JTC1/SC22/WG14
N794
Programming languages - C
Contents
1. Scope................................................... 1
2. Normative references.................................... 2
3. Definitions and conventions............................. 3
4. Compliance.............................................. 7
5. Environment............................................. 9
5.1 Conceptual models................................. 9
5.1.1 Translation environment.................. 9
5.1.2 Execution environments................... 12
5.2 Environmental considerations...................... 20
5.2.1 Character sets........................... 20
5.2.2 Character display semantics.............. 23
5.2.3 Signals and interrupts................... 24
5.2.4 Environmental limits..................... 24
6. Language................................................ 34
6.1 Lexical elements.................................. 34
6.1.1 Keywords................................. 36
6.1.2 Identifiers.............................. 37
6.1.3 Constants................................ 53
6.1.4 String literals.......................... 61
6.1.5 Operators................................ 63
6.1.6 Punctuators.............................. 64
6.1.7 Header names............................. 65
6.1.8 Preprocessing numbers.................... 66
6.1.9 Comments................................. 67
6.2 Conversions....................................... 68
6.2.1 Arithmetic operands...................... 68
6.2.2 Other operands........................... 73
6.3 Expressions....................................... 77
6.3.1 Primary expressions...................... 79
6.3.2 Postfix operators........................ 81
6.3.3 Unary operators.......................... 91
6.3.4 Cast operators........................... 96
6.3.5 Multiplicative operators................. 97
6.3.6 Additive operators....................... 98
6.3.7 Bitwise shift operators.................. 101
6.3.8 Relational operators..................... 102
6.3.9 Equality operators....................... 103
6.3.10 Bitwise AND operator..................... 104
6.3.11 Bitwise exclusive OR operator............ 105
6.3.12 Bitwise inclusive OR operator............ 105
6.3.13 Logical AND operator..................... 106
6.3.14 Logical OR operator...................... 106
6.3.15 Conditional operator..................... 107
6.3.16 Assignment operators..................... 109
6.3.17 Comma operator........................... 111
6.4 Constant expressions.............................. 113
6.5 Declarations...................................... 116
6.5.1 Storage-class specifiers................. 117
6.5.2 Type specifiers.......................... 119
6.5.3 Type qualifiers.......................... 129
6.5.4 Function specifiers...................... 135
6.5.5 Declarators.............................. 137
6.5.6 Type names............................... 147
6.5.7 Type definitions......................... 148
6.5.8 Initialization........................... 151
6.6 Statements........................................ 160
6.6.1 Labeled statements....................... 160
6.6.2 Compound statement, or block............. 161
6.6.3 Expression and null statements........... 162
6.6.4 Selection statements..................... 163
6.6.5 Iteration statements..................... 165
6.6.6 Jump statements.......................... 167
6.7 External definitions.............................. 171
6.7.1 Function definitions..................... 172
6.7.2 External object definitions.............. 175
6.8 Preprocessing directives.......................... 177
6.8.1 Conditional inclusion.................... 180
6.8.2 Source file inclusion.................... 182
6.8.3 Macro replacement........................ 184
6.8.4 Line control............................. 193
6.8.5 Error directive.......................... 194
6.8.6 Pragma directive......................... 194
6.8.7 Null directive........................... 195
6.8.8 Predefined macro names................... 195
6.8.9 Pragma operator.......................... 196
6.9 Future language directions........................ 198
6.9.1 Character escape sequences............... 198
6.9.2 Storage-class specifiers................. 198
6.9.3 Function declarators..................... 198
6.9.4 Function definitions..................... 198
6.9.5 Pragma directives........................ 198
7. Library................................................. 199
7.1 Introduction...................................... 199
7.1.1 Definitions of terms..................... 199
7.1.2 Standard headers......................... 200
7.1.3 Reserved identifiers..................... 202
7.1.4 Errors <errno.h>......................... 203
7.1.5 Limits <float.h> and <limits.h>.......... 204
7.1.6 Common definitions <stddef.h>............ 204
7.1.7 Boolean type and values <stdbool.h>...... 205
7.1.8 Use of library functions................. 206
7.2 Diagnostics <assert.h>............................ 209
7.2.1 Program diagnostics...................... 209
7.3 Character handling <ctype.h>...................... 211
7.3.1 Character testing functions.............. 211
7.3.2 Character case mapping functions......... 216
7.4 Integer types <inttypes.h>........................ 217
7.4.1 Typedef names for integer types.......... 218
7.4.2 Limits of specified-width integer
types.................................... 220
7.4.3 Macros for integer constants............. 223
7.4.4 Macros for format specifiers............. 224
7.4.5 Limits of other integer types............ 226
7.4.6 Conversion functions for greatest-width
integer types............................ 228
7.5 Localization <locale.h>........................... 230
7.5.1 Locale control........................... 231
7.5.2 Numeric formatting convention
inquiry.................................. 233
7.6 Floating-point environment <fenv.h>............... 237
7.6.1 The FENV_ACCESS pragma................... 239
7.6.2 Exceptions............................... 241
7.6.3 Rounding................................. 244
7.6.4 Environment.............................. 245
7.7 Mathematics <math.h>.............................. 248
7.7.1 Treatment of error conditions............ 251
7.7.2 The FP_CONTRACT pragma................... 252
7.7.3 Classification macros.................... 252
7.7.4 Trigonometric functions.................. 256
7.7.5 Hyperbolic functions..................... 259
7.7.6 Exponential and logarithmic
functions................................ 261
7.7.7 Power and absolute value functions....... 267
7.7.8 Error and gamma functions................ 270
7.7.9 Nearest integer functions................ 271
7.7.10 Remainder functions...................... 275
7.7.11 Manipulation functions................... 277
7.7.12 Maximum, minimum, and positive
difference functions..................... 279
7.7.13 Floating multiply-add.................... 281
7.7.14 Comparison macros........................ 281
7.8 Complex arithmetic <complex.h>.................... 285
7.8.1 The CX_LIMITED_RANGE pragma.............. 286
7.8.2 Complex functions........................ 287
7.9 Type-generic math <tgmath.h>...................... 297
7.9.1 Type-generic macros...................... 297
7.10 Nonlocal jumps <setjmp.h>......................... 301
7.10.1 Save calling environment................. 301
7.10.2 Restore calling environment.............. 302
7.11 Signal handling <signal.h>........................ 304
7.11.1 Specify signal handling.................. 305
7.11.2 Send signal.............................. 307
7.12 Variable arguments <stdarg.h>..................... 308
7.12.1 Variable argument list access
macros................................... 308
7.13 Input/output <stdio.h>............................ 313
7.13.1 Introduction............................. 313
7.13.2 Streams.................................. 315
7.13.3 Files.................................... 317
7.13.4 Operations on files...................... 320
7.13.5 File access functions.................... 323
7.13.6 Formatted input/output functions......... 328
7.13.7 Character input/output functions......... 354
7.13.8 Direct input/output functions............ 361
7.13.9 File positioning functions............... 362
7.13.10 Error-handling functions................. 365
7.14 General utilities <stdlib.h>...................... 368
7.14.1 String conversion functions.............. 369
7.14.2 Pseudo-random sequence generation
functions................................ 379
7.14.3 Memory management functions.............. 380
7.14.4 Communication with the environment....... 383
7.14.5 Searching and sorting utilities.......... 386
7.14.6 Integer arithmetic functions............. 388
7.14.7 Multibyte character functions............ 391
7.14.8 Multibyte string functions............... 394
7.15 String handling <string.h>........................ 396
7.15.1 String function conventions.............. 396
7.15.2 Copying functions........................ 396
7.15.3 Concatenation functions.................. 398
7.15.4 Comparison functions..................... 400
7.15.5 Search functions......................... 403
7.15.6 Miscellaneous functions.................. 407
7.16 Date and time <time.h>............................ 409
7.16.1 Components of time....................... 409
7.16.2 Time manipulation functions.............. 411
7.16.3 Time conversion functions................ 417
7.17 Alternative spellings <iso646.h>.................. 424
7.18 Wide-character classification and mapping
utilities <wctype.h>.............................. 425
7.18.1 Introduction............................. 425
7.18.2 Wide-character classification
utilities................................ 426
7.18.3 Wide-character mapping utilities......... 433
7.19 Extended multibyte and wide-character utilities
<wchar.h>......................................... 436
7.19.1 Introduction............................. 436
7.19.2 Formatted wide-character input/output
functions................................ 437
7.19.3 Wide-character input/output
functions................................ 459
7.19.4 General wide-string utilities............ 465
7.19.5 The wcsftime function.................... 486
7.19.6 The wcsfxtime function................... 487
7.19.7 Extended multibyte and wide-character
conversion utilities..................... 487
7.20 Future library directions......................... 496
7.20.1 Errors <errno.h>......................... 496
7.20.2 Character handling <ctype.h>............. 496
7.20.3 Integer types <inttypes.h>............... 496
7.20.4 Localization <locale.h>.................. 496
7.20.5 Signal handling <signal.h>............... 496
7.20.6 Input/output <stdio.h>................... 497
7.20.7 General utilities <stdlib.h>............. 497
7.20.8 Complex arithmetic <complex.h>........... 497
7.20.9 String handling <string.h>............... 497
7.20.10 Wide-character classification and
mapping utilities <wctype.h>............. 498
7.20.11 Extended multibyte and wide-character
utilities <wchar.h>...................... 498
A Bibliography............................................ 499
B Language syntax summary................................. 501
B.1 Lexical grammar................................... 501
B.2 Phrase structure grammar.......................... 507
B.3 Preprocessing directives.......................... 513
C Sequence points......................................... 515
D Library summary......................................... 516
D.1 Errors <errno.h>.................................. 516
D.2 Common definitions <stddef.h>..................... 516
D.3 Boolean type and values <stdbool.h>............... 516
D.4 Diagnostics <assert.h>............................ 516
D.5 Character handling <ctype.h>...................... 517
D.6 Integer types <inttypes.h>........................ 517
D.7 Floating-point environment <fenv.h>............... 523
D.8 Localization <locale.h>........................... 523
D.9 Mathematics <math.h>.............................. 524
D.10 Complex <complex.h>............................... 528
D.11 Type-generic math <tgmath.h>...................... 529
D.12 Nonlocal jumps <setjmp.h>......................... 530
D.13 Signal handling <signal.h>........................ 531
D.14 Variable arguments <stdarg.h>..................... 531
D.15 Input/output <stdio.h>............................ 531
D.16 General utilities <stdlib.h>...................... 534
D.17 String handling <string.h>........................ 536
D.18 Date and time <time.h>............................ 537
D.19 Alternative spellings <iso646.h>.................. 537
D.20 Wide-character classification and mapping
utilities <wctype.h>.............................. 538
D.21 Extended multibyte and wide-character utilities
<wchar.h>......................................... 538
E Implementation limits................................... 543
F IEC 559 floating-point arithmetic....................... 545
F.1 Introduction...................................... 545
F.2 Types............................................. 545
F.3 Operators and functions........................... 546
F.4 Floating to integer conversion.................... 548
F.5 Binary-decimal conversion......................... 549
F.6 Contracted expressions............................ 549
F.7 Environment....................................... 550
F.8 Optimization...................................... 553
F.9 <math.h>.......................................... 558
G IEC 559-compatible complex arithmetic................... 573
G.1 Introduction...................................... 573
G.2 Types............................................. 573
G.3 Conversions....................................... 573
G.4 Binary operators.................................. 574
G.5 <complex.h>....................................... 580
G.6 <tgmath.h>........................................ 588
H Language independent arithmetic......................... 590
H.1 Introduction...................................... 590
H.2 Types............................................. 590
H.3 Notification...................................... 594
I Universal character names for identifiers............... 597
J Common warnings......................................... 599
K Portability issues...................................... 601
K.1 Unspecified behavior.............................. 601
K.2 Undefined behavior................................ 604
K.3 Implementation-defined behavior................... 620
K.4 Locale-specific behavior.......................... 629
K.5 Common extensions................................. 630
Index....................................................... 633
page 1
1. Scope
[#1] This International Standard specifies the form and
establishes the interpretation of programs written in the C
programming language.1 It specifies
- the representation of C programs;
- the syntax and constraints of the C language;
- the semantic rules for interpreting C programs;
- the representation of input data to be processed by C
programs;
- the representation of output data produced by C
programs;
- the restrictions and limits imposed by a conforming
implementation of C.
[#2] This International Standard does not specify
- the mechanism by which C programs are transformed for
use by a data-processing system;
- the mechanism by which C programs are invoked for use
by a data-processing system;
- the mechanism by which input data are transformed for
use by a C program;
- the mechanism by which output data are transformed
after being produced by a C program;
- the size or complexity of a program and its data that
will exceed the capacity of any specific data-
processing system or the capacity of a particular
processor;
__________
1. This International Standard is designed to promote the
portability of C programs among a variety of data-
processing systems. It is intended for use by
implementors and programmers.
page 1 General
page 2
- all minimal requirements of a data-processing system
that is capable of supporting a conforming
implementation.
2. Normative references
[#1] The following standards contain provisions which,
through reference in this text, constitute provisions of
this International Standard. At the time of publication,
the editions indicated were valid. All standards are
subject to revision, and parties to agreements based on this
International Standard are encouraged to investigate the
possibility of applying the most recent editions of the
standards indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
IEC 559:1993, Binary floating-point arithmetic for
microprocessor systems, second edition.
ISO 646:1983, Information processing - ISO 7-bit coded
character set for information interchange.
ISO/IEC 2382-1:1993, Information technology -
Vocabulary - Part 1: Fundamental terms.
ISO 4217:1987, Codes for the representation of
currencies and funds.
ISO 8601:1988, Data elements and interchange formats -
Information interchange - Representation of dates and
times.
ISO/IEC TR 10176, Information technology - Guidelines
for the preparation of programming language standards.
ISO/IEC 10646-1:1993, Information technology -
Universal Multiple-Octet Coded Character Set (UCS) -
Part 1: Architecture and Basic Multilingual Plane.
page 2 General
page 3
3. Definitions and conventions
[#1] In this International Standard, ``shall'' is to be
interpreted as a requirement on an implementation or on a
program; conversely, ``shall not'' is to be interpreted as a
prohibition.
[#2] For the purposes of this International Standard, the
following definitions apply. Other terms are defined where
they appear in italic type or being on the left side of a
syntax rule. Terms explicitly defined in this International
Standard are not to be presumed to refer implicitly to
similar terms defined elsewhere. Terms not defined in this
International Standard are to be interpreted according to
ISO 2382-1.
3.1 Alignment
[#1] A requirement that objects of a particular type be
located on storage boundaries with addresses that are
particular multiples of a byte address.
3.2 Argument
[#1] An expression in the comma-separated list bounded by
the parentheses in a function call expression, or a sequence
of preprocessing tokens in the comma-separated list bounded
by the parentheses in a function-like macro invocation.
Also known as ``actual argument'' or ``actual parameter.''
3.3 Bit
[#1] The unit of data storage in the execution environment
large enough to hold an object that may have one of two
values. It need not be possible to express the address of
each individual bit of an object.
page 3 General
page 4
3.4 Byte
[#1] The unit of data storage large enough to hold any
member of the basic character set of the execution
environment. It shall be possible to express the address of
each individual byte of an object uniquely. A byte is
composed of a contiguous sequence of bits, the number of
which is implementation-defined. The least significant bit
is called the low-order bit; the most significant bit is
called the high-order bit.
3.5 Character
[#1] A bit representation that fits in a byte. The
representation of each member of the basic character set in
both the source and execution environments shall fit in a
byte.
3.6 Constraints
[#1] Restrictions, both syntactic and semantic, by which the
exposition of language elements is to be interpreted.
3.7 Correctly rounded result
[#1] A representation in the result format that is nearest
in value, subject to the effective rounding mode, to what
the result would be given unlimited range and precision.
3.8 Diagnostic message
[#1] A message belonging to an implementation-defined subset
of the implementation's message output.
3.9 Forward references
[#1] References to later subclauses of this International
Standard that contain additional information relevant to
this subclause.
page 4 General
page 5
3.10 Implementation
[#1] A particular set of software, running in a particular
translation environment under particular control options,
that performs translation of programs for, and supports
execution of functions in, a particular execution
environment.
3.11 Implementation-defined behavior
[#1] Unspecified behavior where each implementation shall
document how the choice is made.
3.12 Implementation limits
[#1] Restrictions imposed upon programs by the
implementation.
3.13 Locale-specific behavior
[#1] Behavior that depends on local conventions of
nationality, culture, and language that each implementation
shall document.
3.14 Multibyte character
[#1] A sequence of one or more bytes representing a member
of the extended character set of either the source or the
execution environment. The extended character set is a
superset of the basic character set.
3.15 Object
[#1] A region of data storage in the execution environment,
the contents of which can represent values. Except for
bit-fields, objects are composed of contiguous sequences of
one or more bytes, the number, order, and encoding of which
are either explicitly specified or implementation-defined.
When referenced, an object may be interpreted as having a
particular type; see 6.2.2.1.
page 5 General
page 6
3.16 Parameter
[#1] An object declared as part of a function declaration or
definition that acquires a value on entry to the function,
or an identifier from the comma-separated list bounded by
the parentheses immediately following the macro name in a
function-like macro definition. Also known as ``formal
argument'' or ``formal parameter.''
3.17 Recommended practice
[#1] Sections so entitled contain specification that is
strongly recommended as being in keeping with the intent of
the standard, but that may be impractical for some
implementations.
3.18 Undefined behavior
[#1] Behavior, upon use of a nonportable or erroneous
program construct, of erroneous data, or of indeterminately
valued objects, for which this International Standard
imposes no requirements. Permissible undefined behavior
ranges from ignoring the situation completely with
unpredictable results, to behaving during translation or
program execution in a documented manner characteristic of
the environment (with or without the issuance of a
diagnostic message), to terminating a translation or
execution (with the issuance of a diagnostic message).
[#2] If a ``shall'' or ``shall not'' requirement that
appears outside of a constraint is violated, the behavior is
undefined. Undefined behavior is otherwise indicated in
this International Standard by the words ``undefined
behavior'' or by the omission of any explicit definition of
behavior. There is no difference in emphasis among these
three; they all describe ``behavior that is undefined.''
[#3] The implementation must successfully translate a given
program unless a syntax error is detected, a constraint is
violated, or it can determine that every possible execution
of that program would result in undefined behavior.
page 6 General
page 7
3.19 Unspecified behavior
[#1] Behavior where this International Standard provides two
or more possibilities and imposes no requirements on which
is chosen in any instance. A program that is correct in all
other aspects, operating on correct data, containing
unspecified behavior shall be a correct program and act in
accordance with subclause 5.1.2.3.
Examples
[#2]
1. An example of unspecified behavior is the order in
which the arguments to a function are evaluated.
2. An example of undefined behavior is the behavior on
integer overflow.
3. An example of implementation-defined behavior is the
propagation of the high-order bit when a signed
integer is shifted right.
4. An example of locale-specific behavior is whether the
islower function returns true for characters other
than the 26 lowercase Latin letters.
Forward references: bitwise shift operators (6.3.7),
expressions (6.3), function calls (6.3.2.2), the islower
function (7.3.1.7), localization (7.5).
4. Compliance
[#1] A strictly conforming program shall use only those
features of the language and library specified in this
International Standard.2 It shall not produce output
__________
2. This implies that a strictly conforming program can use
features in a conditionally normative annex provided the
use is conditioned by a #ifdef directive with the
conformance macro for the annex, as in
#ifdef __STDC_IEC_559__ /* FE_UPWARD defined */
/* ... */
fesetround(FE_UPWARD);
/* ... */
page 7 General
page 8
dependent on any unspecified, undefined, or implementation-
defined behavior, and shall not exceed any minimum
implementation limit.
[#2] The two forms of conforming implementation are hosted
and freestanding. A conforming hosted implementation shall
accept any strictly conforming program. A conforming
freestanding implementation shall accept any strictly
conforming program in which the use of the features
specified in the library clause (clause 7) is confined to
the contents of the standard headers <float.h>, <limits.h>,
<stdarg.h>, <stddef.h>, and <iso646.h>. A conforming
implementation may have extensions (including additional
library functions), provided they do not alter the behavior
of any strictly conforming program.3
[#3] A conforming program is one that is acceptable to a
conforming implementation.4
[#4] An implementation shall be accompanied by a document
that defines all implementation-defined characteristics and
all extensions.
Forward references: limits <float.h> and <limits.h>
(7.1.5), variable arguments <stdarg.h> (7.12), common
definitions <stddef.h> (7.1.6), alternate spellings
<iso646.h> (7.17).
____________________________________________________________
#endif
3. This implies that a conforming implementation reserves
no identifiers other than those explicitly reserved in
this International Standard.
4. Strictly conforming programs are intended to be
maximally portable among conforming implementations.
Conforming programs may depend upon nonportable features
of a conforming implementation.
page 8 General
page 9
5. Environment
[#1] An implementation translates C source files and
executes C programs in two data-processing-system
environments, which will be called the translation
environment and the execution environment in this
International Standard. Their characteristics define and
constrain the results of executing conforming C programs
constructed according to the syntactic and semantic rules
for conforming implementations.
Forward references: In the environment clause (clause 5),
only a few of many possible forward references have been
noted.
5.1 Conceptual models
5.1.1 Translation environment
5.1.1.1 Program structure
[#1] A C program need not all be translated at the same
time. The text of the program is kept in units called
source files, also known as preprocessing files, in this
International Standard. A source file together with all the
headers and source files included via the preprocessing
directive #include is known as a preprocessing translation
unit. After preprocessing, a preprocessing translation unit
is called a translation unit. Previously translated
translation units may be preserved individually or in
libraries. The separate translation units of a program
communicate by (for example) calls to functions whose
identifiers have external linkage, manipulation of objects
whose identifiers have external linkage, or manipulation of
data files. Translation units may be separately translated
and then later linked to produce an executable program.
Forward references: conditional inclusion (6.8.1), linkages
of identifiers (6.1.2.2), source file inclusion (6.8.2),
external definitions (6.7), preprocessing directives (6.8).
page 9 Environment
page 10
5.1.1.2 Translation phases
[#1] The precedence among the syntax rules of translation is
specified by the following phases.5
1. Physical source file multibyte characters are mapped
to the source character set (introducing new-line
characters for end-of-line indicators) if necessary.
Any multibyte source file character not in the basic
source character set is replaced by the universal-
character-name that designates that multibyte
character.6 Then, trigraph sequences are replaced by
corresponding single-character internal
representations.
2. Each instance of a backslash character immediately
followed by a newline character is deleted, splicing
physical source lines to form logical source lines.
Only the last backslash on any physical source line
shall be eligible for being part of such a splice. A
source file that is not empty shall end in a new-line
character, which shall not be immediately preceded by
a backslash character before any such splicing takes
place.
3. The source file is decomposed into preprocessing
tokens7 and sequences of white-space characters
__________
5. Implementations must behave as if these separate phases
occur, even though many are typically folded together in
practice.
6. The process of handling extended characters is specified
in terms of mapping to an encoding that uses only the
basic source character set, and, in the case of
character literals and strings, further mapping to the
execution character set. In practical terms, however,
any internal encoding may be used, so long as an actual
extended character encountered in the input, and the
same extended character expressed in the input as a
universal-character-name (i.e., using the \U or \u
notation), are handled equivalently.
7. As described in 6.1, the process of dividing a source
file's characters into preprocessing tokens is context-
dependent. For example, see the handling of < within a
#include preprocessing directive.
page 10 Environment
page 11
(including comments). A source file shall not end in
a partial preprocessing token or comment. Each
comment is replaced by one space character. New-line
characters are retained. Whether each nonempty
sequence of white-space characters other than new-line
is retained or replaced by one space character is
implementation-defined.
4. Preprocessing directives are executed, macro
invocations are expanded, and pragma unary operator
expressions are executed. If a character sequence
that matches the syntax of a universal-character-name
is produced by token concatenation (6.8.3.3), the
behavior is undefined. A #include preprocessing
directive causes the named header or source file to be
processed from phase 1 through phase 4, recursively.
All preprocessing directives are then deleted.
5. Each source character set member, escape sequence, and
universal-character-name in character constants and
string literals is converted to a member of the
execution character set.
6. Adjacent character string literal tokens are
concatenated and adjacent wide string literal tokens
are concatenated.
7. White-space characters separating tokens are no longer
significant. Each preprocessing token is converted
into a token. The resulting tokens are syntactically
and semantically analyzed and translated as a
translation unit.
8. All external object and function references are
resolved. Library components are linked to satisfy
external references to functions and objects not
defined in the current translation. All such
translator output is collected into a program image
which contains information needed for execution in its
execution environment.
Constraints
[#2] A universal-character-name shall not specify a
character short identifier in the range 0000 through 0020 or
007F through 009F inclusive. A universal-character-name
shall not designate a character in the basic source
character set.
page 11 Environment
page 12
Forward references: lexical elements (6.1), preprocessing
directives (6.8), trigraph sequences (5.2.1.1), external
definitions (6.7).
5.1.1.3 Diagnostics
[#1] A conforming implementation shall produce at least one
diagnostic message (identified in an implementation-defined
manner) if a preprocessing translation unit or translation
unit contains a violation of any syntax rule or constraint,
even if the behavior is also explicitly specified as
undefined or implementation-defined. Diagnostic messages
need not be produced in other circumstances.8
Examples
[#2] An implementation shall issue a diagnostic for the
translation unit:
char i;
int i;
because in those cases where wording in this International
Standard describes the behavior for a construct as being
both a constraint error and resulting in undefined behavior,
the constraint error shall be diagnosed.
5.1.2 Execution environments
[#1] Two execution environments are defined: freestanding
and hosted. In both cases, program startup occurs when a
designated C function is called by the execution
environment. All objects in static storage shall be
initialized (set to their initial values) before program
startup. The manner and timing of such initialization are
otherwise unspecified. Program termination returns control
to the execution environment.
__________
8. The intent is that an implementation should identify the
nature of, and where possible localize, each violation.
Of course, an implementation is free to produce any
number of diagnostics as long as a valid program is
still correctly translated. It may also successfully
translate an invalid program.
page 12 Environment
page 13
Forward references: initialization (6.5.8).
5.1.2.1 Freestanding environment
[#1] In a freestanding environment (in which C program
execution may take place without any benefit of an operating
system), the name and type of the function called at program
startup are implementation-defined. Any library facilities
available to a freestanding program are implementation-
defined.
[#2] The effect of program termination in a freestanding
environment is implementation-defined.
5.1.2.2 Hosted environment
[#1] A hosted environment need not be provided, but shall
conform to the following specifications if present.
5.1.2.2.1 Program startup
[#1] The function called at program startup is named main.
The implementation declares no prototype for this function.
It shall be defined with no parameters:
int main(void) { /* ... */ }
or with two parameters (referred to here as argc and argv,
though any names may be used, as they are local to the
function in which they are declared):
int main(int argc, char *argv[]) { /* ... */ }
or equivalent,9 or in some other implementation-defined
manner.
[#2] If they are defined, the parameters to the main
function shall obey the following constraints:
- The value of argc shall be nonnegative.
- argv[argc] shall be a null pointer.
__________
9. Thus, int can be replaced by a typedef name defined as
int, or the type of argv can be written as char ** argv,
and so on.
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- If the value of argc is greater than zero, the array
members argv[0] through argv[argc-1] inclusive shall
contain pointers to strings, which are given
implementation-defined values by the host environment
prior to program startup. The intent is to supply to
the program information determined prior to program
startup from elsewhere in the hosted environment. If
the host environment is not capable of supplying
strings with letters in both uppercase and lowercase,
the implementation shall ensure that the strings are
received in lowercase.
- If the value of argc is greater than zero, the string
pointed to by argv[0] represents the program name;
argv[0][0] shall be the null character if the program
name is not available from the host environment. If
the value of argc is greater than one, the strings
pointed to by argv[1] through argv[argc-1] represent
the program parameters.
- The parameters argc and argv and the strings pointed to
by the argv array shall be modifiable by the program,
and retain their last-stored values between program
startup and program termination.
5.1.2.2.2 Program execution
[#1] In a hosted environment, a program may use all the
functions, macros, type definitions, and objects described
in the library clause (clause 7).
5.1.2.2.3 Program termination
[#1] A return from the initial call to the main function is
equivalent to calling the exit function with the value
returned by the main function as its argument.10 If the }
that terminates the main function is reached, the
termination status returned to the host environment is
unspecified.
__________
10. In accordance with subclause 6.1.2.4, objects with
automatic storage duration declared in main will no
longer have storage guaranteed to be reserved in the
former case even where they would in the latter.
page 14 Environment
page 15
Forward references: definition of terms (7.1.1), the exit
function (7.14.4.3).
5.1.2.3 Program execution
[#1] The semantic descriptions in this International
Standard describe the behavior of an abstract machine in
which issues of optimization are irrelevant.
[#2] Accessing a volatile object, modifying an object,
modifying a file, or calling a function that does any of
those operations are all side effects,11 which are changes
in the state of the execution environment. Evaluation of an
expression may produce side effects. At certain specified
points in the execution sequence called sequence points, all
side effects of previous evaluations shall be complete and
no side effects of subsequent evaluations shall have taken
place.
[#3] In the abstract machine, all expressions are evaluated
as specified by the semantics. An actual implementation
need not evaluate part of an expression if it can deduce
that its value is not used and that no needed side effects
are produced (including any caused by calling a function or
accessing a volatile object).
[#4] When the processing of the abstract machine is
interrupted by receipt of a signal, only the values of
objects as of the previous sequence point may be relied on.
Objects that may be modified between the previous sequence
point and the next sequence point need not have received
their correct values yet.
[#5] An instance of each object with automatic storage
duration is associated with each entry into its block. Such
__________
11. The IEC 559 standard for binary floating-point
arithmetic requires certain status flags and control
modes, with user access. Floating-point operations
implicitly set the status flags; modes affect result
values of floating-point operations. Implementations
that support such floating-point state will need to
regard changes to it as side effects - see Annex F for
details. The floating-point environment library
<fenv.h> provides a programming facility for indicating
when these side effects matter, freeing the
implementations in other cases.
page 15 Environment
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an object exists and retains its last-stored value during
the execution of the block and while the block is suspended
(by a call of a function or receipt of a signal).
[#6] The least requirements on a conforming implementation
are:
- At sequence points, volatile objects are stable in the
sense that previous evaluations are complete and
subsequent evaluations have not yet occurred.
- At program termination, all data written into files
shall be identical to the result that execution of the
program according to the abstract semantics would have
produced.
- The input and output dynamics of interactive devices
shall take place as specified in 7.13.3. The intent of
these requirements is that unbuffered or line-buffered
output appear as soon as possible, to ensure that
prompting messages actually appear prior to a program
waiting for input.
[#7] What constitutes an interactive device is
implementation-defined.
[#8] More stringent correspondences between abstract and
actual semantics may be defined by each implementation.
Examples
1. An implementation might define a one-to-one
correspondence between abstract and actual semantics:
at every sequence point, the values of the actual
objects would agree with those specified by the
abstract semantics. The keyword volatile would then
be redundant.
Alternatively, an implementation might perform various
optimizations within each translation unit, such that
the actual semantics would agree with the abstract
semantics only when making function calls across
translation unit boundaries. In such an
implementation, at the time of each function entry and
function return where the calling function and the
called function are in different translation units,
the values of all externally linked objects and of all
objects accessible via pointers therein would agree
with the abstract semantics. Furthermore, at the time
of each such function entry the values of the
parameters of the called function and of all objects
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accessible via pointers therein would agree with the
abstract semantics. In this type of implementation,
objects referred to by interrupt service routines
activated by the signal function would require
explicit specification of volatile storage, as well as
other implementation-defined restrictions.
2. In executing the fragment
char c1, c2;
/* ... */
c1 = c1 + c2;
the ``integer promotions'' require that the abstract
machine promote the value of each variable to int size
and then add the two ints and truncate the sum.
Provided the addition of two chars can be done without
overflow, or with overflow wrapping silently to
produce the correct result, the actual execution need
only produce the same result, possibly omitting the
promotions.
3. Similarly, in the fragment
float f1, f2;
double d;
/* ... */
f1 = f2 * d;
the multiplication may be executed using single-
precision arithmetic if the implementation can
ascertain that the result would be the same as if it
were executed using double-precision arithmetic (for
example, if d were replaced by the constant 2.0, which
has type double).
4. Implementations employing wide registers must take
care to honor appropriate semantics. Values must be
independent of whether they are represented in a
register or in memory. For example, an implicit
spilling of a register must not alter the value.
Also, an explicit store and load must round to the
precision of the storage type. In particular, casts
and assignments must perform their specified
conversion: for the fragment
double d1, d2;
float f;
d1 = f = expression;
d2 = (float) expressions;
page 17 Environment
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the values assigned to d1 and d2 must have been
converted to float.
5. Rearrangement for floating-point expressions is often
restricted because of limitations in precision as well
as range. The implementation cannot generally apply
the mathematical associative rules for addition or
multiplication, nor the distributive rule, because of
roundoff error, even in the absence of overflow and
underflow. Likewise, implementations cannot generally
replace decimal constants in order to rearrange
expressions. In the following fragment,
rearrangements suggested by mathematical rules for
real numbers are often not valid. See Annex F.8.
double x, y, z;
/* ... */
x = (x * y) * z; // not equivalent to x *= y * z;
z = (x - y) + y ; // not equivalent to z = x;
z = x + x * y; // not equivalent to z = x * (1.0 + y);
y = x / 5.0; // not equivalent of y = x * 0.2;
6. To illustrate the grouping behavior of expressions, in
the following fragment
int a, b;
/* ... */
a = a + 32760 + b + 5;
the expression statement behaves exactly the same as
a = (((a + 32760) + b) + 5);
due to the associativity and precedence of these
operators. Thus, the result of the sum (a + 32760) is
next added to b, and that result is then added to 5
which results in the value assigned to a. On a
machine in which overflows produce an explicit trap
and in which the range of values representable by an
int is [-32768, + 32767], the implementation cannot
rewrite this expression as
a = ((a + b) + 32765);
since if the values for a and b were, respectively, -
32754 and - 15, the sum a + b would produce a trap
while the original expression would not; nor can the
expression be rewritten either as
page 18 Environment
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a = ((a + 32765) + b);
or
a = (a + (b + 32765));
since the values for a and b might have been,
respectively, 4 and -8 or -17 and 12. However on a
machine in which overflow silently generates some
value and where positive and negative overflows
cancel, the above expression statement can be
rewritten by the implementation in any of the above
ways because the same result will occur.
7. The grouping of an expression does not completely
determine its evaluation. In the following fragment
#include <stdio.h>
int sum;
char *p;
/* ... */
sum = sum * 10 - '0' + (*p++ = getchar());
the expression statement is grouped as if it were
written as
sum = (((sum * 10) - '0') + ((*(p++)) = (getchar())));
but the actual increment of p can occur at any time
between the previous sequence point and the next
sequence point (the ;), and the call to getchar can
occur at any point prior to the need of its returned
value.
Forward references: compound statement, or block (6.6.2),
expressions (6.3), files (7.13.3),
sequence points (6.6), the signal function (7.11),
type qualifiers (6.5.3).
page 19 Environment
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5.2 Environmental considerations
5.2.1 Character sets
[#1] Two sets of characters and their associated collating
sequences shall be defined: the set in which source files
are written, and the set interpreted in the execution
environment. The values of the members of the execution
character set are implementation-defined; any additional
members beyond those required by this subclause are locale-
specific.
[#2] In a character constant or string literal, members of
the execution character set shall be represented by
corresponding members of the source character set or by
escape sequences consisting of the backslash \ followed by
one or more characters. A byte with all bits set to 0,
called the null character, shall exist in the basic
execution character set; it is used to terminate a character
string.
[#3] Both the basic source and basic execution character
sets shall have at least the following members: the 26
uppercase letters of the Latin alphabet
A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z
the 26 lowercase letters of the Latin alphabet
a b c d e f g h i j k l m
n o p q r s t u v w x y z
the 10 decimal digits
0 1 2 3 4 5 6 7 8 9
the following 29 graphic characters
! " # % & ' ( ) * + , - . / :
; < = > ? [ \ ] ^ _ { | } ~
the space character, and control characters representing
horizontal tab, vertical tab, and form feed. In both the
source and execution basic character sets, the value of each
character after 0 in the above list of decimal digits shall
be one greater than the value of the previous. In source
files, there shall be some way of indicating the end of each
line of text; this International Standard treats such an
end-of-line indicator as if it were a single new-line
character. In the execution character set, there shall be
page 20 Environment
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control characters representing alert, backspace, carriage
return, and new line. If any other characters are
encountered in a source file (except in a character
constant, a string literal, a header name, a comment, or a
preprocessing token that is never converted to a token), the
behavior is undefined.
[#4] The universal-character-name construct provides a way
to name other characters.
hex-quad:
hexadecimal-digit hexadecimal-digit
hexadecimal-digit hexadecimal-digit
universal-character-name:
\u hex-quad
\U hex-quad hex-quad
[#5] The character designated by the universal-character-
name \Unnnnnnnn is that character whose character short
identifier is nnnnnnnn specified by ISO/IEC 10646-1; the
character designated by the universal-character-name \unnnn
is that character whose character short identifier is
0000nnnn specified by ISO/IEC 10646-1.
Forward references: identifiers (6.1.2), character
constants (6.1.3.4), preprocessing directives (6.8), string
literals (6.1.4), comments (6.1.9), string (7.1.1).
5.2.1.1 Trigraph sequences
[#1] All occurrences in a source file of the following
sequences of three characters (called trigraph sequences12)
are replaced with the corresponding single character.
__________
12. The trigraph sequences enable the input of characters
that are not defined in the Invariant Code Set as
described in ISO/IEC 646:1991, which is a subset of the
seven-bit ASCII code set.
page 21 Environment
page 22
??= #
??( [
??/ \
??) ]
??' ^
??< {
??! |
??> }
??- ~
No other trigraph sequences exist. Each ? that does not
begin one of the trigraphs listed above is not changed.
Examples
[#2] The following source line
printf("Eh???/n");
becomes (after replacement of the trigraph sequence ??/)
printf("Eh?\n");
5.2.1.2 Multibyte characters
[#1] The source character set may contain multibyte
characters, used to represent members of the extended
character set. The execution character set may also contain
multibyte characters, which need not have the same encoding
as for the source character set. For both character sets,
the following shall hold:
- The single-byte characters defined in 5.2.1 shall be
present.
- The presence, meaning, and representation of any
additional members is locale-specific.
- A multibyte character may have a state-dependent
encoding, wherein each sequence of multibyte characters
begins in an initial shift state and enters other
locale-specific shift states when specific multibyte
characters are encountered in the sequence. While in
the initial shift state, all single-byte characters
retain their usual interpretation and do not alter the
shift state. The interpretation for subsequent bytes
in the sequence is a function of the current shift
state.
- A byte with all bits zero shall be interpreted as a
null character independent of shift state.
page 22 Environment
page 23
- A byte with all bits zero shall not occur in the second
or subsequent bytes of a multibyte character.
[#2] For the source character set, the following shall hold:
- A comment, string literal, character constant, or
header name shall begin and end in the initial shift
state.
- A comment, string literal, character constant, or
header name shall consist of a sequence of valid
multibyte characters.
5.2.2 Character display semantics
[#1] The active position is that location on a display
device where the next character output by the fputc function
would appear. The intent of writing a printable character
(as defined by the isprint function) to a display device is
to display a graphic representation of that character at the
active position and then advance the active position to the
next position on the current line. The direction of writing
is locale-specific. If the active position is at the final
position of a line (if there is one), the behavior is
unspecified.
[#2] Alphabetic escape sequences representing nongraphic
characters in the execution character set are intended to
produce actions on display devices as follows:
\a (alert) Produces an audible or visible alert. The active
position shall not be changed.
\b (backspace) Moves the active position to the previous
position on the current line. If the active position is
at the initial position of a line, the behavior is
unspecified.
\f (form feed) Moves the active position to the initial
position at the start of the next logical page.
\n (new line) Moves the active position to the initial
position of the next line.
\r (carriage return) Moves the active position to the
initial position of the current line.
\t (horizontal tab) Moves the active position to the next
horizontal tabulation position on the current line. If
the active position is at or past the last defined
horizontal tabulation position, the behavior is
page 23 Environment
page 24
unspecified.
\v (vertical tab) Moves the active position to the initial
position of the next vertical tabulation position. If
the active position is at or past the last defined
vertical tabulation position, the behavior is
unspecified.
[#3] Each of these escape sequences shall produce a unique
implementation-defined value which can be stored in a single
char object. The external representations in a text file
need not be identical to the internal representations, and
are outside the scope of this International Standard.
Forward references: the isprint function (7.3.1.8), the
fputc function (7.13.7.3).
5.2.3 Signals and interrupts
[#1] Functions shall be implemented such that they may be
interrupted at any time by a signal, or may be called by a
signal handler, or both, with no alteration to earlier, but
still active, invocations' control flow (after the
interruption), function return values, or objects with
automatic storage duration. All such objects shall be
maintained outside the function image (the instructions that
comprise the executable representation of a function) on a
per-invocation basis.
5.2.4 Environmental limits
[#1] Both the translation and execution environments
constrain the implementation of language translators and
libraries. The following summarizes the environmental
limits on a conforming implementation.
5.2.4.1 Translation limits
[#1] The implementation shall be able to translate and
execute at least one program that contains at least one
instance of every one of the following limits:13
- 127 nesting levels of compound statements, iteration
statements, and selection statements
__________
13. Implementations should avoid imposing fixed translation
limits whenever possible.
page 24 Environment
page 25
- 63 nesting levels of conditional inclusion
- 12 pointer, array, and function declarators (in any
combinations) modifying an arithmetic, structure,
union, or incomplete type in a declaration
- 63 nesting levels of parenthesized declarators within a
full declarator
- 63 nesting levels of parenthesized expressions within a
full expression
- 63 significant initial characters in an internal
identifier or a macro name
- 31 significant initial characters in an external
identifier
- 4095 external identifiers in one translation unit
- 511 identifiers with block scope declared in one block
- 4095 macro identifiers simultaneously defined in one
preprocessing translation unit
- 127 parameters in one function definition
- 127 arguments in one function call
- 127 parameters in one macro definition
- 127 arguments in one macro invocation
- 4095 characters in a logical source line
- 4095 characters in a character string literal or wide
string literal (after concatenation)
- 65535 bytes in an object (in a hosted environment only)
- 15 nesting levels for #included files
- 1023 case labels for a switch statement (excluding
those for any nested switch statements)
- 1023 members in a single structure or union
- 1023 enumeration constants in a single enumeration
- 63 levels of nested structure or union definitions in a
single struct-declaration-list
page 25 Environment
page 26
5.2.4.2 Numerical limits
[#1] A conforming implementation shall document all the
limits specified in this subclause, which shall be specified
in the headers <limits.h> and <float.h>.
5.2.4.2.1 Sizes of integer types <limits.h>
[#1] The values given below shall be replaced by constant
expressions suitable for use in #if preprocessing
directives. Moreover, except for CHAR_BIT and MB_LEN_MAX,
the following shall be replaced by expressions that have the
same type as would an expression that is an object of the
corresponding type converted according to the integer
promotions. Their implementation-defined values shall be
equal or greater in magnitude (absolute value) to those
shown, with the same sign.
- number of bits for smallest object that is not a bit-
field (byte)
CHAR_BIT 8
- minimum value for an object of type signed char
SCHAR_MIN -127
- maximum value for an object of type signed char
SCHAR_MAX +127
- maximum value for an object of type unsigned char
UCHAR_MAX 255
- minimum value for an object of type char
CHAR_MIN see below
- maximum value for an object of type char
CHAR_MAX see below
- maximum number of bytes in a multibyte character, for
any supported locale
MB_LEN_MAX 1
- minimum value for an object of type short int
SHRT_MIN -32767
- maximum value for an object of type short int
SHRT_MAX +32767
- maximum value for an object of type unsigned short int
USHRT_MAX 65535
page 26 Environment
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- minimum value for an object of type int
INT_MIN -32767
- maximum value for an object of type int
INT_MAX +32767
- maximum value for an object of type unsigned int
UINT_MAX 65535
- minimum value for an object of type long int
LONG_MIN -2147483647
- maximum value for an object of type long int
LONG_MAX +2147483647
- maximum value for an object of type unsigned long int
ULONG_MAX 4294967295
- minimum value for an object of type long long int
LLONG_MIN -9223372036854775807
- maximum value for an object of type long long int
LLONG_MAX +9223372036854775807
- maximum value for an object of type unsigned long long
int
ULLONG_MAX 18446744073709551615
[#2] If the value of an object of type char is treated as a
signed integer when used in an expression, the value of
CHAR_MIN shall be the same as that of SCHAR_MIN and the
value of CHAR_MAX shall be the same as that of SCHAR_MAX.
Otherwise, the value of CHAR_MIN shall be 0 and the value of
CHAR_MAX shall be the same as that of UCHAR_MAX.14 The
value UCHAR_MAX+1 shall equal 2 raised to the power
CHAR_BIT.
5.2.4.2.2 Characteristics of floating types <float.h>
[#1] The characteristics of floating types are defined in
terms of a model that describes a representation of
floating-point numbers and values that provide information
about an implementation's floating-point arithmetic.15 The
__________
14. See 6.1.2.5.
15. The floating-point model is intended to clarify the
description of each floating-point characteristic and
page 27 Environment
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following parameters are used to define the model for each
floating-point type:
s sign (_1)
b base or radix of exponent representation (an integer > 1)
e exponent (an integer between a minimum e and a maximum e )
p precision (the number of base-b digits inithe significand) max
f nonnegative integers less than b (the significand digits)
k
[#2] A normalized floating-point number x (f > 0 if x / 0)
is defined by the following model: 1
e p -k
x = s x b x R fk x b , emin < e < emax
k=1
[#3] Floating types might include values that are not
normalized floating-point numbers, for example subnormal
numbers (x / 0, e = e , f = 0), infinities, and NaNs. A
NaN is an encodingmisignifying Not-a-Number. A quiet NaN
propagates through almost every arithmetic operation without
raising an exception; a signaling NaN generally raises an
exception when occurring as an arithmetic operand.16
[#4] All integer values in the <float.h> header, except
FLT_ROUNDS, shall be constant expressions suitable for use
in #if preprocessing directives; all floating values shall
be constant expressions. All except FLT_EVAL_METHOD,
FLT_RADIX, and FLT_ROUNDS have separate names for all three
floating-point types. The floating-point model
representation is provided for all values except
FLT_EVAL_METHOD and FLT_ROUNDS.
[#5] The rounding mode for floating-point addition is
characterized by the value of FLT_ROUNDS:17
____________________________________________________________
does not require the floating-point arithmetic of the
implementation to be identical.
16. IEC 559:1993 specifies quiet and signaling NaNs. For
implementations that do not support IEC 559:1993, the
terms quiet NaN and signaling NaN are intended to apply
to encodings with similar behavior.
17. Evaluation of FLT_ROUNDS correctly reflects any
execution-time change of rounding mode through the
function fesetround in <fenv.h>.
page 28 Environment
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-1 indeterminable
0 toward zero
1 to nearest
2 toward positive infinity
3 toward negative infinity
All other values for FLT_ROUNDS characterize
implementation-defined rounding behavior.
[#6] The values of operations with floating operands and
values subject to the usual arithmetic conversions and of
floating constants are evaluated to a format whose range and
precision may be greater than required by the type. The use
of evaluation formats is characterized by the value of
FLT_EVAL_METHOD:18
-1 indeterminable;
0 evaluate all operations and constants just to the range
and precision of the type;
1 evaluate operations and constants of type float and
double to the range and precision of the double type,
evaluate long double operations and constants to the
range and precision of the long double type;
2 evaluate all operations and constants to the range and
precision of the long double type.
All other negative values for FLT_EVAL_METHOD characterize
implementation-defined behavior.
[#7] The values given in the following list shall be
replaced by implementation-defined expressions that shall be
equal or greater in magnitude (absolute value) to those
shown, with the same sign:
- radix of exponent representation, b
FLT_RADIX 2
__________
18. The evaluation method determines evaluation formats of
expressions involving all floating types, not just real
types. For example, if FLT_EVAL_METHOD is 1, then the
product of two float complex operands is represented in
the double complex format, and its parts are evaluated
to double.
page 29 Environment
page 30
- number of base-FLT_RADIX digits in the floating-point
significand, p
FLT_MANT_DIG
DBL_MANT_DIG
LDBL_MANT_DIG
- number of decimal digits, q, such that any floating-
point number with q decimal digits can be rounded into
a floating-point number with p radix b digits and back
again without change to the q decimal digits,
(1 if b is a power of 10
| (p - 1) x log b | + |
| 10 | (0 otherwise
FLT_DIG 6
DBL_DIG 10
LDBL_DIG 10
- minimum negative integer such that FLT_RADIX raised to
that power minus 1 is a normalized floating-point
number, e
min
FLT_MIN_EXP
DBL_MIN_EXP
LDBL_MIN_EXP
- minimum negative integer such that 10 raised to that
power is in the range of normalized floating-point
| e -1 |
numbers, | log b min |
| 10 |
FLT_MIN_10_EXP -37
DBL_MIN_10_EXP -37
LDBL_MIN_10_EXP -37
- maximum integer such that FLT_RADIX raised to that
power minus 1 is a representable finite floating-point
number, e
max
FLT_MAX_EXP
DBL_MAX_EXP
LDBL_MAX_EXP
- maximum integer such that 10 raised to that power is in
the range of representable finite floating-point
| e |
numbers, | log ((1 - b-p) x b max) |
| 10 |
page 30 Environment
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FLT_MAX_10_EXP +37
DBL_MAX_10_EXP +37
LDBL_MAX_10_EXP +37
[#8] The values given in the following list shall be
replaced by implementation-defined expressions with values
that shall be equal to or greater than those shown:
- max-pum reemaxentable finite floating-point number, (1
- b ) x b
FLT_MAX 1E+37
DBL_MAX 1E+37
LDBL_MAX 1E+37
[#9] The values given in the following list shall be
replaced by implementation-defined expressions with values
that shall be equal to or less than those shown:
- the difference between 1 and the least value greater
than 1 that1-ps representable in the given floating
point type, b
FLT_EPSILON 1E-5
DBL_EPSILON 1E-9
LDBL_EPSILON 1E-9
- eini-1m normalized positive floating-point number,
b min
FLT_MIN 1E-37
DBL_MIN 1E-37
LDBL_MIN 1E-37
Examples
[#10]
1. The following describes an artificial floating-point
representation that meets the minimum requirements of
this International Standard, and the appropriate
values in a <float.h> header for type float:
e 6 -k
x = s x 16 x R fk x 16 , -31 < e < +32
k=1
page 31 Environment
page 32
FLT_RADIX 16
FLT_MANT_DIG 6
FLT_EPSILON 9.53674316E-07F
FLT_DIG 6
FLT_MIN_EXP -31
FLT_MIN 2.93873588E-39F
FLT_MIN_10_EXP -38
FLT_MAX_EXP +32
FLT_MAX 3.40282347E+38F
FLT_MAX_10_EXP +38
2. The following describes floating-point representations
that also meet the requirements for single-precision
and double-precision normalized numbers in IEC 559,19
and the appropriate values in a <float.h> header for
types float and double:
e 24 -k
xf = s x 2 x R fk x 2 , -125 < e < +128
k=1
e 53 -k
xd = s x 2 x R fk x 2 , -1021 < e < +1024
k=1
__________
19. The floating-point model in that standard sums powers of
b from zero, so the values of the exponent limits are
one less than shown here.
page 32 Environment
page 33
FLT_RADIX 2
FLT_MANT_DIG 24
FLT_EPSILON 1.19209290E-07F // decimal constant
FLT_EPSILON 0X1P-23F // hex constant
FLT_DIG 6
FLT_MIN_EXP -125
FLT_MIN 1.17549435E-38F // decimal constant
FLT_MIN 0X1P-126F // hex constant
FLT_MIN_10_EXP -37
FLT_MAX_EXP +128
FLT_MAX 3.40282347E+38F // decimal constant
FLT_MAX 0X1.fffffeP127F // hex constant
FLT_MAX_10_EXP +38
DBL_MANT_DIG 53
DBL_EPSILON 2.2204460492503131E-16 // decimal constant
DBL_EPSILON 0X1P-52 // hex constant
DBL_DIG 15
DBL_MIN_EXP -1021
DBL_MIN 2.2250738585072014E-308 // decimal constant
DBL_MIN 0X1P-1022 // hex constant
DBL_MIN_10_EXP -307
DBL_MAX_EXP +1024
DBL_MAX 1.7976931348623157E+308 // decimal constant
DBL_MAX 0X1.ffffffffffffeP1023 // hex constant
DBL_MAX_10_EXP +308
Forward references: conditional inclusion (6.8.1).
page 33 Environment
page 34
6. Language
[#1] In the syntax notation used in the language clause
(clause 6), syntactic categories (nonterminals) are
indicated by italic type, and literal words and character
set members (terminals) by bold type. A colon (:)
following a nonterminal introduces its definition.
Alternative definitions are listed on separate lines, except
when prefaced by the words ``one of.'' An optional symbol
is indicated by the suffix ``-opt,'' so that
{ expression-opt }
indicates an optional expression enclosed in braces.
6.1 Lexical elements
Syntax
[#1]
token:
keyword
identifier
constant
string-literal
operator
punctuator
preprocessing-token:
header-name
identifier
pp-number
character-constant
string-literal
operator
punctuator
each non-white-space character that cannot be one of the above
Constraints
[#2] Each preprocessing token that is converted to a token
shall have the lexical form of a keyword, an identifier, a
constant, a string literal, an operator, or a punctuator.
page 34 Language
page 35
Semantics
[#3] A token is the minimal lexical element of the language
in translation phases 7 and 8. The categories of tokens
are: keywords, identifiers, constants, string literals,
operators, and punctuators. A preprocessing token is the
minimal lexical element of the language in translation
phases 3 through 6. The categories of preprocessing token
are: header names, identifiers, preprocessing numbers,
character constants, string literals, operators,
punctuators, and single non-white-space characters that do
not lexically match the other preprocessing token
categories. If a ' or a " character matches the last
category, the behavior is undefined. Preprocessing tokens
can be separated by white space; this consists of comments
(described later), or white-space characters (space,
horizontal tab, new-line, vertical tab, and form-feed), or
both. As described in 6.8, in certain circumstances during
translation phase 4, white space (or the absence thereof)
serves as more than preprocessing token separation. White
space may appear within a preprocessing token only as part
of a header name or between the quotation characters in a
character constant or string literal.
[#4] If the input stream has been parsed into preprocessing
tokens up to a given character, the next preprocessing token
is the longest sequence of characters that could constitute
a preprocessing token.
[#5] A header name preprocessing token is only recognized
within a #include preprocessing directive, and within such a
directive, a sequence of characters that could be either a
header name or a string literal is recognized as the former.
Examples
1. The program fragment 1Ex is parsed as a preprocessing
number token (one that is not a valid floating or
integer constant token), even though a parse as the
pair of preprocessing tokens 1 and Ex might produce a
valid expression (for example, if Ex were a macro
defined as +1). Similarly, the program fragment 1E1
is parsed as a preprocessing number (one that is a
valid floating constant token), whether or not E is a
macro name.
2. The program fragment x+++++y is parsed as x+++++y,
which violates a constraint on increment operators,
even though the parse x+++++y might yield a correct
expression.
page 35 Language
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Forward references: character constants (6.1.3.4), comments
(6.1.9), expressions (6.3), floating constants (6.1.3.1),
header names (6.1.7), macro replacement (6.8.3), postfix
increment and decrement operators (6.3.2.4), prefix
increment and decrement operators (6.3.3.1), preprocessing
directives (6.8), preprocessing numbers (6.1.8), string
literals (6.1.4).
6.1.1 Keywords
Syntax
[#1]
keyword: one of
auto break case char
complex const continue default
do double else enum
extern float for goto
if imaginary inline int
long register restrict return
short signed sizeof static
struct switch typedef union
unsigned void volatile while
Semantics
[#2] The token complex is reserved in translation units
where the header <complex.h> is included; the token
imaginary is reserved in translation units where both the
header <complex.h> is included and the macro _Imaginary_I is
defined; all other keyword tokens are reserved in all
translation units. When reserved, the above tokens
(entirely in lowercase) are keywords (in translation phases
7 and 8), and shall not be used otherwise. When the token
complex or imaginary is reserved, its use prior to the first
inclusion of the header <complex.h> results in undefined
behavior.
page 36 Language
page 37
6.1.2 Identifiers
Syntax
[#1]
identifier:
nondigit
identifier nondigit
identifier digit
nondigit: one of
universal-character-name
_ a b c d e f g h i j k l m
n o p q r s t u v w x y z
A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z
digit: one of
0 1 2 3 4 5 6 7 8 9
Description
[#2] An identifier is a sequence of nondigit characters
(including the underscore _ and the lowercase and uppercase
letters) and digits. Each universal-character-name in an
identifier shall designate a character whose encoding in ISO
10646-1 falls into one of the ranges specified in Annex
H.20 The first character shall be a nondigit character.
Semantics
[#3] An identifier can denote an object, a function, or one
of the following entities that will be described later: a
tag or a member of a structure, union, or enumeration; a
typedef name; a label name; a macro name; or a macro
parameter. The same identifier can denote different
entities at different points in the program. A member of an
enumeration is called an enumeration constant. Macro names
__________
20. On systems in which linkers cannot accept extended
characters, an encoding of the universal-character-name
may be used in forming valid external identifiers. For
example, some otherwise unused character or sequence of
characters may be used to encode the \u in a universal-
character-name. Extended characters may produce a long
external identifier.
page 37 Language
page 38
and macro parameters are not considered further here,
because prior to the semantic phase of program translation
any occurrences of macro names in the source file are
replaced by the preprocessing token sequences that
constitute their macro definitions.
[#4] There is no specific limit on the maximum length of an
identifier.
[#5] When preprocessing tokens are converted to tokens
during translation phase 7, if a preprocessing token could
be converted to either a keyword or an identifier, it is
converted to a keyword.
Implementation limits
[#6] The implementation shall treat at least the first 63
characters of an internal name (a macro name or an
identifier that does not have external linkage) as
significant. The implementation may further restrict the
significance of an external name (an identifier that has
external linkage) to 31 characters. In both external and
internal names, lower-case and upper-case letters are
different. The number of significant characters in an
identifier is implementation-defined.
[#7] Any identifiers that differ in a significant character
are different identifiers. If two identifiers differ in a
nonsignificant character, the behavior is undefined.
Forward references: linkages of identifiers (6.1.2.2),
macro replacement (6.8.3).
6.1.2.1 Scopes of identifiers
[#1] For each different entity that an identifier
designates, the identifier is visible (i.e., can be used)
only within a region of program text called its scope.
Different entities designated by the same identifier either
have non-overlapping scopes, or are in different name
spaces. There are four kinds of scopes: function, file,
block, and function prototype. (A function prototype is a
declaration of a function that declares the types of its
parameters.)
[#2] A label name is the only kind of identifier that has
function scope. It can be used (in a goto statement)
anywhere in the function in which it appears, and is
declared implicitly by its syntactic appearance (followed by
a : and a statement). Label names shall be unique within a
function.
page 38 Language
page 39
[#3] Every other identifier has scope determined by the
placement of its declaration (in a declarator or type
specifier). If the declarator or type specifier that
declares the identifier appears outside of any block or list
of parameters, the identifier has file scope, which
terminates at the end of the translation unit. If the
declarator or type specifier that declares the identifier
appears inside a block or within the list of parameter
declarations in a function definition, the identifier has
block scope, which terminates at the } that closes the
associated block. If the declarator or type specifier that
declares the identifier appears within the list of parameter
declarations in a function prototype (not part of a function
definition), the identifier has function prototype scope,
which terminates at the end of the function declarator. If
an identifier designates two different entities in the same
name space, the scopes might overlap. If so, the scope of
one entity (the inner scope) will be a strict subset of the
scope of the other entity (the outer scope). Within the
inner scope, the identifier designates the entity declared
in the inner scope; the entity declared in the outer scope
is hidden (and not visible) within the inner scope.
[#4] Unless explicitly stated otherwise, where this
International Standard uses the term identifier to refer to
some entity (as opposed to the syntactic construct), it
refers to the entity in the relevant name space whose
declaration is visible at the point the identifier occurs.
[#5] Two identifiers have the same scope if and only if
their scopes terminate at the same point.
[#6] Structure, union, and enumeration tags have scope that
begins just after the appearance of the tag in a type
specifier that declares the tag. Each enumeration constant
has scope that begins just after the appearance of its
defining enumerator in an enumerator list. Any other
identifier has scope that begins just after the completion
of its declarator.
Forward references: compound statement, or block (6.6.2),
declarations (6.5), enumeration specifiers (6.5.2.2),
function calls (6.3.2.2), function declarators (including
prototypes) (6.5.5.3), function definitions (6.7.1), the
goto statement (6.6.6.1), labeled statements (6.6.1), name
spaces of identifiers (6.1.2.3), scope of macro definitions
(6.8.3.5), source file inclusion (6.8.2), tags (6.5.2.3),
type specifiers (6.5.2).
page 39 Language
page 40
6.1.2.2 Linkages of identifiers
[#1] An identifier declared in different scopes or in the
same scope more than once can be made to refer to the same
object or function by a process called linkage. There are
three kinds of linkage: external, internal, and none.
[#2] In the set of translation units and libraries that
constitutes an entire program, each instance of a particular
identifier with external linkage denotes the same object or
function. Within one translation unit, each instance of an
identifier with internal linkage denotes the same object or
function. Identifiers with no linkage denote unique
entities.
[#3] If the declaration of a file scope identifier for an
object or a function contains the storage-class specifier
static, the identifier has internal linkage.21
[#4] For an identifier declared with the storage-class
specifier extern in a scope in which a prior declaration of
that identifier is visible,22 if the prior declaration
specifies internal or external linkage, the linkage of the
identifier at the later declaration becomes the linkage
specified at the prior declaration. If no prior declaration
is visible, or if the prior declaration specifies no
linkage, then the identifier has external linkage.
[#5] If the declaration of an identifier for a function has
no storage-class specifier, its linkage is determined
exactly as if it were declared with the storage-class
specifier extern. If the declaration of an identifier for
an object has file scope and no storage-class specifier, its
linkage is external.
[#6] The following identifiers have no linkage: an
identifier declared to be anything other than an object or a
function; an identifier declared to be a function parameter;
a block scope identifier for an object declared without the
storage-class specifier extern.
__________
21. A function declaration can contain the storage-class
specifier static only if it is at file scope; see 6.5.1.
22. As specified in 6.1.2.1, the later declaration might
hide the prior declaration.
page 40 Language
page 41
[#7] If, within a translation unit, the same identifier
appears with both internal and external linkage, the
behavior is undefined.
Forward references: compound statement, or block (6.6.2),
declarations (6.5), expressions (6.3), external definitions
(6.7).
6.1.2.3 Name spaces of identifiers
[#1] If more than one declaration of a particular identifier
is visible at any point in a translation unit, the syntactic
context disambiguates uses that refer to different entities.
Thus, there are separate name spaces for various categories
of identifiers, as follows:
- label names (disambiguated by the syntax of the label
declaration and use);
- the tags of structures, unions, and enumerations
(disambiguated by following any23 of the keywords
struct, union, or enum);
- the members of structures or unions; each structure or
union has a separate name space for its members
(disambiguated by the type of the expression used to
access the member via the . or -> operator);
- all other identifiers, called ordinary identifiers
(declared in ordinary declarators or as enumeration
constants).
Forward references: enumeration specifiers (6.5.2.2),
labeled statements (6.6.1), structure and union specifiers
(6.5.2.1), structure and union members (6.3.2.3), tags
(6.5.2.3).
__________
23. There is only one name space for tags even though three
are possible.
page 41 Language
page 42
6.1.2.4 Storage durations of objects
[#1] An object has a storage duration that determines its
lifetime. There are three storage durations: static,
automatic, and allocated. Allocated storage is described in
7.14.3.
[#2] An object whose identifier is declared with external or
internal linkage, or with the storage-class specifier static
has static storage duration. For such an object, storage is
reserved and its stored value is initialized only once,
prior to program startup. The object exists, has a constant
address, and retains its last-stored value throughout the
execution of the entire program.24
[#3] An object whose identifier is declared with no linkage
and without the storage-class specifier static has automatic
storage duration. Storage is guaranteed to be reserved for
a new instance of such an object on each normal entry into
the block with which it is associated. If the block with
which the object is associated is entered by a jump from
outside the block to a labeled statement in the block or in
an enclosed block, then storage is guaranteed to be reserved
provided the object does not have a variable length array
type. If the object is variably modified and the block is
entered by a jump to a labeled statement, then the behavior
is undefined. If an initialization is specified for the
value stored in the object, it is performed on each normal
entry, but not if the block is entered by a jump to a
labeled statement beyond the declaration. A backwards jump
might cause the initializer to be evaluated more than once;
if so, a new value will be stored each time. Storage for
the object is no longer guaranteed to be reserved when
execution of the block ends in any way. (Entering an
enclosed block suspends but does not end execution of the
enclosing block. Calling a function suspends but does not
end execution of the block containing the call.) The value
of a pointer that referred to an object with automatic
storage duration that is no longer guaranteed to be reserved
__________
24. The term constant address means that two pointers to the
object constructed at possibly different times will
compare equal. The address may be different during two
different executions of the same program.
In the case of a volatile object, the last store may not
be explicit in the program.
page 42 Language
page 43
is indeterminate. During execution of the associated block,
the object has a constant address.
Forward references: compound statement, or block (6.6.2),
function calls (6.3.2.2), declarators (6.5.5), array
declarators (6.5.5.2), initialization (6.5.8).
6.1.2.5 Types
[#1] The meaning of a value stored in an object or returned
by a function is determined by the type of the expression
used to access it. (An identifier declared to be an object
is the simplest such expression; the type is specified in
the declaration of the identifier.) Types are partitioned
into object types (types that describe objects), function
types (types that describe functions), and incomplete types
(types that describe objects but lack information needed to
determine their sizes).
[#2] An object declared as type char is large enough to
store any member of the basic execution character set. If a
member of the required source character set enumerated in
5.2.1 is stored in a char object, its value is guaranteed to
be positive. If any other character is stored in a char
object, the resulting value is implementation-defined but
shall be within the range of values that can be represented
in that type.
[#3] There are five standard signed integer types,
designated as signed char, short int, int, long int, and
long long int. (These and other types may be designated in
several additional ways, as described in 6.5.2.) There may
also be implementation-defined extended signed integer
types.25 The standard and extended signed integer types are
collectively called just signed integer types.26
[#4] An object declared as type signed char occupies the
same amount of storage as a ``plain'' char object. A
``plain'' int object has the natural size suggested by the
architecture of the execution environment (large enough to
__________
25. Implementation-defined keywords must have the form of an
identifier reserved for any use as described in 7.1.3.
26. Therefore, any statement in this Standard about signed
integer types also applies to the extended signed
integer types.
page 43 Language
page 44
contain any value in the range INT_MIN to INT_MAX as defined
in the header <limits.h>).
[#5] For each of the signed integer types, there is a
corresponding (but different) unsigned integer type
(designated with the keyword unsigned) that uses the same
amount of storage (including sign information) and has the
same alignment requirements. The unsigned integer types
that correspond to the standard signed integer types are the
standard unsigned integer types. The unsigned integer types
that correspond to the extended signed integer types are the
extended unsigned integer types.
[#6] The extended signed integer types and extended unsigned
integer types are collectively called the extended integer
types.
[#7] For any two types with the same signedness and
different integer conversion rank, the range of values of
the type with smaller integer conversion rank is a subrange
of the values of the other type.
[#8] The range of nonnegative values of a signed integer
type is a subrange of the corresponding unsigned integer
type, and the representation of the same value in each type
is the same.27 A computation involving unsigned operands
can never overflow, because a result that cannot be
represented by the resulting unsigned integer type is
reduced modulo the number that is one greater than the
largest value that can be represented by the resulting
unsigned integer type.
[#9] There are three real floating types, designated as
float, double, and long double. The set of values of the
type float is a subset of the set of values of the type
double; the set of values of the type double is a subset of
the set of values of the type long double.
[#10] There are three complex types, designated as float
complex, double complex, and long double complex.28 The
__________
27. The same representation and alignment requirements are
meant to imply interchangeability as arguments to
functions, return values from functions, and members of
unions.
28. A specification for imaginary types is in informative
Annex G.
page 44 Language
page 45
real floating and complex types are collectively called the
floating types.
[#11] For each floating type there is a corresponding real
type, which is always a real floating type. For real
floating types, it is the same type. For complex types, it
is the type given by deleting the keyword complex from the
type name.
[#12] Each complex type has the same representation and
alignment requirements as an array type containing exactly
two elements of the corresponding real type; the first
element is equal to the real part, and the second element to
the imaginary part, of the complex number.
[#13] The type char, the signed and unsigned integer types,
and the floating types are collectively called the basic
types. Even if the implementation defines two or more basic
types to have the same representation, they are nevertheless
different types.29
[#14] The three types char, signed char, and unsigned char
are collectively called the character types. The
implementation shall define char to have the same range,
representation, and behavior as one of signed char and
unsigned char.30
[#15] An enumeration comprises a set of named integer
constant values. Each distinct enumeration constitutes a
different enumerated type.
[#16] The void type comprises an empty set of values; it is
an incomplete type that cannot be completed.
__________
29. An implementation may define new keywords that provide
alternative ways to designate a basic (or any other)
type. An alternate way to designed a basic type does
not violate the requirement that all basic types be
different. Implementation-defined keywords must have
the form of an identifier reserved for any use as
described in 7.1.3.
30. CHAR_MIN, defined in <limits.h>, will have one of the
values 0 or SCHAR_MIN, and this can be used to
distinguish the two options. Irrespective of the choice
made, char is a separate type from the other two, and it
not compatible with either.
page 45 Language
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[#17] Any number of derived types can be constructed from
the object, function, and incomplete types, as follows:
- An array type describes a contiguously allocated
nonempty set of objects with a particular member object
type, called the element type.31 Array types are
characterized by their element type and by the number
of elements in the array. An array type is said to be
derived from its element type, and if its element type
is T, the array type is sometimes called ``array of
T.'' The construction of an array type from an element
type is called ``array type derivation.''
- A structure type describes a sequentially allocated
nonempty set of member objects, each of which has an
optionally specified name and possibly distinct type.
- A union type describes an overlapping nonempty set of
member objects, each of which has an optionally
specified name and possibly distinct type.
- A function type describes a function with specified
return type. A function type is characterized by its
return type and the number and types of its parameters.
A function type is said to be derived from its return
type, and if its return type is T, the function type is
sometimes called ``function returning T.'' The
construction of a function type from a return type is
called ``function type derivation.''
- A pointer type may be derived from a function type, an
object type, or an incomplete type, called the
referenced type. A pointer type describes an object
whose value provides a reference to an entity of the
referenced type. A pointer type derived from the
referenced type T is sometimes called ``pointer to T.''
The construction of a pointer type from a referenced
type is called ``pointer type derivation.''
[#18] These methods of constructing derived types can be
applied recursively.
[#19] The type char, the signed and unsigned integer types,
and the enumerated types are collectively called integer
__________
31. Since object types do not include incomplete types, an
array of incomplete type cannot be constructed.
page 46 Language
page 47
types. The integer and real floating types are collectively
called real types.
[#20] Integer and floating types are collectively called
arithmetic types. Arithmetic types and pointer types are
collectively called scalar types. Array and structure types
are collectively called aggregate types.32
[#21] Each arithmetic type belongs to one type-domain. The
real type-domain comprises the real types. The complex
type-domain comprises the complex types.
[#22] An array type of unknown size is an incomplete type.
It is completed, for an identifier of that type, by
specifying the size in a later declaration (with internal or
external linkage). A structure or union type of unknown
content (as described in 6.5.2.3) is an incomplete type. It
is completed, for all declarations of that type, by
declaring the same structure or union tag with its defining
content later in the same scope.
[#23] Array, function, and pointer types are collectively
called derived declarator types. A declarator type
derivation from a type T is the construction of a derived
declarator type from T by the application of an array-type,
a function-type, or a pointer-type derivation to T.
[#24] A type is characterized by its type category, which is
either the outermost derivation of a derived type (as noted
above in the construction of derived types), or the type
itself if the type consists of no derived types.
[#25] Any type so far mentioned is an unqualified type.
Each unqualified type has several qualified versions of its
type,33 corresponding to the combinations of one, two, or
all three of the const, volatile, and restrict qualifiers.
The qualified or unqualified versions of a type are distinct
types that belong to the same type category and have the
same representation and alignment requirements.27 A derived
type is not qualified by the qualifiers (if any) of the type
from which it is derived.
__________
32. Note that aggregate type does not include union type
because an object with union type can only contain one
member at a time.
33. See 6.5.3 regarding qualified array and function types.
page 47 Language
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[#26] A pointer to void shall have the same representation
and alignment requirements as a pointer to a character type.
Similarly, pointers to qualified or unqualified versions of
compatible types shall have the same representation and
alignment requirements.27 All pointers to structure types
shall have the same representation and alignment
requirements as each other. All pointers to union types
shall have the same representation and alignment
requirements as each other. Pointers to other types need
not have the same representation or alignment requirements.
Examples
[#27]
1. The type designated as ``float *'' has type ``pointer
to float.'' Its type category is pointer, not a
floating type. The const-qualified version of this
type is designated as ``float * const'' whereas the
type designated as ``const float *'' is not a
qualified type - its type is ``pointer to const-
qualified float'' and is a pointer to a qualified
type.
2. The type designated as ``struct tag (*[5])(float)''
has type ``array of pointer to function returning
struct tag.'' The array has length five and the
function has a single parameter of type float. Its
type category is array.
Forward references: character constants (6.1.3.4),
compatible type and composite type (6.1.2.6), integer
conversion rank (6.2.1.1), declarations (6.5), tags
(6.5.2.3), type qualifiers (6.5.3).
6.1.2.6 Compatible type and composite type
[#1] Two types have compatible type if their types are the
same. Additional rules for determining whether two types
are compatible are described in 6.5.2 for type specifiers,
in 6.5.3 for type qualifiers, and in 6.5.5 for
declarators.34 Moreover, two structure, union, or
enumerated types declared in separate translation units are
compatible if their tags and members satisfy the following
requirements. If one is declared with a tag, the other
__________
34. Two types need not be identical to be compatible.
page 48 Language
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shall be declared with the same tag. If both are completed
types, then the following additional requirements apply:
there shall be a one-to-one correspondence between their
members such that each pair of corresponding members are
declared with compatible types, and such that if one member
of a corresponding pair is declared with a name, the other
member is declared with the same name. For two structures,
corresponding members shall be declared in the same order.
For two structures or unions, corresponding bit-fields shall
have the same widths. For two enumerations, corresponding
members shall have the same values.
[#2] All declarations that refer to the same object or
function shall have compatible type; otherwise, the behavior
is undefined.
[#3] A composite type can be constructed from two types that
are compatible; it is a type that is compatible with both of
the two types and satisfies the following conditions:
- If one type is an array of known constant size, the
composite type is an array of that size; otherwise, if
one type is a variable length array, the composite type
is that type.
- If only one type is a function type with a parameter
type list (a function prototype), the composite type is
a function prototype with the parameter type list.
- If both types are function types with parameter type
lists, the type of each parameter in the composite
parameter type list is the composite type of the
corresponding parameters.
These rules apply recursively to the types from which the
two types are derived.
[#4] For an identifier with internal or external linkage
declared in a scope in which a prior declaration of that
identifier is visible,35 if the prior declaration specifies
internal or external linkage, the type of the identifier at
the later declaration becomes the composite type.
__________
35. As specified in 6.1.2.1, the later declaration might
hide the prior declaration.
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Examples
[#5] Given the following two file scope declarations:
int f(int (*)(), double (*)[3]);
int f(int (*)(char *), double (*)[]);
The resulting composite type for the function is:
int f(int (*)(char *), double (*)[3]);
Forward references: declarators (6.5.5), enumeration
specifiers (6.5.2.2), structure and union specifiers
(6.5.2.1), type definitions (6.5.7), type qualifiers
(6.5.3), type specifiers (6.5.2).
6.1.2.7 Predefined identifiers
[#1] The following identifier shall be defined by the
implementation:
__func__ The name of the lexically-enclosing function.
Forward references: the identifier __func__ (6.3.1.1).
6.1.2.8 Representations of types
[#1] The representations of all types are unspecified except
as stated in this subclause.
6.1.2.8.1 General
[#1] Values of type unsigned char shall be represented using
a pure binary notation.36
[#2] When stored in objects of any other object type, values
of that type consist of n*CHAR_BIT bits, where n is the size
__________
36. A positional representation for integers that uses the
binary digits 0 and 1, in which the values represented
by successive bits are additive, begin with 1, and are
multiplied by successive integral powers of 2, except
perhaps the bit with the highest position. (Adapted
from the American National Dictionary for Information
Processing Systems.) A byte contains CHAR_BIT bits, and
the values of type unsigned char range from 0 to
2CHAR_BIT-1.
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of an object of that type, in bytes. The value may be
copied into an object of type unsigned char [n] (e.g., by
memcpy); the resulting set of bytes is called the object
representation of the value. Two values with the same
object representation shall compare equal, but values that
compare equal might have different object representations.
[#3] Certain object representations might not represent a
value of that type. If the stored value of an object has
such a representation and is accessed by an lvalue
expression that does not have character type, the behavior
is undefined. If such a representation is produced by a
side effect that modifies all or any part of the object by
an lvalue expression that does not have character type, the
behavior is undefined.37 Such representations are called
trap representations.
[#4] When a value is stored in an object of structure or
union type, including in a member object, the bytes of the
object representation that correspond to any padding bytes
take unspecified values.38 The values of padding bytes
shall not affect whether the value of such an object is a
trap representation. Those bits of a structure or union
object that are in the same byte as a bit-field member, but
are not part of that member, shall similarly not affect
whether the value of such an object is a trap
representation.
[#5] When a value is stored in a member of an object of
union type, the bytes of the object representation that do
not correspond to that member but do correspond to other
members take unspecified values, but the value of the union
object shall not thereby become a trap representation.
[#6] Where an operator is applied to a value which has more
than one object representation, which object representation
is used shall not affect the value of the result. Where a
value is stored in an object using a type that has more than
one object representation for that value, it is unspecified
__________
37. Thus an automatic variable can be initialized to a trap
representation without causing undefined behavior, but
the value of the variable cannot be used until a proper
value is stored in it.
38. Thus, for example, structure assignment may be
implemented element-at-a-time or via memcpy.
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which representation is used, but a trap representation
shall not be generated.
6.1.2.8.2 Integer types
[#1] For unsigned integer types other than unsigned char,
the bits of the object representation shall be divided into
two groups: value bits and padding bits (there need not be
any of the latter). If there are N value bits, each bit
shall represent a different power of 2 between 1 and 2N - 1,
so that objects of that type shall be capable of
representing values from 0 to 2N - 1 using a pure binary
representation; this shall be known as the value
representation. The values of any padding bits are
unspecified.39
[#2] For signed integer types, the bits of the object
representation shall be divided into three groups: value
bits, padding bits, and the sign bit. There need not be any
padding bits; there shall be exactly one sign bit. Each
bit that is a value bit shall have the same value as the
same bit in the object representation of the corresponding
unsigned type (if there are M value bits in the signed type
and N in the unsigned type, then M<N). If the sign bit is
zero, it shall not affect the resulting value. If the sign
bit is one, then the value shall be modified in one of the
following ways:
- the corresponding value with sign bit 0 is negated;
- the sign bit has the value -2N;
- the sign bit has the value 1 - 2N.
[#3] The values of any padding bits are unspecified.39 A
valid (non-trap) object representation of a signed integer
type where the sign bit is zero is a valid object
__________
39. Some combinations of padding bits might generate trap
representations, for example, if one padding bit is a
parity bit. Regardless, no arithmetic operation on
valid values can generate a trap representation other
than as part of an exception such as an overflow, and
this cannot occur with unsigned types. All other
combinations of padding bits are alternative object
representations of the value specified by the value
bits.
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representation of the corresponding unsigned type, and shall
represent the same value.
[#4] The precision of an integer type is the number of bits
it uses to represent values, excluding any sign and padding
bits. The width of an integer type is the same but
including any sign bit; thus for unsigned integer types the
two values are the same, while for signed integer types the
width is one greater than the precision.
6.1.3 Constants
Syntax
[#1]
constant:
floating-constant
integer-constant
enumeration-constant
character-constant
Constraints
[#2] The value of a constant shall be in the range of
representable values for its type.
Semantics
[#3] Each constant has a type, determined by its form and
value, as detailed later.
6.1.3.1 Floating constants
Syntax
[#1]
floating-constant:
decimal-floating-constant
hexadecimal-floating-constant
decimal-floating-constant:
fractional-constant exponent-part-opt floating-suffix-opt
digit-sequence exponent-part floating-suffix-opt
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hexadecimal-floating-constant:
0x hexadecimal-fractional-constant
binary-exponent-part floating-suffix-opt
0X hexadecimal-fractional-constant
binary-exponent-part floating-suffix-opt
0x hexadecimal-digit-sequence
binary-exponent-part floating-suffix-opt
0X hexadecimal-digit-sequence
binary-exponent-part floating-suffix-opt
fractional-constant:
digit-sequence-opt . digit-sequence
digit-sequence .
exponent-part:
e sign-opt digit-sequence
E sign-opt digit-sequence
sign: one of
+ -
digit-sequence:
digit
digit-sequence digit
hexadecimal-fractional-constant:
hexadecimal-digit-sequence-opt .
hexadecimal-digit-sequence
hexadecimal-digit-sequence .
binary-exponent-part:
p sign-opt digit-sequence
P sign-opt digit-sequence
hexadecimal-digit-sequence:
hexadecimal-digit
hexadecimal-digit-sequence hexadecimal-digit
hexadecimal-digit: one of
0 1 2 3 4 5 6 7 8 9
a b c d e f
A B C D E F
floating-suffix: one of
f l F L
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Description
[#2] A floating constant has a significand part that may be
followed by an exponent part and a suffix that specifies its
type. The components of the significand part may include a
digit sequence representing the whole-number part, followed
by a period (.), followed by a digit sequence representing
the fraction part. The components of the exponent part are
an e, E, p, or P followed by an exponent consisting of an
optionally signed digit sequence. Either the whole-number
part or the fraction part shall be present; for decimal
floating constants, either the period or the exponent part
shall be present.
Semantics
[#3] The significand part is interpreted as a (decimal or
hexadecimal) rational number; the digit sequence in the
exponent part is interpreted as a decimal integer. For
decimal floating constants, the exponent indicates the power
of 10 by which the significand part is to be scaled. For
hexadecimal floating constants, the exponent indicates the
power of 2 by which the significand part is to be scaled.
For decimal floating constants, and also for hexadecimal
floating constants when FLT_RADIX is not a power of 2, if
the scaled value is in the range of representable values
(for its type) the result is either the nearest
representable value, or the larger or smaller representable
value immediately adjacent to the nearest representable
value, chosen in an implementation-defined manner. For
hexadecimal floating constants, if FLT_RADIX is a power of 2
and the scaled value is in the range of representable values
(for its type), then the result of a hexadecimal floating
constant is correctly rounded.
[#4] An unsuffixed floating constant has type double. If
suffixed by the letter f or F, it has type float. If
suffixed by the letter l or L, it has type long double.
Recommended practice
[#5] The implementation produces a diagnostic message if a
hexadecimal constant cannot be represented exactly in its
evaluation format; the implementation then proceeds with the
translation of the program.
[#6] The translation-time conversion of floating constants
matches the execution-time conversion of character strings
by library functions, such as strtod, given matching inputs
suitable for both conversions, the same result format, and
default execution-time rounding.40
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6.1.3.2 Integer constants
Syntax
[#1]
integer-constant:
decimal-constant integer-suffix-opt
octal-constant integer-suffix-opt
hexadecimal-constant integer-suffix-opt
decimal-constant:
nonzero-digit
decimal-constant digit
octal-constant:
0
octal-constant octal-digit
hexadecimal-constant:
0x hexadecimal-digit
0X hexadecimal-digit
hexadecimal-constant hexadecimal-digit
nonzero-digit: one of
1 2 3 4 5 6 7 8 9
octal-digit: one of
0 1 2 3 4 5 6 7
integer-suffix:
unsigned-suffix long-suffix-opt
long-suffix unsigned-suffix-opt
unsigned-suffix long-long-suffix-opt
long-long-suffix unsigned-suffix-opt
unsigned-suffix: one of
u U
long-suffix: one of
l L
__________
40. The specification for the library functions recommends
more accurate conversion than required for floating
constants. See strtod (7.14.1.5).
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long-long-suffix: one of
ll LL
Description
[#2] An integer constant begins with a digit, but has no
period or exponent part. It may have a prefix that
specifies its base and a suffix that specifies its type.
[#3] A decimal constant begins with a nonzero digit and
consists of a sequence of decimal digits. An octal constant
consists of the prefix 0 optionally followed by a sequence
of the digits 0 through 7 only. A hexadecimal constant
consists of the prefix 0x or 0X followed by a sequence of
the decimal digits and the letters a (or A) through f (or F)
with values 10 through 15 respectively.
Semantics
[#4] The value of a decimal constant is computed base 10;
that of an octal constant, base 8; that of a hexadecimal
constant, base 16. The lexically first digit is the most
significant.
[#5] The type of an integer constant is the first of the
corresponding list in which its value can be represented.
Unsuffixed decimal: int, long int, long long int;
unsuffixed octal or hexadecimal: int, unsigned int, long
int, unsigned long int, long long int, unsigned long long
int; suffixed by the letter u or U: unsigned int, unsigned
long int, unsigned long long int; decimal suffixed by the
letter l or L: long int, long long int; octal or
hexadecimal suffixed by the letter l or L: long int,
unsigned long int, long long int, unsigned long long int;
suffixed by both the letters u or U and l or L: unsigned
long int, unsigned long long int; decimal suffixed by ll or
LL: long long int; octal or hexadecimal suffixed by the
letter ll or LL: long long int, unsigned long long int;
suffixed by both u or U and ll or LL: unsigned long long
int. If an integer constant can not be represented by any
type in its list, it may have an extended integer type, if
the extended integer type can represent its value. If all
of the types in the list for the constant are signed, the
extended integer type shall be signed. If all of the types
in the list for the constant are unsigned, the extended
integer type shall be unsigned. If the list contains both
signed and unsigned types, the extended integer type may be
signed or unsigned.
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6.1.3.3 Enumeration constants
Syntax
[#1]
enumeration-constant:
identifier
Semantics
[#2] An identifier declared as an enumeration constant has
type int.
Forward references: enumeration specifiers (6.5.2.2).
6.1.3.4 Character constants
Syntax
[#1]
character-constant:
'c-char-sequence'
L'c-char-sequence'
c-char-sequence:
c-char
c-char-sequence c-char
c-char:
any member of the source character set except
the single-quote ', backslash \, or new-line character
escape-sequence
universal-character-name
escape-sequence:
simple-escape-sequence
octal-escape-sequence
hexadecimal-escape-sequence
simple-escape-sequence: one of
\' \" \? \\
\a \b \f \n \r \t \v
octal-escape-sequence:
\ octal-digit
\ octal-digit octal-digit
\ octal-digit octal-digit octal-digit
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hexadecimal-escape-sequence:
\x hexadecimal-digit
hexadecimal-escape-sequence hexadecimal-digit
Description
[#2] An integer character constant is a sequence of one or
more multibyte characters enclosed in single-quotes, as in
'x' or 'ab'. A wide character constant is the same, except
prefixed by the letter L. With a few exceptions detailed
later, the elements of the sequence are any members of the
source character set; they are mapped in an implementation-
defined manner to members of the execution character set.
[#3] The single-quote ', the double-quote ", the question-
mark ?, the backslash \, and arbitrary integer values, are
representable according to the following table of escape
sequences:
single-quote ' \'
double-quote " \"
question-mark ? \?
backslash \ \\
octal integer \octal digits
hexadecimal integer \xhexadecimal digits
[#4] The double-quote " and question-mark ? are
representable either by themselves or by the escape
sequences \" and \?, respectively, but the single-quote '
and the backslash \ shall be represented, respectively, by
the escape sequences \' and \\.
[#5] The octal digits that follow the backslash in an octal
escape sequence are taken to be part of the construction of
a single character for an integer character constant or of a
single wide character for a wide character constant. The
numerical value of the octal integer so formed specifies the
value of the desired character or wide character.
[#6] The hexadecimal digits that follow the backslash and
the letter x in a hexadecimal escape sequence are taken to
be part of the construction of a single character for an
integer character constant or of a single wide character for
a wide character constant. The numerical value of the
hexadecimal integer so formed specifies the value of the
desired character or wide character.
[#7] Each octal or hexadecimal escape sequence is the
longest sequence of characters that can constitute the
escape sequence.
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[#8] In addition, certain nongraphic characters are
representable by escape sequences consisting of the
backslash \ followed by a lowercase letter: \a, \b, \f, \n,
\r, \t, and \v.41 If any other escape sequence is
encountered, the behavior is undefined.42
Constraints
[#9] The value of an octal or hexadecimal escape sequence
shall be in the range of representable values for the type
unsigned char for an integer character constant, or the
unsigned type corresponding to wchar_t for a wide character
constant.
Semantics
[#10] An integer character constant has type int. The value
of an integer character constant containing a single
character that maps to a member of the basic execution
character set is the numerical value of the representation
of the mapped character interpreted as an integer. The
value of an integer character constant containing more than
one character, or containing a character or escape sequence
not represented in the basic execution character set, is
implementation-defined. If an integer character constant
contains a single character or escape sequence, its value is
the one that results when an object with type char whose
value is that of the single character or escape sequence is
converted to type int.
[#11] A wide character constant has type wchar_t, an integer
type defined in the <stddef.h> header. The value of a wide
character constant containing a single multibyte character
that maps to a member of the extended execution character
set is the wide character (code) corresponding to that
multibyte character, as defined by the mbtowc function, with
an implementation-defined current locale. The value of a
wide character constant containing more than one multibyte
character, or containing a multibyte character or escape
sequence not represented in the extended execution character
set, is implementation-defined.
__________
41. The semantics of these characters were discussed in
5.2.2.
42. See ``future language directions'' (6.9.1).
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Examples
[#12]
1. The construction '\0' is commonly used to represent
the null character.
2. Consider implementations that use two's-complement
representation for integers and eight bits for objects
that have type char. In an implementation in which
type char has the same range of values as signed char,
the integer character constant '\xFF' has the value -
1; if type char has the same range of values as
unsigned char, the character constant '\xFF' has the
value +255 .
3. Even if eight bits are used for objects that have type
char, the construction '\x123' specifies an integer
character constant containing only one character,
since a hexadecimal escape sequence is terminated only
by a non-hexadecimal character. To specify an integer
character constant containing the two characters whose
values are '\x12' and '3', the construction '\0223'
may be used, since an octal escape sequence is
terminated after three octal digits. (The value of
this two-character integer character constant is
implementation-defined.)
4. Even if 12 or more bits are used for objects that have
type wchar_t, the construction L'\1234' specifies the
implementation-defined value that results from the
combination of the values 0123 and '4'.
Forward references: characters and integers (6.2.1.1),
common definitions <stddef.h> (7.1.6), the mbtowc function
(7.14.7.2).
6.1.4 String literals
Syntax
[#1]
string-literal:
"s-char-sequence-opt"
L"s-char-sequence-opt"
s-char-sequence:
s-char
s-char-sequence s-char
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s-char:
any member of the source character set except
the double-quote ", backslash \, or new-line character
escape-sequence
universal-character-name
Description
[#2] A character string literal is a sequence of zero or
more multibyte characters enclosed in double-quotes, as in
"xyz". A wide string literal is the same, except prefixed
by the letter L.
[#3] The same considerations apply to each element of the
sequence in a character string literal or a wide string
literal as if it were in an integer character constant or a
wide character constant, except that the single-quote ' is
representable either by itself or by the escape sequence \',
but the double-quote " shall be represented by the escape
sequence \".
Semantics
[#4] In translation phase 6, the multibyte character
sequences specified by any sequence of adjacent character
and wide string literal tokens are concatenated into a
single multibyte character sequence. If any of the tokens
are wide string literal tokens, the resulting multibyte
character sequence is treated as a wide string literal;
otherwise, it is treated as a character string literal.
[#5] In translation phase 7, a byte or code of value zero is
appended to each multibyte character sequence that results
from a string literal or literals.43 The multibyte
character sequence is then used to initialize an array of
static storage duration and length just sufficient to
contain the sequence. For character string literals, the
array elements have type char, and are initialized with the
individual bytes of the multibyte character sequence; for
wide string literals, the array elements have type wchar_t,
and are initialized with the sequence of wide characters
corresponding to the multibyte character sequence.
__________
43. A character string literal need not be a string (see
7.1.1), because a null character may be embedded in it
by a \0 escape sequence.
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[#6] These arrays need not be distinct provided their
elements have the appropriate values. If the program
attempts to modify such an array, the behavior is undefined.
Examples
[#7] This pair of adjacent character string literals
"\x12" "3"
produces a single character string literal containing the
two characters whose values are and '3', because escape
sequences are converted into single members of the execution
character set just prior to adjacent string literal
concatenation.
Forward references: common definitions <stddef.h> (7.1.6).
6.1.5 Operators
Syntax
[#1]
operator: one of
[ ] ( ) . ->
++ -- & * + - ~ ! sizeof
/ % << >> < > <= >= == != ^ | && ||
? :
= *= /= %= += -= <<= >>= &= ^= |=
, # ## <: :> %: %:%:
Constraints
[#2] The operators [ ], ( ), and ? : (independent of
spelling) shall occur in pairs, possibly separated by
expressions. The operators # and ## (also spelled %: and
%:%:, respectively) shall occur in macro-defining
preprocessing directives only.
Semantics
[#3] An operator specifies an operation to be performed (an
evaluation) that yields a value, or yields a designator, or
produces a side effect, or a combination thereof. An
operand is an entity on which an operator acts.
[#4] In all aspects of the language, these six tokens
<: :> <% %> %: %:%:
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behave, respectively, the same as these six tokens
[ ] { } # ##
except for their spelling.44
Forward references: expressions (6.3), macro replacement
(6.8.3).
6.1.6 Punctuators
Syntax
[#1]
punctuator: one of
[ ] ( ) { } * , : = ; ... #
<: :> <% %> %:
Constraints
[#2] The punctuators [ ], ( ), and { } (independent of
spelling) shall occur (after translation phase 4) in pairs,
possibly separated by expressions, declarations, or
statements. The punctuator # (also spelled %:) shall occur
in preprocessing directives only.
Semantics
[#3] A punctuator is a symbol that has independent syntactic
and semantic significance but does not specify an operation
to be performed that yields a value. Depending on context,
the same symbol may also represent an operator or part of an
operator.
Forward references: expressions (6.3), declarations (6.5),
preprocessing directives (6.8), statements (6.6).
__________
44. Thus [ and <: behave differently when ``stringized''
(see subclause 6.8.3.2), but can otherwise be freely
interchanged.
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6.1.7 Header names
Syntax
[#1]
header-name:
<h-char-sequence>
"q-char-sequence"
h-char-sequence:
h-char
h-char-sequence h-char
h-char:
any member of the source character set except
the new-line character and >
q-char-sequence:
q-char
q-char-sequence q-char
q-char:
any member of the source character set except
the new-line character and "
Semantics
[#2] The sequences in both forms of header names are mapped
in an implementation-defined manner to headers or external
source file names as specified in 6.8.2.
[#3] If the characters ', \, ", //, or /* occur in the
sequence between the < and > delimiters, the behavior is
undefined. Similarly, if the characters ', \, //, or /*
occur in the sequence between the " delimiters, the behavior
is undefined.45 A header name preprocessing token is
recognized only within a #include preprocessing directive.
__________
45. Thus, sequences of characters that resemble escape
sequences cause undefined behavior.
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Examples
[#4] The following sequence of characters:
0x3<1/a.h>1e2
#include <1/a.h>
#define const.member@$
forms the following sequence of preprocessing tokens (with
each individual preprocessing token delimited by a { on the
left and a } on the right).
{0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}
{#}{include} {<1/a.h>}
{#}{define} {const}{.}{member}{@}{$}
Forward references: source file inclusion (6.8.2).
6.1.8 Preprocessing numbers
Syntax
[#1]
pp-number:
digit
. digit
pp-number digit
pp-number nondigit
pp-number e sign
pp-number E sign
pp-number p sign
pp-number P sign
pp-number .
Description
[#2] A preprocessing number begins with a digit optionally
preceded by a period (.) and may be followed by letters,
underscores, digits, periods, and e+, e-, E+, E-, p+, p-,
P+, or P- character sequences.
[#3] Preprocessing number tokens lexically include all
floating and integer constant tokens.
Semantics
[#4] A preprocessing number does not have type or a value;
it acquires both after a successful conversion (as part of
translation phase 7) to a floating constant token or an
integer constant token.
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6.1.9 Comments
[#1] Except within a character constant, a string literal,
or a comment, the characters /* introduce a comment. The
contents of a comment are examined only to identify
multibyte characters and to find the characters */ that
terminate it.46
[#2] Except within a character constant, a string literal,
or a comment, the characters // introduce a comment that
includes all multibyte characters up to, but not including,
the next new-line character. The contents of such a comment
are examined only to identify multibyte characters and to
find the terminating new-line character.
Examples
[#3]
"a//b" // four-character string literal
#include "//e" // undefined behavior
// */ // comment, not syntax error
f = g/**//h; // equivalent to f = g / h;
//\
i(); // part of a two-line comment
/\
/ j(); // part of a two-line comment
#define glue(x,y) x##y
glue(/,/) k(); // syntax error, not comment
/*//*/ l(); // equivalent to l();
m = n//**/o
+ p; // equivalent to m = n + p;
__________
46. Thus, /* ... */ comments do not nest.
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6.2 Conversions
[#1] Several operators convert operand values from one type
to another automatically. This subclause specifies the
result required from such an implicit conversion, as well as
those that result from a cast operation (an explicit
conversion). The list in 6.2.1.7 summarizes the conversions
performed by most ordinary operators; it is supplemented as
required by the discussion of each operator in 6.3.
[#2] Conversion of an operand value to a compatible type
causes no change to the value or the representation.
Forward references: cast operators (6.3.4).
6.2.1 Arithmetic operands
6.2.1.1 Characters and integers
[#1] Every integer type has an integer conversion rank
defined as follows:
- No two signed integer types shall have the same rank,
even if they have the same representation.
- The rank of a signed integer type shall be greater than
the rank of any signed integer type with less
precision.
- The rank of any standard signed integer type shall be
greater than the rank of any extended signed integer
type with the same precision.
- The rank of long long int shall be greater than the
rank of long int, which shall be greater than the rank
of int, which shall be greater than the rank of short
int, which shall be greater than the rank of signed
char.
- The rank of any unsigned integer type shall equal the
rank of the corresponding signed integer type.
- The rank of char shall equal the rank of signed char
and unsigned char.
- The rank of any enumerated type shall equal the rank of
the compatible integer type.
- The rank of any extended signed integer type relative
to another extended signed integer type with the same
precision is implementation-defined, but still subject
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to the other rules for determining the integer
conversion rank.
- For all integer types T1, T2, and T3, if T1 has greater
rank than T2 and T2 has greater rank than T3, then T1
has greater rank than T3.
[#2] The following may be used in an expression wherever an
int or unsigned int may be used.
- An object or expression with an integer type whose
integer conversion rank is less than the rank of int
and unsigned int.
- A bit-field of type int, signed int, or unsigned int.
[#3] If an int can represent all values of the original
type, the value is converted to an int; otherwise, it is
converted to an unsigned int. These are called the integer
promotions.47 All other types are unchanged by the integer
promotions.
[#4] The integer promotions preserve value including sign.
As discussed earlier, whether a ``plain'' char is treated as
signed is implementation-defined.
Forward references: enumeration specifiers (6.5.2.2),
structure and union specifiers (6.5.2.1).
6.2.1.2 Signed and unsigned integers
[#1] When a value with integer type is converted to another
integer type, if the value can be represented by the new
type, it is unchanged.
[#2] Otherwise, if the new type is unsigned, the value is
converted by repeatedly adding or subtracting one more than
the maximum value that can be represented in the new type
until the value is in the range of the new type.
__________
47. The integer promotions are applied only as part of the
usual arithmetic conversions, to certain argument
expressions, to the operands of the unary +, -, and ~
operators, and to both operands of the shift operators,
as specified by their respective subclauses.
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[#3] Otherwise, the new type is signed and the value cannot
be represented in it; the result is implementation-defined.
6.2.1.3 Real floating and integer
[#1] When a value of real floating type is converted to
integer type, the fractional part is discarded. If the
value of the integral part cannot be represented by the
integer type, the behavior is undefined.48
[#2] When a value of integer type is converted to real
floating type, if the value being converted is in the range
of values that can be represented but cannot be represented
exactly, the result is either the nearest higher or nearest
lower value, chosen in an implementation-defined manner. If
the value being converted is outside the range of values
that can be represented, the behavior is undefined.
6.2.1.4 Real floating types
[#1] When a float is promoted to double or long double, or a
double is promoted to long double, its value is unchanged.
[#2] When a double is demoted to float or a long double to
double or float, if the value being converted is outside the
range of values that can be represented, the behavior is
undefined. If the value being converted is in the range of
values that can be represented but cannot be represented
exactly, the result is either the nearest higher or nearest
lower value, chosen in an implementation-defined manner.
6.2.1.5 Complex types
[#1] When a value of complex type is converted to another
complex type, both the real and imaginary parts follow the
conversion rules for the corresponding real types.
__________
48. The remaindering operation performed when a value of
integer type is converted to unsigned type need not be
performed when a value of real floating type is
converted to unsigned type. Thus, the range of portable
real floating values is (-1,Utype_MAX+1).
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6.2.1.6 Real and complex
[#1] When a value of real type is converted to a complex
type, the real part of the complex result value is
determined by the rules of conversion to the corresponding
real type and the imaginary part of the complex result value
is a positive zero or an unsigned zero.
[#2] When a value of complex type is converted to a real
type, the imaginary part of the complex value is discarded
and the value of the real part is converted according to the
conversion rules for the corresponding real type.
6.2.1.7 Usual arithmetic conversions
[#1] Many operators that expect operands of arithmetic type
cause conversions and yield result types in a similar way.
The purpose is to determine a common real type for the
operands and result. For the specified operands, each
operand is converted, without change of type-domain, to a
type whose corresponding real type is the common real type.
Unless explicitly stated otherwise, the common real type is
also the corresponding real type of the result, whose type-
domain is determined by the operator. This pattern is called
the usual arithmetic conversions:
First, if the corresponding real type of either operand
is long double, the other operand is converted, without
change of type-domain, to a type whose corresponding
real type is long double.
Otherwise, if the corresponding real type of either
operand is double, the other operand is converted,
without change of type-domain, to a type whose
corresponding real type is double.
Otherwise, if the corresponding real type of either
operand is float, the other operand is converted,
without change of type-domain, to a type whose
corresponding real type is float.49
Otherwise, the integer promotions are performed on both
operands. Then the following rules are applied to the
__________
49. For example, addition of a double complex and a float
entails just the conversion of the float operand to
double (and yields a double complex result).
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promoted operands:
If both operands have the same type, then no
further conversion is needed.
Otherwise, if both operands have signed integer
types or both have unsigned integer types, the
operand with the type of lesser integer conversion
rank is converted to the type of the operand with
greater rank.
Otherwise, if the operand that has unsigned
integer type has rank greater or equal to the rank
of the type of the other operand, then the operand
with signed integer type is converted to the type
of the operand with unsigned integer type.
Otherwise, if the type of the operand with signed
integer type can represent all of the values of
the type of the operand with unsigned integer
type, then the operand with unsigned integer type
is converted to the type of the operand with
signed integer type.
Otherwise, both operands are converted to the
unsigned integer type corresponding to the type of
the operand with signed integer type.
[#2] The values of floating operands and of the results of
floating expressions may be represented in greater precision
and range than that required by the type; the types are not
changed thereby.50
__________
50. The cast and assignment operators still must perform
their specified conversions, as described in 6.2.1.3 and
6.2.1.4.
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6.2.2 Other operands
6.2.2.1 Lvalues and function designators
[#1] An lvalue is an expression (with an object type or an
incomplete type other than void) that designates an
object.51 When an object is said to have a particular type,
the type is specified by the lvalue used to designate the
object. A modifiable lvalue is an lvalue that does not have
array type, does not have an incomplete type, does not have
a const-qualified type, and if it is a structure or union,
does not have any member (including, recursively, any member
or element of all contained aggregates or unions) with a
const-qualified type.
[#2] Except when it is the operand of the sizeof operator,
the unary & operator, the ++ operator, the -- operator, or
the left operand of the . operator or an assignment
operator, an lvalue that does not have array type is
converted to the value stored in the designated object (and
is no longer an lvalue). If the lvalue has qualified type,
the value has the unqualified version of the type of the
lvalue; otherwise, the value has the type of the lvalue. If
the lvalue has an incomplete type and does not have array
type, the behavior is undefined.
[#3] Except when it is the operand of the sizeof operator or
the unary & operator, or is a character string literal used
to initialize an array of character type, or is a wide
string literal used to initialize an array with element type
compatible with wchar_t, an lvalue that has type ``array of
type'' is converted to an expression that has type ``pointer
to type'' that points to the initial element of the array
object and is not an lvalue. If the array object has
register storage class, the behavior is undefined.
__________
51. The name ``lvalue'' comes originally from the assignment
expression E1 = E2, in which the left operand E1 must be
a (modifiable) lvalue. It is perhaps better considered
as representing an object ``locator value.'' What is
sometimes called ``rvalue'' is in this International
Standard described as the ``value of an expression.''
An obvious example of an lvalue is an identifier of an
object. As a further example, if E is a unary
expression that is a pointer to an object, *E is an
lvalue that designates the object to which E points.
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[#4] A function designator is an expression that has
function type. Except when it is the operand of the sizeof
operator52 or the unary & operator, a function designator
with type ``function returning type'' is converted to an
expression that has type ``pointer to function returning
type.''
Forward references: address and indirection operators
(6.3.3.2), assignment operators (6.3.16), common definitions
<stddef.h> (7.1.6), initialization (6.5.8), postfix
increment and decrement operators (6.3.2.4), prefix
increment and decrement operators (6.3.3.1), the sizeof
operator (6.3.3.4), structure and union members (6.3.2.3).
6.2.2.2 void
[#1] The (nonexistent) value of a void expression (an
expression that has type void) shall not be used in any way,
and implicit or explicit conversions (except to void) shall
not be applied to such an expression. If an expression of
any other type occurs in a context where a void expression
is required, its value or designator is discarded. (A void
expression is evaluated for its side effects.)
6.2.2.3 Pointers
[#1] A pointer to void may be converted to or from a pointer
to any incomplete or object type. A pointer to any
incomplete or object type may be converted to a pointer to
void and back again; the result shall compare equal to the
original pointer.
[#2] For any qualifier q, a pointer to a non-q-qualified
type may be converted to a pointer to the q-qualified
version of the type; the values stored in the original and
converted pointers shall compare equal.
[#3] An integer constant expression with the value 0, or
such an expression cast to type void *, is called a null
pointer constant.53 If a null pointer constant is assigned
__________
52. Because this conversion does not occur, the operand of
the sizeof operator remains a function designator and
violates the constraint in 6.3.3.4.
53. The macro NULL is defined in <stddef.h> as a null
pointer constant; see 7.1.6.
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to or compared for equality to a pointer, the constant is
converted to a pointer of that type. Such a pointer, called
a null pointer, is guaranteed to compare unequal to a
pointer to any object or function.
[#4] Conversion of a null pointer to another pointer type
yields a null pointer of that type. Any two null pointers
shall compare equal.
[#5] An integer may be converted to any pointer type. The
result is implementation-defined, might not be properly
aligned, and might not point to an entity of the referenced
type.54
[#6] Any pointer type may be converted to an integer type;
the result is implementation-defined. If the result cannot
be represented in the integer type, the behavior is
undefined. The result need not be in the range of values of
any integer type.55
[#7] A pointer to an object or incomplete type may be
converted to a pointer to a different object or incomplete
type. If the resulting pointer is not correctly aligned56
for the pointed to type, the behavior is undefined.
Otherwise, when converted back again, the result shall
compare equal to the original pointer.
[#8] A pointer to a function of one type may be converted to
a pointer to a function of another type and back again; the
result shall compare equal to the original pointer. If a
converted pointer is used to call a function that has a type
that is not compatible with the type of the called function,
the behavior is undefined.
__________
54. The mapping functions for converting a pointer to an
integer or an integer to a pointer are intended to be
consistent with the addressing structure of the
execution environment.
55. Thus, if the conversion is to unsigned int but yields a
negative value, the behavior is undefined.
56. In general, the concept correctly aligned is transitive:
if a pointer to type A is correctly aligned for a
pointer to type B, which in turn is correctly aligned
for a pointer to type C, then a pointer to type A is
correctly aligned for a pointer to type C.
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Forward references: cast operators (6.3.4), equality
operators (6.3.9), simple assignment (6.3.16.1).
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6.3 Expressions
[#1] An expression is a sequence of operators and operands
that specifies computation of a value, or that designates an
object or a function, or that generates side effects, or
that performs a combination thereof.
[#2] Between the previous and next sequence point an object
shall have its stored value modified at most once by the
evaluation of an expression. Furthermore, the prior value
shall be accessed only to determine the value to be
stored.57
[#3] Except as indicated by the syntax58 or otherwise
specified later (for the function-call operator (), &&, ||,
?:, and comma operators), the order of evaluation of
subexpressions and the order in which side effects take
place are both unspecified.
__________
57. This paragraph renders undefined statement expressions
such as
i = ++i + 1;
while allowing
i = i + 1;
58. The syntax specifies the precedence of operators in the
evaluation of an expression, which is the same as the
order of the major subclauses of this subclause, highest
precedence first. Thus, for example, the expressions
allowed as the operands of the binary + operator (6.3.6)
shall be those expressions defined in 6.3.1 through
6.3.6. The exceptions are cast expressions (6.3.4) as
operands of unary operators (6.3.3), and an operand
contained between any of the following pairs of
operators: grouping parentheses () (6.3.1),
subscripting brackets [] (6.3.2.1), function-call
parentheses () (6.3.2.2), and the conditional operator
?: (6.3.15).
Within each major subclause, the operators have the same
precedence. Left- or right-associativity is indicated
in each subclause by the syntax for the expressions
discussed therein.
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[#4] Some operators (the unary operator ~, and the binary
operators <<, >>, &, ^, and |, collectively described as
bitwise operators) shall have operands that have integer
type. These operators return values that depend on the
internal representations of integers, and have
implementation-defined and undefined aspects for signed
types.
[#5] If an exception occurs during the evaluation of an
expression (that is, if the result is not mathematically
defined or not in the range of representable values for its
type), the behavior is undefined.
[#6] The effective type of an object for an access to its
stored value is the declared type of the object, if it has
one. If a value is stored into an object having no declared
type through an lvalue having a type that is not a character
type, then the type of the lvalue becomes the effective type
of the object for that access and for subsequent accesses
that do not modify the stored value. If a value is copied
into an object having no declared type using memcpy or
memmove, or is copied as an array of character type, then
the effective type of the modified object for that access
and for subsequent accesses that do not modify the value is
the effective type of the object from which the value is
copied, if it has one. For all other accesses to an object
having no declared type, the effective type of the object is
simply the type of the lvalue used for the access.
[#7] An object shall have its stored value accessed only by
an lvalue expression that has one of the following types:59
- a type compatible with the effective type of the
object,
- a qualified version of a type compatible with the
effective type of the object,
- a type that is the signed or unsigned type
corresponding to the effective type of the object,
- a type that is the signed or unsigned type
corresponding to a qualified version of the effective
__________
59. The intent of this list is to specify those
circumstances in which an object may or may not be
aliased.
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type of the object,
- an aggregate or union type that includes one of the
aforementioned types among its members (including,
recursively, a member of a subaggregate or contained
union), or
- a character type.
[#8] A floating expression may be contracted, that is,
evaluated as though it were an atomic operation, thereby
omitting rounding errors implied by the source code and the
expression evaluation method.60 The FP_CONTRACT pragma in
<math.h> provides a way to disallow contracted expressions.
Otherwise, whether and how expressions are contracted is
implementation-defined.61
6.3.1 Primary expressions
Syntax
[#1]
primary-expr:
identifier
constant
string-literal
( expression )
Semantics
[#2] An identifier is a primary expression, provided it has
been declared as designating an object (in which case it is
an lvalue) or a function (in which case it is a function
designator).62
__________
60. A contracted expression might also omit the raising of
floating-point exception flags.
61. This license is specifically intended to allow
implementations to exploit fast machine instructions
that combine multiple C operators. As contractions
potentially undermine predictability, and can even
decrease accuracy for containing expressions, their use
must be well-defined and clearly documented.
62. Thus, an undeclared identifier is a violation of the
syntax.
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[#3] A constant is a primary expression. Its type depends
on its form and value, as detailed in 6.1.3.
[#4] A string literal is a primary expression. It is an
lvalue with type as detailed in 6.1.4.
[#5] A parenthesized expression is a primary expression.
Its type and value are identical to those of the
unparenthesized expression. It is an lvalue, a function
designator, or a void expression if the unparenthesized
expression is, respectively, an lvalue, a function
designator, or a void expression.
Forward references: declarations (6.5).
6.3.1.1 The identifier __func__
Semantics
[#1] The identifier __func__ is implicitly declared by the
translator as if, immediately following the opening brace of
each function definition, the declaration
static const char __func__[] = "function-name";
appeared, where function-name is the name of the lexically-
enclosing function.63 This name is the unadorned name of
the function.
[#2] This name is encoded as if the implicit declaration had
been written in the source character set and then translated
into the execution character set as indicated in translation
phase 5.
Examples
[#3] Consider the code fragment:
__________
63. Note that since the name __func__ is reserved for any
use by the implementation (7.1.3), if any other
identifier is explicitly declared using the name
__func__, the behavior is undefined.
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#include <stdio.h>
void myfunc(void)
{
printf("%s\n", __func__);
/* ... */
}
Each time the function is called, it will print to the
standard output stream:
myfunc
6.3.2 Postfix operators
Syntax
[#1]
postfix-expr:
primary-expr
postfix-expr [ expression ]
postfix-expr ( argument-expression-list-opt )
postfix-expr . identifier
postfix-expr -> identifier
postfix-expr ++
postfix-expr --
( type-name ) { initializer-list }
( type-name ) { initializer-list , }
argument-expression-list:
assignment-expr
argument-expression-list , assignment-expr
6.3.2.1 Array subscripting
Constraints
[#1] One of the expressions shall have type ``pointer to
object type,'' the other expression shall have integer type,
and the result has type ``type.''
Semantics
[#2] A postfix expression followed by an expression in
square brackets [] is a subscripted designation of an
element of an array object. The definition of the subscript
operator [] is that E1[E2] is identical to (*(E1+(E2))).
Because of the conversion rules that apply to the binary +
operator, if E1 is an array object (equivalently, a pointer
to the initial element of an array object) and E2 is an
integer, E1[E2] designates the E2-th element of E1 (counting
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from zero).
[#3] Successive subscript operators designate an element of
a multidimensional array object. If E is an n-dimensional
array (n>2) with dimensions ixjx ... xk, then E (used as
other than an lvalue) is converted to a pointer to an (n-
1)-dimensional array with dimensions jx ... x k. If the
unary * operator is applied to this pointer explicitly, or
implicitly as a result of subscripting, the result is the
pointed-to (n - 1)-dimensional array, which itself is
converted into a pointer if used as other than an lvalue.
It follows from this that arrays are stored in row-major
order (last subscript varies fastest).
Examples
[#4] Consider the array object defined by the declaration
int x[3][5];
Here x is a 3x5 array of ints; more precisely, x is an array
of three element objects, each of which is an array of five
ints. In the expression x[i], which is equivalent to
(*(x+(i))), x is first converted to a pointer to the initial
array of five ints. Then i is adjusted according to the
type of x, which conceptually entails multiplying i by the
size of the object to which the pointer points, namely an
array of five int objects. The results are added and
indirection is applied to yield an array of five ints. When
used in the expression x[i][j], that in turn is converted to
a pointer to the first of the ints, so x[i][j] yields an
int.
Forward references: additive operators (6.3.6), address and
indirection operators (6.3.3.2), array declarators
(6.5.5.2).
6.3.2.2 Function calls
Constraints
[#1] The expression that denotes the called function64 shall
have type pointer to function returning void or returning an
object type other than an array type.
__________
64. Most often, this is the result of converting an
identifier that is a function designator.
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[#2] If the expression that denotes the called function has
a type that includes a prototype, the number of arguments
shall agree with the number of parameters. Each argument
shall have a type such that its value may be assigned to an
object with the unqualified version of the type of its
corresponding parameter.
Semantics
[#3] A postfix expression followed by parentheses ()
containing a possibly empty, comma-separated list of
expressions is a function call. The postfix expression
denotes the called function. The list of expressions
specifies the arguments to the function.
[#4] An argument may be an expression of any object type.
In preparing for the call to a function, the arguments are
evaluated, and each parameter is assigned the value of the
corresponding argument.65 If the expression that denotes
the called function has type pointer to function returning
an object type, the function call expression has the same
type as that object type, and has the value determined as
specified in 6.6.6.4. Otherwise, the function call has type
void.
[#5] If the expression that denotes the called function has
a type that does not include a prototype, the integer
promotions are performed on each argument, and arguments
that have type float are promoted to double. These are
called the default argument promotions. If the number of
arguments does not agree with the number of parameters, the
behavior is undefined. If the function is defined with a
type that does not include a prototype, and the types of the
arguments after promotion are not compatible with those of
the parameters after promotion, the behavior is undefined,
except for the following cases:
- one promoted type is a signed integer type, the other
promoted type is the corresponding unsigned integer
__________
65. A function may change the values of its parameters, but
these changes cannot affect the values of the arguments.
On the other hand, it is possible to pass a pointer to
an object, and the function may change the value of the
object pointed to. A parameter declared to have array
or function type is converted to a parameter with a
pointer type as described in 6.7.1.
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type, and the value is representable in both types;
- one type is pointer to void and the other is a pointer
to a character type.
[#6] If the function is defined with a type that includes a
prototype, and the types of the arguments after promotion
are not compatible with the types of the parameters, or if
the prototype ends with an ellipsis (, ...), the behavior is
undefined.
[#7] If the expression that denotes the called function has
a type that includes a prototype, the arguments are
implicitly converted, as if by assignment, to the types of
the corresponding parameters, taking the type of each
parameter to be the unqualified version of its declared
type. The ellipsis notation in a function prototype
declarator causes argument type conversion to stop after the
last declared parameter. The default argument promotions
are performed on trailing arguments.
[#8] If the function is defined with a type that is not
compatible with the type (of the expression) pointed to by
the expression that denotes the called function, the
behavior is undefined.
[#9] No other conversions are performed implicitly; in
particular, the number and types of arguments are not
compared with those of the parameters in a function
definition that does not include a function prototype
declarator.
[#10] The order of evaluation of the function designator,
the arguments, and subexpressions within the arguments is
unspecified, but there is a sequence point before the actual
call.
[#11] Recursive function calls shall be permitted, both
directly and indirectly through any chain of other
functions.
Examples
[#12] In the function call
(*pf[f1()]) (f2(), f3() + f4())
the functions f1, f2, f3, and f4 may be called in any order.
All side effects shall be completed before the function
pointed to by pf[f1()] is entered.
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Forward references: function declarators (including
prototypes) (6.5.5.3), function definitions (6.7.1), the
return statement (6.6.6.4), simple assignment (6.3.16.1).
6.3.2.3 Structure and union members
Constraints
[#1] The first operand of the . operator shall have a
qualified or unqualified structure or union type, and the
second operand shall name a member of that type.
[#2] The first operand of the -> operator shall have type
``pointer to qualified or unqualified structure'' or
``pointer to qualified or unqualified union,'' and the
second operand shall name a member of the type pointed to.
Semantics
[#3] A postfix expression followed by the . operator and an
identifier designates a member of a structure or union
object. The value is that of the named member, and is an
lvalue if the first expression is an lvalue. If the first
expression has qualified type, the result has the so-
qualified version of the type of the designated member.
[#4] A postfix expression followed by the -> operator and an
identifier designates a member of a structure or union
object. The value is that of the named member of the object
to which the first expression points, and is an lvalue.66
If the first expression is a pointer to a qualified type,
the result has the so-qualified version of the type of the
designated member.
[#5] With one exception, if the value of a member of a union
object is used when the most recent store to the object was
to a different member, the behavior is implementation-
defined.67 One special guarantee is made in order to
__________
66. If &E is a valid pointer expression (where & is the
``address-of'' operator, which generates a pointer to
its operand), the expression (&E)->MOS is the same as
E.MOS.
67. The ``byte orders'' for scalar types are invisible to
isolated programs that do not indulge in type punning
(for example, by assigning to one member of a union and
inspecting the storage by accessing another member that
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simplify the use of unions: If a union contains several
structures that share a common initial sequence (see below),
and if the union object currently contains one of these
structures, it is permitted to inspect the common initial
part of any of them anywhere that a declaration of the
completed type of the union is visible. Two structures
share a common initial sequence if corresponding members
have compatible types (and, for bit-fields, the same widths)
for a sequence of one or more initial members.
Examples
[#6]
1. If f is a function returning a structure or union, and
x is a member of that structure or union, f().x is a
valid postfix expression but is not an lvalue.
2. The following is a valid fragment:
union {
struct {
int alltypes;
} n;
struct {
int type;
int intnode;
} ni;
struct {
int type;
double doublenode;
} nf;
} u;
u.nf.type = 1;
u.nf.doublenode = 3.14;
/* ... */
if (u.n.alltypes == 1)
if (sin(u.nf.doublenode) == 0.0)
/* ... */
____________________________________________________________
is an appropriately sized array of character type), but
must be accounted for when conforming to externally
imposed storage layouts.
page 86 Language
page 87
3. The following is not a valid fragment (because the
union type is not visible within function f):
struct t1 { int m; };
struct t2 { int m; };
int f(struct t1 * p1, struct t2 * p2)
{
if (p1->m < 0)
p2->m = -p2->m;
return p1->m;
}
int g()
{
union {
struct t1 s1;
struct t2 s2;
} u;
/* ... */
return f(&u.s1, &u.s2);
}
Forward references: address and indirection operators
(6.3.3.2), structure and union specifiers (6.5.2.1).
6.3.2.4 Postfix increment and decrement operators
Constraints
[#1] The operand of the postfix increment or decrement
operator shall have qualified or unqualified real or pointer
type and shall be a modifiable lvalue.
Semantics
[#2] The result of the postfix ++ operator is the value of
the operand. After the result is obtained, the value of the
operand is incremented. (That is, the value 1 of the
appropriate type is added to it.) See the discussions of
additive operators and compound assignment for information
on constraints, types, and conversions and the effects of
operations on pointers. The side effect of updating the
stored value of the operand shall occur between the previous
and the next sequence point.
[#3] The postfix -- operator is analogous to the postfix ++
operator, except that the value of the operand is
decremented (that is, the value 1 of the appropriate type is
subtracted from it).
page 87 Language
page 88
Forward references: additive operators (6.3.6), compound
assignment (6.3.16.2).
6.3.2.5 Compound literals
Constraints
[#1] The type name shall specify an object type or an array
of unknown size.
[#2] No initializer shall attempt to provide a value for an
object not contained within the entire unnamed object
specified by the compound literal.
[#3] If the compound literal occurs outside the body of a
function, the initializer list shall consist of constant
expressions.
Semantics
[#4] A postfix expression that consists of a parenthesized
type name followed by a brace-enclosed list of initializers
is a compound literal. It provides an unnamed object whose
value is given by the initializer list.68
[#5] If the type name specifies an array of unknown size,
the size is determined by the initializer list as specified
in 6.5.7, and the type of the compound literal is that of
the completed array type. Otherwise (when the type name
specifies an object type), the type of the compound literal
is that specified by the type name. In either case, the
result is an lvalue.
[#6] The value of the compound literal is that of an unnamed
object initialized by the initializer list. The object has
static storage duration if and only if the compound literal
occurs outside the body of a function; otherwise, it has
automatic storage duration associated with the enclosing
block.
[#7] All the semantic rules and constraints for initializer
lists in 6.5.8 are applicable to compound literals.69
__________
68. Note that this differs from a cast expression. For
example, a cast specifies a conversion to scalar types
or void only, and the result of a cast expression is not
an lvalue.
page 88 Language
page 89
[#8] String literals, and compound literals with const-
qualified types, need not designate distinct objects.70
Examples
[#9]
1. The file scope definition
int *p = (int []){2, 4};
initializes p to point to the first element of an
array of two ints, the first having the value two and
the second, four. The expressions in this compound
literal must be constant. The unnamed object has
static storage duration.
2. In contrast, in
void f(void)
{
int *p;
/*...*/
p = (int [2]){*p};
/*...*/
}
p is assigned the address of the first element of an
array of two ints, the first having the value
previously pointed to by p and the second, zero. The
expressions in this compound literal need not be
constant. The unnamed object has automatic storage
duration.
3. Initializers with designations can be combined with
compound literals. Structure objects created using
compound literals can be passed to functions without
depending on member order:
____________________________________________________________
69. For example, subobjects without explicit initializers
are initialized to zero.
70. This allows implementations to share storage for string
literals and constant compound literals with the same or
overlapping representations.
page 89 Language
page 90
drawline((struct point){.x=1, .y=1},
(struct point){.x=3, .y=4});
Or, if drawline instead expected pointers to struct
point:
drawline(&(struct point){.x=1, .y=1},
&(struct point){.x=3, .y=4});
4. A read-only compound literal can be specified through
constructions like:
(const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}
5. The following three expressions have different
meanings:
"/tmp/fileXXXXXX"
(char []){"/tmp/fileXXXXXX"}
(const char[]){"/tmp/fileXXXXXX"}
The first always has static storage duration and has
type array of char, but need not be modifiable; the
last two have automatic storage duration when they
occur within the body of a function, and the first of
these two is modifiable.
6. Like string literals, const-qualified compound
literals can be placed into read-only memory and can
even be shared. For example,
(const char[]){"abc"} == "abc"
might yield 1 if the literals' storage is shared.
7. Since compound literals are unnamed, a single compound
literal cannot specify a circularly linked object.
For example, there is no way to write a self-
referential compound literal that could be used as the
function argument in place of the named object
endless_zeros below:
struct int_list { int car; struct int_list *cdr; };
struct int_list endless_zeros = {0, &endless_zeros};
eval(endless_zeros);
8. Outside the body of a function, a compound literal is
an initialization of a static object; however, inside
a function body, it is an assignment to an automatic
object. Therefore, the following two loops produce
the same sequence of values for the objects associated
page 90 Language
page 91
with their respective compound literals.
for (int i = 0; i < 10; i++) {
f((struct s){.a = i, .b = 42});
}
for (int i = 0; i < 10; i++)
f((struct s){.a = i, .b = 42});
9. Each compound literal creates only a single object in
a given scope:
struct s { int i; };
int f (void)
{
struct s *p = 0, *q;
int j;
for (j = 0; j < 2; j++)
q = p, p = &((struct s){ j });
return p == q && q.i == 1;
}
The function f() always returns the value 1.
Note that if the body of the for loop were enclosed in
braces, the lifetime of the unnamed object would be
the body of the loop only, and on entry next time
around p would be pointing to an object which is no
longer guaranteed to exist, which is undefined
behavior.
6.3.3 Unary operators
Syntax
[#1]
unary-expr:
postfix-expr
++ unary-expr
-- unary-expr
unary-operator cast-expr
sizeof unary-expr
sizeof ( type-name )
unary-operator: one of
& * + - ~ !
page 91 Language
page 92
6.3.3.1 Prefix increment and decrement operators
Constraints
[#1] The operand of the prefix increment or decrement
operator shall have qualified or unqualified real or pointer
type and shall be a modifiable lvalue.
Semantics
[#2] The value of the operand of the prefix ++ operator is
incremented. The result is the new value of the operand
after incrementation. The expression ++E is equivalent to
(E+=1). See the discussions of additive operators and
compound assignment for information on constraints, types,
side effects, and conversions and the effects of operations
on pointers.
[#3] The prefix -- operator is analogous to the prefix ++
operator, except that the value of the operand is
decremented.
Forward references: additive operators (6.3.6), compound
assignment (6.3.16.2).
6.3.3.2 Address and indirection operators
Constraints
[#1] The operand of the unary & operator shall be either a
function designator, the result of a [] or unary * operator,
or an lvalue that designates an object that is not a bit-
field and is not declared with the register storage-class
specifier.
[#2] The operand of the unary * operator shall have pointer
type.
Semantics
[#3] The result of the unary & (address-of) operator is a
pointer to the object or function designated by its operand.
If the operand has type ``type'', the result has type
``pointer to type''. If the operand is the result of a
unary * operator, neither that operator nor the & operator
are evaluated, and the result shall be as if both were
omitted, even if the intermediate object does not exist,
except that the constraints on the operators still apply and
the result is not an lvalue. Similarly, if the operand is
the result of a [] operator, neither the & operator nor the
unary * that is implied by the [] are evaluated, and the
page 92 Language
page 93
result shall be as if the & operator was removed and the []
operator was changed to a + operator.
[#4] The unary * operator denotes indirection. If the
operand points to a function, the result is a function
designator; if it points to an object, the result is an
lvalue designating the object. If the operand has type
``pointer to type'', the result has type ``type''. If an
invalid value has been assigned to the pointer, the behavior
of the unary * operator is undefined.71
Forward references: storage-class specifiers (6.5.1),
structure and union specifiers (6.5.2.1).
6.3.3.3 Unary arithmetic operators
Constraints
[#1] The operand of the unary + or - operator shall have
arithmetic type; of the ~ operator, integer type; of the !
operator, scalar type.
Semantics
[#2] The result of the unary + operator is the value of its
operand. The integer promotion is performed on the operand,
and the result has the promoted type.
[#3] The result of the unary - operator is the negative of
its operand. The integer promotion is performed on the
operand, and the result has the promoted type.
__________
71. Thus &*E is equivalent to E (even if E is a null
pointer), and &(E1[E2]]) to (E1+(E2)). It is always
true that if E is a function designator or an lvalue
that is a valid operand of the unary & operator, *&E is
a function designator or an lvalue equal to E. If *P is
an lvalue and T is the name of an object pointer type,
*(T)P is an lvalue that has a type compatible with that
to which T points.
Among the invalid values for dereferencing a pointer by
the unary * operator are a null pointer, an address
inappropriately aligned for the type of object pointed
to, and the address of an automatic storage duration
object when execution of the block with which the object
is associated has terminated.
page 93 Language
page 94
[#4] The result of the ~ operator is the bitwise complement
of its operand (that is, each bit in the result is set if
and only if the corresponding bit in the converted operand
is not set). The integer promotion is performed on the
operand, and the result has the promoted type. The
expression ~E is equivalent to (ULLONG_MAX-E) if E is
promoted to type unsigned long long, to (ULONG_MAX-E) if E
is promoted to type unsigned long, to (UINT_MAX-E) if E is
promoted to type unsigned int. (The constants ULLONG_MAX,
ULONG_MAX, and UINT_MAX are defined in the header
<limits.h>.)
[#5] The result of the logical negation operator ! is 0 if
the value of its operand compares unequal to 0, 1 if the
value of its operand compares equal to 0. The result has
type int. The expression !E is equivalent to (0==E).
Forward references: limits <float.h> and <limits.h>
(7.1.5).
6.3.3.4 The sizeof operator
Constraints
[#1] The sizeof operator shall not be applied to an
expression that has function type or an incomplete type, to
the parenthesized name of such a type, or to an lvalue that
designates a bit-field object.
Semantics
[#2] The sizeof operator yields the size (in bytes) of its
operand, which may be an expression or the parenthesized
name of a type. The size is determined from the type of the
operand. The result is an integer. If the type of the
operand is a variable length array type, the operand is
evaluated; otherwise, the operand is not evaluated and the
result is an integer constant.
[#3] When applied to an operand that has type char, unsigned
char, or signed char, (or a qualified version thereof) the
result is 1. When applied to an operand that has array
type, the result is the total number of bytes in the
array.72 When applied to an operand that has structure or
__________
72. When applied to a parameter declared to have array or
function type, the sizeof operator yields the size of
the pointer obtained by converting as in 6.2.2.1; see
page 94 Language
page 95
union type, the result is the total number of bytes in such
an object, including internal and trailing padding.
[#4] The value of the result is implementation-defined, and
its type (an unsigned integer type) is size_t defined in the
<stddef.h> header.
Examples
[#5]
1. A principal use of the sizeof operator is in
communication with routines such as storage allocators
and I/O systems. A storage-allocation function might
accept a size (in bytes) of an object to allocate and
return a pointer to void. For example:
extern void *alloc(size_t);
double *dp = alloc(sizeof *dp);
The implementation of the alloc function should ensure
that its return value is aligned suitably for
conversion to a pointer to double.
2. Another use of the sizeof operator is to compute the
number of elements in an array:
sizeof array / sizeof array[0]
3. In this example, the size of a variable-length array
is computed and returned from a function:
size_t fsize3 (int n)
{
char b[n+3]; // Variable length array.
return sizeof b; // Execution time sizeof.
}
int main()
{
size_t size;
size = fsize3(10); // fsize3 returns 13.
return 0;
}
____________________________________________________________
6.7.1.
page 95 Language
page 96
Forward references: common definitions <stddef.h> (7.1.6),
declarations (6.5), structure and union specifiers
(6.5.2.1), type names (6.5.6), array declarators (6.5.5.2).
6.3.4 Cast operators
Syntax
[#1]
cast-expr:
unary-expr
( type-name ) cast-expr
Constraints
[#2] Unless the type name specifies a void type, the type
name shall specify qualified or unqualified scalar type and
the operand shall have scalar type.
[#3] Conversions that involve pointers, other than where
permitted by the constraints of 6.3.16.1, shall be specified
by means of an explicit cast.
Semantics
[#4] Preceding an expression by a parenthesized type name
converts the value of the expression to the named type.
This construction is called a cast.73 A cast that specifies
no conversion has no effect on the type or value of an
expression.74
__________
73. A cast does not yield an lvalue. Thus, a cast to a
qualified type has the same effect as a cast to the
unqualified version of the type.
74. If the value of the expression is represented with
greater precision or range than required by the type
named by the cast (6.2.1.7), then the cast specifies a
conversion even if the type of the expression is the
same as the named type.
page 96 Language
page 97
Forward references: equality operators (6.3.9), function
declarators (including prototypes) (6.5.5.3), simple
assignment (6.3.16.1), type names (6.5.6).
6.3.5 Multiplicative operators
Syntax
[#1]
multiplicative-expr:
cast-expr
multiplicative-expr * cast-expr
multiplicative-expr / cast-expr
multiplicative-expr % cast-expr
Constraints
[#2] Each of the operands shall have arithmetic type. The
operands of the % operator shall have integer type.
Semantics
[#3] The usual arithmetic conversions are performed on the
operands.
[#4] The result of the binary * operator is the product of
the operands.
[#5] The result of the / operator is the quotient from the
division of the first operand by the second; the result of
the % operator is the remainder. In both operations, if the
value of the second operand is zero, the behavior is
undefined.
[#6] When integers are divided, the result of the / operator
is the algebraic quotient with any fractional part
discarded.75 If the quotient a/b is representable, the
expression (a/b)*b + a%b shall equal a.
[#7] If either operand has complex type, the result has
complex type.
__________
75. This is often called ``truncation toward zero''.
page 97 Language
page 98
6.3.6 Additive operators
Syntax
[#1]
additive-expr:
multiplicative-expr
additive-expr + multiplicative-expr
additive-expr - multiplicative-expr
Constraints
[#2] For addition, either both operands shall have
arithmetic type, or one operand shall be a pointer to an
object type and the other shall have integer type.
(Incrementing is equivalent to adding 1.)
[#3] For subtraction, one of the following shall hold:
- both operands have arithmetic type;
- both operands are pointers to qualified or unqualified
versions of compatible object types; or
- the left operand is a pointer to an object type and the
right operand has integer type. (Decrementing is
equivalent to subtracting 1.)
Semantics
[#4] If both operands have arithmetic type, the usual
arithmetic conversions are performed on them.
[#5] The result of the binary + operator is the sum of the
operands.
[#6] The result of the binary - operator is the difference
resulting from the subtraction of the second operand from
the first.
[#7] For the purposes of these operators, a pointer to a
nonarray object behaves the same as a pointer to the first
element of an array of length one with the type of the
object as its element type.
[#8] When an expression that has integer type is added to or
subtracted from a pointer, the result has the type of the
pointer operand. If the pointer operand points to an
element of an array object, and the array is large enough,
the result points to an element offset from the original
page 98 Language
page 99
element such that the difference of the subscripts of the
resulting and original array elements equals the integer
expression. In other words, if the expression P points to
the i-th element of an array object, the expressions (P)+N
(equivalently, N+(P)) and (P)-N (where N has the value n)
point to, respectively, the i+n-th and i- n-th elements of
the array object, provided they exist. Moreover, if the
expression P points to the last element of an array object,
the expression (P)+1 points one past the last element of the
array object, and if the expression Q points one past the
last element of an array object, the expression (Q)-1 points
to the last element of the array object. If both the
pointer operand and the result point to elements of the same
array object, or one past the last element of the array
object, the evaluation shall not produce an overflow;
otherwise, the behavior is undefined. Unless both the
pointer operand and the result point to elements of the same
array object, or the pointer operand points one past the
last element of an array object and the result points to an
element of the same array object, the behavior is undefined
if the result is used as an operand of a unary * operator
that is actually evaluated.
[#9] When two pointers to elements of the same array object
are subtracted, the result is the difference of the
subscripts of the two array elements. The size of the
result is implementation-defined, and its type (a signed
integer type) is ptrdiff_t defined in the <stddef.h> header.
If the result is not representable in an object of that
type, the behavior is undefined. In other words, if the
expressions P and Q point to, respectively, the i-th and j-
th elements of an array object, the expression (P)-(Q) has
the value i-j provided the value fits in an object of type
ptrdiff_t. Moreover, if the expression P points either to
an element of an array object or one past the last element
of an array object, and the expression Q points to the last
element of the same array object, the expression ((Q)+1)-(P)
has the same value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and
has the value zero if the expression P points one past the
last element of the array object, even though the expression
(Q)+1 does not point to an element of the array object.
Unless both pointers point to elements of the same array
object, or one past the last element of the array object,
the behavior is undefined.76
__________
76. Another way to approach pointer arithmetic is first to
convert the pointer(s) to character pointer(s): In this
scheme the integer expression added to or subtracted
page 99 Language
page 100
[#10] If either operand has complex type, the result has
complex type.
Examples
[#11] Pointer arithmetic is well defined with pointers to
variable length array types.
{
int n = 4, m = 3;
int a[n][m];
int (*p)[m] = a; // p == &a[0]
p += 1; // p == &a[1]
(*p)[2] = 99; // a[1][2] == 99
n = p - a; // n == 1
}
[#12] If array a in the above example is declared to be an
array of known constant size, and pointer p is declared to
be a pointer to an array of the same know constant size that
points to a, the results are the same.
Forward references: array declarators (6.5.5.2), common
definitions <stddef.h> (7.1.6).
____________________________________________________________
from the converted pointer is first multiplied by the
size of the object originally pointed to, and the
resulting pointer is converted back to the original
type. For pointer subtraction, the result of the
difference between the character pointers is similarly
divided by the size of the object originally pointed to.
When viewed in this way, an implementation need only
provide one extra byte (which may overlap another object
in the program) just after the end of the object in
order to satisfy the ``one past the last element''
requirements.
page 100 Language
page 101
6.3.7 Bitwise shift operators
Syntax
[#1]
shift-expr:
additive-expr
shift-expr << additive-expr
shift-expr >> additive-expr
Constraints
[#2] Each of the operands shall have integer type.
Semantics
[#3] The integer promotions are performed on each of the
operands. The type of the result is that of the promoted
left operand. If the value of the right operand is negative
or is greater than or equal to the number of value and sign
bits in the object representation of the promoted left
operand, the behavior is undefined.
[#4] The result of E1 << E2 is E1 left-shifted E2 bit
positions; vacated bits are filled with zeros. If E1 has an
unsigned type, the value of the result is E1 x 2E2, reduced
modulo ULLONG_MAX+1 if E1 has type unsigned long long,
ULONG_MAX+1 if E1 has type unsigned long, UINT_MAX+1
otherwise. (The constants ULLONG_MAX, ULONG_MAX, and
UINT_MAX are defined in the header <limits.h>.) If E1 has a
signed type and nonnegative value, and E1x2E2 is less than
or equal to INT_MAX (if E1 has type int), LONG_MAX (if E1
has type long int), or LLONG_MAX (if E1 has type long long
int), then that is the resulting value. Otherwise, the
behavior is undefined.
[#5] The result of E1 >> E2 is E1 right-shifted E2 bit
positions. If E1 has an unsigned type or if E1 has a signed
type and a nonnegative value, the value of the result is the
integral part of the quotient of E1 divided by the quantity,
2 raised to the power E2. If E1 has a signed type and a
negative value, the resulting value is implementation-
defined.
page 101 Language
page 102
6.3.8 Relational operators
Syntax
[#1]
relational-expr:
shift-expr
relational-expr < shift-expr
relational-expr > shift-expr
relational-expr <= shift-expr
relational-expr >= shift-expr
Constraints
[#2] One of the following shall hold:
- both operands have real type;
- both operands are pointers to qualified or unqualified
versions of compatible object types; or
- both operands are pointers to qualified or unqualified
versions of compatible incomplete types.
Semantics
[#3] If both of the operands have arithmetic type, the usual
arithmetic conversions are performed.
[#4] For the purposes of these operators, a pointer to a
nonarray object behaves the same as a pointer to the first
element of an array of length one with the type of the
object as its element type.
[#5] When two pointers are compared, the result depends on
the relative locations in the address space of the objects
pointed to. If two pointers to object or incomplete types
both point to the same object, or both point one past the
last element of the same array object, they compare equal.
If the objects pointed to are members of the same aggregate
object, pointers to structure members declared later compare
greater than pointers to members declared earlier in the
structure, and pointers to array elements with larger
subscript values compare greater than pointers to elements
of the same array with lower subscript values. All pointers
to members of the same union object compare equal. If the
expression P points to an element of an array object and the
expression Q points to the last element of the same array
object, the pointer expression Q+1 compares greater than P.
In all other cases, the behavior is undefined.
page 102 Language
page 103
[#6] Each of the operators < (less than), > (greater than),
<= (less than or equal to), and >= (greater than or equal
to) shall yield 1 if the specified relation is true and 0 if
it is false.77 The result has type int.
6.3.9 Equality operators
Syntax
[#1]
equality-expr:
relational-expr
equality-expr == relational-expr
equality-expr != relational-expr
Constraints
[#2] One of the following shall hold:
- both operands have arithmetic type;
- both operands are pointers to qualified or unqualified
versions of compatible types;
- one operand is a pointer to an object or incomplete
type and the other is a pointer to a qualified or
unqualified version of void; or
- one operand is a pointer and the other is a null
pointer constant.
Semantics
[#3] The == (equal to) and the != (not equal to) operators
are analogous to the relational operators except for their
lower precedence.78 Where the operands have types and
values suitable for the relational operators, the semantics
detailed in 6.3.8 apply.
__________
77. The expression a<b<c is not interpreted as in ordinary
mathematics. As the syntax indicates, it means (a<b)<c;
in other words, ``if a is less than b compare 1 to c;
otherwise, compare 0 to c.''
78. Because of the precedences, a<b == c<d is 1 whenever a<b
and c<d have the same truth-value.
page 103 Language
page 104
[#4] If two pointers to object or incomplete types are both
null pointers, they compare equal. If two pointers to
object or incomplete types compare equal, they both are null
pointers, or both point to the same object, or both point
one past the last element of the same array object.79 If
two pointers to function types are both null pointers or
both point to the same function, they compare equal. If two
pointers to function types compare equal, either both are
null pointers, or both point to the same function. If one
of the operands is a pointer to an object or incomplete type
and the other has type pointer to a qualified or unqualified
version of void, the pointer to an object or incomplete type
is converted to the type of the other operand.
[#5] Values of complex types are equal if and only if both
their real parts are equal and also their imaginary parts
are equal. Any two values of arithmetic types from
different type-domains are equal if and only if the results
of their conversion to the complex type corresponding to the
common real type determined by the usual arithmetic
conversions are equal.
6.3.10 Bitwise AND operator
Syntax
[#1]
AND-expr:
equality-expr
AND-expr & equality-expr
Constraints
[#2] Each of the operands shall have integer type.
Semantics
[#3] The usual arithmetic conversions are performed on the
operands.
[#4] The result of the binary & operator is the bitwise AND
of the operands (that is, each bit in the result is set if
__________
79. If invalid prior pointer operations, such as accesses
outside array bounds, produced undefined behavior, the
effect of subsequent comparisons is undefined.
page 104 Language
page 105
and only if each of the corresponding bits in the converted
operands is set).
6.3.11 Bitwise exclusive OR operator
Syntax
[#1]
exclusive-OR-expr:
AND-expr
exclusive-OR-expr ^ AND-expr
Constraints
[#2] Each of the operands shall have integer type.
Semantics
[#3] The usual arithmetic conversions are performed on the
operands.
[#4] The result of the ^ operator is the bitwise exclusive
OR of the operands (that is, each bit in the result is set
if and only if exactly one of the corresponding bits in the
converted operands is set).
6.3.12 Bitwise inclusive OR operator
Syntax
[#1]
inclusive-OR-expr:
exclusive-OR-expr
inclusive-OR-expr | exclusive-OR-expr
Constraints
[#2] Each of the operands shall have integer type.
Semantics
[#3] The usual arithmetic conversions are performed on the
operands.
[#4] The result of the | operator is the bitwise inclusive
OR of the operands (that is, each bit in the result is set
if and only if at least one of the corresponding bits in the
converted operands is set).
page 105 Language
page 106
6.3.13 Logical AND operator
Syntax
[#1]
logical-AND-expr:
inclusive-OR-expr
logical-AND-expr && inclusive-OR-expr
Constraints
[#2] Each of the operands shall have scalar type.
Semantics
[#3] The && operator shall yield 1 if both of its operands
compare unequal to 0; otherwise, it yields 0. The result
has type int.
[#4] Unlike the bitwise binary & operator, the && operator
guarantees left-to-right evaluation; there is a sequence
point after the evaluation of the first operand. If the
first operand compares equal to 0, the second operand is not
evaluated.
6.3.14 Logical OR operator
Syntax
[#1]
logical-OR-expr:
logical-AND-expr
logical-OR-expr || logical-AND-expr
Constraints
[#2] Each of the operands shall have scalar type.
Semantics
[#3] The || operator shall yield 1 if either of its operands
compare unequal to 0; otherwise, it yields 0. The result
has type int.
[#4] Unlike the bitwise | operator, the || operator
guarantees left-to-right evaluation; there is a sequence
point after the evaluation of the first operand. If the
first operand compares unequal to 0, the second operand is
not evaluated.
page 106 Language
page 107
6.3.15 Conditional operator
Syntax
[#1]
conditional-expr:
logical-OR-expr
logical-OR-expr ? expr : conditional-expr
Constraints
[#2] The first operand shall have scalar type.
[#3] One of the following shall hold for the second and
third operands:
- both operands have arithmetic type;
- both operands have compatible structure or union types;
- both operands have void type;
- both operands are pointers to qualified or unqualified
versions of compatible types;
- one operand is a pointer and the other is a null
pointer constant; or
- one operand is a pointer to an object or incomplete
type and the other is a pointer to a qualified or
unqualified version of void.
Semantics
[#4] The first operand is evaluated; there is a sequence
point after its evaluation. The second operand is evaluated
only if the first compares unequal to 0; the third operand
is evaluated only if the first compares equal to 0; the
value of the second or third operand (whichever is
evaluated) is the result.80
[#5] If both the second and third operands have arithmetic
type, the usual arithmetic conversions are performed to
bring them to a common type and the result has that type.
__________
80. A conditional expression does not yield an lvalue.
page 107 Language
page 108
If both the operands have structure or union type, the
result has that type. If both operands have void type, the
result has void type.
[#6] If both the second and third operands are pointers or
one is a null pointer constant and the other is a pointer,
the result type is a pointer to a type qualified with all
the type qualifiers of the types pointed-to by both
operands. Furthermore, if both operands are pointers to
compatible types or differently qualified versions of a
compatible type, the result has the composite type; if one
operand is a null pointer constant, the result has the type
of the other operand; otherwise, one operand is a pointer to
void or a qualified version of void, in which case the other
operand is converted to type pointer to void, and the result
has that type.
Examples
[#7] The common type that results when the second and third
operands are pointers is determined in two independent
stages. The appropriate qualifiers, for example, do not
depend on whether the two pointers have compatible types.
[#8] Given the declarations
const void *c_vp;
void *vp;
const int *c_ip;
volatile int *v_ip;
int *ip;
const char *c_cp;
the third column in the following table is the common type
that is the result of a conditional expression in which the
first two columns are the second and third operands (in
either order):
c_vp c_ip const void *
v_ip 0 volatile int *
c_ip v_ip const volatile int *
vp c_cp const void *
ip c_ip const int *
vp ip void *
page 108 Language
page 109
6.3.16 Assignment operators
Syntax
[#1]
assignment-expr:
conditional-expr
unary-expr assignment-operator assignment-expr
assignment-operator: one of
= *= /= %= += -= <<= >>= &= ^= |=
Constraints
[#2] An assignment operator shall have a modifiable lvalue
as its left operand.
Semantics
[#3] An assignment operator stores a value in the object
designated by the left operand. An assignment expression
has the value of the left operand after the assignment, but
is not an lvalue. The type of an assignment expression is
the type of the left operand unless the left operand has
qualified type, in which case it is the unqualified version
of the type of the left operand. The side effect of
updating the stored value of the left operand shall occur
between the previous and the next sequence point.
[#4] The order of evaluation of the operands is unspecified.
6.3.16.1 Simple assignment
Constraints
[#1] One of the following shall hold:81
- the left operand has qualified or unqualified
arithmetic type and the right has arithmetic type;
__________
81. The asymmetric appearance of these constraints with
respect to type qualifiers is due to the conversion
(specified in 6.2.2.1) that changes lvalues to ``the
value of the expression'' which removes any type
qualifiers from the type category of the expression.
page 109 Language
page 110
- the left operand has a qualified or unqualified version
of a structure or union type compatible with the type
of the right;
- both operands are pointers to qualified or unqualified
versions of compatible types, and the type pointed to
by the left has all the qualifiers of the type pointed
to by the right;
- one operand is a pointer to an object or incomplete
type and the other is a pointer to a qualified or
unqualified version of void, and the type pointed to by
the left has all the qualifiers of the type pointed to
by the right; or
- the left operand is a pointer and the right is a null
pointer constant.
Semantics
[#2] In simple assignment (=), the value of the right
operand is converted to the type of the assignment
expression and replaces the value stored in the object
designated by the left operand.
[#3] If the value being stored in an object is accessed from
another object that overlaps in any way the storage of the
first object, then the overlap shall be exact and the two
objects shall have qualified or unqualified versions of a
compatible type; otherwise, the behavior is undefined.
Examples
[#4]
1. In the program fragment
int f(void);
char c;
/* ... */
if ((c = f()) == -1)
/* ... */
the int value returned by the function may be
truncated when stored in the char, and then converted
back to int width prior to the comparison. In an
implementation in which ``plain'' char has the same
range of values as unsigned char (and char is narrower
than int), the result of the conversion cannot be
negative, so the operands of the comparison can never
compare equal. Therefore, for full portability, the
page 110 Language
page 111
variable c should be declared as int.
2. In the fragment:
char c;
int i;
long l;
l = (c = i);
the value of i is converted to the type of the
assignment-expression c = i, that is, char type. The
value of the expression enclosed in parentheses is
then converted to the type of the outer assignment-
expression, that is, long type.
6.3.16.2 Compound assignment
Constraints
[#1] For the operators += and -= only, either the left
operand shall be a pointer to an object type and the right
shall have integer type, or the left operand shall have
qualified or unqualified arithmetic type and the right shall
have arithmetic type.
[#2] For the other operators, each operand shall have
arithmetic type consistent with those allowed by the
corresponding binary operator.
Semantics
[#3] A compound assignment of the form E1 op= E2 differs
from the simple assignment expression E1 = E1 op (E2) only
in that the lvalue E1 is evaluated only once.
6.3.17 Comma operator
Syntax
[#1]
expression:
assignment-expr
expression , assignment-expr
page 111 Language
page 112
Semantics
[#2] The left operand of a comma operator is evaluated as a
void expression; there is a sequence point after its
evaluation. Then the right operand is evaluated; the result
has its type and value.82
Examples
[#3] As indicated by the syntax, in contexts where a comma
is a punctuator (in lists of arguments to functions and
lists of initializers) the comma operator as described in
this subclause cannot appear. On the other hand, it can be
used within a parenthesized expression or within the second
expression of a conditional operator in such contexts. In
the function call
f(a, (t=3, t+2), c)
the function has three arguments, the second of which has
the value 5.
Forward references: initialization (6.5.8).
__________
82. A comma operator does not yield an lvalue.
page 112 Language
page 113
6.4 Constant expressions
Syntax
[#1]
constant-expression:
conditional-expression
Description
[#2] A constant expression can be evaluated during
translation rather than runtime, and accordingly may be used
in any place that a constant may be.
Constraints
[#3] Constant expressions shall not contain assignment,
increment, decrement, function-call, or comma operators,
except when they are contained within the operand of a
sizeof operator.83
[#4] Each constant expression shall evaluate to a constant
that is in the range of representable values for its type.
Semantics
[#5] An expression that evaluates to a constant is required
in several contexts.84 If a floating expression is
evaluated in the translation environment, the arithmetic
precision and range shall be at least as great as if the
expression were being evaluated in the execution
environment.
[#6] An integer constant expression shall have integer type
and shall only have operands that are integer constants,
__________
83. The operand of a sizeof operator is not evaluated
(6.3.3.4), and thus any operator in 6.3 may be used.
84. An integer constant expression must be used to specify
the size of a bit-field member of a structure, the value
of an enumeration constant, the size of an array, or the
value of a case constant. Further constraints that
apply to the integer constant expressions used in
conditional-inclusion preprocessing directives are
discussed in 6.8.1.
page 113 Language
page 114
enumeration constants, character constants, sizeof
expressions whose operand does not have variable length
array type or a parenthesized name of such a type, and
floating constants that are the immediate operands of casts.
Cast operators in an integer constant expression shall only
convert arithmetic types to integer types, except as part of
an operand to the sizeof operator.
[#7] More latitude is permitted for constant expressions in
initializers. Such a constant expression shall be, or
evaluate to, one of the following:
- an arithmetic constant expression,
- a null pointer constant,
- an address constant, or
- an address constant for an object type plus or minus an
integer constant expression.
[#8] An arithmetic constant expression shall have arithmetic
type and shall only have operands that are integer
constants, floating constants, enumeration constants,
character constants, and sizeof expressions. Cast operators
in an arithmetic constant expression shall only convert
arithmetic types to arithmetic types, except as part of an
operand to the sizeof operator.
[#9] An address constant is a null pointer, a pointer to an
lvalue designating an object of static storage duration, or
to a function designator; it shall be created explicitly
using the unary & operator or an integer constant cast to
pointer type, or implicitly by the use of an expression of
array or function type. The array-subscript [] and member-
access . and -> operators, the address & and indirection *
unary operators, and pointer casts may be used in the
creation of an address constant, but the value of an object
shall not be accessed by use of these operators.
[#10] An implementation may accept other forms of constant
expressions.
[#11] The semantic rules for the evaluation of a constant
expression are the same as for nonconstant expressions.85
__________
85. Thus, in the following initialization,
page 114 Language
page 115
Forward references: array declarators (6.5.5.2),
initialization (6.5.8).
____________________________________________________________
static int i = 2 || 1 / 0;
the expression is a valid integer constant expression
with value one.
page 115 Language
page 116
6.5 Declarations
Syntax
[#1]
declaration:
declaration-specifiers init-declarator-list-opt ;
declaration-specifiers:
storage-class-specifier declaration-specifiers-opt
type-specifier declaration-specifiers-opt
type-qualifier declaration-specifiers-opt
function-specifiers
init-declarator-list:
init-declarator
init-declarator-list , init-declarator
init-declarator:
declarator
declarator = initializer
Constraints
[#2] A declaration shall declare at least a declarator
(excluding the parameters of a function or the members of a
structure or union), a tag, or the members of an
enumeration.
[#3] If an identifier has no linkage, there shall be no more
than one declaration of the identifier (in a declarator or
type specifier) with the same scope and in the same name
space, except for tags as specified in 6.5.2.3.
[#4] All declarations in the same scope that refer to the
same object or function shall specify compatible types.
Semantics
[#5] A declaration specifies the interpretation and
attributes of a set of identifiers. A definition of an
identifier is a declaration for that identifier that:
- for an object, causes storage to be reserved for that
object;
- for a function, includes the function body;86
page 116 Language
page 117
- for an enumeration constant or typedef name, is the
(only) declaration of the identifier.
[#6] The declaration specifiers consist of a sequence of
specifiers that indicate the linkage, storage duration, and
part of the type of the entities that the declarators
denote. The init-declarator-list is a comma-separated
sequence of declarators, each of which may have additional
type information, or an initializer, or both. The
declarators contain the identifiers (if any) being declared.
[#7] If an identifier for an object is declared with no
linkage, the type for the object shall be complete by the
end of its declarator, or by the end of its init-declarator
if it has an initializer.
Forward references: declarators (6.5.5), enumeration
specifiers (6.5.2.2), initialization (6.5.8), tags
(6.5.2.3).
6.5.1 Storage-class specifiers
Syntax
[#1]
storage-class-specifier:
typedef
extern
static
auto
register
Constraints
[#2] At most, one storage-class specifier may be given in
the declaration specifiers in a declaration.87
__________
86. Function definitions have a different syntax, described
in 6.7.1.
87. See ``future language directions'' (6.9.2).
page 117 Language
page 118
Semantics
[#3] The typedef specifier is called a ``storage-class
specifier'' for syntactic convenience only; it is discussed
in 6.5.7. The meanings of the various linkages and storage
durations were discussed in 6.1.2.2 and 6.1.2.4.
[#4] A declaration of an identifier for an object with
storage-class specifier register suggests that access to the
object be as fast as possible. The extent to which such
suggestions are effective is implementation-defined.88
[#5] The declaration of an identifier for a function that
has block scope shall have no explicit storage-class
specifier other than extern.
[#6] If an aggregate or union object is declared with a
storage-class specifier other than typedef, the properties
resulting from the storage-class specifier, except with
respect to linkage, also apply to the members of the object,
and so on recursively for any aggregate or union member
objects.
Forward references: type definitions (6.5.7).
__________
88. The implementation may treat any register declaration
simply as an auto declaration. However, whether or not
addressable storage is actually used, the address of any
part of an object declared with storage-class specifier
register may not be computed, either explicitly (by use
of the unary & operator as discussed in 6.3.3.2) or
implicitly (by converting an array name to a pointer as
discussed in 6.2.2.1). Thus the only operator that can
be applied to an array declared with storage-class
specifier register is sizeof.
page 118 Language
page 119
6.5.2 Type specifiers
Syntax
[#1]
type-specifier:
void
char
short
int
long
float
double
complex
signed
unsigned
struct-or-union-specifier
enum-specifier
typedef-name
Constraints
[#2] At least one type specifier shall be given in the
declaration specifiers in a declaration. Each list of type
specifiers shall be one of the following sets (delimited by
commas, when there is more than one set on a line); the type
specifiers may occur in any order, possibly intermixed with
the other declaration specifiers.
- void
- char
- signed char
- unsigned char
- short, signed short, short int, or signed short int
- unsigned short, or unsigned short int
- int, signed, or signed int
- unsigned, or unsigned int
- long, signed long, long int, or signed long int
- unsigned long, or unsigned long int
page 119 Language
page 120
- long long, signed long long, long long int, or signed
long long int
- unsigned long long, or unsigned long long int
- float
- double
- long double
- float complex
- double complex
- long double complex
- struct-or-union specifier
- enum-specifier
- typedef-name
Semantics
[#3] Specifiers for structures, unions, and enumerations are
discussed in 6.5.2.1 through 6.5.2.3. Declarations of
typedef names are discussed in 6.5.7. The characteristics
of the other types are discussed in 6.1.2.5.
[#4] Each of the comma-separated sets designates the same
type, except that for bit-fields, it is implementation-
defined whether the specified int is the same type as signed
int or is the same type as unsigned int.
Forward references: enumeration specifiers (6.5.2.2),
structure and union specifiers (6.5.2.1), tags (6.5.2.3),
type definitions (6.5.7).
6.5.2.1 Structure and union specifiers
Syntax
[#1]
struct-or-union-specifier:
struct-or-union identifier-opt { struct-declaration-list }
struct-or-union identifier
page 120 Language
page 121
struct-or-union:
struct
union
struct-declaration-list:
struct-declaration
struct-declaration-list struct-declaration
struct-declaration:
specifier-qualifier-list struct-declarator-list ;
specifier-qualifier-list:
type-specifier specifier-qualifier-list-opt
type-qualifier specifier-qualifier-list-opt
struct-declarator-list:
struct-declarator
struct-declarator-list , struct-declarator
struct-declarator:
declarator
declarator-opt : constant-expression
Constraints
[#2] A structure or union shall not contain a member with
incomplete or function type, except that the last element of
a structure may have incomplete array type. Hence it shall
not contain an instance of itself (but may contain a pointer
to an instance of itself).
[#3] The expression that specifies the width of a bit-field
shall be an integer constant expression that has nonnegative
value that shall not exceed the number of bits in an object
of the type that is specified if the colon and expression
are omitted. If the value is zero, the declaration shall
have no declarator.
Semantics
[#4] As discussed in 6.1.2.5, a structure is a type
consisting of a sequence of members, whose storage is
allocated in an ordered sequence, and a union is a type
consisting of a sequence of members whose storage overlap.
[#5] Structure and union specifiers have the same form.
[#6] The presence of a struct-declaration-list in a struct-
or-union-specifier declares a new type, within a translation
unit. The struct-declaration-list is a sequence of
declarations for the members of the structure or union. If
page 121 Language
page 122
the struct-declaration-list contains no named members, the
behavior is undefined. The type is incomplete until after
the } that terminates the list.
[#7] A member of a structure or union may have any object
type other than a variably modified type.89 In addition, a
member may be declared to consist of a specified number of
bits (including a sign bit, if any). Such a member is
called a bit-field;90 its width is preceded by a colon.
[#8] A bit-field shall have a type that is a qualified or
unqualified version of signed int or unsigned int. A bit-
field is interpreted as a signed or unsigned integer type
consisting of the specified number of bits.91
[#9] An implementation may allocate any addressable storage
unit large enough to hold a bit-field. If enough space
remains, a bit-field that immediately follows another bit-
field in a structure shall be packed into adjacent bits of
the same unit. If insufficient space remains, whether a
bit-field that does not fit is put into the next unit or
overlaps adjacent units is implementation-defined. The
order of allocation of bit-fields within a unit (high-order
to low-order or low-order to high-order) is implementation-
defined. The alignment of the addressable storage unit is
unspecified.
[#10] A bit-field declaration with no declarator, but only a
colon and a width, indicates an unnamed bit-field.92 As a
special case of this, a bit-field structure member with a
__________
89. A structure or union can not contain a member with a
variably modified type because member names are not
ordinary identifiers as defined in 6.1.2.3.
90. The unary & (address-of) operator may not be applied to
a bit-field object; thus, there are no pointers to or
arrays of bit-field objects.
91. As specified in 6.5.2 above, if the actual type
specifier used is int or there is no type specifier, or
is a typedef-name defined using either of these, then it
is implementation-defined whether the bit-field is
signed or unsigned.
92. An unnamed bit-field structure member is useful for
padding to conform to externally imposed layouts.
page 122 Language
page 123
width of 0 indicates that no further bit-field is to be
packed into the unit in which the previous bit-field, if
any, was placed.
[#11] Each non-bit-field member of a structure or union
object is aligned in an implementation-defined manner
appropriate to its type.
[#12] Within a structure object, the non-bit-field members
and the units in which bit-fields reside have addresses that
increase in the order in which they are declared. A pointer
to a structure object, suitably converted, points to its
initial member (or if that member is a bit-field, then to
the unit in which it resides), and vice versa. There may be
unnamed padding within a structure object, but not at its
beginning.
[#13] The size of a union is sufficient to contain the
largest of its members. The value of at most one of the
members can be stored in a union object at any time. A
pointer to a union object, suitably converted, points to
each of its members (or if a member is a bit-field, then to
the unit in which it resides), and vice versa.
[#14] There may be unnamed padding at the end of a structure
or union, were the structure or union to be an element of an
array.
[#15] As a special case, the last element of a structure may
be an incomplete array type. This is called a flexible
array member, and the size of the structure shall be equal
to the offset of the last element of an otherwise identical
structure that replaces the flexible array member with an
array of one element. When an lvalue whose type is a
structure with a flexible array member is used to access an
object, it behaves as if that member were replaced by the
longest array that would not make the structure larger than
the object being accessed. If this array would have no
elements, then it behaves as if it has one element, but the
behavior is undefined if any attempt is made to access that
element.
Examples
[#16] After the declarations:
struct s { int n; double d[]; };
struct ss { int n; double d[1]; };
the three expressions:
page 123 Language
page 124
sizeof (struct s)
offsetof(struct s, d)
offsetof(struct ss, d)
have the same value. The structure struct s has a flexible
array member d.
[#17] If sizeof (double) is 8, then after the following code
is executed:
struct s *s1;
struct s *s2;
s1 = malloc(sizeof (struct s) + 64);
s2 = malloc(sizeof (struct s) + 46);
and assuming that the calls to malloc succeed, s1 and s2
behave as if they had been declared as:
struct { int n; double d[8]; } *s1;
struct { int n; double d[5]; } *s2;
[#18] Following the further successful assignments:
s1 = malloc(sizeof (struct s) + 10);
s2 = malloc(sizeof (struct s) + 6);
they then behave as if they had been declared as:
struct { int n; double d[1]; } *s1, *s2;
and:
double *dp;
dp = &(s1->d[0]); // Permitted
*dp = 42; // Permitted
dp = &(s2->d[0]); // Permitted
*dp = 42; // Undefined behavior
Forward references: tags (6.5.2.3).
6.5.2.2 Enumeration specifiers
Syntax
[#1]
enum-specifier:
enum identifier-opt { enumerator-list }
enum identifier-opt { enumerator-list , }
enum identifier
page 124 Language
page 125
enumerator-list:
enumerator
enumerator-list , enumerator
enumerator:
enumeration-constant
enumeration-constant = constant-expression
Constraints
[#2] The expression that defines the value of an enumeration
constant shall be an integer constant expression that has a
value representable as an int.
Semantics
[#3] The identifiers in an enumerator list are declared as
constants that have type int and may appear wherever such
are permitted.93 An enumerator with = defines its
enumeration constant as the value of the constant
expression. If the first enumerator has no =, the value of
its enumeration constant is 0. Each subsequent enumerator
with no = defines its enumeration constant as the value of
the constant expression obtained by adding 1 to the value of
the previous enumeration constant. (The use of enumerators
with = may produce enumeration constants with values that
duplicate other values in the same enumeration.) The
enumerators of an enumeration are also known as its members.
[#4] Each enumerated type shall be compatible with an
integer type. The choice of type is implementation-defined,
but shall be capable of representing the values of all the
members of the enumeration.
[#5] The enumerated type is complete at the } that
terminates the list of enumerator declarations.
__________
93. Thus, the identifiers of enumeration constants declared
in the same scope shall all be distinct from each other
and from other identifiers declared in ordinary
declarators.
page 125 Language
page 126
Examples
[#6]
enum hue { chartreuse, burgundy, claret=20, winedark };
enum hue col, *cp;
col = claret;
cp = &col;
if (*cp != burgundy)
/* ... */
makes hue the tag of an enumeration, and then declares col
as an object that has that type and cp as a pointer to an
object that has that type. The enumerated values are in the
set {0, 1, 20, 21}.
Forward references: tags (6.5.2.3).
6.5.2.3 Tags
Constraints
[#1] A specific type shall have its content defined at most
once.
[#2] A type specifier of the form
enum identifier
without an enumerator list shall only appear after the type
it specifies is completed.
Semantics
[#3] All declarations of structure, union, or enumerated
types that have the same scope and use the same tag declare
the same type. The type is complete94 until the closing
brace of the list defining the content, and complete
__________
94. An incomplete type may only by used when the size of an
object of that type is not needed. It is not needed,
for example, when a typedef name is declared to be a
specifier for a structure or union, or when a pointer to
or a function returning a structure or union is being
declared. (See incomplete types in 6.1.2.5.) The
specification shall be complete before such a function
is called or defined.
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thereafter.
[#4] Two declarations of structure, union, or enumerated
types which are in different scopes or use different tags
declare distinct types. Each declaration of a structure,
union, or enumerated type which does not include a tag
declares a distinct type.
[#5] A type specifier of the form
struct-or-union identifier-opt { struct-declaration-list }
or
enum identifier { enumerator-list }
or
enum identifier { enumerator-list , }
declares a structure, union, or enumerated type. The list
defines the structure content, union content, or enumeration
content. If an identifier is provided,95 the type
specifier also declares the identifier to be the tag of that
type.
[#6] A declaration of the form
struct-or-union identifier
specifies a structure of union type and declares the
identifier as a tag of that type.96
[#7] If a type specifier of the form
struct-or-union identifier
occurs other than as part of one of the above forms, and no
other declaration of the identifier as a tag is visible,
then it declares an incomplete structure or union type, and
declares the identifier as the tag of that type.96
__________
95. If there is no identifier, the type can, within the
translation unit, only be referred to by the declaration
of which it is a part. Of course, when the declaration
is of a typedef name, subsequent declarations can make
use of that typedef name to declare objects having the
specified structure, union, or enumerated type.
96. A similar construction with enum does not exist.
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[#8] If a type specifier of the form
struct-or-union identifier
or
enum identifier
occurs other than as part of one of the above forms, and a
declaration of the identifier as a tag is visible, then it
specifies the same type as that other declaration, and does
not redeclare the tag.
Examples
[#9]
1. This mechanism allows declaration of a self-
referential structure.
struct tnode {
int count;
struct tnode *left, *right;
};
specifies a structure that contains an integer and two
pointers to objects of the same type. Once this
declaration has been given, the declaration
struct tnode s, *sp;
declares s to be an object of the given type and sp to
be a pointer to an object of the given type. With
these declarations, the expression sp->left refers to
the left struct tnode pointer of the object to which
sp points; the expression s.right->count designates
the count member of the right struct tnode pointed to
from s.
The following alternative formulation uses the typedef
mechanism:
typedef struct tnode TNODE;
struct tnode {
int count;
TNODE *left, *right;
};
TNODE s, *sp;
2. To illustrate the use of prior declaration of a tag to
specify a pair of mutually referential structures, the
declarations
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struct s1 { struct s2 *s2p; /* ... */ }; // D1
struct s2 { struct s1 *s1p; /* ... */ }; // D2
specify a pair of structures that contain pointers to
each other. Note, however, that if s2 were already
declared as a tag in an enclosing scope, the
declaration D1 would refer to it, not to the tag s2
declared in D2. To eliminate this context
sensitivity, the declaration
struct s2;
may be inserted ahead of D1. This declares a new tag
s2 in the inner scope; the declaration D2 then
completes the specification of the new type.
3. An enumeration type is compatible with some integer
type. An implementation may delay the choice of which
integer type until all enumeration constants have been
seen. Thus in:
enum f { c = sizeof (enum f) };
the behavior is undefined since the size of the
respective enumeration type is not necessarily known
when sizeof is encountered.
Forward references: declarators (6.5.5), array declarators
(6.5.5.2), type definitions (6.5.7).
6.5.3 Type qualifiers
Syntax
[#1]
type-qualifier:
const
restrict
volatile
Constraints
[#2] Types other than pointer types derived from object or
incomplete types shall not be restrict-qualified.
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Semantics
[#3] The properties associated with qualified types are
meaningful only for expressions that are lvalues.97
[#4] If the same qualifier appears more than once in the
same specifier-qualifier-list, either directly or via one or
more typedefs, the behavior is the same as if it appeared
only once.
[#5] If an attempt is made to modify an object defined with
a const-qualified type through use of an lvalue with non-
const-qualified type, the behavior is undefined. If an
attempt is made to refer to an object defined with a
volatile-qualified type through use of an lvalue with non-
volatile-qualified type, the behavior is undefined.98
[#6] An object that has volatile-qualified type may be
modified in ways unknown to the implementation or have other
unknown side effects. Therefore any expression referring to
such an object shall be evaluated strictly according to the
rules of the abstract machine, as described in 5.1.2.3.
Furthermore, at every sequence point the value last stored
in the object shall agree with that prescribed by the
abstract machine, except as modified by the unknown factors
mentioned previously.99 What constitutes an access to an
object that has volatile-qualified type is implementation-
defined.
__________
97. The implementation may place a const object that is not
volatile in a read-only region of storage. Moreover,
the implementation need not allocate storage for such an
object if its address is never used.
98. This applies to those objects that behave as if they
were defined with qualified types, even if they are
never actually defined as objects in the program (such
as an object at a memory-mapped input/output address).
99. A volatile declaration may be used to describe an object
corresponding to a memory-mapped input/output port or an
object accessed by an asynchronously interrupting
function. Actions on objects so declared shall not be
``optimized out'' by an implementation or reordered
except as permitted by the rules for evaluating
expressions.
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[#7] An object that is referenced through a restrict-
qualified pointer has a special association with that
pointer. This association, defined in 6.5.3.1 below,
requires that all references to that object shall use,
directly or indirectly, the value of that pointer. For
example, a statement that assigns a value returned by malloc
to a single pointer establishes this association between the
allocated object and the pointer. The intended use of the
restrict qualifier (like the register storage class) is to
promote optimization, and deleting all instances of the
qualifier from a conforming program does not change its
meaning (i.e., observable behavior).
[#8] If the specification of an array type includes any type
qualifiers, the element type is so-qualified, not the array
type. If the specification of a function type includes any
type qualifiers, the behavior is undefined.100
[#9] For two qualified types to be compatible, both shall
have the identically qualified version of a compatible type;
the order of type qualifiers within a list of specifiers or
qualifiers does not affect the specified type.
Examples
[#10]
1. An object declared
extern const volatile int real_time_clock;
may be modifiable by hardware, but cannot be assigned
to, incremented, or decremented.
2. The following declarations and expressions illustrate
the behavior when type qualifiers modify an aggregate
type:
__________
100. Both of these can occur through the use of typedefs.
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const struct s { int mem; } cs = { 1 };
struct s ncs; // the object ncs is modifiable
typedef int A[2][3];
const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of
// const int
int *pi;
const int *pci;
ncs = cs; // valid
cs = ncs; // violates modifiable lvalue constraint for =
pi = &ncs.mem; // valid
pi = &cs.mem; // violates type constraints for =
pci = &cs.mem; // valid
pi = a[0]; // invalid: a[0] has type ``const int *''
6.5.3.1 Formal definition of restrict
[#1] Let D be a declaration of an ordinary identifier that
provides a means of designating an object P as a restrict-
qualified pointer.
[#2] If D appears inside a block and does not have storage
class extern, let B denote the block. If D appears in the
list of parameter declarations of a function definition, let
B denote the associated block. Otherwise, let B denote the
block of main (or the block of whatever function is called
at program startup in a freestanding environment).
[#3] In what follows, a pointer expression E is said to be
based on object P if (at some sequence point in the
execution of B prior to the evaluation of E) modifying P to
point to a copy of the array object into which it formerly
pointed would change the value of E. (In other words, E
depends on the value of P itself rather than on the value of
an object referenced indirectly through P. For example, if
identifier p has type (int **restrict), then the pointer
expressions p and p+1 are based on the restricted pointer
object designated by p, but the pointer expressions *p and
p[1] are not.) Note that ``based'' is defined only for
expressions with pointer types.
[#4] During each execution of B, let A be the array object
that is determined dynamically by all references through
pointer expressions based on P. Then all references to
values of A shall be through pointer expressions based on P.
Furthermore, if P is assigned the value of a pointer
expression E that is based on another restricted pointer
object P2, associated with block B2, then either the
execution of B2 shall begin before the execution of B, or
the execution of B2 shall end prior to the assignment. If
these requirements are not met, then the behavior is
undefined.
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[#5] Here an execution of B means that portion of the
execution of the program during which storage is guaranteed
to be reserved for an instance of an object that is
associated with B and that has automatic storage duration.
A reference to a value means either an access to or a
modification of the value. During an execution of B,
attention is confined to those references that are actually
evaluated. (This excludes references that appear in
unevaluated expressions, and also excludes references that
are ``available'', in the sense of employing visible
identifiers, but do not actually appear in the text of B.)
[#6] A translator is free to ignore any or all aliasing
implications of uses of restrict.
Examples
[#7]
1. The file scope declarations
int * restrict a;
int * restrict b;
extern int c[];
assert that if an object is referenced using the value
of one of a, b, or c, then it is never referenced
using the value of either of the other two.
2. The function parameter declarations in the following
example
void f(int n, int * restrict p, int * restrict q)
{
while (n-- > 0)
*p++ = *q++;
}
assert that, during each execution of the function, if
an object is referenced through one of the pointer
parameters, then it is not also referenced through the
other.
The benefit of the restrict qualifiers is that they
enable a translator to make an effective dependence
analysis of function f without examining any of the
calls of f in the program. The cost is that the
programmer must examine all of those calls to ensure
that none give undefined behavior. For example, the
second call of f in g has undefined behavior because
each of d[1] through d[49] is referenced through both
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p and q.
void g(void)
{
extern float d[100];
f(50, d + 50, d); // ok
f(50, d + 1, d); // undefined behavior
}
3. The function parameter declarations
void h(int n, int * const restrict p,
int * const q, int * const r)
{
int i;
for (i = 0; i < n; i++)
p[i] = q[i] + r[i];
}
show how const can be used in conjunction with
restrict. The const qualifiers imply, without the
need to examine the body of h, that q and r cannot
become based on p. The fact that p is restrict-
qualified therefore implies that an object referenced
through p is never referenced through either of q or
r. This is the precise assertion required to optimize
the loop. Note that a call of the form h(100, a, b,
b) has defined behavior, which would not be true if
all three of p, q, and r were restrict-qualified.
4. The rule limiting assignments between restricted
pointers does not distinguish between a function call
and an equivalent nested block. With one exception,
only ``outer-to-inner'' assignments between restricted
pointers declared in nested blocks have defined
behavior.
{
int * restrict p1;
int * restrict q1;
p1 = q1; // undefined behavior
{
int * restrict p2 = p1; // ok
int * restrict q2 = q1; // ok
p1 = q2; // undefined behavior
p2 = q2; // undefined behavior
}
}
The exception allows the value of a restricted pointer
to be carried out of the block in which it (or, more
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precisely, the ordinary identifier used to designate
it) is declared when that block finishes execution.
For example, this permits new_vector to return a
vector.
typedef struct { int n; float * restrict v; } vector;
vector new_vector(int n)
{
vector t;
t.n = n;
t.v = malloc(n * sizeof (float));
return t;
}
6.5.4 Function specifiers
Syntax
[#1]
function-specifier:
inline
Constraints
[#2] Function specifiers shall be used only in the
declaration of an identifier for a function.
[#3] An inline definition (see below) of a function with
external linkage shall not contain a definition of an object
with static storage duration that can be modified, and shall
not contain a reference to an identifier with internal
linkage.
[#4] The inline function specifier shall not appear in a
declaration of main.
Semantics
[#5] A function declared with an inline function specifier
is an inline function. Making a function an inline function
suggests that calls to the function be as fast as possible
by using, for example, an alternative to the usual function
call mechanism known as ``inline substitution''.101 The
__________
101. Inline substitution is not textual substitution, nor
does it create a new function. Therefore, for example,
the expansion of a macro used within the body of the
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extent to which such suggestions are effective is
implementation-defined.102
[#6] Any function with internal linkage can be an inline
function. For a function with external linkage, the
following restrictions apply. If a function is declared
with an inline function specifier, then it shall also be
defined in the same translation unit. If all of the file
scope declarations for a function in a translation unit
include the inline function specifier without extern, then
the definition in that translation unit is an inline
definition. An inline definition does not provide an
external definition for the function, and does not forbid an
external definition in another translation unit. An inline
definition provides an alternative to an external
definition, which a translator may use to implement any call
to the function in the same translation unit. It is
unspecified whether a call to the function uses the inline
definition or the external definition.
Examples
[#7] The declaration of an inline function with external
linkage can result in either an external definition, or a
definition available for use only within the translation
unit. A file scope declaration with extern creates an
external definition. The following example shows an entire
translation unit.
____________________________________________________________
function uses the definition it had at the point the
function body appears, and not where the function is
called; and identifiers refer to the declarations in
scope where the body occurs. Similarly, the address of
the function is not affected by the function's being
inlined.
102. For example, an implementation might never perform
inline substitution, or might only perform inline
substitutions to calls in the scope of an inline
declaration.
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page 137
inline double fahr(double t)
{
return (9.0 * t) / 5.0 + 32.0;
}
inline double cels(double t)
{
return (5.0 * (t - 32.0)) / 9.0;
}
/* Creates an external definition. */
extern double fahr(double);
double convert(int is_fahr, double temp)
{
/* A translator may perform inline substitutions. */
return is_fahr ? cels(temp) : fahr(temp);
}
[#8] Note that the definition of fahr is an external
definition because fahr is also declared with extern, but
the definition of cels is an inline definition. Because
there is a call to cels, an external definition of cels in
another translation unit is still required by 6.7.
6.5.5 Declarators
Syntax
[#1]
declarator:
pointer-opt direct-declarator
direct-declarator:
identifier
( declarator )
direct-declarator [ assignment-expression-opt ]
direct-declarator [ * ]
direct-declarator ( parameter-type-list )
direct-declarator ( identifier-list-opt )
pointer:
* type-qualifier-list-opt
* type-qualifier-list-opt pointer
type-qualifier-list:
type-qualifier
type-qualifier-list type-qualifier
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parameter-type-list:
parameter-list
parameter-list , ...
parameter-list:
parameter-declaration
parameter-list , parameter-declaration
parameter-declaration:
declaration-specifiers declarator
declaration-specifiers abstract-declarator-opt
identifier-list:
identifier
identifier-list , identifier
Semantics
[#2] Each declarator declares one identifier, and asserts
that when an operand of the same form as the declarator
appears in an expression, it designates a function or object
with the scope, storage duration, and type indicated by the
declaration specifiers.
[#3] A full declarator is a declarator that is not part of
another declarator. The end of a full declarator is a
sequence point. If the nested sequence of declarators in a
full declarator contains a variable length array type, the
type specified by the full declarator is said to be variably
modified.
[#4] In the following subclauses, consider a declaration
T D1
where T contains the declaration specifiers that specify a
type T (such as int) and D1 is a declarator that contains an
identifier ident. The type specified for the identifier
ident in the various forms of declarator is described
inductively using this notation.
[#5] If, in the declaration ``T D1'', D1 has the form
identifier
then the type specified for ident is T.
[#6] If, in the declaration ``T D1'', D1 has the form
( D )
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then ident has the type specified by the declaration ``T
D''. Thus, a declarator in parentheses is identical to the
unparenthesized declarator, but the binding of complicated
declarators may be altered by parentheses.
Implementation limits
[#7] The implementation shall allow the specification of
types that have at least 12 pointer, array, and function
declarators (in any valid combinations) modifying an
arithmetic, structure, union, or incomplete type, either
directly or via one or more typedefs.
Forward references: array declarators (6.5.5.2), type
definitions (6.5.7).
6.5.5.1 Pointer declarators
Semantics
[#1] If, in the declaration ``T D1'', D1 has the form
* type-qualifier-list-opt D
and the type specified for ident in the declaration ``T D''
is ``derived-declarator-type-list T'', then the type
specified for ident is ``derived-declarator-type-list type-
qualifier-list pointer to T''. For each type qualifier in
the list, ident is a so-qualified pointer.
[#2] For two pointer types to be compatible, both shall be
identically qualified and both shall be pointers to
compatible types.
Examples
[#3] The following pair of declarations demonstrates the
difference between a ``variable pointer to a constant
value'' and a ``constant pointer to a variable value''.
const int *ptr_to_constant;
int *const constant_ptr;
The contents of an object pointed to by ptr_to_constant
shall not be modified through that pointer, but
ptr_to_constant itself may be changed to point to another
object. Similarly, the contents of the int pointed to by
constant_ptr may be modified, but constant_ptr itself shall
always point to the same location.
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[#4] The declaration of the constant pointer constant_ptr
may be clarified by including a definition for the type
``pointer to int''.
typedef int *int_ptr;
const int_ptr constant_ptr;
declares constant_ptr as an object that has type ``const-
qualified pointer to int''.
6.5.5.2 Array declarators
Constraints
[#1] The [ and ] may delimit an expression or *. If [ and ]
delimit an expression (which specifies the size of an
array), it shall have an integer type. If the expression is
a constant expression then it shall have a value greater
than zero. The element type shall not be an incomplete or
function type.
[#2] Only ordinary identifiers (as defined in 6.1.2.3) with
block scope or function prototype scope and without linkage
can have a variably modified type. If an identifier is
declared to be an object with static storage duration, it
shall not have a variable length array type.
Semantics
[#3] If, in the declaration ``T D1'', D1 has the form
D[assignment-expr-opt]
or
D[*]
and the type specified for ident in the declaration ``T D''
is ``derived-declarator-type-list T'', then the type
specified for ident is ``derived-declarator-type-list array
of T''.103 If the size is not present, the array type is an
incomplete type. If * is used instead of a size expression,
the array type is a variable length array type of
unspecified size, which can only be used in declarations
__________
103. When several ``array of'' specifications are adjacent,
a multidimensional array is declared.
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with function prototype scope. If the size expression is an
integer constant expression and the element type has a known
constant size, the array type is not a variable length array
type. Otherwise, the array type is a variable length array
type. If the size expression is not a constant expression,
and it is evaluated at program execution time, it shall
evaluate to a value greater than zero. It is unspecified
whether side effects are produced when the size expression
is evaluated. The size of each instance of a variable
length array type does not change during its lifetime.
[#4] For two array types to be compatible, both shall have
compatible element types, and if both size specifiers are
present, and are integer constant expressions, then both
size specifiers shall have the same constant value. If the
two array types are used in a context which requires them to
be compatible, it is undefined behavior if the two size
specifiers evaluate to unequal values.
Examples
[#5]
1. float fa[11], *afp[17];
declares an array of float numbers and an array of
pointers to float numbers.
2. Note the distinction between the declarations
extern int *x;
extern int y[];
The first declares x to be a pointer to int; the
second declares y to be an array of int of unspecified
size (an incomplete type), the storage for which is
defined elsewhere.
3. The following declarations demonstrate the
compatibility rules for variably modified types.
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extern int n;
extern int m;
void fcompat(void)
{
int a[n][6][m];
int (*p)[4][n+1];
int c[n][n][6][m];
int (*r)[n][n][n+1];
p = a; // Error - not compatible because 4 != 6.
r = c; // Compatible, but defined behavior
// only if n == 6 and m == n+1.
}
4. All declarations of variably modified (VM) types must
be declared at either block scope or function
prototype scope. Array objects declared with the
static or extern storage class specifier cannot have a
variable length array (VLA) type. However, an object
declared with the static storage class specifier can
have a VM type (that is, a pointer to a VLA type).
Finally, all identifiers declared with a VM type must
be ordinary identifiers, and can not, therefore, be
members of structures or unions.
extern int n;
int A[n]; // Error - file scope VLA.
extern int (*p2)[n]; // Error - file scope VM.
int B[100]; // OK - file scope but not VM.
void fvla(int n, int C[m][m]) // OK - VLA with prototype scope.
{
typedef int VLA[m][m] // OK - block scope typedef VLA.
struct tag {
int (*y)[n]; // Error - y not ordinary identifier.
int z[n]; // Error - z not ordinary identifier.
};
int D[m]; // OK - auto VLA.
static int E[m]; // Error - static block scope VLA.
extern int F[m]; // Error - F has linkage and is VLA.
int (*s)[m]; // OK - auto pointer to VLA.
extern int (*r)[m]; // Error - r had linkage and is
// a pointer to VLA.
static int (*q)[m] = &B; // OK - q is a static block
// pointer to VLA.
}
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Forward references: function definitions (6.7.1),
initialization (6.5.8).
6.5.5.3 Function declarators (including prototypes)
Constraints
[#1] A function declarator shall not specify a return type
that is a function type or an array type.
[#2] The only storage-class specifier that shall occur in a
parameter declaration is register.
[#3] An identifier list in a function declarator that is not
part of a function definition shall be empty.
[#4] After all rewrites, the parameters in a parameter-
type-list that is part of a function definition shall not
have incomplete type.104
Semantics
[#5] If, in the declaration ``T D1'', D1 has the form
D(parameter-type-list)
or
D(identifier-list-opt)
and the type specified for ident in the declaration ``T D''
is ``derived-declarator-type-list T'', then the type
specified for ident is ``derived-declarator-type-list
function returning T''.
[#6] A parameter type list specifies the types of, and may
declare identifiers for, the parameters of the function. A
declared parameter that is a member of a parameter type list
that is not part of a function definition, may use the [*]
notation in its sequence of declarator specifiers to specify
a variable length array type. If the list terminates with
an ellipsis (, ...), no information about the number or
types of the parameters after the comma is supplied.105 The
__________
104. Arrays and functions are rewritten as pointers.
105. The macros defined in the <stdarg.h> header (7.12) may
be used to access arguments that correspond to the
ellipsis.
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special case of an unnamed parameter of type void as the
only item in the list specifies that the function has no
parameters.
[#7] If, in a parameter declaration, an identifier can be
treated as a typedef name or as a parameter name, it shall
be taken as a typedef name.
[#8] If the function declarator is not part of a function
definition, the parameters may have incomplete type.
[#9] The storage-class specifier in the declaration
specifiers for a parameter declaration, if present, is
ignored unless the declared parameter is one of the members
of the parameter type list for a function definition.
[#10] An identifier list declares only the identifiers of
the parameters of the function. An empty list in a function
declarator that is part of a function definition specifies
that the function has no parameters. The empty list in a
function declarator that is not part of a function
definition specifies that no information about the number or
types of the parameters is supplied.106
[#11] For two function types to be compatible, both shall
specify compatible return types.107 Moreover, the parameter
type lists, if both are present, shall agree in the number
of parameters and in use of the ellipsis terminator;
corresponding parameters shall have compatible types. If
one type has a parameter type list and the other type is
specified by a function declarator that is not part of a
function definition and that contains an empty identifier
list, the parameter list shall not have an ellipsis
terminator and the type of each parameter shall be
compatible with the type that results from the application
of the default argument promotions. If one type has a
parameter type list and the other type is specified by a
function definition that contains a (possibly empty)
identifier list, both shall agree in the number of
parameters, and the type of each prototype parameter shall
be compatible with the type that results from the
application of the default argument promotions to the type
__________
106. See ``future language directions'' (6.9.3).
107. If both function types are ``old style'', parameter
types are not compared.
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of the corresponding identifier. (In the determination of
type compatibility and of a composite type, each parameter
declared with function or array type is taken as having the
type that results from conversion to a pointer type, as in
6.7.1, and each parameter declared with qualified type is
taken as having the unqualified version of its declared
type.)
Examples
[#12]
1. The declaration
int f(void), *fip(), (*pfi)();
declares a function f with no parameters returning an
int, a function fip with no parameter specification
returning a pointer to an int, and a pointer pfi to a
function with no parameter specification returning an
int. It is especially useful to compare the last two.
The binding of *fip() is *(fip()), so that the
declaration suggests, and the same construction in an
expression requires, the calling of a function fip,
and then using indirection through the pointer result
to yield an int. In the declarator (*pfi)(), the
extra parentheses are necessary to indicate that
indirection through a pointer to a function yields a
function designator, which is then used to call the
function; it returns an int.
If the declaration occurs outside of any function, the
identifiers have file scope and external linkage. If
the declaration occurs inside a function, the
identifiers of the functions f and fip have block
scope and either internal or external linkage
(depending on what file scope declarations for these
identifiers are visible), and the identifier of the
pointer pfi has block scope and no linkage.
2. The declaration
int (*apfi[3])(int *x, int *y);
declares an array apfi of three pointers to functions
returning int. Each of these functions has two
parameters that are pointers to int. The identifiers
x and y are declared for descriptive purposes only and
go out of scope at the end of the declaration of apfi.
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3. The declaration
int (*fpfi(int (*)(long), int))(int, ...);
declares a function fpfi that returns a pointer to a
function returning an int. The function fpfi has two
parameters: a pointer to a function returning an int
(with one parameter of type long), and an int. The
pointer returned by fpfi points to a function that has
one int parameter and accepts zero or more additional
arguments of any type.
4. The following prototype has a variably modified
parameter.
void addscalar(int n, int m,
double a[n][n*m+300], double x);
int main()
{
double b[4][308];
addscalar(4, 2, b, 2.17);
return 0;
}
void addscalar(int n, int m,
double a[n][n*m+300], double x)
{
for (int i = 0; i < n; i++)
for (int j = 0, k = n*m+300; j < k; j++)
// a is a pointer to a VLA
// with n*m+300 elements
a[i][j] += x;
}
5. The following are all compatible function prototype
declarators.
double maximum(int n, int m, double a[n][m]);
double maximum(int n, int m, double a[*][*]);
double maximum(int n, int m, double a[ ][*]);
double maximum(int n, int m, double a[ ][m]);
Forward references: function definitions (6.7.1), type
names (6.5.6).
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6.5.6 Type names
Syntax
[#1]
type-name:
specifier-qualifier-list abstract-declarator-opt
abstract-declarator:
pointer
pointer-opt direct-abstract-declarator
direct-abstract-declarator:
( abstract-declarator )
direct-abstract-declarator-opt [ assignment-expression-opt ]
direct-abstract-declarator-opt [ * ]
direct-abstract-declarator-opt ( parameter-type-list-opt )
Semantics
[#2] In several contexts, it is desired to specify a type.
This is accomplished using a type name, which is
syntactically a declaration for a function or an object of
that type that omits the identifier.108
Examples
[#3] The constructions
(a) int
(b) int *
(c) int *[3]
(d) int (*)[3]
(e) int *()
(f) int (*)(void)
(g) int (*const [])(unsigned int, ...)
name respectively the types (a) int, (b) pointer to int, (c)
array of three pointers to int, (d) pointer to an array of
three ints, (e) function with no parameter specification
returning a pointer to int, (f) pointer to function with no
__________
108. As indicated by the syntax, empty parentheses in a type
name are interpreted as ``function with no parameter
specification'', rather than redundant parentheses
around the omitted identifier.
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parameters returning an int, and (g) array of an unspecified
number of constant pointers to functions, each with one
parameter that has type unsigned int and an unspecified
number of other parameters, returning an int.
6.5.7 Type definitions
Syntax
[#1]
typedef-name:
identifier
Constraints
[#2] If a typedef name specifies a variably modified type
then it shall have block scope.
Semantics
[#3] In a declaration whose storage-class specifier is
typedef, each declarator defines an identifier to be a
typedef name that specifies the type specified for the
identifier in the way described in 6.5.5. Any array size
expressions associated with variable length array
declarators shall be evaluated with the typedef name at the
beginning of its scope upon each normal entry to the block.
A typedef declaration does not introduce a new type, only a
synonym for the type so specified. That is, in the
following declarations:
typedef T type_ident;
type_ident D;
type_ident is defined as a typedef name with the type
specified by the declaration specifiers in T (known as T),
and the identifier in D has the type ``derived-declarator-
type-list T'' where the derived-declarator-type-list is
specified by the declarators of D. A typedef name shares
the same name space as other identifiers declared in
ordinary declarators. If the identifier is redeclared in an
inner scope or is declared as a member of a structure or
union in the same or an inner scope, the type specifiers
shall not be omitted in the inner declaration.
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Examples
[#4]
1. After
typedef int MILES, KLICKSP();
typedef struct { double hi, lo; } range;
the constructions
MILES distance;
extern KLICKSP *metricp;
range x;
range z, *zp;
are all valid declarations. The type of distance is
int, that of metricp is ``pointer to function with no
parameter specification returning int'', and that of x
and z is the specified structure; zp is a pointer to
such a structure. The object distance has a type
compatible with any other int object.
2. After the declarations
typedef struct s1 { int x; } t1, *tp1;
typedef struct s2 { int x; } t2, *tp2;
type t1 and the type pointed to by tp1 are compatible.
Type t1 is also compatible with type struct s1, but
not compatible with the types struct s2, t2, the type
pointed to by tp2, and int.
3. The following obscure constructions
typedef signed int t;
typedef int plain;
struct tag {
unsigned t:4;
const t:5;
plain r:5;
};
declare a typedef name t with type signed int, a
typedef name plain with type int, and a structure with
three bit-field members, one named t that contains
values in the range [0, 15], an unnamed const-
qualified bit-field which (if it could be accessed)
would contain values in at least the range [-15, +15],
and one named r that contains values in the range [0,
31] or values in at least the range [-15, +15]. (The
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choice of range is implementation-defined.) The first
two bit-field declarations differ in that unsigned is
a type specifier (which forces t to be the name of a
structure member), while const is a type qualifier
(which modifies t which is still visible as a typedef
name). If these declarations are followed in an inner
scope by
t f(t (t));
long t;
then a function f is declared with type ``function
returning signed int with one unnamed parameter with
type pointer to function returning signed int with one
unnamed parameter with type signed int'', and an
identifier t with type long.
4. On the other hand, typedef names can be used to
improve code readability. All three of the following
declarations of the signal function specify exactly
the same type, the first without making use of any
typedef names.
typedef void fv(int), (*pfv)(int);
void (*signal(int, void (*)(int)))(int);
fv *signal(int, fv *);
pfv signal(int, pfv);
5. The following is a block scope declaration of a
typedef name A with a variable length array type.
void tdef(int n)
{
typedef int A[n];
A a;
A *p;
p = &a;
}
6. The size expression that is part of the variable
length array type named by typedef name B is evaluated
each time function copyt is entered. However, the
size of the variable length array type does not change
if the value of n is subsequently changed.
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void copyt(int n)
{
typedef int B[n]; // B is n ints, n evaluated now.
n += 1;
{
B a; // a is n ints, n without += 1.
int b[n]; // a and b are different sizes
for (i = 1; i < n; i++)
a[i-1] = b[i];
}
}
Forward references: the signal function (7.11.1.1).
6.5.8 Initialization
Syntax
[#1]
initializer:
assignment-expression
{ initializer-list }
{ initializer-list , }
initializer-list:
designation-opt initializer
initializer-list , designation-opt initializer
designation:
designator-list =
designator-list:
designator
designator-list designator
designator:
[ constant-expression ]
. identifier
Constraints
[#2] No initializer shall attempt to provide a value for an
object not contained within the entity being initialized.
[#3] The type of the entity to be initialized shall be an
array of unknown size or an object type that is not a
variable length array type.
[#4] All the expressions in an initializer for an object
that has static storage duration shall be constant
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expressions or string literals.
[#5] If the declaration of an identifier has block scope,
and the identifier has external or internal linkage, the
declaration shall have no initializer for the identifier.
[#6] If a designator has the form
[ constant-expression ]
then the current object (defined below) shall have array
type and the expression shall be an integer constant
expression. If the array is of unknown size, any
nonnegative value is valid.
[#7] If a designator has the form
. identifier
then the current object (defined below) shall have structure
or union type and the identifier shall be a member of that
type.
Semantics
[#8] An initializer specifies the initial value stored in an
object.
[#9] Except where explicitly stated otherwise, for the
purposes of this subclause unnamed members of objects of
structure and union type do not participate in
initialization. Unnamed members of structure objects have
indeterminate value even after initialization. A union
object containing only unnamed members has indeterminate
value even after initialization.
[#10] If an object that has automatic storage duration is
not initialized explicitly, its value is indeterminate. If
an object that has static storage duration is not
initialized explicitly, then:
- if it has pointer type, it is initialized to a null
pointer;
- if it has arithmetic type, it is initialized to zero;
- if it is an aggregate, every member is initialized
(recursively) according to these rules;
- if it is a union, the first named member is initialized
(recursively) according to these rules.
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[#11] The initializer for a scalar shall be a single
expression, optionally enclosed in braces. The initial
value of the object, including unnamed members, is that of
the expression; the same type constraints and conversions as
for simple assignment apply, taking the type of the scalar
to be the unqualified version of its declared type.
[#12] Each brace-enclosed initializer list has an associated
current object. When no designations are present,
subobjects of the current object are initialized in order
according to the type of the current object: array elements
in increasing subscript order, structure members in
declaration order, and the first named member of a
union.109 In contrast, a designation causes the following
initializer to begin initialization of the subobject
described by the designator. Initialization then continues
forward in order, beginning with the next subobject after
that described by the designator.110
[#13] Each designator list begins its description with the
current object associated with the closest surrounding brace
pair. Each item in the designator list (in order) specifies
a particular member of its current object and changes the
current object for the next designator (if any) to be that
member.111 The current object that results at the end of
the designator list is the subobject to be initialized by
the following initializer.
[#14] The initialization shall occur in initializer list
order, each initializer provided for a particular subobject
__________
109. If the initializer list for a subaggregate or
contained union does not begin with a left brace, its
subobjects are initialized as usual, but the
subaggregate or contained union does not become the
current object: current objects are associated only
with brace-enclosed initializer lists.
110. After a union member is initialized, the next object
is not the next member of the union; instead, it
is the next subobject of an object containing the
union.
111. Thus, a designator can only specify a strict subobject
of the aggregate or union that is associated with the
surrounding brace pair. Note, too, that each separate
designator list is independent.
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page 154
overriding any previously listed initializer for the same
subobject; all subobjects that are not initialized
explicitly shall be initialized implicitly the same as
objects that have static storage duration.
[#15] The initializer for a structure or union object that
has automatic storage duration either shall be an
initializer list as described below, or shall be a single
expression that has compatible structure or union type. In
the latter case, the initial value of the object is that of
the expression.
[#16] The rest of this subclause deals with initializers for
objects that have aggregate or union type.
[#17] An array of character type may be initialized by a
character string literal, optionally enclosed in braces.
Successive characters of the character string literal
(including the terminating null character if there is room
or if the array is of unknown size) initialize the elements
of the array.
[#18] An array with element type compatible with wchar_t may
be initialized by a wide string literal, optionally enclosed
in braces. Successive codes of the wide string literal
(including the terminating zero-valued code if there is room
or if the array is of unknown size) initialize the elements
of the array.
[#19] Otherwise, the initializer for an object that has
aggregate type shall be a brace-enclosed list of
initializers for the named members of the aggregate, written
in increasing subscript or member order; and the initializer
for an object that has union type shall be a brace-enclosed
initializer for the first named member of the union.
[#20] If the aggregate contains members that are aggregates
or unions, or if the first member of a union is an aggregate
or union, the rules apply recursively to the subaggregates
or contained unions. If the initializer of a subaggregate
or contained union begins with a left brace, the
initializers enclosed by that brace and its matching right
brace initialize the members of the subaggregate or the
first member of the contained union. Otherwise, only enough
initializers from the list are taken to account for the
members of the subaggregate or the first member of the
contained union; any remaining initializers are left to
initialize the next member of the aggregate of which the
current subaggregate or contained union is a part.
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[#21] If there are fewer initializers in a brace-enclosed
list than there are members of an aggregate, or fewer
characters in a string literal used to initialize an array
of known size than there are elements in the array, the
remainder of the aggregate shall be initialized implicitly
the same as objects that have static storage duration.
[#22] If an array of unknown size is initialized, its size
is determined by the largest indexed element with an
explicit initializer. At the end of its initializer list,
the array no longer has incomplete type.
[#23] The order in which any side effects occur among the
initialization list expressions is unspecified.112
Examples
[#24]
1. The declaration
int x[] = { 1, 3, 5 };
defines and initializes x as a one-dimensional array
object that has three elements, as no size was
specified and there are three initializers.
2. The declaration
int y[4][3] = {
{ 1, 3, 5 },
{ 2, 4, 6 },
{ 3, 5, 7 },
};
is a definition with a fully bracketed initialization:
1, 3, and 5 initialize the first row of y (the array
object y[0]), namely y[0][0], y[0][1], and y[0][2].
Likewise the next two lines initialize y[1] and y[2].
The initializer ends early, so y[3] is initialized
with zeros. Precisely the same effect could have been
achieved by
__________
112. In particular, the evaluation order need not be the
same as the order of subobject initialization.
page 155 Language
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int y[4][3] = {
1, 3, 5, 2, 4, 6, 3, 5, 7
};
The initializer for y[0] does not begin with a left
brace, so three items from the list are used.
Likewise the next three are taken successively for
y[1] and y[2].
3. The declaration
int z[4][3] = {
{ 1 }, { 2 }, { 3 }, { 4 }
};
initializes the first column of z as specified and
initializes the rest with zeros.
4. The declaration
struct { int a[3], b; } w[] = { { 1 }, 2 };
is a definition with an inconsistently bracketed
initialization. It defines an array with two element
structures: w[0].a[0] is 1 and w[1].a[0] is 2; all
the other elements are zero.
5. The declaration
short q[4][3][2] = {
{ 1 },
{ 2, 3 },
{ 4, 5, 6 }
};
contains an incompletely but consistently bracketed
initialization. It defines a three-dimensional array
object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1]
is 3, and 4, 5, and 6 initialize q[2][0][0],
q[2][0][1], and q[2][1][0], respectively; all the rest
are zero. The initializer for q[0][0] does not begin
with a left brace, so up to six items from the current
list may be used. There is only one, so the values
for the remaining five elements are initialized with
zero. Likewise, the initializers for q[1][0] and
q[2][0] do not begin with a left brace, so each uses
up to six items, initializing their respective two-
dimensional subaggregates. If there had been more
than six items in any of the lists, a diagnostic
message would have been issued. The same
initialization result could have been achieved by:
page 156 Language
page 157
short q[4][3][2] = {
1, 0, 0, 0, 0, 0,
2, 3, 0, 0, 0, 0,
4, 5, 6
};
or by:
short q[4][3][2] = {
{
{ 1 },
},
{
{ 2, 3 },
},
{
{ 4, 5 },
{ 6 },
}
};
in a fully bracketed form.
Note that the fully bracketed and minimally bracketed
forms of initialization are, in general, less likely
to cause confusion.
6. One form of initialization that completes array types
involves typedef names. Given the declaration
typedef int A[]; // OK - declared with block scope
the declaration
A a = { 1, 2 }, b = { 3, 4, 5 };
is identical to
int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
due to the rules for incomplete types.
7. The declaration
char s[] = "abc", t[3] = "abc";
defines ``plain'' char array objects s and t whose
elements are initialized with character string
literals. This declaration is identical to
page 157 Language
page 158
char s[] = { 'a', 'b', 'c', '\0' },
t[] = { 'a', 'b', 'c' };
The contents of t>
<HR><H3>Transfer interrupted!</H3>
other hand, the declaration
char *p = "abc";
defines p with type ``pointer to char'' that is
initialized to point to an object with type ``array of
char'' with length 4 whose elements are initialized
with a character string literal. If an attempt is
made to use p to modify the contents of the array, the
behavior is undefined.
8. Arrays can be initialized to correspond to the
elements of an enumeration by using designators:
enum { member_one, member_two };
const char *nm[] = {
[member_two] = "member two",
[member_one] = "member one",
};
9. Structure members can be initialized to nonzero values
without depending on their order:
div_t answer = { .quot = 2, .rem = -1 };
10. Designators can be used to provide explicit
initialization when unadorned initializer lists might
be misunderstood:
struct { int a[3], b; } w[] =
{ [0].a = {1}, [1].a[0] = 2 };
11. Space can be ``allocated'' from both ends of an array
by using a single designator:
int a[MAX] = {
1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
};
In the above, if MAX is greater than ten, there will
be some zero-valued elements in the middle; if it is
less than ten, some of the values provided by the
first five initializers will be overridden by the
second five.
12. Any member of a union can be initialized:
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union { /* ... */ } u = { .any_member = 42 };
Forward references: common definitions <stddef.h> (7.1.6).
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6.6 Statements
Syntax
[#1]
statement:
labeled-statement
compound-statement
expression-statement
selection-statement
iteration-statement
jump-statement
Semantics
[#2] A statement specifies an action to be performed.
Except as indicated, statements are executed in sequence.
[#3] A full expression is an expression that is not part of
another expression. Each of the following is a full
expression: an initializer; the expression in an expression
statement; the controlling expression of a selection
statement (if or switch); the controlling expression of a
while or do statement; each of the (optional) expressions of
a for statement; the (optional) expression in a return
statement. The end of a full expression is a sequence
point.
Forward references: expression and null statements (6.6.3),
selection statements (6.6.4), iteration statements (6.6.5),
the return statement (6.6.6.4).
6.6.1 Labeled statements
Syntax
[#1]
labeled-statement:
identifier : statement
case constant-expr : statement
default : statement
Constraints
[#2] A case or default label shall appear only in a switch
statement. Further constraints on such labels are discussed
under the switch statement.
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page 161
Semantics
[#3] Any statement may be preceded by a prefix that declares
an identifier as a label name. Labels in themselves do not
alter the flow of control, which continues unimpeded across
them.
Forward references: the goto statement (6.6.6.1), the
switch statement (6.6.4.2).
6.6.2 Compound statement, or block
Syntax
[#1]
compound-statement:
{ block-item-list-opt }
block-item-list:
block-item
block-item-list block-item
block-item:
declaration
statement
Semantics
[#2] A compound statement (also called a block) allows a set
of statements to be grouped into one syntactic unit, which
may have its own set of declarations and initializations (as
discussed in 6.1.2.4). The initializers of objects that
have automatic storage duration, and the variable length
array declarators of ordinary identifiers with block scope
are evaluated and the values are stored in the objects
(including storing an indeterminate value in objects without
an initializer) each time that the declaration is reached in
the order of execution, as if it were a statement, and
within each declaration in the order that declarators
appear.
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6.6.3 Expression and null statements
Syntax
[#1]
expression-statement:
expression-opt ;
Semantics
[#2] The expression in an expression statement is evaluated
as a void expression for its side effects.113
[#3] A null statement (consisting of just a semicolon)
performs no operations.
Examples
[#4]
1. If a function call is evaluated as an expression
statement for its side effects only, the discarding of
its value may be made explicit by converting the
expression to a void expression by means of a cast:
int p(int);
/* ... */
(void)p(0);
2. In the program fragment
char *s;
/* ... */
while (*s++ != '\0')
;
a null statement is used to supply an empty loop body
to the iteration statement.
3. A null statement may also be used to carry a label
just before the closing } of a compound statement.
__________
113. Such as assignments, and function calls which have side
effects.
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page 163
while (loop1) {
/* ... */
while (loop2) {
/* ... */
if (want_out)
goto end_loop1;
/* ... */
}
/* ... */
end_loop1: ;
}
Forward references: iteration statements (6.6.5).
6.6.4 Selection statements
Syntax
[#1]
selection-statement:
if ( expression ) statement
if ( expression ) statement else statement
switch ( expression ) statement
Semantics
[#2] A selection statement selects among a set of statements
depending on the value of a controlling expression.
6.6.4.1 The if statement
Constraints
[#1] The controlling expression of an if statement shall
have scalar type.
Semantics
[#2] In both forms, the first substatement is executed if
the expression compares unequal to 0. In the else form, the
second substatement is executed if the expression compares
equal to 0. If the first substatement is reached via a
label, the second substatement is not executed.
[#3] An else is associated with the lexically nearest
preceeding if that is allowed by the grammar.
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6.6.4.2 The switch statement
Constraints
[#1] The controlling expression of a switch statement shall
have integer type, and shall not cause a block to be entered
by a jump from outside the block to a statement that follows
a case or default label in the block (or an enclosed block)
if that block contains the declaration of a variably
modified object or variably modified typedef name. The
expression of each case label shall be an integer constant
expression. No two of the case constant expressions in the
same switch statement shall have the same value after
conversion. There may be at most one default label in a
switch statement. (Any enclosed switch statement may have a
default label or case constant expressions with values that
duplicate case constant expressions in the enclosing switch
statement.)
Semantics
[#2] A switch statement causes control to jump to, into, or
past the statement that is the switch body, depending on the
value of a controlling expression, and on the presence of a
default label and the values of any case labels on or in the
switch body. A case or default label is accessible only
within the closest enclosing switch statement.
[#3] The integer promotions are performed on the controlling
expression. The constant expression in each case label is
converted to the promoted type of the controlling
expression. If a converted value matches that of the
promoted controlling expression, control jumps to the
statement following the matched case label. Otherwise, if
there is a default label, control jumps to the labeled
statement. If no converted case constant expression matches
and there is no default label, no part of the switch body is
executed.
Implementation limits
[#4] As discussed previously (5.2.4.1), the implementation
may limit the number of case values in a switch statement.
Examples
[#5] In the artificial program fragment
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page 165
switch (expr)
{
int i = 4;
f(i);
case 0:
i = 17;
/* falls through into default code */
default:
printf("%d\n", i);
}
the object whose identifier is i exists with automatic
storage duration (within the block) but is never
initialized, and thus if the controlling expression has a
nonzero value, the call to the printf function will access
an indeterminate value. Similarly, the call to the function
f cannot be reached.
6.6.5 Iteration statements
Syntax
[#1]
iteration-statement:
while ( expression ) statement
do statement while ( expression ) ;
for ( expr-opt ; expr-opt ; expr-opt ) statement
for ( declaration ; expr-opt ; expr-opt ) statement
Constraints
[#2] The controlling expression of an iteration statement
shall have scalar type.
[#3] The declaration part of a for statement shall only
declare identifiers for objects having storage class auto or
register.
Semantics
[#4] An iteration statement causes a statement called the
loop body to be executed repeatedly until the controlling
expression compares equal to 0.
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6.6.5.1 The while statement
[#1] The evaluation of the controlling expression takes
place before each execution of the loop body.
6.6.5.2 The do statement
[#1] The evaluation of the controlling expression takes
place after each execution of the loop body.
6.6.5.3 The for statement
[#1] Except for the behavior of a continue statement in the
loop body, the statement
for ( clause-1 ; expr-2 ; expr-3 ) statement
and the sequence of statements
{
clause-1 ;
while ( expr-2 ) {
statement
expr-3 ;
}
}
are equivalent (where clause-1 can be an expression or a
declaration).114
[#2] Both clause-1 and expr-3 can be omitted. If either or
both are an expression, they are evaluated as a void
expression. An omitted expr-2 is replaced by a nonzero
constant.
__________
114. Thus, clause-1 specifies initialization for the loop,
possibly declaring one or more variables for use in the
loop; expr-2, the controlling expression, specifies an
evaluation made before each iteration, such that
execution of the loop continues until the expression
compares equal to 0; expr-3 specifies an operation (such
as incrementing) that is performed after each iteration.
If clause-1 is a declaration, then the scope of any
variable it declares is the remainder of the declaration
and the entire loop, including the other two
expressions.
page 166 Language
page 167
Forward references: the continue statement (6.6.6.2).
6.6.6 Jump statements
Syntax
[#1]
jump-statement:
goto identifier ;
continue ;
break ;
return expression-opt ;
Semantics
[#2] A jump statement causes an unconditional jump to
another place.
6.6.6.1 The goto statement
Constraints
[#1] The identifier in a goto statement shall name a label
located somewhere in the enclosing function. A goto
statement shall not cause a block to be entered by a jump
from outside the block to a labeled statement in the block
(or an enclosed block) if that block contains the
declaration of a variably modified object or variably
modified typedef name.
Semantics
[#2] A goto statement causes an unconditional jump to the
statement prefixed by the named label in the enclosing
function.
Examples
[#3]
1. It is sometimes convenient to jump into the middle of
a complicated set of statements. The following
outline presents one possible approach to a problem
based on these three assumptions:
1. The general initialization code accesses objects
only visible to the current function.
2. The general initialization code is too large to
warrant duplication.
page 167 Language
page 168
3. The code to determine the next operation must be
at the head of the loop. (To allow it to be
reached by continue statements, for example.)
/* ... */
goto first_time;
for (;;) {
// determine next operation
/* ... */
if (need to reinitialize) {
// reinitialize-only code
/* ... */
first_time:
// general initialization code
/* ... */
continue;
}
// handle other operations
/* ... */
}
2. A goto statement is not allowed to jump past any
declarations of objects with variably modified types.
A jump within the block, however, is permitted.
goto lab3; // Error: going INTO scope of VLA.
{
double a[n];
a[j] = 4.4;
lab3:
a[j] = 3.3;
goto lab 4; // OK, going WITHIN scope of VLA.
a[j] = 5.5;
lab4:
a[j] = 6.6;
}
goto lab4; // Error: going INTO scope of VLA.
6.6.6.2 The continue statement
Constraints
[#1] A continue statement shall appear only in or as a loop
body.
Semantics
[#2] A continue statement causes a jump to the loop-
continuation portion of the smallest enclosing iteration
statement; that is, to the end of the loop body. More
precisely, in each of the statements
page 168 Language
page 169
while (/* ... */) { do { for (/* ... */) {
/* ... */ /* ... */ /* ... */
continue; continue; continue;
/* ... */ /* ... */ /* ... */
contin: ; contin: ; contin: ;
} } while (/* ... */); }
unless the continue statement shown is in an enclosed
iteration statement (in which case it is interpreted within
that statement), it is equivalent to goto contin;.115
6.6.6.3 The break statement
Constraints
[#1] A break statement shall appear only in or as a switch
body or loop body.
Semantics
[#2] A break statement terminates execution of the smallest
enclosing switch or iteration statement.
6.6.6.4 The return statement
Constraints
[#1] A return statement with an expression shall not appear
in a function whose return type is void. A return statement
without an expression shall only appear in a function whose
return type is void.
Semantics
[#2] A return statement terminates execution of the current
function and returns control to its caller. A function may
have any number of return statements.
[#3] If a return statement with an expression is executed,
the value of the expression is returned to the caller as the
value of the function call expression. If the expression
has a type different from the return type of the function in
which it appears, the value is converted as if by assignment
to an object having the return type of the function.116
__________
115. Following the contin: label is a null statement.
116. The return statement is not an assignment. The overlap
page 169 Language
page 170
[#4] If a return statement without an expression is
executed, and the value of the function call is used by the
caller, the behavior is undefined.
Examples
[#5] In:
struct s { double i; } f(void);
union {
struct {
int f1;
struct s f2;
} u1;
struct {
struct s f3;
int f4;
} u2;
} g;
struct s f(void)
{
return g.u1.f2;
}
/* ... */
g.u2.f3 = f();
there is no undefined behavior.
____________________________________________________________
restriction of subclause 6.3.16.1 does not apply to the
case of function return.
page 170 Language
page 171
6.7 External definitions
Syntax
[#1]
translation-unit:
external-declaration
translation-unit external-declaration
external-declaration:
function-definition
declaration
Constraints
[#2] The storage-class specifiers auto and register shall
not appear in the declaration specifiers in an external
declaration.
[#3] There shall be no more than one external definition for
each identifier declared with internal linkage in a
translation unit. Moreover, if an identifier declared with
internal linkage is used in an expression (other than as a
part of the operand of a sizeof operator), there shall be
exactly one external definition for the identifier in the
translation unit.
Semantics
[#4] As discussed in 5.1.1.1, the unit of program text after
preprocessing is a translation unit, which consists of a
sequence of external declarations. These are described as
``external'' because they appear outside any function (and
hence have file scope). As discussed in 6.5, a declaration
that also causes storage to be reserved for an object or a
function named by the identifier is a definition.
[#5] An external definition is an external declaration that
is also a definition of a function or an object. If an
identifier declared with external linkage is used in an
expression (other than as part of the operand of a sizeof
operator), somewhere in the entire program there shall be
exactly one external definition for the identifier;
otherwise, there shall be no more than one.117
__________
117. Thus, if an identifier declared with external linkage
is not used in an expression, there need be no external
page 171 Language
page 172
6.7.1 Function definitions
Syntax
[#1]
function-definition:
declaration-specifiers declarator declaration-list-opt compound-statement
Constraints
[#2] The identifier declared in a function definition (which
is the name of the function) shall have a function type, as
specified by the declarator portion of the function
definition.118
[#3] The return type of a function shall be void or an
object type other than array type.
[#4] The storage-class specifier, if any, in the declaration
specifiers shall be either extern or static.
[#5] If the declarator includes a parameter type list, the
declaration of each parameter shall include an identifier
(except for the special case of a parameter list consisting
of a single parameter of type void, in which there shall not
be an identifier). No declaration list shall follow.
[#6] If the declarator includes an identifier list, each
declaration in the declaration list shall have at least one
declarator, those declarators shall declare only identifiers
____________________________________________________________
definition for it.
118. The intent is that the type category in a function
definition cannot be inherited from a typedef:
typedef int F(void); /* type F is ``function of no arguments returning int'' */
F f, g; /* f and g both have type compatible with F */
F f { /* ... */ } /* WRONG: syntax/constraint error */
F g() { /* ... */ } /* WRONG: declares that g returns a function */
int f(void) { /* ... */ } /* RIGHT: f has type compatible with F */
int g() { /* ... */ } /* RIGHT: g has type compatible with F */
F *e(void) { /* ... */ } /* e returns a pointer to a function */
F *((e))(void) { /* ... */ } /* same: parentheses irrelevant */
int (*fp)(void); /* fp points to a function that has type F */
F *Fp; /* Fp points to a function that has type F */
page 172 Language
page 173
from the identifier list, and every identifier in the
identifier list shall be declared. An identifier declared
as a typedef name shall not be redeclared as a parameter.
The declarations in the declaration list shall contain no
storage-class specifier other than register and no
initializations.
Semantics
[#7] The declarator in a function definition specifies the
name of the function being defined and the identifiers of
its parameters. If the declarator includes a parameter type
list, the list also specifies the types of all the
parameters; such a declarator also serves as a function
prototype for later calls to the same function in the same
translation unit. If the declarator includes an identifier
list,119 the types of the parameters shall be declared in a
following declaration list.
[#8] If a function that accepts a variable number of
arguments is defined without a parameter type list that ends
with the ellipsis notation, the behavior is undefined.
[#9] Each parameter has automatic storage duration. Its
identifier is an lvalue.120 The layout of the storage for
parameters is unspecified.
[#10] On entry to the function all size expressions of its
variably modified parameters are evaluated, and the value of
each argument expression shall be converted to the type of
its corresponding parameter, as if by assignment to the
parameter. Array expressions and function designators as
arguments are converted to pointers before the call. A
declaration of a parameter as ``array of type'' shall be
adjusted to ``pointer to type,'' and a declaration of a
parameter as ``function returning type'' shall be adjusted
to ``pointer to function returning type,'' as in 6.2.2.1.
The resulting parameter type shall be an object type.
__________
119. See ``future language directions'' (6.9.4).
120. A parameter is in effect declared at the head of the
compound statement that constitutes the function body,
and therefore may not be redeclared in the function body
(except in an enclosed block).
page 173 Language
page 174
[#11] After all parameters have been assigned, the compound
statement that constitutes the body of the function
definition is executed.
[#12] If the } that terminates a function is reached, and
the value of the function call is used by the caller, the
behavior is undefined.
Examples
[#13]
1. In the following:
extern int max(int a, int b)
{
return a > b ? a : b;
}
extern is the storage-class specifier and int is the
type specifier; max(int a, int b) is the function
declarator; and
{ return a > b ? a : b; }
is the function body. The following similar
definition uses the identifier-list form for the
parameter declarations:
extern int max(a, b)
int a, b;
{
return a > b ? a : b;
}
Here int a, b; is the declaration list for the
parameters. The difference between these two
definitions is that the first form acts as a prototype
declaration that forces conversion of the arguments of
subsequent calls to the function, whereas the second
form may not.
2. To pass one function to another, one might say
int f(void);
/* ... */
g(f);
Then the definition of g might read
page 174 Language
page 175
void g(int (*funcp)(void))
{
/* ... */ (*funcp)() /* or funcp() ... */
}
or, equivalently,
void g(int func(void))
{
/* ... */ func() /* or (*func)() ... */
}
6.7.2 External object definitions
Semantics
[#1] If the declaration of an identifier for an object has
file scope and an initializer, the declaration is an
external definition for the identifier.
[#2] A declaration of an identifier for an object that has
file scope without an initializer, and without a storage-
class specifier or with the storage-class specifier static,
constitutes a tentative definition. If a translation unit
contains one or more tentative definitions for an
identifier, and the translation unit contains no external
definition for that identifier, then the behavior is exactly
as if the translation unit contains a file scope declaration
of that identifier, with the composite type as of the end of
the translation unit, with an initializer equal to 0.
[#3] If the declaration of an identifier for an object is a
tentative definition and has internal linkage, the declared
type shall not be an incomplete type.
Examples
[#4]
1.
int i1 = 1; // definition, external linkage
static int i2 = 2; // definition, internal linkage
extern int i3 = 3; // definition, external linkage
int i4; // tentative definition, external linkage
static int i5; // tentative definition, internal linkage
page 175 Language
page 176
int i1; // valid tentative definition, refers to previous
int i2; // 6.1.2.2 renders undefined, linkage disagreement
int i3; // valid tentative definition, refers to previous
int i4; // valid tentative definition, refers to previous
int i5; // 6.1.2.2 renders undefined, linkage disagreement
extern int i1; // refers to previous, whose linkage is external
extern int i2; // refers to previous, whose linkage is internal
extern int i3; // refers to previous, whose linkage is external
extern int i4; // refers to previous, whose linkage is external
extern int i5; // refers to previous, whose linkage is internal
2. If at the end of the translation unit containing
int i[];
the array i still has incomplete type, the array is
assumed to have one element. This element is
initialized to zero on program startup.
page 176 Language
page 177
6.8 Preprocessing directives
Syntax
[#1]
preprocessing-file:
group-opt
group:
group-part
group group-part
group-part:
pp-tokens-opt new-line
if-section
control-line
if-section:
if-group elif-groups-opt else-group-opt endif-line
if-group:
# if constant-expr new-line group-opt
# ifdef identifier new-line group-opt
# ifndef identifier new-line group-opt
elif-groups:
elif-group
elif-groups elif-group
elif-group:
# elif constant-expr new-line group-opt
else-group:
# else new-line group-opt
endif-line:
# endif new-line
page 177 Language
page 178
control-line:
# include pp-tokens new-line
# define identifier replacement-list new-line
# define identifier lparen identifier-list-opt )
replacement-list new-line
# define identifier lparen ... ) replacement-list new-line
# define identifier lparen identifier-list , ... )
replacement-list new-line
# undef identifier new-line
# line pp-tokens new-line
# error pp-tokens-opt new-line
# pragma pp-tokens-opt new-line
# new-line
lparen:
the left-parenthesis character without preceding white-space
replacement-list:
pp-tokens-opt
pp-tokens:
preprocessing-token
pp-tokens preprocessing-token
new-line:
the new-line character
Description
[#2] A preprocessing directive consists of a sequence of
preprocessing tokens that begins with a # preprocessing
token that (at the start of translation phase 4) is either
the first character in the source file (optionally after
white space containing no new-line characters) or that
follows white space containing at least one new-line
character, and is ended by the next new-line character.121 A
new-line character ends the preprocessing directive even if
it occurs within what would otherwise be an invocation of a
function-like macro.
__________
121. Thus, preprocessing directives are commonly called
``lines.'' These ``lines'' have no other syntactic
significance, as all white space is equivalent except in
certain situations during preprocessing (see the #
character string literal creation operator in 6.8.3.2,
for example).
page 178 Language
page 179
Constraints
[#3] The only white-space characters that shall appear
between preprocessing tokens within a preprocessing
directive (from just after the introducing # preprocessing
token through just before the terminating new-line
character) are space and horizontal-tab (including spaces
that have replaced comments or possibly other white-space
characters in translation phase 3).
[#4] In the definition of an object-like macro, if the first
character of a replacement list is not a character required
by subclause 5.2.1, then there shall be white-space
separation between the identifier and the replacement
list.122
Semantics
[#5] The implementation can process and skip sections of
source files conditionally, include other source files, and
replace macros. These capabilities are called
preprocessing, because conceptually they occur before
translation of the resulting translation unit.
[#6] The preprocessing tokens within a preprocessing
directive are not subject to macro expansion unless
otherwise stated.
Examples
[#7] In:
#define EMPTY
EMPTY # include <file.h>
the sequence of preprocessing tokens on the second line is
not a preprocessing directive, because it does not begin
with a # at the start of translation phase 4, even though it
will do so after the macro EMPTY has been replaced.
__________
122. This allows an implementation to choose to interpret
the directive:
#define THIS$AND$THAT(a, b) ((a) + (b))
as defining a function-like macro THIS$AND$THAT, rather
than an object-like macro THIS. Whichever choice it
makes, it must also issue a diagnostic.
page 179 Language
page 180
6.8.1 Conditional inclusion
Constraints
[#1] The expression that controls conditional inclusion
shall be an integer constant expression except that: it
shall not contain a cast; identifiers (including those
lexically identical to keywords) are interpreted as
described below;123 and it may contain unary operator
expressions of the form
defined identifier
or
defined ( identifier )
which evaluate to 1 if the identifier is currently defined
as a macro name (that is, if it is predefined or if it has
been the subject of a #define preprocessing directive
without an intervening #undef directive with the same
subject identifier), 0 if it is not.
Semantics
[#2] Preprocessing directives of the forms
# if constant-expr new-line group-opt
# elif constant-expr new-line group-opt
check whether the controlling constant expression evaluates
to nonzero.
[#3] Prior to evaluation, macro invocations in the list of
preprocessing tokens that will become the controlling
constant expression are replaced (except for those macro
names modified by the defined unary operator), just as in
normal text. If the token defined is generated as a result
of this replacement process or use of the defined unary
operator does not match one of the two specified forms prior
to macro replacement, the behavior is undefined. After all
replacements due to macro expansion and the defined unary
operator have been performed, all remaining identifiers are
replaced with the pp-number 0, and then each preprocessing
__________
123. Because the controlling constant expression is
evaluated during translation phase 4, all identifiers
either are or are not macro names - there simply are no
keywords, enumeration constants, etc.
page 180 Language
page 181
token is converted into a token. The resulting tokens
compose the controlling constant expression which is
evaluated according to the rules of 6.4, except that all
signed integer types and all unsigned integer types act as
if they have the same representation as, respectively, the
types intmax_t and uintmax_t defined in the header
<inttypes.h>. This includes interpreting character
constants, which may involve converting escape sequences
into execution character set members. Whether the numeric
value for these character constants matches the value
obtained when an identical character constant occurs in an
expression (other than within a #if or #elif directive) is
implementation-defined.124 Also, whether a single-character
character constant may have a negative value is
implementation-defined.
[#4] Preprocessing directives of the forms
# ifdef identifier new-line group-opt
# ifndef identifier new-line group-opt
check whether the identifier is or is not currently defined
as a macro name. Their conditions are equivalent to #if
defined identifier and #if !defined identifier respectively.
[#5] Each directive's condition is checked in order. If it
evaluates to false (zero), the group that it controls is
skipped: directives are processed only through the name
that determines the directive in order to keep track of the
level of nested conditionals; the rest of the directives'
preprocessing tokens are ignored, as are the other
preprocessing tokens in the group. Only the first group
whose control condition evaluates to true (nonzero) is
processed. If none of the conditions evaluates to true, and
there is a #else directive, the group controlled by the
#else is processed; lacking a #else directive, all the
groups until the #endif are skipped.125
__________
124. Thus, the constant expression in the following #if
directive and if statement is not guaranteed to evaluate
to the same value in these two contexts.
#if 'z' - 'a' == 25
if ('z' - 'a' == 25)
125. As indicated by the syntax, a preprocessing token shall
not follow a #else or #endif directive before the
page 181 Language
page 182
Forward references: macro replacement (6.8.3), source file
inclusion (6.8.2), largest integer types (7.4.1.5).
6.8.2 Source file inclusion
Constraints
[#1] A #include directive shall identify a header or source
file that can be processed by the implementation.
Semantics
[#2] A preprocessing directive of the form
# include <h-char-sequence> new-line
searches a sequence of implementation-defined places for a
header identified uniquely by the specified sequence between
the < and > delimiters, and causes the replacement of that
directive by the entire contents of the header. How the
places are specified or the header identified is
implementation-defined.
[#3] A preprocessing directive of the form
# include "q-char-sequence" new-line
causes the replacement of that directive by the entire
contents of the source file identified by the specified
sequence between the " delimiters. The named source file is
searched for in an implementation-defined manner. If this
search is not supported, or if the search fails, the
directive is reprocessed as if it read
# include <h-char-sequence> new-line
with the identical contained sequence (including >
characters, if any) from the original directive.
[#4] A preprocessing directive of the form
# include pp-tokens new-line
____________________________________________________________
terminating new-line character. However, comments may
appear anywhere in a source file, including within a
preprocessing directive.
page 182 Language
page 183
(that does not match one of the two previous forms) is
permitted. The preprocessing tokens after include in the
directive are processed just as in normal text. (Each
identifier currently defined as a macro name is replaced by
its replacement list of preprocessing tokens.) The
directive resulting after all replacements shall match one
of the two previous forms.126 The method by which a
sequence of preprocessing tokens between a < and a >
preprocessing token pair or a pair of " characters is
combined into a single header name preprocessing token is
implementation-defined.
[#5] The implementation shall provide unique mappings for
sequences consisting of one or more letters or digits (as
defined in 5.2.1) followed by a period (.) and a single
letter. The first character shall be a letter. The
implementation may ignore the distinctions of alphabetical
case and restrict the mapping to eight significant
characters before the period.
[#6] A #include preprocessing directive may appear in a
source file that has been read because of a #include
directive in another file, up to an implementation-defined
nesting limit (see 5.2.4.1).
Examples
[#7]
1. The most common uses of #include preprocessing
directives are as in the following:
#include <stdio.h>
#include "myprog.h"
2. This illustrates macro-replaced #include directives:
__________
126. Note that adjacent string literals are not concatenated
into a single string literal (see the translation phases
in 5.1.1.2); thus, an expansion that results in two
string literals is an invalid directive.
page 183 Language
page 184
#if VERSION == 1
#define INCFILE "vers1.h"
#elif VERSION == 2
#define INCFILE "vers2.h" // and so on
#else
#define INCFILE "versN.h"
#endif
#include INCFILE
Forward references: macro replacement (6.8.3).
6.8.3 Macro replacement
Constraints
[#1] Two replacement lists are identical if and only if the
preprocessing tokens in both have the same number, ordering,
spelling, and white-space separation, where all white-space
separations are considered identical.
[#2] An identifier currently defined as a macro without use
of lparen (an object-like macro) shall not be redefined by
another #define preprocessing directive unless the second
definition is an object-like macro definition and the two
replacement lists are identical.
[#3] An identifier currently defined as a macro using lparen
(a function-like macro) shall not be redefined by another
#define preprocessing directive unless the second definition
is a function-like macro definition that has the same number
and spelling of parameters, and the two replacement lists
are identical.
[#4] If the identifier-list in the macro definition does not
end with an ellipsis, the number of arguments, including
those arguments consisting of no preprocessing tokens, in an
invocation of a function-like macro shall agree with the
number of parameters in the macro definition. Otherwise,
there shall be more arguments in the invocation than there
are parameters in the macro definition (excluding the ...).
There shall exist a ) preprocessing token that terminates
the invocation.
[#5] The identifier __VA_ARGS__ shall only occur in the
replacement-list of a #define preprocessing directive using
the ellipsis notation in the arguments.
[#6] A parameter identifier in a function-like macro shall
be uniquely declared within its scope.
page 184 Language
page 185
Semantics
[#7] The identifier immediately following the define is
called the macro name. There is one name space for macro
names. Any white-space characters preceding or following
the replacement list of preprocessing tokens are not
considered part of the replacement list for either form of
macro.
[#8] If a # preprocessing token, followed by an identifier,
occurs lexically at the point at which a preprocessing
directive could begin, the identifier is not subject to
macro replacement.
[#9] A preprocessing directive of the form
# define identifier replacement-list new-line
defines an object-like macro that causes each subsequent
instance of the macro name127 to be replaced by the
replacement list of preprocessing tokens that constitute the
remainder of the directive. The replacement list is then
rescanned for more macro names as specified below.
[#10] A preprocessing directive of the form
# define identifier lparen identifier-list-opt ) replacement-list new-line
# define identifier lparen ... ) replacement-list new-line
# define identifier lparen identifier-list , ... ) replacement-list new-line
defines a function-like macro with arguments, similar
syntactically to a function call. The parameters are
specified by the optional list of identifiers, whose scope
extends from their declaration in the identifier list until
the new-line character that terminates the #define
preprocessing directive. Each subsequent instance of the
function-like macro name followed by a ( as the next
preprocessing token introduces the sequence of preprocessing
tokens that is replaced by the replacement list in the
definition (an invocation of the macro). The replaced
sequence of preprocessing tokens is terminated by the
__________
127. Since, by macro-replacement time, all character
constants and string literals are preprocessing tokens,
not sequences possibly containing identifier-like
subsequences (see 5.1.1.2, translation phases), they are
never scanned for macro names or parameters.
page 185 Language
page 186
matching ) preprocessing token, skipping intervening matched
pairs of left and right parenthesis preprocessing tokens.
Within the sequence of preprocessing tokens making up an
invocation of a function-like macro, new-line is considered
a normal white-space character.
[#11] The sequence of preprocessing tokens bounded by the
outside-most matching parentheses forms the list of
arguments for the function-like macro. The individual
arguments within the list are separated by comma
preprocessing tokens, but comma preprocessing tokens between
matching inner parentheses do not separate arguments. If
there are sequences of preprocessing tokens within the list
of arguments that would otherwise act as preprocessing
directives, the behavior is undefined.
[#12] If there is a ... in the identifier-list in the macro
definition, then the trailing arguments, including any
separating comma preprocessing tokens, are merged to form a
single item: the variable arguments. The number of
arguments so combined is such that, following merger, the
number of arguments is one more than the number of
parameters in the macro definition (excluding the ...).
6.8.3.1 Argument substitution
[#1] After the arguments for the invocation of a function-
like macro have been identified, argument substitution takes
place. A parameter in the replacement list, unless preceded
by a # or ## preprocessing token or followed by a ##
preprocessing token (see below), is replaced by the
corresponding argument after all macros contained therein
have been expanded. Before being substituted, each
argument's preprocessing tokens are completely macro
replaced as if they formed the rest of the preprocessing
file; no other preprocessing tokens are available.
[#2] An identifier __VA_ARGS__ that occurs in the
replacement list shall be treated as if it were a parameter,
and the variable arguments shall form the preprocessing
tokens used to replace it.
page 186 Language
page 187
6.8.3.2 The # operator
Constraints
[#1] Each # preprocessing token in the replacement list for
a function-like macro shall be followed by a parameter as
the next preprocessing token in the replacement list.
Semantics
[#2] If, in the replacement list, a parameter is immediately
preceded by a # preprocessing token, both are replaced by a
single character string literal preprocessing token that
contains the spelling of the preprocessing token sequence
for the corresponding argument. Each occurrence of white
space between the argument's preprocessing tokens becomes a
single space character in the character string literal.
White space before the first preprocessing token and after
the last preprocessing token comprising the argument is
deleted. Otherwise, the original spelling of each
preprocessing token in the argument is retained in the
character string literal, except for special handling for
producing the spelling of string literals and character
constants: a \ character is inserted before each " and \
character of a character constant or string literal
(including the delimiting " characters). If the replacement
that results is not a valid character string literal, the
behavior is undefined. The character string literal
corresponding to an empty argument is "". The order of
evaluation of # and ## operators is unspecified.
6.8.3.3 The ## operator
Constraints
[#1] A ## preprocessing token shall not occur at the
beginning or at the end of a replacement list for either
form of macro definition.
Semantics
[#2] If, in the replacement list, a parameter is immediately
preceded or followed by a ## preprocessing token, the
parameter is replaced by the corresponding argument's
preprocessing token sequence; however, if an argument
consists of no preprocessing tokens, the parameter is
replaced by a placemarker preprocessing token instead.
[#3] For both object-like and function-like macro
invocations, before the replacement list is reexamined for
more macro names to replace, each instance of a ##
page 187 Language
page 188
preprocessing token in the replacement list (not from an
argument) is deleted and the preceding preprocessing token
is concatenated with the following preprocessing token
(placemarker preprocessing tokens are handled specially:
concatenation of two placemarkers results in a single
placemarker preprocessing token; concatenation of a
placemarker with a non - placemarker preprocessing token
results in the non-placemarker preprocessing token). If the
result is not a valid preprocessing token, the behavior is
undefined. The resulting token is available for further
macro replacement. The order of evaluation of ## operators
is unspecified.
Examples
[#4]
#define hash_hash # ## #
#define mkstr(a) # a
#define in_between(a) mkstr(a)
#define join(c, d) in_between(c hash_hash d)
char p[] = join(x, y); // equivalent to
// char p[] = "x ## y";
The expansion produces, at various stages:
join(x, y)
in_between(x hash_hash y)
in_between(x ## y)
mkstr(x ## y)
"x ## y"
In other words, expanding hash_hash produces a new token,
consisting of two adjacent sharp signs, but this new token
is not the catenation operator.
6.8.3.4 Rescanning and further replacement
[#1] After all parameters in the replacement list have been
substituted and # and ## processing has taken place, all
placemarker preprocessing tokens are removed, then the
resulting preprocessing token sequence is rescanned with all
subsequent preprocessing tokens of the source file for more
macro names to replace.
page 188 Language
page 189
[#2] If the name of the macro being replaced is found during
this scan of the replacement list (not including the rest of
the source file's preprocessing tokens), it is not replaced.
Further, if any nested replacements encounter the name of
the macro being replaced, it is not replaced. These
nonreplaced macro name preprocessing tokens are no longer
available for further replacement even if they are later
(re)examined in contexts in which that macro name
preprocessing token would otherwise have been replaced.
[#3] The resulting completely macro-replaced preprocessing
token sequence is not processed as a preprocessing directive
even if it resembles one, but all pragma unary operator
expressions within it are then processed as specified in
6.8.9 below.
6.8.3.5 Scope of macro definitions
[#1] A macro definition lasts (independent of block
structure) until a corresponding #undef directive is
encountered or (if none is encountered) until the end of
translation phase 4.
[#2] A preprocessing directive of the form
# undef identifier new-line
causes the specified identifier no longer to be defined as a
macro name. It is ignored if the specified identifier is
not currently defined as a macro name.
Examples
[#3]
1. The simplest use of this facility is to define a
``manifest constant,'' as in
#define TABSIZE 100
int table[TABSIZE];
2. The following defines a function-like macro whose
value is the maximum of its arguments. It has the
advantages of working for any compatible types of the
arguments and of generating in-line code without the
overhead of function calling. It has the
disadvantages of evaluating one or the other of its
arguments a second time (including side effects) and
generating more code than a function if invoked
several times. It also cannot have its address taken,
as it has none.
page 189 Language
page 190
#define max(a, b) ((a) > (b) ? (a) : (b))
The parentheses ensure that the arguments and the
resulting expression are bound properly.
3. To illustrate the rules for redefinition and
reexamination, the sequence
#define x 3
#define f(a) f(x * (a))
#undef x
#define x 2
#define g f
#define z z[0]
#define h g(~
#define m(a) a(w)
#define w 0,1
#define t(a) a
#define p() int
#define q(x) x
#define r(x,y) x ## y
#define str(x) # x
f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
g(x+(3,4)-w) | h 5) & m
(f)^m(m);
p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
char c[2][6] = { str(hello), str() };
results in
f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
int i[] = { 1, 23, 4, 5, };
char c[2][6] = { "hello", "" };
4. To illustrate the rules for creating character string
literals and concatenating tokens, the sequence
page 190 Language
page 191
#define str(s) # s
#define xstr(s) str(s)
#define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
x ## s, x ## t)
#define INCFILE(n) vers ## n // from previous #include example
#define glue(a, b) a ## b
#define xglue(a, b) glue(a, b)
#define HIGHLOW "hello"
#define LOW LOW ", world"
debug(1, 2);
fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
== 0) str(: @\n), s);
#include xstr(INCFILE(2).h)
glue(HIGH, LOW);
xglue(HIGH, LOW)
results in
printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
fputs(
"strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
s);
#include "vers2.h" (after macro replacement, before file access)
"hello";
"hello" ", world"
or, after concatenation of the character string
literals,
printf("x1= %d, x2= %s", x1, x2);
fputs(
"strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
s);
#include "vers2.h" (after macro replacement, before file access)
"hello";
"hello, world"
Space around the # and ## tokens in the macro
definition is optional.
5. To illustrate the rules for
placemarker ## placemarker
the sequence
#define t(x,y,z) x ## y ## z
int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
t(10,,), t(,11,), t(,,12), t(,,) };
results in
page 191 Language
page 192
int j[] = { 123, 45, 67, 89,
10, 11, 12, };
6. To demonstrate the redefinition rules, the following
sequence is valid.
#define OBJ_LIKE (1-1)
#define OBJ_LIKE /* white space */ (1-1) /* other */
#define FUNC_LIKE(a) ( a )
#define FUNC_LIKE( a )( /* note the white space */ \
a /* other stuff on this line
*/ )
But the following redefinitions are invalid:
#define OBJ_LIKE (0) /* different token sequence */
#define OBJ_LIKE (1 - 1) /* different white space */
#define FUNC_LIKE(b) ( a ) /* different parameter usage */
#define FUNC_LIKE(b) ( b ) /* different parameter spelling */
7. Finally, to show the variable argument list macro
facilities:
#define debug(...) fprintf(stderr, __VA_ARGS__)
#define showlist(...) puts(#__VA_ARGS__)
#define report(test, ...) ((test)?puts(#test):\
printf(__VA_ARGS__))
debug("Flag");
debug("X = %d\n", x);
showlist(The first, second, and third items.);
report(x>y, "x is %d but y is %d", x, y);
results in
fprintf(stderr, "Flag" );
fprintf(stderr, "X = %d\n", x );
puts( "The first, second, and third items." );
((x>y)?puts("x>y"):
printf("x is %d but y is %d", x, y));
page 192 Language
page 193
6.8.4 Line control
Constraints
[#1] The string literal of a #line directive, if present,
shall be a character string literal.
Semantics
[#2] The line number of the current source line is one
greater than the number of new-line characters read or
introduced in translation phase 1 (5.1.1.2) while processing
the source file to the current token.
[#3] A preprocessing directive of the form
# line digit-sequence new-line
causes the implementation to behave as if the following
sequence of source lines begins with a source line that has
a line number as specified by the digit sequence
(interpreted as a decimal integer). The digit sequence
shall not specify zero, nor a number greater than
2147483647.
[#4] A preprocessing directive of the form
# line digit-sequence "s-char-sequence-opt" new-line
sets the line number similarly and changes the presumed name
of the source file to be the contents of the character
string literal.
[#5] A preprocessing directive of the form
# line pp-tokens new-line
(that does not match one of the two previous forms) is
permitted. The preprocessing tokens after line on the
directive are processed just as in normal text (each
identifier currently defined as a macro name is replaced by
its replacement list of preprocessing tokens). The
directive resulting after all replacements shall match one
of the two previous forms and is then processed as
appropriate.
page 193 Language
page 194
6.8.5 Error directive
Semantics
[#1] A preprocessing directive of the form
# error pp-tokens-opt new-line
causes the implementation to produce a diagnostic message
that includes the specified sequence of preprocessing
tokens.
6.8.6 Pragma directive
Semantics
[#1] A preprocessing directive of the form
# pragma pp-tokens-opt new-line
where the preprocessing token STDC does not immediately
follow the pragma on the directive causes the implementation
to behave in a manner which it shall document. The behavior
might cause translation to fail or the resulting program to
behave in a non-conforming manner. Any such pragma that is
not recognized by the implementation is ignored.
[#2] If the preprocessing token STDC does immediately follow
the pragma on the directive, then no macro replacements are
performed on the directive, and the directive shall have one
of the following forms whose meaning is described elsewhere:
#pragma STDC FP_CONTRACT on-off-switch
#pragma STDC FENV_ACCESS on-off-switch
#pragma STDC CX_LIMITED_RANGE on-off-switch
on-off-switch: one of
ON OFF DEFAULT
Forward references: the FP_CONTRACT pragma (7.7.2), the
FENV_ACCESS pragma (7.6.1), the CX_LIMITED_RANGE pragma
(7.8.1).
page 194 Language
page 195
6.8.7 Null directive
Semantics
[#1] A preprocessing directive of the form
# new-line
has no effect.
6.8.8 Predefined macro names
[#1] The following macro names shall be defined by the
implementation:
__LINE__ The line number of the current source line (a
decimal constant).
__FILE__ The presumed name of the source file (a character
string literal).
__DATE__ The date of translation of the source file (a
character string literal of the form "Mmm dd yyyy",
where the names of the months are the same as those
generated by the asctime function, and the first
character of dd is a space character if the value
is less than 10). If the date of translation is
not available, an implementation-defined valid date
shall be supplied.
__TIME__ The time of translation of the source file (a
character string literal of the form "hh:mm:ss" as
in the time generated by the asctime function). If
the time of translation is not available, an
implementation-defined valid time shall be
supplied.
__STDC__ The decimal constant 1, intended to indicate a
conforming implementation.
__STDC_VERSION__ The decimal constant 199901L.128
[#2] The following macro names are conditionally defined by
the implementation: 624.nr:c 0u+000m'unu
__________
128. The value in ISO/IEC 9899:1994 was 199409L.
page 195 Language
page 196
__STDC_IEC_559__ The decimal constant 1, intended to
indicate conformance to the specifications in Annex F (IEC
559 floating-point arithmetic).
__STDC_IEC_559_COMPLEX__ The decimal constant 1, intended to
indicate adherence to the specifications in informative
Annex G (IEC 559 compatible complex arithmetic).
[#3] The values of the predefined macros (except for
__LINE__ and __FILE__) remain constant throughout the
translation unit.
[#4] None of these macro names, nor the identifier defined,
shall be the subject of a #define or a #undef preprocessing
directive. All predefined macro names shall begin with a
leading underscore followed by an uppercase letter or a
second underscore.
Forward references: the asctime function (7.16.3.1).
6.8.9 Pragma operator
Semantics
[#1] A unary operator expression of the form:
_Pragma ( string-literal )
is processed as follows. The string-literal is destringized
by deleting the L prefix, if present, deleting the leading
and trailing double-quotes, replacing each escape sequence
\" by a double-quote, and replacing each escape sequence \\
by a single backslash. The resulting sequence of characters
is processed through translation phase 3 to produce
preprocessing tokens that are executed as if they were the
pp-tokens in a pragma directive. The original four
preprocessing tokens in the unary operator expression are
removed.
Examples
[#2] A directive of the form:
#pragma list on "..\listing.dir"
can also be expressed as:
_Pragma ( "listing on \"..\\listing.dir\"" )
The latter form is processed in the same way whether it
appears literally as shown, or results from macro
page 196 Language
page 197
replacement, as in:
#define LISTING(x) PRAGMA(listing on #x)
#define PRAGMA(x) _Pragma(#x)
LISTING ( ..\listing.dir )
page 197 Language
page 198
6.9 Future language directions
6.9.1 Character escape sequences
[#1] Lowercase letters as escape sequences are reserved for
future standardization. Other characters may be used in
extensions.
6.9.2 Storage-class specifiers
[#1] The placement of a storage-class specifier other than
at the beginning of the declaration specifiers in a
declaration is an obsolescent feature.
6.9.3 Function declarators
[#1] The use of function declarators with empty parentheses
(not prototype-format parameter type declarators) is an
obsolescent feature.
6.9.4 Function definitions
[#1] The use of function definitions with separate parameter
identifier and declaration lists (not prototype-format
parameter type and identifier declarators) is an obsolescent
feature.
6.9.5 Pragma directives
[#1] Pragmas whose first pp-token is STDC are reserved for
future standardization.
page 198 Language
page 199
7. Library
7.1 Introduction
7.1.1 Definitions of terms
[#1] A string is a contiguous sequence of characters
terminated by and including the first null character. A
``pointer to'' a string is a pointer to its initial (lowest
addressed) character. The ``length'' of a string is the
number of characters preceding the null character and its
``value'' is the sequence of the values of the contained
characters, in order.
[#2] A letter is a printing character in the execution
character set corresponding to any of the 52 required
lowercase and uppercase letters in the source character set,
listed in 5.2.1.
[#3] The decimal-point character is the character used by
functions that convert floating-point numbers to or from
character sequences to denote the beginning of the
fractional part of such character sequences.129 It is
represented in the text and examples by a period, but may be
changed by the setlocale function.
[#4] A wide character is a code value (a binary encoded
integer) of an object of type wchar_t that corresponds to a
member of the extended character set.130
[#5] A null wide character is a wide character with code
value zero.
[#6] A wide string is a contiguous sequence of wide
characters terminated by and including the first null wide
__________
129. The functions that make use of the decimal-point
character are atof, fprintf, fscanf, fwprintf, fwscanf,
localeconv, printf, scanf, sprintf, sscanf, strtod,
swprintf, swscanf, vfprintf, vfscanf, vfwprintf,
vfwscanf, vprintf, vscanf, vsprintf, vsscanf, vswprintf,
vswscanf, vwprintf, vwscanf, wprintf, and wscanf.
130. An equivalent definition can be found in subclause
6.1.3.4.
page 199 Library
page 200
character. A pointer to a wide string is a pointer to its
initial (lowest addressed) wide character. The length of a
wide string is the number of wide characters preceding the
null wide character and the value of a wide string is the
sequence of code values of the contained wide characters, in
order.
[#7] A shift sequence is a contiguous sequence of bytes
within a multibyte string that (potentially) causes a change
in shift state. (See subclause 5.2.1.2.) A shift sequence
shall not have a corresponding wide character; it is instead
taken to be an adjunct to an adjacent multibyte
character.131
Forward references: character handling (7.3), the setlocale
function (7.5.1.1).
7.1.2 Standard headers
[#1] Each library function is declared, with a type that
includes a prototype, in a header,132 whose contents are
made available by the #include preprocessing directive. The
header declares a set of related functions, plus any
necessary types and additional macros needed to facilitate
their use. Declarations of types described in this clause
shall not include type qualifiers, unless explicity stated
otherwise.
[#2] The standard headers are
__________
131. For state-dependent encodings, the values for
MB_CUR_MAX and MB_LEN_MAX must thus be large enough to
count all the bytes in any complete multibyte character
plus at least one adjacent shift sequence of maximum
length. Whether these counts provide for more than one
shift sequence is the implementation's choice.
132. A header is not necessarily a source file, nor are the
< and > delimited sequences in header names necessarily
valid source file names.
page 200 Library
page 201
<assert.h> <complex.h> <ctype.h>
<errno.h> <fenv.h> <float.h>
<inttypes.h> <iso646.h> <limits.h>
<locale.h> <math.h> <setjmp.h>
<signal.h> <stdarg.h> <stdbool.h>
<stddef.h> <stdio.h> <stdlib.h>
<string.h> <tgmath.h> <time.h>
<wchar.h> <wctype.h>
[#3] If a file with the same name as one of the above < and
> delimited sequences, not provided as part of the
implementation, is placed in any of the standard places for
a source file to be included, the behavior is undefined.
[#4] Standard headers may be included in any order; each may
be included more than once in a given scope, with no effect
different from being included only once, except that the
effect of including <assert.h> depends on the definition of
NDEBUG. If used, a header shall be included outside of any
external declaration or definition, and it shall first be
included before the first reference to any of the functions
or objects it declares, or to any of the types or macros it
defines. However, if an identifier is declared or defined
in more than one header, the second and subsequent
associated headers may be included after the initial
reference to the identifier. The program shall not have any
macros with names lexically identical to keywords currently
defined prior to the inclusion.
[#5] Any definition of an object-like macro described in
this clause shall expand to code that is fully protected by
parentheses where necessary, so that it groups in an
arbitrary expression as if it were a single identifier.
[#6] Any declaration of a library function shall have
external linkage.
Forward references: diagnostics (7.2).
page 201 Library
page 202
7.1.3 Reserved identifiers
[#1] Each header declares or defines all identifiers listed
in its associated subclause, and optionally declares or
defines identifiers listed in its associated future library
directions subclause and identifiers which are always
reserved either for any use or for use as file scope
identifiers.
- All identifiers that begin with an underscore and
either an uppercase letter or another underscore are
always reserved for any use.
- All identifiers that begin with an underscore are
always reserved for use as macros and as identifiers
with file scope in both the ordinary and tag name
spaces.
- Each macro name in any of the following subclauses
(including the future library directions) is reserved
for use as specified if any of its associated headers
is included; unless explicitly stated otherwise (see
7.1.8).
- All identifiers with external linkage in any of the
following subclauses (including the future library
directions) are always reserved for use as identifiers
with external linkage.133
- Each identifier with file scope listed in any of the
following subclauses (including the future library
directions) is reserved for use as macro and as an
identifier with file scope in the same name space if
any of its associated headers is included.
[#2] No other identifiers are reserved. If the program
declares or defines an identifier that is reserved in that
context (other than as allowed by 7.1.8), the behavior is
undefined.134
__________
133. The list of reserved identifiers with external linkage
includes errno, setjmp, and va_end.
134. Since macro names are replaced whenever found,
independent of scope and name space, macro names
matching any of the reserved identifier names must not
be defined if an associated header, if any, is included.
page 202 Library
page 203
[#3] If the program removes (with #undef) any macro
definition of an identifier in the first group listed above,
the behavior is undefined.
7.1.4 Errors <errno.h>
[#1] The header <errno.h> defines several macros, all
relating to the reporting of error conditions.
[#2] The macros are
EDOM
EILSEQ
ERANGE
which expand to integer constant expressions with type int,
distinct positive values, and which are suitable for use in
#if preprocessing directives; and
errno
which expands to a modifiable lvalue135 that has type int,
the value of which is set to a positive error number by
several library functions. It is unspecified whether errno
is a macro or an identifier declared with external linkage.
If a macro definition is suppressed in order to access an
actual object, or a program defines an identifier with the
name errno, the behavior is undefined.
[#3] The value of errno is zero at program startup, but is
never set to zero by any library function.136 The value of
errno may be set to nonzero by a library function call
whether or not there is an error, provided the use of errno
is not documented in the description of the function in this
International Standard.
__________
135. The macro errno need not be the identifier of an
object. It might expand to a modifiable lvalue
resulting from a function call (for example, *errno()).
136. Thus, a program that uses errno for error checking
should set it to zero before a library function call,
then inspect it before a subsequent library function
call. Of course, a library function can save the value
of errno on entry and then set it to zero, as long as
the original value is restored if errno's value is still
zero just before the return.
page 203 Library
page 204
[#4] Additional macro definitions, beginning with E and a
digit or E and an uppercase letter,137 may also be specified
by the implementation.
7.1.5 Limits <float.h> and <limits.h>
[#1] The headers <float.h> and <limits.h> define several
macros that expand to various limits and parameters.
[#2] The macros, their meanings, and the constraints (or
restrictions) on their values are listed in 5.2.4.2.
7.1.6 Common definitions <stddef.h>
[#1] The following types and macros are defined in the
standard header <stddef.h>. Some are also defined in other
headers, as noted in their respective subclauses.
[#2] The types are
ptrdiff_t
which is the signed integer type of the result of
subtracting two pointers;
size_t
which is the unsigned integer type of the result of the
sizeof operator; and
wchar_t
which is an integer type whose range of values can represent
distinct codes for all members of the largest extended
character set specified among the supported locales; the
null character shall have the code value zero and each
member of the basic character set defined in 5.2.1 shall
have a code value equal to its value when used as the lone
character in an integer character constant.
[#3] The macros are
NULL
which expands to an implementation-defined null pointer
__________
137. See ``future library directions'' (7.20.1).
page 204 Library
page 205
constant; and
offsetof(type, member-designator)
which expands to an integer constant expression that has
type size_t, the value of which is the offset in bytes, to
the structure member (designated by member-designator), from
the beginning of its structure (designated by type). The
member-designator shall be such that given
static type t;
then the expression &(t.member-designator) evaluates to an
address constant. (If the specified member is a bit-field,
the behavior is undefined.)
Forward references: localization (7.5).
7.1.7 Boolean type and values <stdbool.h>
[#1] The header <stdbool.h> defines one type and three
macros.
[#2] The type is
bool
which is an integer type that promotes to int or unsigned
int, and that is suitable to be used as the type of a bit-
field. A bit-field of any width and type bool shall be
capable for representing the value 1.138
__________
138. The traditional choice for type bool has been int, but
this is not a requirement of this International
Standard. Other available choices include, but are not
limited to, char, unsigned int, and an enumeration type.
If an enumeration type is chosen, the names of its true
and false members are "masked" by the macros true and
false, but the member names might be available to the
debugger:
typedef enum { false=0, true=1 } bool;
#define false 0
#define true 1
The type is suitable for bit-fields if it is int,
unsigned int, signed int, or some type allowed by an
page 205 Library
page 206
[#3] The macros are
true
which expands to the decimal constant 1,
false
which expands to the decimal constant 0, and
__bool_true_false_are_defined
which expands to the decimal constant 1. The macros are
suitable for use in #if preprocessing directives.
7.1.8 Use of library functions
[#1] Each of the following statements applies unless
explicitly stated otherwise in the detailed descriptions
that follow. If an argument to a function has an invalid
value (such as a value outside the domain of the function,
or a pointer outside the address space of the program, or a
null pointer) or a type (after promotion) not expected by a
function with variable number of arguments, the behavior is
undefined. If a function argument is described as being an
array, the pointer actually passed to the function shall
have a value such that all address computations and accesses
to objects (that would be valid if the pointer did point to
the first element of such an array) are in fact valid. Any
function declared in a header may be additionally
implemented as a function-like macro defined in the header,
so if a library function is declared explicitly when its
header is included, one of the techniques shown below can be
used to ensure the declaration is not affected by such a
macro. Any macro definition of a function can be suppressed
locally by enclosing the name of the function in
parentheses, because the name is then not followed by the
left parenthesis that indicates expansion of a macro
function name. For the same syntactic reason, it is
permitted to take the address of a library function even if
it is also defined as a macro.139 The use of #undef to
____________________________________________________________
implementation extension. It is required that a bool
bit-field of width 1 be unsigned. Thus, bool cannot be
signed int, nor can it be plain int if width 1 plain int
bit-fields are signed.
139. This means that an implementation must provide an
page 206 Library
page 207
remove any macro definition will also ensure that an actual
function is referred to. Any invocation of a library
function that is implemented as a macro shall expand to code
that evaluates each of its arguments exactly once, fully
protected by parentheses where necessary, so it is generally
safe to use arbitrary expressions as arguments.140
Likewise, those function-like macros described in the
following subclauses may be invoked in an expression
anywhere a function with a compatible return type could be
called.141 All object-like macros listed as expanding to
integer constant expressions shall additionally be suitable
for use in #if preprocessing directives.
[#2] Provided that a library function can be declared
without reference to any type defined in a header, it is
also permissible to declare the function and use it without
including its associated header.
____________________________________________________________
actual function for each library function, even if it
also provides a macro for that function.
140. Such macros might not contain the sequence points that
the corresponding function calls do.
141. Because external identifiers and some macro names
beginning with an underscore are reserved,
implementations may provide special semantics for such
names. For example, the identifier _BUILTIN_abs could
be used to indicate generation of in-line code for the
abs function. Thus, the appropriate header could
specify
#define abs(x) _BUILTIN_abs(x)
for a compiler whose code generator will accept it.
In this manner, a user desiring to guarantee that a
given library function such as abs will be a genuine
function may write
#undef abs
whether the implementation's header provides a macro
implementation of abs or a built-in implementation. The
prototype for the function, which precedes and is hidden
by any macro definition, is thereby revealed also.
page 207 Library
page 208
[#3] There is a sequence point immediately before a library
function return.
[#4] The functions in the standard library are not
guaranteed to be reentrant and may modify objects with
static storage duration.142
Examples
[#5] The function atoi may be used in any of several ways:
- by use of its associated header (possibly generating a
macro expansion)
#include <stdlib.h>
const char *str;
/* ... */
i = atoi(str);
- by use of its associated header (assuredly generating a
true function reference)
#include <stdlib.h>
#undef atoi
const char *str;
/* ... */
i = atoi(str);
or
#include <stdlib.h>
const char *str;
/* ... */
i = (atoi)(str);
- by explicit declaration
extern int atoi(const char *);
const char *str;
/* ... */
i = atoi(str);
__________
142. Thus, a signal handler cannot, in general, call
standard library functions.
page 208 Library
page 209
7.2 Diagnostics <assert.h>
[#1] The header <assert.h> defines the assert macro and
refers to another macro,
NDEBUG
which is not defined by <assert.h>. If NDEBUG is defined as
a macro name at the point in the source file where
<assert.h> is included, the assert macro is defined simply
as
#define assert(ignore) ((void)0)
[#2] The assert macro shall be implemented as a macro, not
as an actual function. If the macro definition is
suppressed in order to access an actual function, the
behavior is undefined.
7.2.1 Program diagnostics
7.2.1.1 The assert macro
Synopsis
[#1]
#include <assert.h>
void assert(int expression);
Description
[#2] The assert macro puts diagnostic tests into programs.
When it is executed, if expression is false (that is,
compares equal to 0), the assert macro writes information
about the particular call that failed (including the text of
the argument, the name of the source file, and the source
line number -- the latter are respectively the values of
the preprocessing macros __FILE__ and __LINE__ and the
identifier __func__) on the standard error file in an
implementation-defined format.143 It then calls the abort
function.
__________
143. The message written might be of the form
Assertion failed: expression, function abc, file xyz,
line nnn
page 209 Library
page 210
Returns
[#3] The assert macro returns no value.
Forward references: the abort function (7.14.4.1).
page 210 Library
page 211
7.3 Character handling <ctype.h>
[#1] The header <ctype.h> declares several functions useful
for testing and mapping characters.144 In all cases the
argument is an int, the value of which shall be
representable as an unsigned char or shall equal the value
of the macro EOF. If the argument has any other value, the
behavior is undefined.
[#2] The behavior of these functions is affected by the
current locale. Those functions that have locale-specific
aspects only when not in the "C" locale are noted below.
[#3] The term printing character refers to a member of a
locale-specific set of characters, each of which occupies
one printing position on a display device; the term control
character refers to a member of a locale-specific set of
characters that are not printing characters.145
Forward references: EOF (7.13.1), localization (7.5).
7.3.1 Character testing functions
[#1] The functions in this subclause return nonzero (true)
if and only if the value of the argument c conforms to that
in the description of the function.
7.3.1.1 The isalnum function
Synopsis
[#1]
#include <ctype.h>
int isalnum(int c);
__________
144. See ``future library directions'' (7.20.2).
145. In an implementation that uses the seven-bit ASCII
character set, the printing characters are those whose
values lie from 0x20 (space) through 0x7E (tilde); the
control characters are those whose values lie from 0
(NUL) through 0x1F (US), and the character 0x7F (DEL).
page 211 Library
page 212
Description
[#2] The isalnum function tests for any character for which
isalpha or isdigit is true.
7.3.1.2 The isalpha function
Synopsis
[#1]
#include <ctype.h>
int isalpha(int c);
Description
[#2] The isalpha function tests for any character for which
isupper or islower is true, or any character that is one of
a locale-specific set of characters for which none of
iscntrl, isdigit, ispunct, or isspace is true.146 In the
"C" locale, isalpha returns true only for the characters for
which isupper or islower is true.
7.3.1.3 The isblank function
Synopsis
[#1]
#include <ctype.h>
int isblank(int c);
Description
[#2] The isblank function tests for any character for that
is a standard blank character or is one of a locale-specific
set of characters, for which isalnum is false. The standard
blank characters are the following: space (' '), and
horizontal tab ('\t'). In the "C" locale, isblank returns
true only for the standard blank characters.
__________
146. The functions islower and isupper test true or false
separately for each of these additional characters; all
four combinations are possible.
page 212 Library
page 213
7.3.1.4 The iscntrl function
Synopsis
[#1]
#include <ctype.h>
int iscntrl(int c);
Description
[#2] The iscntrl function tests for any control character.
7.3.1.5 The isdigit function
Synopsis
[#1]
#include <ctype.h>
int isdigit(int c);
Description
[#2] The isdigit function tests for any decimal-digit
character (as defined in 5.2.1).
7.3.1.6 The isgraph function
Synopsis
[#1]
#include <ctype.h>
int isgraph(int c);
Description
[#2] The isgraph function tests for any printing character
except space (' ').
7.3.1.7 The islower function
Synopsis
[#1]
#include <ctype.h>
int islower(int c);
page 213 Library
page 214
Description
[#2] The islower function tests for any character that is a
lowercase letter or is one of a locale-specific set of
characters for which none of iscntrl, isdigit, ispunct, or
isspace is true. In the "C" locale, islower returns true
only for the characters defined as lowercase letters (as
defined in 5.2.1).
7.3.1.8 The isprint function
Synopsis
[#1]
#include <ctype.h>
int isprint(int c);
Description
[#2] The isprint function tests for any printing character
including space (' ').
7.3.1.9 The ispunct function
Synopsis
[#1]
#include <ctype.h>
int ispunct(int c);
Description
[#2] The ispunct function tests for any printing character
that is one of a locale-specific set of characters for which
neither isspace nor isalnum is true.
7.3.1.10 The isspace function
Synopsis
[#1]
#include <ctype.h>
int isspace(int c);
page 214 Library
page 215
Description
[#2] The isspace function tests for any character that is a
standard white-space character or is one of a locale-
specific set of characters for which isalnum is false. The
standard white-space characters are the following: space
(' '), form feed ('\f'), new-line ('\n'), carriage return
('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In
the "C" locale, isspace returns true only for the standard
white-space characters.
7.3.1.11 The isupper function
Synopsis
[#1]
#include <ctype.h>
int isupper(int c);
Description
[#2] The isupper function tests for any character that is an
uppercase letter or is one of a locale-specific set of
characters for which none of iscntrl, isdigit, ispunct, or
isspace is true. In the "C" locale, isupper returns true
only for the characters defined as uppercase letters (as
defined in 5.2.1).
7.3.1.12 The isxdigit function
Synopsis
[#1]
#include <ctype.h>
int isxdigit(int c);
Description
[#2] The isxdigit function tests for any hexadecimal-digit
character (as defined in 6.1.3.1).
page 215 Library
page 216
7.3.2 Character case mapping functions
7.3.2.1 The tolower function
Synopsis
[#1]
#include <ctype.h>
int tolower(int c);
Description
[#2] The tolower function converts an uppercase letter to a
corresponding lowercase letter.
Returns
[#3] If the argument is a character for which isupper is
true and there are one or more corresponding characters, as
specified by the current locale, for which islower is true,
the tolower function returns one of the corresponding
characters (always the same one for any given locale);
otherwise, the argument is returned unchanged.
7.3.2.2 The toupper function
Synopsis
[#1]
#include <ctype.h>
int toupper(int c);
Description
[#2] The toupper function converts a lowercase letter to a
corresponding uppercase letter.
Returns
[#3] If the argument is a character for which islower is
true and there are one or more corresponding characters, as
specified by the current locale, for which isupper is true,
the toupper function returns one of the corresponding
characters (always the same one for any given locale);
otherwise, the argument is returned unchanged.
page 216 Library
page 217
7.4 Integer types <inttypes.h>
[#1] The header <inttypes.h> defines sets of typedef names
for integer types having specified widths, and defines
corresponding sets of macros. It also defines macros that
specify limits of integer types corresponding to typedef
names defined in other standard headers, and declares four
functions for converting numeric character strings to
greatest-width integers.
[#2] Typedef names are defined in the following categories:
- integer types having certain exact widths;
- integer types having at least certain specified widths;
- fastest integer types having at least certain specified
widths;
- integer types wide enough to hold pointers to objects;
- integer types having greatest width.
(Some of these typedef names may denote the same type.)
[#3] Corresponding macros specify limits of the defined
types, construct suitable character constants, and provide
conversion specifiers for use with the formatted
input/output functions.
[#4] For each typedef name described herein that can be
defined as a type existing in the implementation,147
<inttypes.h> shall define that typedef name, and it shall
define the associated macros. Conversely, for each typedef
name described herein that cannot be defined as a type
existing in the implementation, <inttypes.h> shall not
define that typedef name, nor shall it define the associated
macros.
__________
147. Some of these typedef names may denote implementation-
defined extended integer types.
page 217 Library
page 218
7.4.1 Typedef names for integer types
[#1] When typedef names differing only in the absence or
presence of the initial u are defined, they shall denote
corresponding signed and unsigned types as described in
subclause 6.1.2.5.
7.4.1.1 Exact-width integer types
[#1] Each of the following typedef names designates an
integer type that has exactly the specified width. These
typedef names have the general form of intn_t or uintn_t
where n is the required width. For example, uint8_t denotes
an unsigned integer type that has a width of exactly 8 bits.
[#2] The following designate exact-width signed integer
types:
int8_t int16_t int32_t int64_t
[#3] The following designate exact-width unsigned integer
types:
uint8_t uint16_t uint32_t uint64_t
(Any of these types might not exist.)
7.4.1.2 Minimum-width integer types
[#1] Each of the following typedef names designates an
integer type that has at least the specified width, such
that no integer type of lesser size has at least the
specified width. These typedef names have the general form
of int_leastn_t or uint_leastn_t where n is the minimum
required width. For example, int_least32_t denotes a signed
integer type that has a width of at least 32 bits.
[#2] The following designate minimum-width signed integer
types:
int_least8_t int_least16_t
int_least32_t int_least64_t
[#3] The following designate minimum-width unsigned integer
types:
uint_least8_t uint_least16_t
uint_least32_t uint_least64_t
(These types must exist.)
page 218 Library
page 219
7.4.1.3 Fastest minimum-width integer types
[#1] Each of the following typedef names designates an
integer type that is usually fastest148 to operate with
among all integer types that have at least the specified
width. These typedef names have the general form of
int_fastn_t or uint_fastn_t where n is the minimum required
width. For example, int_fast16_t denotes the fastest signed
integer type that has a width of at least 16 bits.
[#2] The following designate fastest minimum-width signed
integer types:
int_fast8_t int_fast16_t
int_fast32_t int_fast64_t
[#3] The following designate fastest minimum-width unsigned
integer types:
uint_fast8_t uint_fast16_t
uint_fast32_t uint_fast64_t
(These types must exist.)
7.4.1.4 Integer types capable of holding object pointers
[#1] The following typedef name designates a signed integer
type with the property that any valid pointer to void can be
converted to this type, then converted back to pointer to
void, and the result will compare equal to the original
pointer:
intptr_t
[#2] The following typedef name designates an unsigned
integer type with the property that any valid pointer to
void can be converted to this type, then converted back to
pointer to void, and the result will compare equal to the
original pointer:
__________
148. The designated type is not guaranteed to be fastest for
all purposes; if the implementation has no clear grounds
for choosing one type over another, it will simply pick
some integer type satisfying the signedness and width
requirements.
page 219 Library
page 220
uintptr_t
(Either or both of these types might not exist.)
7.4.1.5 Greatest-width integer types
[#1] The following typedef name designates a signed integer
type capable of representing any value of any signed integer
type:
intmax_t
[#2] The following typedef name designates an unsigned
integer type capable of representing any value of any
unsigned integer type:
uintmax_t
(These types must exist.)
7.4.2 Limits of specified-width integer types
[#1] The following object-like macros149 specify the minimum
and maximum limits of integer types corresponding to the
typedef names defined in <inttypes.h>. Each macro name
corresponds to a similar typedef name in subclause 7.4.1.
[#2] Each instance of any defined macro shall be replaced by
a constant expression suitable for use in #if preprocessing
directives, and this expression shall have the same type as
would an expression that is an object of the corresponding
type converted according to the integer promotions. Its
implementation-defined value shall be equal to or greater in
magnitude (absolute value) than the corresponding value
given below, with the same sign.
__________
149. C++ implementations should define these macros only
when __STDC_LIMIT_MACROS is defined before <inttypes.h>
is included.
page 220 Library
page 221
7.4.2.1 Limits of exact-width integer types
- minimum values of exact-width signed integer types
INT8_MIN -127
INT16_MIN -32767
INT32_MIN -2147483647
INT64_MIN -9223372036854775807
(The value must be either that given or exactly 1
less.)
- maximum values of exact-width signed integer types
INT8_MAX +127
INT16_MAX +32767
INT32_MAX +2147483647
INT64_MAX +9223372036854775807
(The value must be exactly that given.)
- maximum values of exact-width unsigned integer types
UINT8_MAX 255
UINT16_MAX 65535
UINT32_MAX 4294967295
UINT64_MAX 18446744073709551615
(The value must be exactly that given.)
7.4.2.2 Limits of minimum-width integer types
- minimum values of minimum-width signed integer types
INT_LEAST8_MIN -127
INT_LEAST16_MIN -32767
INT_LEAST32_MIN -2147483647
INT_LEAST64_MIN -9223372036854775807
- maximum values of minimum-width signed integer types
INT_LEAST8_MAX +127
INT_LEAST16_MAX +32767
INT_LEAST32_MAX +2147483647
INT_LEAST64_MAX +9223372036854775807
- maximum values of minimum-width unsigned integer types
UINT_LEAST8_MAX 255
UINT_LEAST16_MAX 65535
UINT_LEAST32_MAX 4294967295
UINT_LEAST64_MAX 18446744073709551615
page 221 Library
page 222
7.4.2.3 Limits of fastest minimum-width integer types
- minimum values of fastest minimum-width signed integer
types
INT_FAST8_MIN -127
INT_FAST16_MIN -32767
INT_FAST32_MIN -2147483647
INT_FAST64_MIN -9223372036854775807
- maximum values of fastest minimum-width signed integer
types
INT_FAST8_MAX +127
INT_FAST16_MAX +32767
INT_FAST32_MAX +2147483647
INT_FAST64_MAX +9223372036854775807
- maximum values of fastest minimum-width unsigned
integer types
UINT_FAST8_MAX 255
UINT_FAST16_MAX 65535
UINT_FAST32_MAX 4294967295
UINT_FAST64_MAX 18446744073709551615
7.4.2.4 Limits of integer types capable of holding object
pointers
- minimum value of pointer-holding signed integer type
INTPTR_MIN -32767
- maximum value of pointer-holding signed integer type
INTPTR_MAX +32767
- maximum value of pointer-holding unsigned integer type
UINTPTR_MAX 65535
7.4.2.5 Limits of greatest-width integer types
- minimum value of greatest-width signed integer type
INTMAX_MIN -9223372036854775807
- maximum value of greatest-width signed integer type
INTMAX_MAX +9223372036854775807
- maximum value of greatest-width unsigned integer type
UINTMAX_MAX 18446744073709551615
page 222 Library
page 223
7.4.3 Macros for integer constants
[#1] The following function-like macros150 expand to integer
constants suitable for initializing objects that have
integer types corresponding to typedef names defined in
<inttypes.h>. Each macro name corresponds to a similar
typedef name in subclause 7.4.1.2 or 7.4.1.5.
[#2] The argument in any instance of these macros shall be a
decimal, octal, or hexadecimal constant (as defined in
subclause 6.1.3.2) with a value that does not exceed the
limits for the corresponding type.
7.4.3.1 Macros for minimum-width integer constants
[#1] Each of the following macros expands to an integer
constant having the value specified by its argument and a
type with at least the specified width. These macro names
have the general form of INTn_C or UINTn_C where n is the
minimum required width. For example, UINT64_C(0x123) might
expand to the integer constant 0x123ULL.
[#2] The following expand to integer constants that have
signed integer types:
INT8_C(value) INT16_C(value)
INT32_C(value) INT64_C(value)
[#3] The following expand to integer constants that have
unsigned integer types:
UINT8_C(value) UINT16_C(value)
UINT32_C(value) UINT64_C(value)
__________
150. C++ implementations should define these macros only
when __STDC_CONSTANT_MACROS is defined before
<inttypes.h> is included.
page 223 Library
page 224
7.4.3.2 Macros for greatest-width integer constants
[#1] The following macro expands to an integer constant
having the value specified by its argument and the type
intmax_t:
INTMAX_C(value)
[#2] The following macro expands to an integer constant
having the value specified by its argument and the type
uintmax_t:
UINTMAX_C(value)
7.4.4 Macros for format specifiers
[#1] Each of the following object-like macros151 expands to
a string literal containing a conversion specifier, possibly
modified by a prefix such as hh, h, l, or ll, suitable for
use within the format argument of a formatted input/output
function when converting the corresponding integer type.
These macro names have the general form of PRI (character
string literals for the fprintf family) or SCN (character
string literals for the fscanf family),152 followed by the
conversion specifier, followed by a name corresponding to a
similar typedef name in subclause 7.4.1. For example,
PRIdFAST32 can be used in a format string to print the value
of an integer of type int_fast32_t.
[#2] The fprintf macros for signed integers are:
__________
151. C++ implementations should define these macros only
when __STDC_FORMAT_MACROS is defined before <inttypes.h>
is included.
152. Separate macros are given for use with fprintf and
fscanf functions because, typically, different format
specifiers are required for fprintf and fscanf even when
the type is the same.
page 224 Library
page 225
PRId8 PRId16 PRId32 PRId64
PRIdLEAST8 PRIdLEAST16 PRIdLEAST32 PRIdLEAST64
PRIdFAST8 PRIdFAST16 PRIdFAST32 PRIdFAST64
PRIdMAX PRIdPTR
PRIi8 PRIi16 PRIi32 PRIi64
PRIiLEAST8 PRIiLEAST16 PRIiLEAST32 PRIiLEAST64
PRIiFAST8 PRIiFAST16 PRIiFAST32 PRIiFAST64
PRIiMAX PRIiPTR
[#3] The fprintf macros for unsigned integers are:
PRIo8 PRIo16 PRIo32 PRIo64
PRIoLEAST8 PRIoLEAST16 PRIoLEAST32 PRIoLEAST64
PRIoFAST8 PRIoFAST16 PRIoFAST32 PRIoFAST64
PRIoMAX PRIoPTR
PRIu8 PRIu16 PRIu32 PRIu64
PRIuLEAST8 PRIuLEAST16 PRIuLEAST32 PRIuLEAST64
PRIuFAST8 PRIuFAST16 PRIuFAST32 PRIuFAST64
PRIuMAX PRIuPTR
PRIx8 PRIx16 PRIx32 PRIx64
PRIxLEAST8 PRIxLEAST16 PRIxLEAST32 PRIxLEAST64
PRIxFAST8 PRIxFAST16 PRIxFAST32 PRIxFAST64
PRIxMAX PRIxPTR
PRIX8 PRIX16 PRIX32 PRIX64
PRIXLEAST8 PRIXLEAST16 PRIXLEAST32 PRIXLEAST64
PRIXFAST8 PRIXFAST16 PRIXFAST32 PRIXFAST64
PRIXMAX PRIXPTR
[#4] The fscanf macros for signed integers are:
SCNd8 SCNd16 SCNd32 SCNd64
SCNdLEAST8 SCNdLEAST16 SCNdLEAST32 SCNdLEAST64
SCNdFAST8 SCNdFAST16 SCNdFAST32 SCNdFAST64
SCNdMAX SCNdPTR
SCNi8 SCNi16 SCNi32 SCNi64
SCNiLEAST8 SCNiLEAST16 SCNiLEAST32 SCNiLEAST64
SCNiFAST8 SCNiFAST16 SCNiFAST32 SCNiFAST64
SCNiMAX SCNiPTR
[#5] The fscanf macros for unsigned integers are:
page 225 Library
page 226
SCNo8 SCNo16 SCNo32 SCNo64
SCNoLEAST8 SCNoLEAST16 SCNoLEAST32 SCNoLEAST64
SCNoFAST8 SCNoFAST16 SCNoFAST32 SCNoFAST64
SCNoMAX SCNoPTR
SCNu8 SCNu16 SCNu32 SCNu64
SCNuLEAST8 SCNuLEAST16 SCNuLEAST32 SCNuLEAST64
SCNuFAST8 SCNuFAST16 SCNuFAST32 SCNuFAST64
SCNuMAX SCNuPTR
SCNx8 SCNx16 SCNx32 SCNx64
SCNxLEAST8 SCNxLEAST16 SCNxLEAST32 SCNxLEAST64
SCNxFAST8 SCNxFAST16 SCNxFAST32 SCNxFAST64
SCNxMAX SCNxPTR
[#6] Because the default argument promotions do not affect
pointer parameters, there might not exist suitable fscanf
format specifiers for some of the typedef names defined in
this header. Consequently, as a special exception to the
requirement that the implementation shall define all macros
associated with each typedef name defined in this header, in
such a case the problematic fscanf macros may be left
undefined.
Examples
#include <inttypes.h>
#include <wchar.h>
int main(void)
{
uintmax_t i = UINTMAX_MAX; // this type always exists
wprintf(L"The largest integer value is %020"
PRIxMAX "\n", i);
return 0;
}
7.4.5 Limits of other integer types
[#1] The following object-like macros151 specify the minimum
and maximum limits of integer types corresponding to typedef
names defined in other standard headers.
[#2] Each instance of these macros shall be replaced by a
constant expression suitable for use in #if preprocessing
directives, and this expression shall have the same type as
would an expression that is an object of the corresponding
type converted according to the integer promotions. Its
implementation-defined value shall be equal to or greater in
magnitude (absolute value) than the corresponding value
given below, with the same sign.
page 226 Library
page 227
- limits of ptrdiff_t
PTRDIFF_MIN -65535
PTRDIFF_MAX +65535
- limits of sig_atomic_t
SIG_ATOMIC_MIN see below
SIG_ATOMIC_MAX see below
- limit of size_t
SIZE_MAX 65535
- limits of wchar_t
WCHAR_MIN see below
WCHAR_MAX see below
- limits of wint_t
WINT_MIN see below
WINT_MAX see below
[#3] If sig_atomic_t is defined as a signed integer type,
the value of SIG_ATOMIC_MIN shall be no greater than -127
and the value of SIG_ATOMIC_MAX shall be no less than 127;
otherwise, sig_atomic_t is defined as an unsigned integer
type, and the value of SIG_ATOMIC_MIN shall be 0 and the
value of SIG_ATOMIC_MAX shall be no less than 255.
[#4] If wchar_t is defined as a signed integer type, the
value of WCHAR_MIN shall be no greater than -127 and the
value of WCHAR_MAX shall be no less than 127; otherwise,
wchar_t is defined as an unsigned integer type, and the
value of WCHAR_MIN shall be 0 and the value of WCHAR_MAX
shall be no less than 255.
[#5] If wint_t is defined as a signed integer type, the
value of WINT_MIN shall be no greater than -32767 and the
value of WINT_MAX shall be no less than 32767; otherwise,
wint_t is defined as an unsigned integer type, and the value
of WINT_MIN shall be 0 and the value of WINT_MAX shall be no
less than 65535.
page 227 Library
page 228
7.4.6 Conversion functions for greatest-width integer types
7.4.6.1 The strtoimax function
Synopsis
[#1]
#include <inttypes.h>
intmax_t strtoimax(const char * restrict nptr,
char ** restrict endptr, int base);
Description
[#2] The strtoimax function is equivalent to strtol, except
that the initial portion of the string is converted to
intmax_t representation.
Returns
[#3] The strtoimax function returns the converted value, if
any. If no conversion could be performed zero is returned.
If the correct value is outside the range of representable
values, INTMAX_MAX or INTMAX_MIN is returned (according to
the sign of the value), and the value of the macro ERANGE is
stored in errno.
7.4.6.2 The strtoumax function
Synopsis
[#1]
#include <inttypes.h>
uintmax_t strtoumax(const char * restrict nptr,
char ** restrict endptr, int base);
Description
[#2] The strtoumax function is equivalent to strtoul, except
that the initial portion of the string is converted to
uintmax_t representation.
Returns
[#3] The strtoumax function returns the converted value, if
any. If no conversion could be performed zero is returned.
If the correct value is outside the range of representable
values, UINTMAX_MAX is returned, and the value of the macro
ERANGE is stored in errno.
page 228 Library
page 229
7.4.6.3 The wcstoimax function
Synopsis
[#1]
#include <stddef.h> // for wchar_t
#include <inttypes.h>
intmax_t wcstoimax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
Description
[#2] The wcstoimax function is equivalent to wcstol, except
that the initial portion of the wide string is converted to
intmax_t representation.
Returns
[#3] The wcstoimax function returns the converted value, if
any. If no conversion could be performed zero is returned.
If the correct value is outside the range of representable
values, INTMAX_MAX or INTMAX_MIN is returned (according to
the sign of the value), and the value of the macro ERANGE is
stored in errno.
7.4.6.4 The wcstoumax function
Synopsis
[#1]
#include <stddef.h> // for wchar_t
#include <inttypes.h>
uintmax_t wcstoumax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
Description
[#2] The wcstoumax function is equivalent to wcstoul, except
that the initial portion of the wide string is converted to
uintmax_t representation.
Returns
[#3] The wcstoumax function returns the converted value, if
any. If no conversion could be performed zero is returned.
If the correct value is outside the range of representable
values, UINTMAX_MAX is returned, and the value of the macro
ERANGE is stored in errno.
page 229 Library
page 230
7.5 Localization <locale.h>
[#1] The header <locale.h> declares two functions, one type,
and defines several macros.
[#2] The type is
struct lconv
which contains members related to the formatting of numeric
values. The structure shall contain at least the following
members, in any order. The semantics of the members and
their normal ranges is explained in 7.5.2.1. In the "C"
locale, the members shall have the values specified in the
comments.
char *decimal_point; // "."
char *thousands_sep; // ""
char *grouping; // ""
char *int_curr_symbol; // ""
char *currency_symbol; // ""
char *mon_decimal_point; // ""
char *mon_thousands_sep; // ""
char *mon_grouping; // ""
char *positive_sign; // ""
char *negative_sign; // ""
char int_frac_digits; // CHAR_MAX
char frac_digits; // CHAR_MAX
char p_cs_precedes; // CHAR_MAX
char p_sep_by_space; // CHAR_MAX
char n_cs_precedes; // CHAR_MAX
char n_sep_by_space; // CHAR_MAX
char p_sign_posn; // CHAR_MAX
char n_sign_posn; // CHAR_MAX
[#3] The macros defined are NULL (described in 7.1.6);
and153
__________
153. ISO/IEC 9945-2, Information technology - Portable
operating system interface (POSIX) - Part 2: shell and
utilities specifies locale and charmap formats that may
be used to specify locales for C.
page 230 Library
page 231
LC_ALL
LC_COLLATE
LC_CTYPE
LC_MONETARY
LC_NUMERIC
LC_TIME
which expand to integer constant expressions with distinct
values, suitable for use as the first argument to the
setlocale function. Additional macro definitions, beginning
with the characters LC_ and an uppercase letter,154 may also
be specified by the implementation.
7.5.1 Locale control
7.5.1.1 The setlocale function
Synopsis
[#1]
#include <locale.h>
char *setlocale(int category, const char *locale);
Description
[#2] The setlocale function selects the appropriate portion
of the program's locale as specified by the category and
locale arguments. The setlocale function may be used to
change or query the program's entire current locale or
portions thereof. The value LC_ALL for category names the
program's entire locale; the other values for category name
only a portion of the program's locale. LC_COLLATE affects
the behavior of the strcoll and strxfrm functions. LC_CTYPE
affects the behavior of the character handling functions155
and the multibyte functions. LC_MONETARY affects the
monetary formatting information returned by the localeconv
function. LC_NUMERIC affects the decimal-point character
for the formatted input/output functions and the string
conversion functions, as well as the nonmonetary formatting
information returned by the localeconv function. LC_TIME
affects the behavior of the strftime function.
__________
154. See ``future library directions'' (7.20.4).
155. The only functions in 7.3 whose behavior is not
affected by the current locale are isdigit and isxdigit.
page 231 Library
page 232
[#3] A value of "C" for locale specifies the minimal
environment for C translation; a value of "" for locale
specifies the locale-specific native environment. Other
implementation-defined strings may be passed as the second
argument to setlocale.
[#4] At program startup, the equivalent of
setlocale(LC_ALL, "C");
is executed.
[#5] The implementation shall behave as if no library
function calls the setlocale function.
Returns
[#6] If a pointer to a string is given for locale and the
selection can be honored, the setlocale function returns a
pointer to the string associated with the specified category
for the new locale. If the selection cannot be honored, the
setlocale function returns a null pointer and the program's
locale is not changed.
[#7] A null pointer for locale causes the setlocale function
to return a pointer to the string associated with the
category for the program's current locale; the program's
locale is not changed.156
[#8] The pointer to string returned by the setlocale
function is such that a subsequent call with that string
value and its associated category will restore that part of
the program's locale. The string pointed to shall not be
modified by the program, but may be overwritten by a
subsequent call to the setlocale function.
Forward references: formatted input/output functions
(7.13.6), the multibyte character functions (7.14.7), the
multibyte string functions (7.14.8), string conversion
functions (7.14.1), the strcoll function (7.15.4.3), the
strftime function (7.16.3.6), the strxfrm function
(7.15.4.5).
__________
156. The implementation must arrange to encode in a string
the various categories due to a heterogeneous locale
when category has the value LC_ALL.
page 232 Library
page 233
7.5.2 Numeric formatting convention inquiry
7.5.2.1 The localeconv function
Synopsis
[#1]
#include <locale.h>
struct lconv *localeconv(void);
Description
[#2] The localeconv function sets the components of an
object with type struct lconv with values appropriate for
the formatting of numeric quantities (monetary and
otherwise) according to the rules of the current locale.
[#3] The members of the structure with type char * are
pointers to strings, any of which (except decimal_point) can
point to "", to indicate that the value is not available in
the current locale or is of zero length. Apart from
grouping and mon_grouping, the strings shall start and end
in the initial shift state. The members with type char are
nonnegative numbers, any of which can be CHAR_MAX to
indicate that the value is not available in the current
locale. The members include the following:
char *decimal_point
The decimal-point character used to format
nonmonetary quantities.
char *thousands_sep
The character used to separate groups of digits
before the decimal-point character in formatted
nonmonetary quantities.
char *grouping
A string whose elements indicate the size of each
group of digits in formatted nonmonetary quantities.
char *int_curr_symbol
The international currency symbol applicable to the
current locale. The first three characters contain
the alphabetic international currency symbol in
accordance with those specified in ISO 4217:1987.
The fourth character (immediately preceding the null
character) is the character used to separate the
international currency symbol from the monetary
quantity.
page 233 Library
page 234
char *currency_symbol
The local currency symbol applicable to the current
locale.
char *mon_decimal_point
The decimal-point used to format monetary quantities.
char *mon_thousands_sep
The separator for groups of digits before the
decimal-point in formatted monetary quantities.
char *mon_grouping
A string whose elements indicate the size of each
group of digits in formatted monetary quantities.
char *positive_sign
The string used to indicate a nonnegative-valued
formatted monetary quantity.
char *negative_sign
The string used to indicate a negative-valued
formatted monetary quantity.
char int_frac_digits
The number of fractional digits (those after the
decimal-point) to be displayed in an internationally
formatted monetary quantity.
char frac_digits
The number of fractional digits (those after the
decimal-point) to be displayed in a formatted
monetary quantity.
char p_cs_precedes
Set to 1 or 0 if the currency_symbol respectively
precedes or succeeds the value for a nonnegative
formatted monetary quantity.
char p_sep_by_space
Set to 1 or 0 if the currency_symbol respectively is
or is not separated by a space from the value for a
nonnegative formatted monetary quantity.
char n_cs_precedes
Set to 1 or 0 if the currency_symbol respectively
precedes or succeeds the value for a negative
formatted monetary quantity.
char n_sep_by_space
Set to 1 or 0 if the currency_symbol respectively is
or is not separated by a space from the value for a
page 234 Library
page 235
negative formatted monetary quantity.
char p_sign_posn
Set to a value indicating the positioning of the
positive_sign for a nonnegative formatted monetary
quantity.
char n_sign_posn
Set to a value indicating the positioning of the
negative_sign for a negative formatted monetary
quantity.
[#4] The elements of grouping and mon_grouping are
interpreted according to the following:
CHAR_MAX No further grouping is to be performed.
0 The previous element is to be repeatedly used for
the remainder of the digits.
other The integer value is the number of digits that
comprise the current group. The next element is
examined to determine the size of the next group
of digits before the current group.
[#5] The value of p_sign_posn and n_sign_posn is interpreted
according to the following:
0 Parentheses surround the quantity and currency_symbol.
1 The sign string precedes the quantity and
currency_symbol.
2 The sign string succeeds the quantity and
currency_symbol.
3 The sign string immediately precedes the currency_symbol.
4 The sign string immediately succeeds the currency_symbol.
[#6] The implementation shall behave as if no library
function calls the localeconv function.
Returns
[#7] The localeconv function returns a pointer to the
filled-in object. The structure pointed to by the return
value shall not be modified by the program, but may be
overwritten by a subsequent call to the localeconv function.
In addition, calls to the setlocale function with categories
LC_ALL, LC_MONETARY, or LC_NUMERIC may overwrite the
page 235 Library
page 236
contents of the structure.
Examples
[#8] The following table illustrates the rules which may
well be used by four countries to format monetary
quantities.
Country Positive format Negative formatInternational format
Italy L.1.234 -L.1.234 ITL.1.234
Netherlands F 1.234,56 F -1.234,56 NLG 1.234,56
Norway kr1.234,56 kr1.234,56- NOK 1.234,56
Switzerland SFrs.1,234.56 SFrs.1,234.56C CHF 1,234.56
[#9] For these four countries, the respective values for the
monetary members of the structure returned by localeconv
are:
Italy Netherlands NorwaySwitzerland
int_curr_symbol "ITL." "NLG " "NOK " "CHF "
currency_symbol "L." "F" "kr" "SFrs."
mon_decimal_point "" "," ",""."
mon_thousands_sep "." "." "."","
mon_grouping "\3" "\3" "\3" "\3"
positive_sign "" "" "" ""
negative_sign "-" "-" "-" "C"
int_frac_digits 0 2 2 2
frac_digits 0 2 2 2
p_cs_precedes 1 1 1 1
p_sep_by_space 0 1 0 0
n_cs_precedes 1 1 1 1
n_sep_by_space 0 1 0 0
p_sign_posn 1 1 1 1
n_sign_posn 1 4 2 2
page 236 Library
page 237
7.6 Floating-point environment <fenv.h>
[#1] The header <fenv.h> declares two types and several
macros and functions to provide access to the floating-point
environment. The floating-point environment refers
collectively to any floating-point status flags and control
modes supported by the implementation.157 A floating-point
status flag is a system variable whose value is set as a
side effect of the arithmetic to provide auxiliary
information. A floating-point control mode is a system
variable whose value may be set by the user to affect the
subsequent behavior of the arithmetic.
[#2] Certain programming conventions support the intended
model of use for the floating-point environment:158
- a function call must not alter its caller's modes,
clear its caller's flags, nor depend on the state of
its caller's flags unless the function is so
documented;
- a function call is assumed to require default modes,
unless its documentation promises otherwise or unless
the function is known not to use floating-point;
- a function call is assumed to have the potential for
raising floating-point exceptions, unless its
documentation promises otherwise, or unless the
function is known not to use floating-point.
[#3] The type
fenv_t
represents the entire floating-point environment.
__________
157. This header is designed to support the exception status
flags and directed-rounding control modes required by
IEC 559, and other similar floating-point state
information. Also it is designed to facilitate code
portability among all systems.
158. With these conventions, a programmer can safely assume
default modes (or be unaware of them). The
responsibilities associated with accessing the
floating-point environment fall on the programmer or
program that does so explicitly.
page 237 Library
page 238
[#4] The type
fexcept_t
represents the floating-point exception flags collectively,
including any status the implementation associates with the
flags.
[#5] Each of the macros
FE_DIVBYZERO
FE_INEXACT
FE_INVALID
FE_OVERFLOW
FE_UNDERFLOW
is defined if and only if the implementation supports the
exception by means of the functions in 7.6.2. The defined
macros expand to integer constant expressions with values
such that bitwise ORs of all combinations of the macros
result in distinct values.
[#6] The macro
FE_ALL_EXCEPT
is simply the bitwise OR of all exception macros defined by
the implementation.
[#7] Each of the macros
FE_DOWNWARD
FE_TONEAREST
FE_TOWARDZERO
FE_UPWARD
is defined if and only if the implementation supports
getting and setting the represented rounding direction by
means of the fegetround and fesetround functions. The
defined macros expand to integer constant expressions whose
values are distinct nonnegative values.159
__________
159. Even though the rounding direction macros may expand to
constants corresponding to the values of FLT_ROUNDS,
they are not required to do so.
page 238 Library
page 239
[#8] The macro
FE_DFL_ENV
represents the default floating-point environment - the one
installed at program startup - and has type pointer to
const-qualified fenv_t. It can be used as an argument to
<fenv.h> functions that manage the floating-point
environment.
[#9] Additional macro definitions, beginning with FE_ and
having type pointer to const-qualified fenv_t, may also be
specified by the implementation.
7.6.1 The FENV_ACCESS pragma
Synopsis
[#1]
#include <fenv.h>
#pragma STDC FENV_ACCESS on-off-switch
Description
[#2] The FENV_ACCESS pragma provides a means to inform the
implementation when a program might access the floating-
point environment to test flags or run under non-default
modes.160 The pragma can occur either outside external
declarations or preceding all explicit declarations and
statements inside a compound statement. When outside
external declarations, the pragma takes effect from its
occurrence until another FENV_ACCESS pragma is encountered,
or until the end of the translation unit. When inside a
compound statement, the pragma takes effect from its
occurrence until another FENV_ACCESS pragma is encountered
(within a nested compound statement), or until the end of
the compound statement; at the end of a compound statement
the state for the pragma is restored to its condition just
__________
160. The purpose of the FENV_ACCESS pragma is to allow
certain optimizations, for example global common
subexpression elimination, code motion, and constant
folding, that could subvert flag tests and mode changes.
In general, if the state of FENV_ACCESS is off then the
translator can assume that default modes are in effect
and the flags are not tested.
page 239 Library
page 240
before the compound statement. If this pragma is used in
any other context, the behavior is undefined. If part of a
program tests flags or runs under non-default mode settings,
but was translated with the state for the FENV_ACCESS pragma
off, then the behavior of that program is undefined. The
default state (on or off) for the pragma is implementation-
defined.
Examples
[#3]
#include <fenv.h>
void f(double x)
{
#pragma STDC FENV_ACCESS ON
void g(double);
void h(double);
/* ... */
g(x + 1);
h(x + 1);
/* ... */
}
If the function g might depend on status flags set as a side
effect of the first x + 1, or if the second x + 1 might
depend on control modes set as a side effect of the call to
function g, then the program must contain an appropriately
placed invocation of #pragma STDC FENV_ACCESS ON.161
__________
161. The side effects impose a temporal ordering that
requires two evaluations of x + 1. On the other hand,
without the #pragma STDC FENV_ACCESS ON pragma, and
assuming the default state is off, just one evaluation
of x + 1 would suffice.
page 240 Library
page 241
7.6.2 Exceptions
[#1] The following functions provide access to the exception
flags.162 The int input argument for the functions
represents a subset of floating-point exceptions, and can be
constructed by bitwise ORs of the exception macros, for
example FE_OVERFLOW | FE_INEXACT. For other argument values
the behavior of these functions is undefined.
7.6.2.1 The feclearexcept function
Synopsis
[#1]
#include <fenv.h>
void feclearexcept(int excepts);
Description
[#2] The feclearexcept function clears the supported
exceptions represented by its argument.
7.6.2.2 The fegetexceptflag function
Synopsis
[#1]
#include <fenv.h>
void fegetexceptflag(fexcept_t *flagp,
int excepts);
Description
[#2] The fegetexceptflag function stores an implementation-
defined representation of the exception flags indicated by
the argument excepts in the object pointed to by the
argument flagp.
__________
162. The functions fetestexcept, feraiseexcept, and
feclearexcept support the basic abstraction of flags
that are either set or clear. An implementation may
endow exception flags with more information - for
example, the address of the code which first raised the
exception; the functions fegetexceptflag and
fesetexceptflag deal with the full content of flags.
page 241 Library
page 242
7.6.2.3 The feraiseexcept function
Synopsis
[#1]
#include <fenv.h>
void feraiseexcept(int excepts);
Description
[#2] The feraiseexcept function raises the supported
exceptions represented by its argument.163 The order in
which these exceptions are raised is unspecified, except as
stated in F.7.6. Whether the feraiseexcept function
additionally raises the inexact exception whenever it raises
the overflow or underflow exception is implementation-
defined.
7.6.2.4 The fesetexceptflag function
Synopsis
[#1]
#include <fenv.h>
void fesetexceptflag(const fexcept_t *flagp,
int excepts);
Description
[#2] The fesetexceptflag function sets the complete status
for those exception flags indicated by the argument excepts,
according to the representation in the object pointed to by
flagp. The value of *flagp must have been set by a previous
call to fegetexceptflag whose second argument represented at
least those exceptions represented by the argument excepts;
if not, the effect on the indicated exception flags is
undefined. This function does not raise exceptions, but
only sets the state of the flags.
__________
163. The effect is intended to be similar to that of
exceptions raised by arithmetic operations. Hence,
enabled traps for exceptions raised by this function are
taken. The specification in F.7.6 is in the same
spirit.
page 242 Library
page 243
7.6.2.5 The fetestexcept function
Synopsis
[#1]
#include <fenv.h>
int fetestexcept(int excepts);
Description
[#2] The fetestexcept function determines which of a
specified subset of the exception flags are currently set.
The excepts argument specifies the exception flags to be
queried.164
Returns
[#3] The fetestexcept function returns the value of the
bitwise OR of the exception macros corresponding to the
currently set exceptions included in excepts.
Examples
[#4] Call f if invalid is set, then g if overflow is set:
#include <fenv.h>
/* ... */
{
#pragma STDC FENV_ACCESS ON
int set_excepts;
// maybe raise exceptions
set_excepts =
fetestexcept(FE_INVALID | FE_OVERFLOW);
if (set_excepts & FE_INVALID) f();
if (set_excepts & FE_OVERFLOW) g();
/* ... */
}
__________
164. This mechanism allows testing several exceptions with
just one function call.
page 243 Library
page 244
7.6.3 Rounding
[#1] The fegetround and fesetround functions provide control
of rounding direction modes.
7.6.3.1 The fegetround function
Synopsis
[#1]
#include <fenv.h>
int fegetround(void);
Description
[#2] The fegetround function gets the current rounding
direction.
Returns
[#3] The fegetround function returns the value of the
rounding direction macro representing the current rounding
direction.
7.6.3.2 The fesetround function
Synopsis
[#1]
#include <fenv.h>
int fesetround(int round);
Description
[#2] The fesetround function establishes the rounding
direction represented by its argument round. If the
argument does not match a rounding direction macro, the
rounding direction is not changed.
Returns
[#3] The fesetround function returns a nonzero value if and
only if the argument matches a rounding direction macro
(that is, if and only if the requested rounding direction
can be established).
page 244 Library
page 245
Examples
[#4] Save, set, and restore the rounding direction. Report
an error and abort if setting the rounding direction fails.
#include <fenv.h>
#include <assert.h>
/* ... */
{
#pragma STDC FENV_ACCESS ON
int save_round;
int setround_ok;
save_round = fegetround();
setround_ok = fesetround(FE_UPWARD);
assert(setround_ok);
/* ... */
fesetround(save_round);
/* ... */
}
7.6.4 Environment
[#1] The functions in this section manage the floating-point
environment - status flags and control modes - as one
entity.
7.6.4.1 The fegetenv function
Synopsis
[#1]
#include <fenv.h>
void fegetenv(fenv_t *envp);
Description
[#2] The fegetenv function stores the current floating-point
environment in the object pointed to by envp.
7.6.4.2 The feholdexcept function
Synopsis
[#1]
#include <fenv.h>
int feholdexcept(fenv_t *envp);
page 245 Library
page 246
Description
[#2] The feholdexcept function saves the current environment
in the object pointed to by envp, clears the exception
flags, and installs a non-stop (continue on exceptions)
mode, if available, for all exceptions.165
Returns
[#3] The feholdexcept function returns nonzero if and only
if non-stop exception handling was successfully installed.
7.6.4.3 The fesetenv function
Synopsis
[#1]
#include <fenv.h>
void fesetenv(const fenv_t *envp);
Description
[#2] The fesetenv function establishes the floating-point
environment represented by the object pointed to by envp.
The argument envp must point to an object set by a call to
fegetenv or feholdexcept, or equal the macro FE_DFL_ENV or
an implementation-defined environment macro. Note that
fesetenv merely installs the state of the exception flags
represented through its argument, and does not raise these
exceptions.
__________
165. IEC 559 systems have a default non-stop mode, and
typically at least one other mode for trap handling or
aborting; if the system provides only the non-stop mode
then installing it is trivial. For such systems, the
feholdexcept function can be used in conjunction with
the feupdateenv function to write routines that hide
spurious exceptions from their callers.
page 246 Library
page 247
7.6.4.4 The feupdateenv function
Synopsis
[#1]
#include <fenv.h>
void feupdateenv(const fenv_t *envp);
Description
[#2] The feupdateenv function saves the currently raised
exceptions in its automatic storage, installs the
environment represented through envp, and then raises the
saved exceptions. The argument envp must point to an object
set by a call to feholdexcept or fegetenv, or equal the
macro FE_DFL_ENV or an implementation-defined environment
macro.
Examples
[#3] Hide spurious underflow exceptions:
#include <fenv.h>
double f(double x)
{
#pragma STDC FENV_ACCESS ON
double result;
fenv_t save_env;
feholdexcept(&save_env);
// compute result
if (/* test spurious underflow */)
feclearexcept(FE_UNDERFLOW);
feupdateenv(&save_env);
return result;
}
page 247 Library
page 248
7.7 Mathematics <math.h>
[#1] The header <math.h> declares two types and several
mathematical functions and defines several macros. Most
synopses specify a function which takes one or more double
arguments and returns a double value; for each such
function, there are functions with the same name but with f
and l suffixes which are corresponding functions with float
and long double arguments and return values.166 Some
synopses specify a function which takes a double argument
and returns an integer-type value; for each such function,
there are functions with the same name but with f and l
suffixes which are corresponding functions with float and
long double arguments. Integer arithmetic functions and
conversion functions are discussed later.
[#2] The types
float_t
double_t
are floating types at least as wide as float and double,
respectively, and such that double_t is at least as wide as
float_t. If FLT_EVAL_METHOD equals 0, float_t and double_t
are float and double, respectively; if FLT_EVAL_METHOD
equals 1, they are both double; if FLT_EVAL_METHOD equals 2,
they are both long double; and for other values of
FLT_EVAL_METHOD, they are otherwise implementation-
defined.167
[#3] The macro
HUGE_VAL
expands to a positive double constant expression, not
__________
166. Particularly on systems with wide expression
evaluation, a <math.h> function might pass arguments and
return values in wider format than the synopsis
prototype indicates.
167. The types float_t and double_t are intended to be the
implementation's most efficient types at least as wide
as float and double, respectively. For FLT_EVAL_METHOD
equal 0, 1, or 2, the type float_t is the narrowest type
used by the implementation to evaluate floating
expressions.
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necessarily representable as a float. The macros
HUGE_VALF
HUGE_VALL
are respectively float and long double analogs of
HUGE_VAL.168
[#4] The macro
INFINITY
expands to a constant expression of type float representing
an implementation-defined positive or unsigned infinity, if
available, else to a positive constant of type float that
overflows at translation time.
[#5] The macro
NAN
is defined if and only if the implementation supports quiet
NaNs for the float type. It expands to a constant
expression of type float representing an implementation-
defined quiet NaN.
[#6] The macros
FP_INFINITE
FP_NAN
FP_NORMAL
FP_SUBNORMAL
FP_ZERO
are for number classification. They represent the mutually
exclusive kinds of floating-point values. They expand to
integer constant expressions with distinct values.
[#7] The macro
FP_FAST_FMA
is optionally defined. If defined, it indicates the fma
__________
168. HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive
infinities in an implementation that supports
infinities.
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function generally executes about as fast as a multiply and
an add of double operands.169 The macros
FP_FAST_FMAF
FP_FAST_FMAL
are, respectively, float and long double analogs of
FP_FAST_FMA.
[#8] The macros
FP_ILOGB0
FP_ILOGBNAN
expand to integer constant expressions whose values are
returned by ilogb(x) if x is zero or NaN, respectively. The
value of FP_ILOGB0 shall be either INT_MIN or -INT_MAX. The
value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN.
[#9] The macro
DECIMAL_DIG
expands to an integer constant expression whose value is
implementation-defined. It represents a number of decimal
digits supported by conversion between decimal and all
internal floating-point formats.170
Recommended practice
[#10] Conversion from (at least) double to decimal with
DECIMAL_DIG digits and back is the identity function.171
__________
169. Typically, the FP_FAST_FMA macro is defined if and only
if the fma function is implemented directly with a
hardware multiply-add instruction. Software
implementations are expected to be substantially slower.
170. DECIMAL_DIG is intended to give an appropriate number
of digits to carry in canonical decimal representations.
171. In order that correctly rounded conversion from an
internal floating-point format with precision m to
decimal with DECIMAL_DIG digits and back be the identity
function, DECIMAL_DIG should be a positive integer n
satisfying the inequality:
n>m if FLT_RADIX is 10
n-1 m otherwise
10 >FLT_RADIX
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7.7.1 Treatment of error conditions
[#1] The behavior of each of the functions in <math.h> is
specified for all representable values of its input
arguments, except where stated otherwise.
[#2] For all functions, a domain error occurs if an input
argument is outside the domain over which the mathematical
function is defined. The description of each function lists
any required domain errors; an implementation may define
additional domain errors, provided that such errors are
consistent with the mathematical definition of the
function.172 On a domain error, the function returns an
implementation-defined value; whether the integer
expression errno acquires the value EDOM is implementation-
defined.
[#3] Similarly, a range error occurs if the mathematical
result of the function cannot be represented in an object of
the specified type, due to extreme magnitude. A floating
result overflows if the magnitude of the mathematical result
is finite but so large that the mathematical result cannot
be represented, without extraordinary roundoff error, in an
object of the specified type. If a floating result
overflows and default rounding is in effect, or if the
mathematical result is an exact infinity (for example
log(0.0)), then the function returns the value of the macro
HUGE_VAL, HUGE_VALF, or HUGE_VALL appropriate to the
specified result type, with the same sign as the correct
value of the function; whether errno acquires the value
ERANGE when a range error occurs is implementation-defined.
The result underflows if the magnitude of the mathematical
result is so small that the mathematical result cannot be
represented, without extraordinary roundoff error, in an
object of the specified type.173 If the result underflows,
the function returns a value whose magnitude is no greater
than the smallest normalized positive number in the
____________________________________________________________
172. In an implementation that supports infinities, this
allows an infinity as an argument to be a domain error
if the mathematical domain of the function does not
include the infinity.
173. The term underflow here is intended to encompass both
gradual underflow as in IEC 559 and also flush-to-zero
underflow.
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specified type and is otherwise implementation-defined;
whether errno acquires the value ERANGE is implementation-
defined.
7.7.2 The FP_CONTRACT pragma
Synopsis
[#1]
#include <math.h>
#pragma STDC FP_CONTRACT on-off-switch
Description
[#2] The FP_CONTRACT pragma can be used to allow (if the
state is on) or disallow (if the state is off) the
implementation to contract expressions (6.3). Each pragma
can occur either outside external declarations or preceding
all explicit declarations and statements inside a compound
statement. When outside external declarations, the pragma
takes effect from its occurrence until another FP_CONTRACT
pragma is encountered, or until the end of the translation
unit. When inside a compound statement, the pragma takes
effect from its occurrence until another FP_CONTRACT pragma
is encountered (within a nested compound statement), or
until the end of the compound statement; at the end of a
compound statement the state for the pragma is restored to
its condition just before the compound statement. If this
pragma is used in any other context, the behavior is
undefined. The default state (on or off) for the pragma is
implementation-defined.
7.7.3 Classification macros
[#1] In the synopses in this subclause, real-floating
indicates that the argument must be an expression of real
floating type. The result is undefined if an argument is
not of real floating type.
7.7.3.1 The fpclassify macro
Synopsis
[#1]
#include <math.h>
int fpclassify(real-floating x);
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Description
[#2] The fpclassify macro classifies its argument value as
NaN, infinite, normal, subnormal, or zero. First, an
argument represented in a format wider than its semantic
type is converted to its semantic type. Then classification
is based on the type of the argument.174
Returns
[#3] The fpclassify macro returns the value of the number
classification macro appropriate to the value of its
argument.
Examples
[#4] The fpclassify macro might be implemented in terms of
ordinary functions as
#define fpclassify(x) \
((sizeof (x) == sizeof (float)) ? \
__fpclassifyf(x) \
: (sizeof (x) == sizeof (double)) ? \
__fpclassifyd(x) \
: __fpclassifyl(x))
7.7.3.2 The signbit macro
Synopsis
[#1]
#include <math.h>
int signbit(real-floating x);
Description
[#2] The signbit macro determines whether the sign of its
argument value is negative.175
__________
174. Since an expression can be evaluated with more range
and precision than its type has, it is important to know
the type that classification is based on. For example,
a normal long double value might become subnormal when
converted to double, and zero when converted to float.
175. The signbit macro reports the sign of all values,
including infinities, zeros, and NaNs.
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Returns
[#3] The signbit macro returns a nonzero value if and only
if the sign of its argument value is negative.
7.7.3.3 The isfinite macro
Synopsis
[#1]
#include <math.h>
int isfinite(real-floating x);
Description
[#2] The isfinite macro determines whether its argument has
a finite value (zero, subnormal, or normal, and not infinite
or NaN). First, an argument represented in a format wider
than its semantic type is converted to its semantic type.
Then determination is based on the type of the argument.
Returns
[#3] The isfinite macro returns a nonzero value if and only
if its argument has a finite value.
7.7.3.4 The isnormal macro
Synopsis
[#1]
#include <math.h>
int isnormal(real-floating x);
Description
[#2] The isnormal macro determines whether its argument
value is normal (neither zero, subnormal, infinite, nor
NaN). First, an argument represented in a format wider than
its semantic type is converted to its semantic type. Then
determination is based on the type of the argument.
Returns
[#3] The isnormal macro returns a nonzero value if and only
if its argument has a normal value.
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7.7.3.5 The isnan macro
Synopsis
[#1]
#include <math.h>
int isnan(real-floating x);
Description
[#2] The isnan macro determines whether its argument value
is a NaN. First, an argument represented in a format wider
than its semantic type is converted to its semantic type.
Then determination is based on the type of the argument.176
Returns
[#3] The isnan macro returns a nonzero value if and only if
its argument has a NaN value.
7.7.3.6 The isinf macro
Synopsis
[#1]
#include <math.h>
int isinf(real-floating x);
Description
[#2] The isinf macro determines whether its argument value
is an infinity (positive or negative). First, an argument
represented in a format wider than its semantic type is
converted to its semantic type. Then determination is based
on the type of the argument.
__________
176. For the isnan macro, the type for determination doesn't
matter unless the implementation supports NaNs in the
evaluation type but not in the semantic type.
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Returns
[#3] The isinf macro returns a nonzero value if and only if
its argument has an infinite value.
7.7.4 Trigonometric functions
7.7.4.1 The acos function
Synopsis
[#1]
#include <math.h>
double acos(double x);
Description
[#2] The acos function computes the principal value of the
arc cosine of x. A domain error occurs for arguments not in
the range [-1, +1].
Returns
[#3] The acos function returns the arc cosine in the range
[0, pi] radians.
7.7.4.2 The asin function
Synopsis
[#1]
#include <math.h>
double asin(double x);
Description
[#2] The asin function computes the principal value of the
arc sine of x. A domain error occurs for arguments not in
the range [-1, +1].
Returns
[#3] The asin function returns the arc sine in the range [ -
pi/2, +pi/2] radians.
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7.7.4.3 The atan function
Synopsis
[#1]
#include <math.h>
double atan(double x);
Description
[#2] The atan function computes the principal value of the
arc tangent of x.
Returns
[#3] The atan function returns the arc tangent in the range
[-pi/2, +pi/2] radians.
7.7.4.4 The atan2 function
Synopsis
[#1]
#include <math.h>
double atan2(double y, double x);
Description
[#2] The atan2 function computes the principal value of the
arc tangent of y / x, using the signs of both arguments to
determine the quadrant of the return value. A domain error
may occur if both arguments are zero.
Returns
[#3] The atan2 function returns the arc tangent of y / x, in
the range [-pi, +pi] radians.
7.7.4.5 The cos function
Synopsis
[#1]
#include <math.h>
double cos(double x);
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Description
[#2] The cos function computes the cosine of x (measured in
radians).
Returns
[#3] The cos function returns the cosine value.
7.7.4.6 The sin function
Synopsis
[#1]
#include <math.h>
double sin(double x);
Description
[#2] The sin function computes the sine of x (measured in
radians).
Returns
[#3] The sin function returns the sine value.
7.7.4.7 The tan function
Synopsis
[#1]
#include <math.h>
double tan(double x);
Description
[#2] The tan function returns the tangent of x (measured in
radians).
Returns
[#3] The tan function returns the tangent value.
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7.7.5 Hyperbolic functions
7.7.5.1 The cosh function
Synopsis
[#1]
#include <math.h>
double cosh(double x);
Description
[#2] The cosh function computes the hyperbolic cosine of x.
A range error occurs if the magnitude of x is too large.
Returns
[#3] The cosh function returns the hyperbolic cosine value.
7.7.5.2 The sinh function
Synopsis
[#1]
#include <math.h>
double sinh(double x);
Description
[#2] The sinh function computes the hyperbolic sine of x. A
range error occurs if the magnitude of x is too large.
Returns
[#3] The sinh function returns the hyperbolic sine value.
7.7.5.3 The tanh function
Synopsis
[#1]
#include <math.h>
double tanh(double x);
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Description
[#2] The tanh function computes the hyperbolic tangent of x.
Returns
[#3] The tanh function returns the hyperbolic tangent value.
7.7.5.4 The acosh function
Synopsis
[#1]
#include <math.h>
double acosh(double x);
Description
[#2] The acosh function computes the (nonnegative) arc
hyperbolic cosine of x. A domain error occurs for arguments
less than 1.
Returns
[#3] The acosh function returns the arc hyperbolic cosine in
the range [0, +oo].
7.7.5.5 The asinh function
Synopsis
[#1]
#include <math.h>
double asinh(double x);
Description
[#2] The asinh function computes the arc hyperbolic sine of
x.
Returns
[#3] The asinh function returns the arc hyperbolic sine
value.
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7.7.5.6 The atanh function
Synopsis
[#1]
#include <math.h>
double atanh(double x);
Description
[#2] The atanh function computes the arc hyperbolic tangent
of x. A domain error occurs for arguments not in the range
[-1, +1].
Returns
[#3] The atanh function returns the arc hyperbolic tangent
value.
7.7.6 Exponential and logarithmic functions
7.7.6.1 The exp function
Synopsis
[#1]
#include <math.h>
double exp(double x);
Description
[#2] The exp function computes the exponential function of
x. A range error occurs if the magnitude of x is too large.
Returns
[#3] The exp function returns the exponential value.
7.7.6.2 The frexp function
Synopsis
[#1]
#include <math.h>
double frexp(double value, int *exp);
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Description
[#2] The frexp function breaks a floating-point number into
a normalized fraction and an integral power of 2. It stores
the integer in the int object pointed to by exp.
Returns
[#3] The frexp function returns the value x, such that x is
a double with magnitude in the interval [1/2, 1) or zero,
and value equals x x 2*exp. If value is zero, both parts of
the result are zero.
7.7.6.3 The ldexp function
Synopsis
[#1]
#include <math.h>
double ldexp(double x, int exp);
Description
[#2] The ldexp function multiplies a floating-point number
by an integral power of 2. A range error may occur.
Returns
[#3] The ldexp function returns the value of x x 2exp.
7.7.6.4 The log function
Synopsis
[#1]
#include <math.h>
double log(double x);
Description
[#2] The log function computes the natural logarithm of x.
A domain error occurs if the argument is negative. A range
error may occur if the argument is zero.
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Returns
[#3] The log function returns the natural logarithm value.
7.7.6.5 The log10 function
Synopsis
[#1]
#include <math.h>
double log10(double x);
Description
[#2] The log10 function computes the base-ten logarithm of
x. A domain error occurs if the argument is negative. A
range error may occur if the argument is zero.
Returns
[#3] The log10 function returns the base-ten logarithm
value.
7.7.6.6 The modf function
Synopsis
[#1]
#include <math.h>
double modf(double value, double *iptr);
Description
[#2] The modf function breaks the argument value into
integral and fractional parts, each of which has the same
sign as the argument. It stores the integral part as a
double in the object pointed to by iptr.
Returns
[#3] The modf function returns the value of the signed
fractional part of value.
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7.7.6.7 The exp2 function
Synopsis
[#1]
#include <math.h>
double exp2(double x);
Description
[#2] The exp2 function computes the base-2 exponential of x:
2x. A range error occurs if the magnitude of x is too
large.
Returns
[#3] The exp2 function returns the base-2 exponential value.
7.7.6.8 The expm1 function
Synopsis
[#1]
#include <math.h>
double expm1(double x);
Description
[#2] The expm1 function computes the base-e exponential of
the argument, minus 1: ex-1.177 A range error occurs if x
is too large.
Returns
[#3] The expm1 function returns the value of ex-1.
__________
177. For small magnitude x, expm1(x) is expected to be more
accurate than exp(x) - 1.
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7.7.6.9 The log1p function
Synopsis
[#1]
#include <math.h>
double log1p(double x);
Description
[#2] The log1p function computes the base-e logarithm of 1
plus the argument.178 A domain error occurs if the argument
is less than -1. A range error may occur if the argument
equals -1.
Returns
[#3] The log1p function returns the value of the base-e
logarithm of 1 plus the argument.
7.7.6.10 The log2 function
Synopsis
[#1]
#include <math.h>
double log2(double x);
Description
[#2] The log2 function computes the base-2 logarithm of x.
A domain error occurs if the argument is less than zero. A
range error may occur if the argument is zero.
Returns
[#3] The log2 function returns the base-2 logarithm value.
__________
178. For small magnitude x, log1p(x) is expected to be more
accurate than log(1 + x).
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7.7.6.11 The logb function
Synopsis
[#1]
#include <math.h>
double logb(double x);
Description
[#2] The logb function extracts the exponent of x, as a
signed integer value in the format of x. If x is subnormal
it is treated as though it were normalized; thus for
positive finite x,
1 < x x FLT_RADIX-logb(x) < FLT_RADIX
A range error may occur if the argument is zero.
Returns
[#3] The logb function returns the signed exponent of its
argument.
7.7.6.12 The scalbn function
Synopsis
[#1]
#include <math.h>
double scalbn(double x, int n);
Description
[#2] The scalbn function computes x x FLT_RADIXn
efficiently, not normally by computing FLT_RADIXn
explicitly. A range error may occur.
Returns
[#3] The scalbn function returns the value of x x
FLT_RADIXn.
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7.7.6.13 The scalbln function
Synopsis
[#1]
#include <math.h>
double scalbln(double x, long int n);
Description
[#2] The scalbln function is equivalent to the scalbn
function, except that the integer argument is long int.
7.7.6.14 The ilogb function
Synopsis
[#1]
#include <math.h>
int ilogb(double x);
Description
[#2] The ilogb function extracts the exponent of x as a
signed int value. It is equivalent to (int) logb(x), for
finite nonzero x; it computes the value FP_ILOGB0 if x is
zero; it computes the value INT_MAX if x is infinite; and it
computes the value FP_ILOGBNAN if x is a NaN. A range error
may occur if x is 0.
Returns
[#3] The ilogb function returns the exponent of x as a
signed int value.
7.7.7 Power and absolute value functions
7.7.7.1 The fabs function
Synopsis
[#1]
#include <math.h>
double fabs(double x);
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Description
[#2] The fabs function computes the absolute value of a
floating-point number x.
Returns
[#3] The fabs function returns the absolute value of x.
7.7.7.2 The pow function
Synopsis
[#1]
#include <math.h>
double pow(double x, double y);
Description
[#2] The pow function computes x raised to the power y. A
domain error occurs if x is negative and y is finite and not
an integer value. A domain error occurs if the result
cannot be represented when x is zero and y is less than or
equal to zero. A range error may occur.
Returns
[#3] The pow function returns the value of x raised to the
power y.
7.7.7.3 The sqrt function
Synopsis
[#1]
#include <math.h>
double sqrt(double x);
Description
[#2] The sqrt function computes the nonnegative square root
of x. A domain error occurs if the argument is less than
zero.
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Returns
[#3] The sqrt function returns the value of the square root.
7.7.7.4 The cbrt function
Synopsis
[#1]
#include <math.h>
double cbrt(double x);
Description
[#2] The cbrt function computes the real cube root of x.
Returns
[#3] The cbrt function returns the value of the cube root.
7.7.7.5 The hypot function
Synopsis
[#1]
#include <math.h>
double hypot(double x, double y);
Description
[#2] The hypot function computes the square root of the sum
of the squares of x and y, without undue overflow or
underflow. A range error may occur.
[#3]
Returns
[#4] The hypot function returns the value of the square root
of the sum of the squares.
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7.7.8 Error and gamma functions
[#1]
7.7.8.1 The erf function
Synopsis
[#1]
#include <math.h>
double erf(double x);
Description
[#2] The erf function computes the error function of x.
Returns
[#3] The erf function returns the error function value.
7.7.8.2 The erfc function
Synopsis
[#1]
#include <math.h>
double erfc(double x);
Description
[#2] The erfc function computes the complementary error
function of x. A range error occurs if x is too large.
Returns
[#3] The erfc function returns the complementary error
function value.
7.7.8.3 The gamma function
Synopsis
[#1]
#include <math.h>
double gamma(double x);
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Description
[#2] The gamma function computes the gamma function of x: G
(x). A domain error occurs if x is a negative integer or
zero. A range error may occur if the magnitude of x is too
large.
Returns
[#3] The gamma function returns the gamma function value.
7.7.8.4 The lgamma function
Synopsis
[#1]
#include <math.h>
double lgamma(double x);
Description
[#2] The lgamma function computes the natural logarithm of
the absolute value of gamma of x: log (|G(x)|). A range
error occurs if x is too large or if x isea negative integer
or zero.
Returns
[#3] The lgamma function returns the value of the natural
logarithm of the absolute value of gamma of x.
7.7.9 Nearest integer functions
7.7.9.1 The ceil function
Synopsis
[#1]
#include <math.h>
double ceil(double x);
Description
[#2] The ceil function computes the smallest integer value
not less than x.
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Returns
[#3] The ceil function returns the smallest integer value
not less than x, expressed as a double.
7.7.9.2 The floor function
Synopsis
[#1]
#include <math.h>
double floor(double x);
Description
[#2] The floor function computes the largest integer value
not greater than x.
Returns
[#3] The floor function returns the largest integer value
not greater than x, expressed as a double.
7.7.9.3 The nearbyint function
Synopsis
[#1]
#include <math.h>
double nearbyint(double x);
Description
[#2] The nearbyint function differs from the rint function
(7.7.9.4) only in that the nearbyint function does not raise
the inexact exception. (See F.9.6.3-F.9.6.4.)
Returns
[#3] The nearbyint function returns the rounded integer
value.
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7.7.9.4 The rint function
Synopsis
[#1]
#include <math.h>
double rint(double x);
Description
[#2] The rint function rounds its argument to an integer
value in floating-point format, using the current rounding
direction.
Returns
[#3] The rint function returns the rounded integer value.
7.7.9.5 The lrint function
Synopsis
[#1]
#include <math.h>
long int lrint(double x);
Description
[#2] The lrint function rounds its argument to the nearest
integer value, rounding according to the current rounding
direction. If the rounded value is outside the range of
long int, the numeric result is unspecified. A range error
may occur if the magnitude of x is too large.
Returns
[#3] The lrint function returns the rounded integer value,
using the current rounding direction.
7.7.9.6 The llrint function
Synopsis
[#1]
#include <math.h>
long long llrint(double x);
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Description
[#2] The llrint function is equivalent to the lrint
function, except that the returned value has type long long.
7.7.9.7 The round function
Synopsis
[#1]
#include <math.h>
double round(double x);
Description
[#2] The round function rounds its argument to the nearest
integer value in floating-point format, rounding halfway
cases away from zero, regardless of the current rounding
direction.
Returns
[#3] The round function returns the rounded integer value.
7.7.9.8 The lround function
Synopsis
[#1]
#include <math.h>
long int lround(double x);
Description
[#2] The lround function rounds its argument to the nearest
integer value, rounding halfway cases away from zero,
regardless of the current rounding direction. If the
rounded value is outside the range of long int, the numeric
result is unspecified. A range error may occur if the
magnitude of x is too large.
Returns
[#3] The lround function returns the rounded integer value.
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7.7.9.9 The llround function
Synopsis
[#1]
#include <math.h>
long long llround(double x);
Description
[#2] The llround function is equivalent to the lround
function, except that the returned value has type long long.
7.7.9.10 The trunc function
Synopsis
[#1]
#include <math.h>
double trunc(double x);
Description
[#2] The trunc function rounds its argument to the integer
value, in floating format, nearest to but no larger in
magnitude than the argument.
Returns
[#3] The trunc function returns the truncated integer value.
7.7.10 Remainder functions
7.7.10.1 The fmod function
Synopsis
[#1]
#include <math.h>
double fmod(double x, double y);
Description
[#2] The fmod function computes the floating-point remainder
of x / y.
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Returns
[#3] The fmod function returns the value x - n x y, for some
integer n such that, if y is nonzero, the result has the
same sign as x and magnitude less than the magnitude of y.
If y is zero, whether a domain error occurs or the fmod
function returns zero is implementation-defined.
7.7.10.2 The remainder function
Synopsis
[#1]
#include <math.h>
double remainder(double x, double y);
Description
[#2] The remainder function computes the remainder x REM y
required by IEC 559.179
Returns
[#3] The remainder function returns the value of x REM y.
__________
179. ``When
y / 0,
the remainder r = x REM y is defined regardless of the
rounding mode by the mathematical relation r = x -
y * n, where n is the integer nearest the exact value
of x / y; whenever |n - x/y| = 1/2, then n is even.
Thus, the remainder is always exact. If r = 0, its sign
shall be that of x.'' This definition is applicable for
all implementations.
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7.7.10.3 The remquo function
Synopsis
[#1]
#include <math.h>
double remquo(double x, double y, int *quo);
Description
[#2] The remquo function computes the same remainder as the
remainder function. In the object pointed to by quo it
stores a value whose sign is the sign of x / y and whose
magnitude is congruent mod 2n to the magnitude of the
integral quotient of x / y, where n is an implementation-
defined integer at least 3.
Returns
[#3] The remquo function returns the value of x REM y.
7.7.11 Manipulation functions
7.7.11.1 The copysign function
Synopsis
[#1]
#include <math.h>
double copysign(double x, double y);
Description
[#2] The copysign function produces a value with the
magnitude of x and the sign of y. It produces a NaN (with
the sign of y) if x is a NaN. On implementations that
represent a signed zero but do not treat negative zero
consistently in arithmetic operations, the copysign function
regards the sign of zero as positive.
Returns
[#3] The copysign function returns a value with the
magnitude of x and the sign of y.
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7.7.11.2 The nan function
Synopsis
[#1]
#include <math.h>
double nan(const char *tagp);
Description
[#2] If the implementation supports quiet NaNs for the
double type, then the call nan("n-char-sequence") is
equivalent to strtod("NAN(n-char-sequence)", (char**) NULL);
the call nan("") is equivalent to strtod("NAN()", (char**)
NULL). If tagp does not point to an n-char-sequence string
then the result NaN's content is unspecified. If the
implementation does not support quiet NaNs for the double
type, a call to the nan function is unspecified.
Returns
[#3] The nan function returns a quiet NaN, if available,
with content indicated through tagp.
7.7.11.3 The nextafter function
Synopsis
[#1]
#include <math.h>
double nextafter(double x, double y);
Description
[#2] The nextafter function determines the next
representable value, in the type of the function, after x in
the direction of y, where x and y are first converted to the
type of the function.180 The nextafter function returns y
if x equals y.
__________
180. The argument values are converted to the type of the
function, even by a macro implementation of the
function.
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Returns
[#3] The nextafter function returns the next representable
value in the specified format after x in the direction of y.
7.7.11.4 The nextafterx function
Synopsis
[#1]
#include <math.h>
double nextafterx(double x, long double y);
Description
[#2] The nextafterx function is equivalent to the nextafter
function except that the second parameter has type long
double.181
7.7.12 Maximum, minimum, and positive difference functions
7.7.12.1 The fdim function
Synopsis
[#1]
#include <math.h>
double fdim(double x, double y);
Description
[#2] The fdim function determines the positive difference
between its arguments:
x - y if x > y
+0 if x < y
A range error may occur.
__________
181. The result of the nextafterx function is determined in
the type of the function, without loss of range or
precision in a floating second argument.
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Returns
[#3] The fdim function returns the positive difference
value.
7.7.12.2 The fmax function
Synopsis
[#1]
#include <math.h>
double fmax(double x, double y);
Description
[#2] The fmax function determines the maximum numeric value
of its arguments.182
Returns
[#3] The fmax function returns the maximum numeric value of
its arguments.
7.7.12.3 The fmin function
Synopsis
[#1]
#include <math.h>
double fmin(double x, double y);
Description
[#2] The fmin function determines the minimum numeric value
of its arguments.183
__________
182. NaN arguments are treated as missing data: if one
argument is a NaN and the other numeric, then fmax
chooses the numeric value. See F.9.9.2.
183. fmin is analogous to fmax in its treatment of NaNs.
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Returns
[#3] The fmin function returns the minimum numeric value of
its arguments.
7.7.13 Floating multiply-add
7.7.13.1 The fma function
Synopsis
[#1]
#include <math.h>
double fma(double x, double y, double z);
Description
[#2] The fma function computes the sum z plus the product x
times y, rounded as one ternary operation: it computes the
sum z plus the product x times y (as if) to infinite
precision and rounds once to the result format, according to
the rounding mode characterized by the value of FLT_ROUNDS.
Returns
[#3] The fma function returns the sum z plus the product x
times y, rounded as one ternary operation.
7.7.14 Comparison macros
[#1] The relational and equality operators support the usual
mathematical relationships between numeric values. For any
ordered pair of numeric values exactly one of the
relationships - less, greater, and equal - is true.
Relational operators may raise the invalid exception when
argument values are NaNs. For a NaN and a numeric value, or
for two NaNs, just the unordered relationship is true.184
The following subclauses provide macros that are quiet (non
exception raising) versions of the relational operators, and
other comparison macros that facilitate writing efficient
__________
184. IEC 559 requires that the built-in relational operators
raise the invalid exception if the operands compare
unordered, as an error indicator for programs written
without consideration of NaNs; the result in these cases
is false.
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code that accounts for NaNs without suffering the invalid
exception. In the synopses in this subclause, real-floating
indicates that the argument must be an expression of real
floating type.
7.7.14.1 The isgreater macro
Synopsis
[#1]
#include <math.h>
int isgreater(real-floating x, real-floating y);
Description
[#2] The isgreater macro determines whether its first
argument is greater than its second argument. The value of
isgreater(x,y) is always equal to (x) > (y); however, unlike
(x) > (y), isgreater(x,y) does not raise the invalid
exception when x and y are unordered.
Returns
[#3] The isgreater macro returns the value of (x) > (y).
7.7.14.2 The isgreaterequal macro
Synopsis
[#1]
#include <math.h>
int isgreaterequal(real-floating x, real-floating y);
Description
[#2] The isgreaterequal macro determines whether its first
argument is greater than or equal to its second argument.
The value of isgreaterequal(x,y) is always equal to (x) >=
(y); however, unlike (x) >= (y), isgreaterequal(x,y) does
not raise the invalid exception when x and y are unordered.
Returns
[#3] The isgreaterequal macro returns the value of (x) >=
(y).
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7.7.14.3 The isless macro
Synopsis
[#1]
#include <math.h>
int isless(real-floating x, real-floating y);
Description
[#2] The isless macro determines whether its first argument
is less than its second argument. The value of isless(x,y)
is always equal to (x) < (y); however, unlike (x) < (y),
isless(x,y) does not raise the invalid exception when x and
y are unordered.
Returns
[#3] The isless macro returns the value of (x) < (y).
7.7.14.4 The islessequal macro
Synopsis
[#1]
#include <math.h>
int islessequal(real-floating x, real-floating y);
Description
[#2] The islessequal macro determines whether its first
argument is less than or equal to its second argument. The
value of islessequal(x,y) is always equal to (x) <= (y);
however, unlike (x) <= (y), islessequal(x,y) does not raise
the invalid exception when x and y are unordered.
Returns
[#3] The islessequal macro returns the value of (x) <= (y).
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7.7.14.5 The islessgreater macro
Synopsis
[#1]
#include <math.h>
int islessgreater(real-floating x, real-floating y);
Description
[#2] The islessgreater macro determines whether its first
argument is less than or greater than its second argument.
The islessgreater(x,y) macro is similar to (x) < (y) ||
(x) > (y); however, islessgreater(x,y) does not raise the
invalid exception when x and y are unordered (nor does it
evaluate x and y twice).
Returns
[#3] The islessgreater macro returns the value of (x) < (y)
|| (x) > (y).
7.7.14.6 The isunordered macro
Synopsis
[#1]
#include <math.h>
int isunordered(real-floating x, real-floating y);
Description
[#2] The isunordered macro determines whether its arguments
are unordered.
Returns
[#3] The isunordered macro returns 1 if its arguments are
unordered and 0 otherwise.
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7.8 Complex arithmetic <complex.h>
[#1] The header <complex.h> defines macros and declares
functions that support complex arithmetic. Each synopsis
specifies a function with one or two double complex
parameters and returning a double complex or double value;
for each such function, there are similar functions with the
same name but with f and l suffixes. The f suffix indicates
that float (instead of double) is the corresponding real
type for the parameters and result. Similarly the l suffix
indicates that long double is the corresponding real type
for the parameters and result.
[#2] The macro
_Complex_I
expands to a constant expression of type const float
complex, with the value of the imaginary unit.185 The macro
_Imaginary_I
is defined if and only if the implementation supports
imaginary types;186 it expands to a constant expression of
type const float imaginary, with the value of the imaginary
unit.
[#3] The macro
I
is defined to be _Complex_I or, if defined, _Imaginary_I.
Notwithstanding the provisions of subclause 7.1.3, it is
permitted to undefine the macro I.
__________
185. The imaginary unit is a number i such that i * i = -1.
186. A specification for imaginary types is in informative
Annex G.
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7.8.1 The CX_LIMITED_RANGE pragma
Synopsis
[#1]
#include <complex.h>
#pragma STDC CX_LIMITED_RANGE on-off-switch
Description
[#2] The usual mathematical formula for multiplication of
two complex numbers and the one for division by a complex
number are problematic because of their treatment of
infinities and because of undue overflow and underflow. The
CX_LIMITED_RANGE pragma can be used to inform the
implementation that (where the state is on) the usual
mathematical formulas for multiplication and division are
acceptable.187 The pragma can occur either outside external
declarations or preceding all explicit declarations and
statements inside a compound statement. When outside
external declarations, the pragma takes effect from its
occurrence until another CX_LIMITED_RANGE pragma is
encountered, or until the end of the translation unit. When
inside a compound statement, the pragma takes effect from
its occurrence until another CX_LIMITED_RANGE pragma is
encountered (within a nested compound statement), or until
the end of the compound statement; at the end of a compound
statement the state for the pragma is restored to its
condition just before the compound statement. If this
pragma is used in any other context, the behavior is
undefined. The default state for the pragma is off.
__________
187. The purpose of the pragma is to allow the
implementation to use the formulas
(x + y*i) * (u + v*i) = (x*u - y*v) + (y*u + x*v)*i
(x + y*i) / (u + v*i) = (x*u + y*v) / (u*u + v*v) +
((y*u - x*v) / (u*u + v*v))*i
where the programmer can determine they are safe.
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7.8.2 Complex functions
[#1] Values are interpreted as radians, not degrees. An
implementation may set errno but is not required to.
7.8.2.1 Branch cuts
[#1] Some of the functions below have branch cuts, across
which the function is discontinuous. For implementations
with a signed zero (including all IEC 559 implementations)
that follow the specification of Annex G, the sign of zero
distinguishes one side of a cut from another so the function
is continuous (except for format limitations) as the cut is
approached from either side. For example, for the square
root function, which has a branch cut along the negative
real axis, the top of the cut, with imaginary part +0, maps
to the positive imaginary axis, and the bottom of the cut,
with imaginary part -0, maps to the negative imaginary axis.
[#2] Implementations that do not support a signed zero (see
Annex F) cannot distinguish the sides of branch cuts. These
implementations must map a cut so the function is continuous
as the cut is approached coming around the finite endpoint
of the cut in a counter clockwise direction. (Branch cuts
for the functions specified here have just one finite
endpoint.) For example, for the square root function,
coming counter clockwise around the finite endpoint of the
cut along the negative real axis approaches the cut from
above, so the cut maps to the positive imaginary axis.
7.8.2.2 The cacos function
Synopsis
[#1]
#include <complex.h>
double complex cacos(double complex z);
Description
[#2] The cacos function computes the complex arc cosine of
z, with branch cuts outside the interval [-1, 1] along the
real axis.
Returns
[#3] The cacos function returns the complex arc cosine
value, in the range of a strip mathematically unbounded
along the imaginary axis and in the interval [0, pi] along
the real axis.
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7.8.2.3 The casin function
Synopsis
[#1]
#include <complex.h>
double complex casin(double complex z);
Description
[#2] The casin function computes the complex arc sine of z,
with branch cuts outside the interval [-1, 1] along the real
axis.
Returns
[#3] The casin function returns the complex arc sine value,
in the range of a strip mathematically unbounded along the
imaginary axis and in the interval [-pi/2, pi/2] along the
real axis.
7.8.2.4 The catan function
Synopsis
[#1]
#include <complex.h>
double complex catan(double complex z);
Description
[#2] The catan function computes the complex arc tangent of
z, with branch cuts outside the interval [-i, i] along the
imaginary axis.
Returns
[#3] The catan function returns the complex arc tangent
value, in the range of a strip mathematically unbounded
along the imaginary axis and in the interval [ - pi/2, pi/2]
along the real axis.
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7.8.2.5 The ccos function
Synopsis
[#1]
#include <complex.h>
double complex ccos(double complex z);
Description
[#2] The ccos function computes the complex cosine of z.
Returns
[#3] The ccos function returns the complex cosine value.
7.8.2.6 The csin function
Synopsis
[#1]
#include <complex.h>
double complex csin(double complex z);
Description
[#2] The csin function computes the complex sine of z.
Returns
[#3] The csin function returns the complex sine value.
7.8.2.7 The ctan function
Synopsis
[#1]
#include <complex.h>
double complex ctan(double complex z);
Description
[#2] The ctan function computes the complex tangent of z.
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Returns
[#3] The ctan function returns the complex tangent value.
7.8.2.8 The cacosh function
Synopsis
[#1]
#include <complex.h>
double complex cacosh(double complex z);
Description
[#2] The cacosh function computes the complex arc hyperbolic
cosine of z, with a branch cut at values less than 1 along
the real axis.
Returns
[#3] The cacosh function returns the complex arc hyperbolic
cosine value, in the range of a half-strip of non-negative
values along the real axis and in the interval [ - ipi, ipi]
along the imaginary axis.
7.8.2.9 The casinh function
Synopsis
[#1]
#include <complex.h>
double complex casinh(double complex z);
Description
[#2] The casinh function computes the complex arc hyperbolic
sine of z, with branch cuts outside the interval [-i, i]
along the imaginary axis.
Returns
[#3] The casinh function returns the complex arc hyperbolic
sine value, in the range of a strip mathematically unbounded
along the real axis and in the interval [ - ipi/2, ipi/2]
along the imaginary axis.
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7.8.2.10 The catanh function
Synopsis
[#1]
#include <complex.h>
double complex catanh(double complex z);
Description
[#2] The catanh function computes the complex arc hyperbolic
tangent of z, with branch cuts outside the interval [-1, 1]
along the real axis.
Returns
[#3] The catanh function returns the complex arc hyperbolic
tangent value, in the range of a strip mathematically
unbounded along the real axis and in the interval [ -
ipi/2, ipi/2] along the imaginary axis.
7.8.2.11 The ccosh function
Synopsis
[#1]
#include <complex.h>
double complex ccosh(double complex z);
Description
[#2] The ccosh function computes the complex hyperbolic
cosine of z.
Returns
[#3] The ccosh function returns the complex hyperbolic
cosine value.
7.8.2.12 The csinh function
Synopsis
[#1]
#include <complex.h>
double complex csinh(double complex z);
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Description
[#2] The csinh function computes the complex hyperbolic sine
of z.
Returns
[#3] The csinh function returns the complex hyperbolic sine
value.
7.8.2.13 The ctanh function
Synopsis
[#1]
#include <complex.h>
double complex ctanh(double complex z);
Description
[#2] The ctanh function computes the complex hyperbolic
tangent of z.
Returns
[#3] The ctanh function returns the complex hyperbolic
tangent value.
7.8.2.14 The cexp function
Synopsis
[#1]
#include <complex.h>
double complex cexp(double complex z);
Description
[#2] The cexp function computes the complex base-e
exponential of z.
Returns
[#3] The cexp function returns the complex base-e
exponential value.
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7.8.2.15 The clog function
Synopsis
[#1]
#include <complex.h>
double complex clog(double complex z);
Description
[#2] The clog function computes the complex natural (base-e)
logarithm of z, with a branch cut along the negative real
axis.
Returns
[#3] The clog function returns the complex natural logarithm
value, in the range of a strip mathematically unbounded
along the real axis and in the interval [ - ipi, ipi] along
the imaginary axis.
7.8.2.16 The csqrt function
Synopsis
[#1]
#include <complex.h>
double complex csqrt(double complex z);
Description
[#2] The csqrt function computes the complex square root of
z, with a branch cut along the negative real axis.
Returns
[#3] The csqrt function returns the complex square root
value, in the range of the right half-plane (including the
imaginary axis).
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7.8.2.17 The cabs function
Synopsis
[#1]
#include <complex.h>
double cabs(double complex z);
Description
[#2] The cabs function computes the complex absolute value
(also called norm, modulus, or magnitude) of z.
Returns
[#3] The cabs function returns the complex absolute value.
7.8.2.18 The cpow function
Synopsis
[#1]
#include <complex.h>
double complex cpow(double complex x, double complex y);
Description
[#2] The cpow function computes the complex power function
xy, with a branch cut for the first parameter along the
negative real axis.
Returns
[#3] The cpow function returns the complex power function
value.
7.8.2.19 The carg function
Synopsis
[#1]
#include <complex.h>
double carg(double complex z);
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Description
[#2] The carg function computes the argument (also called
phase angle) of z, with a branch cut along the negative real
axis.
Returns
[#3] The carg function returns the value of the argument in
the range [-pi, pi].
7.8.2.20 The conj function
Synopsis
[#1]
#include <complex.h>
double complex conj(double complex z);
Description
[#2] The conj function computes the complex conjugate of z,
by reversing the sign of its imaginary part.
Returns
[#3] The conj function returns the complex conjugate value.
7.8.2.21 The cimag function
Synopsis
[#1]
#include <complex.h>
double cimag(double complex z);
Description
[#2] The cimag function computes the imaginary part of z.188
__________
188. For a variable z of complex type, z == creal(z) +
cimag(z)*I.
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Returns
[#3] The cimag function returns the imaginary part value (as
a real).
7.8.2.22 The cproj function
Synopsis
[#1]
#include <complex.h>
double complex cproj(double complex z);
Description
[#2] The cproj function computes a projection of z onto the
Riemann sphere: z projects to z except that all complex
infinities (even those with one infinite part and one NaN
part) project to positive infinity on the real axis. If z
has an infinite part, then cproj(z) is equivalent to
INFINITY + I * copysign(7.8.2.23 The creal function
Synopsis
[#1]
#include <complex.h>
double creal(double complex z);
Description
[#2] The creal function computes the real part of z.
Returns
[#3] The creal function returns the real part value.
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7.9 Type-generic math <tgmath.h>
[#1] The header <tgmath.h> includes the headers <math.h> and
<complex.h> and defines several type-generic macros.
7.9.1 Type-generic macros
[#1] Of the <math.h> and <complex.h> functions without an f
(float) or l (long double) suffix, several have one or more
parameters whose corresponding real type is double. For
each such function, except modf, there is a corresponding
type-generic macro.189 The parameters whose corresponding
real type is double in the function synopsis are generic
parameters. Use of the macro invokes a function whose
corresponding real type and type-domain are determined by
the arguments for the generic parameters.190
[#2] Use of the macro invokes a function whose generic
parameters have the corresponding real type determined as
follows:
- First, if any argument for generic parameters has type
long double, the type determined is long double.
- Otherwise, if any argument for generic parameters has
type double or is of integer type, the type determined
is double.
- Otherwise, the type determined is float.
[#3] For each unsuffixed function in <math.h> for which
there is a function in <complex.h> with the same name except
for a c prefix, the corresponding type-generic macro (for
both functions) has the same name as the function in
<math.h>. The corresponding type-generic macro for fabs and
cabs is fabs.
__________
189. Like other function-like macros in Standard libraries,
each type-generic macro can be suppressed to make
available the corresponding ordinary function.
190. If the type of the argument is incompatible with the
type of the parameter for the selected function, the
behavior is undefined.
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center;
ce ce ce
le le le.
<math.h> function <complex.h> function type-generic macro
_ _ _
acos cacos acos
asin casin asin
atan catan atan
acosh cacosh acosh
asinh casinh asinh
atanh catanh atanh
cos ccos cos
sin csin sin
tan ctan tan
cosh ccosh cosh
sinh csinh sinh
tanh ctanh tanh
exp cexp exp
log clog log
pow cpow pow
sqrt csqrt sqrt
fabs cabs fabs
[#4] If at least one argument for a generic parameter is
complex, then use of the macro invokes a complex function;
otherwise, use of the macro invokes a real function.
[#5] For each unsuffixed function in <math.h> without a c-
prefixed counterpart in <complex.h>, the corresponding
type-generic macro has the same name as the function. These
type-generic macros are:
center;
le le le.
atan2 cbrt ceil
copysign erf erfc
exp2 expm1 fdim
floor fma fmax
fmin fmod frexp
gamma hypot ilogb
ldexp lgamma llrint
llround log10 log1p
log2 logb lrint
lround nearbyint nextafter
nextafterx remainder remquo
rint round scalbn
scalbln trunc
[#6] If all arguments for generic parameters are real, then
use of the macro invokes a real function; otherwise, use of
the macro results in undefined behavior.
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[#7] For each unsuffixed function in <complex.h> that is not
a c-prefixed counterpart to a function in <math.h>, the
corresponding type-generic macro has the same name as the
function. These type-generic macros are:
center;
le le le.
carg cimag conj
cproj creal
[#8] Use of the macro with any real or complex argument
invokes a complex function.
Examples
[#9] With the declarations
#include <tgmath.h>
int n;
float f;
double d;
long double ld;
float complex fc;
double complex dc;
long double complex ldc;
functions invoked by use of type-generic macros are shown in
the following table:
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center;
ce ce
le le.
macro use invokes
_ _
exp(n) exp(n), the function
acosh(f) acoshf(f)
sin(d) sin(d), the function
atan(ld) atanl(ld)
log(fc) clogf(fc)
sqrt(dc) csqrt(dc)
pow(ldc, f) cpowl(ldc, f)
remainder(n, n) remainder(n, n), the function
nextafter(d, f) nextafter(d, f), the function
nextafterx(f, ld) nextafterxf(f, ld)
copysign(n, ld) copysignl(n, ld)
ceil(fc) undefined behavior
rint(dc) undefined behavior
fmax(ldc, ld) undefined behavior
carg(n) carg(n), the function
cproj(f) cprojf(f)
creal(d) creal(d), the function
cimag(ld) cimagl(ld)
cabs(fc) cabsf(fc)
carg(dc) carg(dc), the function
cproj(ldc) cprojl(ldc)
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7.10 Nonlocal jumps <setjmp.h>
[#1] The header <setjmp.h> defines the macro setjmp, and
declares one function and one type, for bypassing the normal
function call and return discipline.191
[#2] The type declared is
jmp_buf
which is an array type suitable for holding the information
needed to restore a calling environment.
[#3] It is unspecified whether setjmp is a macro or an
identifier declared with external linkage. If a macro
definition is suppressed in order to access an actual
function, or a program defines an external identifier with
the name setjmp, the behavior is undefined.
7.10.1 Save calling environment
7.10.1.1 The setjmp macro
Synopsis
[#1]
#include <setjmp.h>
int setjmp(jmp_buf env);
Description
[#2] The setjmp macro saves its calling environment in its
jmp_buf argument for later use by the longjmp function.
Returns
[#3] If the return is from a direct invocation, the setjmp
macro returns the value zero. If the return is from a call
to the longjmp function, the setjmp macro returns a nonzero
value.
__________
191. These functions are useful for dealing with unusual
conditions encountered in a low-level function of a
program.
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Environmental restriction
[#4] An invocation of the setjmp macro shall appear only in
one of the following contexts:
- the entire controlling expression of a selection or
iteration statement;
- one operand of a relational or equality operator with
the other operand an integer constant expression, with
the resulting expression being the entire controlling
expression of a selection or iteration statement;
- the operand of a unary ! operator with the resulting
expression being the entire controlling expression of a
selection or iteration statement; or
- the entire expression of an expression statement
(possibly cast to void).
[#5] If the invocation appears in any other context, the
behavior is undefined.
7.10.2 Restore calling environment
7.10.2.1 The longjmp function
Synopsis
[#1]
#include <setjmp.h>
void longjmp(jmp_buf env, int val);
Description
[#2] The longjmp function restores the environment saved by
the most recent invocation of the setjmp macro in the same
invocation of the program, with the corresponding jmp_buf
argument. If there has been no such invocation, or if the
function containing the invocation of the setjmp macro has
terminated execution192 in the interim, the behavior is
__________
192. For example, by executing a return statement or because
another longjmp call has caused a transfer to a setjmp
invocation in a function earlier in the set of nested
calls.
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undefined.
[#3] All accessible objects have values as of the time
longjmp was called, except that the values of objects of
automatic storage duration that are local to the function
containing the invocation of the corresponding setjmp macro
that do not have volatile-qualified type and have been
changed between the setjmp invocation and longjmp call are
indeterminate.
Returns
[#4] After longjmp is completed, program execution continues
as if the corresponding invocation of the setjmp macro had
just returned the value specified by val. The longjmp
function cannot cause the setjmp macro to return the value
0; if val is 0, the setjmp macro returns the value 1.
Examples
[#5] The longjmp function that returns control back to the
point of the setjmp invocation might cause memory associated
with a variable length array object to be squandered.
#include <setjmp.h>
jmp_buf buf;
void g(int n);
void h(int n);
int n = 6;
void f(void)
{
int x[n]; // OK, f is not terminated.
setjmp(buf);
g(n);
}
void g(int n)
{
int a[n]; // a may remain allocated.
h(n);
}
void h(int n)
{
int b[n]; // b may remain allocated.
longjmp(buf,2); // might cause memory loss.
}
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7.11 Signal handling <signal.h>
[#1] The header <signal.h> declares a type and two functions
and defines several macros, for handling various signals
(conditions that may be reported during program execution).
[#2] The type defined is
sig_atomic_t
which is the (possibly volatile-qualified) integer type of
an object that can be accessed as an atomic entity, even in
the presence of asynchronous interrupts.
[#3] The macros defined are
SIG_DFL
SIG_ERR
SIG_IGN
which expand to positive integer constant expressions with
type int and distinct values that have type compatible with
the second argument to and the return value of the signal
function, and whose value compares unequal to the address of
any declarable function; and the following, which expand to
positive integer constant expressions with distinct values
that are the signal numbers, each corresponding to the
specified condition:
SIGABRT abnormal termination, such as is initiated by the
abort function
SIGFPE an erroneous arithmetic operation, such as zero
divide or an operation resulting in overflow
SIGILL detection of an invalid function image, such as an
illegal instruction
SIGINT receipt of an interactive attention signal
SIGSEGV an invalid access to storage
SIGTERM a termination request sent to the program
[#4] An implementation need not generate any of these
signals, except as a result of explicit calls to the raise
function. Additional signals and pointers to undeclarable
functions, with macro definitions beginning, respectively,
with the letters SIG and an uppercase letter or with SIG_
and an uppercase letter,193 may also be specified by the
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implementation. The complete set of signals, their
semantics, and their default handling is implementation-
defined; all signal numbers shall be positive.
7.11.1 Specify signal handling
7.11.1.1 The signal function
Synopsis
[#1]
#include <signal.h>
void (*signal(int sig, void (*func)(int)))(int);
Description
[#2] The signal function chooses one of three ways in which
receipt of the signal number sig is to be subsequently
handled. If the value of func is SIG_DFL, default handling
for that signal will occur. If the value of func is
SIG_IGN, the signal will be ignored. Otherwise, func shall
point to a function to be called when that signal occurs.
An invocation of such a function because of a signal, or
(recursively) of any further functions called by that
invocation (other than functions in the standard library),
is called a signal handler.
[#3] When a signal occurs and func points to a function, it
is implementation-defined whether the equivalent of
signal(sig, SIG_DFL); is executed or the implementation
prevents some implementation-defined set of signals (at
least including sig) from occuring until the current signal
handling has completed; in the case of SIGILL, the
implementation may alternatively define that no action is
taken. Then the equivalent of (*func)(sig); is executed.
If and when the function returns, if the value of sig is
SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined
value corresponding to a computational exception, the
behavior is undefined; otherwise the program will resume
__________
193. See ``future library directions'' (7.20.6). The names
of the signal numbers reflect the following terms
(respectively): abort, floating-point exception,
illegal instruction, interrupt, segmentation violation,
and termination.
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execution at the point it was interrupted.
[#4] If the signal occurs as the result of calling the abort
or raise function, the signal handler shall not call the
raise function.
[#5] If the signal occurs other than as the result of
calling the abort or raise function, the behavior is
undefined if the signal handler refers to any object with
static storage duration other than by assigning a value to
an object declared as volatile sig_atomic_t, or the signal
handler calls any function in the standard library other
than the abort function or the signal function with the
first argument equal to the signal number corresponding to
the signal that caused the invocation of the handler.
Furthermore, if such a call to the signal function results
in a SIG_ERR return, the value of errno is indeterminate.194
[#6] At program startup, the equivalent of
signal(sig, SIG_IGN);
may be executed for some signals selected in an
implementation-defined manner; the equivalent of
signal(sig, SIG_DFL);
is executed for all other signals defined by the
implementation.
[#7] The implementation shall behave as if no library
function calls the signal function.
Returns
[#8] If the request can be honored, the signal function
returns the value of func for the most recent successful
call to signal for the specified signal sig. Otherwise, a
value of SIG_ERR is returned and a positive value is stored
in errno.
__________
194. If any signal is generated by an asynchronous signal
handler, the behavior is undefined.
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Forward references: the abort function (7.14.4.1), the exit
function (7.14.4.3).
7.11.2 Send signal
7.11.2.1 The raise function
Synopsis
[#1]
#include <signal.h>
int raise(int sig);
Description
[#2] The raise function carries out the actions described in
subclause 7.11.1.1 for the signal sig. If a signal handler
is called, the raise function shall not return until after
the signal handler does.
Returns
[#3] The raise function returns zero if successful, nonzero
if unsuccessful.
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7.12 Variable arguments <stdarg.h>
[#1] The header <stdarg.h> declares a type and defines four
macros, for advancing through a list of arguments whose
number and types are not known to the called function when
it is translated.
[#2] A function may be called with a variable number of
arguments of varying types. As described in 6.7.1, its
parameter list contains one or more parameters. The
rightmost parameter plays a special role in the access
mechanism, and will be designated parmN in this description.
[#3] The type declared is
va_list
which is an object type suitable for holding information
needed by the macros va_start, va_arg, va_end, and va_copy.
If access to the varying arguments is desired, the called
function shall declare an object (referred to as ap in this
subclause) having type va_list. The object ap may be passed
as an argument to another function; if that function invokes
the va_arg macro with parameter ap, the value of ap in the
calling function is indeterminate and shall be passed to the
va_end macro prior to any further reference to ap.195
7.12.1 Variable argument list access macros
[#1] The va_start, va_arg, and va_copy macros described in
this subclause shall be implemented as macros, not
functions. It is unspecified whether va_end is a macro or
an identifier declared with external linkage. If a macro
definition is suppressed in order to access an actual
function, or a program defines an external identifier with
the name va_end, the behavior is undefined. Each invocation
of the va_start or va_copy macros shall be matched by a
corresponding invocation of the va_end macro in the function
accepting a varying number of arguments.
__________
195. It is permitted to create a pointer to a va_list and
pass that pointer to another function, in which case the
original function may make further use of the original
list after the other function returns.
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7.12.1.1 The va_start macro
Synopsis
[#1]
#include <stdarg.h>
void va_start(va_list ap, parmN);
Description
[#2] The va_start macro shall be invoked before any access
to the unnamed arguments.
[#3] The va_start macro initializes ap for subsequent use by
va_arg and va_end. va_start shall not be invoked again for
the same ap without an intervening invocation of va_end for
the same ap.
[#4] The parameter parmN is the identifier of the rightmost
parameter in the variable parameter list in the function
definition (the one just before the , ...). If the
parameter parmN is declared with the register storage class,
with a function or array type, or with a type that is not
compatible with the type that results after application of
the default argument promotions, the behavior is undefined.
Returns
[#5] The va_start macro returns no value.
7.12.1.2 The va_arg macro
Synopsis
[#1]
#include <stdarg.h>
type va_arg(va_list ap, type);
Description
[#2] The va_arg macro expands to an expression that has the
type and value of the next argument in the call. The
parameter ap shall be the same as the va_list ap initialized
by va_start. Each invocation of va_arg modifies ap so that
the values of successive arguments are returned in turn.
The parameter type is a type name specified such that the
type of a pointer to an object that has the specified type
can be obtained simply by postfixing a * to type. If there
is no actual next argument, or if type is not compatible
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with the type of the actual next argument (as promoted
according to the default argument promotions), the behavior
is undefined.
Returns
[#3] The first invocation of the va_arg macro after that of
the va_start macro returns the value of the argument after
that specified by parmN. Successive invocations return the
values of the remaining arguments in succession.
7.12.1.3 The va_copy macro
Synopsis
[#1]
#include <stdarg.h>
void va_copy(va_list dest, va_list src);
Description
[#2] The va_copy macro makes the va_list dest be a copy of
the va_list src, as if the va_start macro had been applied
to it followed by the same sequence of uses of the va_arg
macro as had previously been used to reach the present state
of src.
Returns
[#3] The va_copy macro returns no value.
7.12.1.4 The va_end macro
Synopsis
[#1]
#include <stdarg.h>
void va_end(va_list ap);
Description
[#2] The va_end macro facilitates a normal return from the
function whose variable argument list was referred to by the
expansion of va_start that initialized the va_list ap. The
va_end macro may modify ap so that it is no longer usable
(without an intervening invocation of va_start). If there
is no corresponding invocation of the va_start macro, or if
the va_end macro is not invoked before the return, the
behavior is undefined.
page 310 Library
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Returns
[#3] The va_end macro returns no value.
Examples
[#4] The function f1 gathers into an array a list of
arguments that are pointers to strings (but not more than
MAXARGS arguments), then passes the array as a single
argument to function f2. The number of pointers is
specified by the first argument to f1.
#include <stdarg.h>
#define MAXARGS 31
void f1(int n_ptrs, ...)
{
va_list ap;
char *array[MAXARGS];
int ptr_no = 0;
if (n_ptrs > MAXARGS)
n_ptrs = MAXARGS;
va_start(ap, n_ptrs);
while (ptr_no < n_ptrs)
array[ptr_no++] = va_arg(ap, char *);
va_end(ap);
f2(n_ptrs, array);
}
Each call to f1 shall have visible the definition of the
function or a declaration such as
void f1(int, ...);
[#5] The function f3 is similar, but saves the status of the
variable argument list after the indicated number of
arguments; after f2 has been called once with the whole
list, the trailing part of the list is gathered again and
passed to function f4.
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#include <stdarg.h>
#define MAXARGS 31
void f3(int n_ptrs, int f4_after, ...)
{
va_list ap, ap_save;
char *array[MAXARGS];
int ptr_no = 0;
if (n_ptrs > MAXARGS)
n_ptrs = MAXARGS;
va_start(ap, n_ptrs);
while (ptr_no < n_ptrs) {
array[ptr_no++] = va_arg(ap, char *);
if (ptr_no == f4_after)
va_copy(ap_save, ap);
}
va_end(ap);
f2(n_ptrs, array);
// Now process the saved copy.
n_ptrs -= f4_after;
ptr_no = 0;
while (ptr_no < n_ptrs)
array[ptr_no++] = va_arg(ap_save, char *);
va_end(ap_save);
f4(n_ptrs, array);
}
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7.13 Input/output <stdio.h>
7.13.1 Introduction
[#1] The header <stdio.h> declares three types, several
macros, and many functions for performing input and output.
[#2] The types declared are size_t (described in 7.1.6);
FILE
which is an object type capable of recording all the
information needed to control a stream, including its file
position indicator, a pointer to its associated buffer (if
any), an error indicator that records whether a read/write
error has occurred, and an end-of-file indicator that
records whether the end of the file has been reached; and
fpos_t
which is an object type other than an array type capable of
recording all the information needed to specify uniquely
every position within a file.
[#3] The macros are NULL (described in 7.1.6);
_IOFBF
_IOLBF
_IONBF
which expand to integer constant expressions with distinct
values, suitable for use as the third argument to the
setvbuf function;
BUFSIZ
which expands to an integer constant expression, which is
the size of the buffer used by the setbuf function;
EOF
which expands to an integer constant expression, with type
int and a negative value, that is returned by several
functions to indicate end-of-file, that is, no more input
from a stream;
FOPEN_MAX
which expands to an integer constant expression that is the
minimum number of files that the implementation guarantees
can be open simultaneously;
page 313 Library
page 314
FILENAME_MAX
which expands to an integer constant expression that is the
size needed for an array of char large enough to hold the
longest file name string that the implementation guarantees
can be opened;196
L_tmpnam
which expands to an integer constant expression that is the
size needed for an array of char large enough to hold a
temporary file name string generated by the tmpnam function;
SEEK_CUR
SEEK_END
SEEK_SET
which expand to integer constant expressions with distinct
values, suitable for use as the third argument to the fseek
function;
TMP_MAX
which expands to an integer constant expression that is the
minimum number of unique file names that shall be generated
by the tmpnam function;
stderr
stdin
stdout
which are expressions of type ``pointer to FILE'' that point
to the FILE objects associated, respectively, with the
standard error, input, and output streams.
[#4] The header <wchar.h> declares a number of functions
useful for wide-character input and output. The wide-
character input/output functions described in that subclause
__________
196. If the implementation imposes no practical limit on the
length of file name strings, the value of FILENAME_MAX
should instead be the recommended size of an array
intended to hold a file name string. Of course, file
name string contents are subject to other system-
specific constraints; therefore all possible strings of
length FILENAME_MAX cannot be expected to be opened
successfully.
page 314 Library
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provide operations analogous to most of those described
here, except that the fundamental units internal to the
program are wide characters. The external representation
(in the file) is a sequence of ``generalized'' multibyte
characters, as described further in subclause 7.13.3.
[#5] The input/output functions are given the following
collective terms:
- The wide-character input functions - those functions
described in these subclauses that perform input into
wide characters and wide strings: fgetwc, fgetws,
getwc, getwchar, fwscanf, wscanf, vfwscanf, and
vwscanf.
- The wide-character output functions - those functions
described in these subclauses that perform output from
wide characters and wide strings: fputwc, fputws,
putwc, putwchar, fwprintf, wprintf, vfwprintf, and
vwprintf.
- The wide-character input/output functions - the union
of the ungetwc function, the wide-character input
functions, and the wide-character output functions.
- The byte input/output functions - those functions
described in these subclauses that perform
input/output: fgetc, fgets, fprintf, fputc, fputs,
fread, fscanf, fwrite, getc, getchar, gets, printf,
putc, putchar, puts, scanf, ungetc, vfprintf, vfscanf,
vprintf, and vscanf.
Forward references: files (7.13.3), the fseek function
(7.13.9.2), streams (7.13.2), the tmpnam function
(7.13.4.4), <wchar.h> (7.19).
7.13.2 Streams
[#1] Input and output, whether to or from physical devices
such as terminals and tape drives, or whether to or from
files supported on structured storage devices, are mapped
into logical data streams, whose properties are more uniform
than their various inputs and outputs. Two forms of mapping
are supported, for text streams and for binary streams.197
__________
197. An implementation need not distinguish between text
streams and binary streams. In such an implementation,
there need be no new-line characters in a text stream
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[#2] A text stream is an ordered sequence of characters
composed into lines, each line consisting of zero or more
characters plus a terminating new-line character. Whether
the last line requires a terminating new-line character is
implementation-defined. Characters may have to be added,
altered, or deleted on input and output to conform to
differing conventions for representing text in the host
environment. Thus, there need not be a one-to-one
correspondence between the characters in a stream and those
in the external representation. Data read in from a text
stream will necessarily compare equal to the data that were
earlier written out to that stream only if: the data
consist only of printable characters and the control
characters horizontal tab and new-line; no new-line
character is immediately preceded by space characters; and
the last character is a new-line character. Whether space
characters that are written out immediately before a new-
line character appear when read in is implementation-
defined.
[#3] A binary stream is an ordered sequence of characters
that can transparently record internal data. Data read in
from a binary stream shall compare equal to the data that
were earlier written out to that stream, under the same
implementation. Such a stream may, however, have an
implementation-defined number of null characters appended to
the end of the stream.
[#4] Each stream has an orientation. After a stream is
associated with an external file, but before any operations
are performed on it, the stream is without orientation. Once
a wide-character input/output function has been applied to a
stream without orientation, the stream becomes wide-
oriented. Similarly, once a byte input/output function has
been applied to a stream without orientation, the stream
becomes byte-oriented. Only a call to the freopen function
or the fwide function can otherwise alter the orientation of
a stream. (A successful call to freopen removes any
orientation.)198
[#5] Byte input/output functions shall not be applied to a
wide-oriented stream; and wide-character input/output
____________________________________________________________
nor any limit to the length of a line.
198. The three predefined streams stdin, stdout, and stderr
are unoriented at program startup.
page 316 Library
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functions shall not be applied to a byte-oriented stream.
The remaining stream operations do not affect and are not
affected by a stream's orientation, except for the following
additional restrictions:
- Binary wide-oriented streams have the file-positioning
restrictions ascribed to both text and binary streams.
- For wide-oriented streams, after a successful call to a
file-positioning function that leaves the file position
indicator prior to the end-of-file, a wide-character
output function can overwrite a partial multibyte
character; any file contents beyond the byte(s) written
are henceforth indeterminate.
[#6] Each wide-oriented stream has an associated mbstate_t
object that stores the current parse state of the stream. A
successful call to fgetpos stores a representation of the
value of this mbstate_t object as part of the value of the
fpos_t object. A later successful call to fsetpos using the
same stored fpos_t value restores the value of the
associated mbstate_t object as well as the position within
the controlled stream.
Environmental limits
[#7] An implementation shall support text files with lines
containing at least 254 characters, including the
terminating new-line character. The value of the macro
BUFSIZ shall be at least 256.
Forward references: freopen (7.13.5.4), fwide (7.19.3.10),
mbstate_t (7.18.1), fgetpos (7.13.9.1), and fsetpos
(7.13.9.3).
7.13.3 Files
[#1] A stream is associated with an external file (which may
be a physical device) by opening a file, which may involve
creating a new file. Creating an existing file causes its
former contents to be discarded, if necessary. If a file
can support positioning requests (such as a disk file, as
opposed to a terminal), then a file position indicator
associated with the stream is positioned at the start
(character number zero) of the file, unless the file is
opened with append mode in which case it is implementation-
defined whether the file position indicator is initially
positioned at the beginning or the end of the file. The
file position indicator is maintained by subsequent reads,
writes, and positioning requests, to facilitate an orderly
progression through the file.
page 317 Library
page 318
[#2] Binary files are not truncated, except as defined in
7.13.5.3. Whether a write on a text stream causes the
associated file to be truncated beyond that point is
implementation-defined.
[#3] When a stream is unbuffered, characters are intended to
appear from the source or at the destination as soon as
possible. Otherwise characters may be accumulated and
transmitted to or from the host environment as a block.
When a stream is fully buffered, characters are intended to
be transmitted to or from the host environment as a block
when a buffer is filled. When a stream is line buffered,
characters are intended to be transmitted to or from the
host environment as a block when a new-line character is
encountered. Furthermore, characters are intended to be
transmitted as a block to the host environment when a buffer
is filled, when input is requested on an unbuffered stream,
or when input is requested on a line buffered stream that
requires the transmission of characters from the host
environment. Support for these characteristics is
implementation-defined, and may be affected via the setbuf
and setvbuf functions.
[#4] A file may be disassociated from a controlling stream
by closing the file. Output streams are flushed (any
unwritten buffer contents are transmitted to the host
environment) before the stream is disassociated from the
file. The value of a pointer to a FILE object is
indeterminate after the associated file is closed (including
the standard text streams). Whether a file of zero length
(on which no characters have been written by an output
stream) actually exists is implementation-defined.
[#5] The file may be subsequently reopened, by the same or
another program execution, and its contents reclaimed or
modified (if it can be repositioned at its start). If the
main function returns to its original caller, or if the exit
function is called, all open files are closed (hence all
output streams are flushed) before program termination.
Other paths to program termination, such as calling the
abort function, need not close all files properly.
[#6] The address of the FILE object used to control a stream
may be significant; a copy of a FILE object may not
necessarily serve in place of the original.
[#7] At program startup, three text streams are predefined
and need not be opened explicitly - standard input (for
reading conventional input), standard output (for writing
conventional output), and standard error (for writing
diagnostic output). When opened, the standard error stream
page 318 Library
page 319
is not fully buffered; the standard input and standard
output streams are fully buffered if and only if the stream
can be determined not to refer to an interactive device.
[#8] Functions that open additional (nontemporary) files
require a file name, which is a string. The rules for
composing valid file names are implementation-defined.
Whether the same file can be simultaneously open multiple
times is also implementation-defined.
[#9] Although both text and binary wide-oriented streams are
conceptually sequences of wide characters, the external file
associated with a wide-oriented stream is a sequence of
multibyte characters, generalized as follows:
- Multibyte encodings within files may contain embedded
null bytes (unlike multibyte encodings valid for use
internal to the program).
- A file need not begin nor end in the initial shift
state.199
[#10] Moreover, the encodings used for multibyte characters
may differ among files. Both the nature and choice of such
encodings are implementation-defined.
[#11] The wide-character input functions read multibyte
characters from the stream and convert them to wide
characters as if they were read by successive calls to the
getwc function. Each conversion occurs as if by a call to
the mbrtowc function, with the conversion state described by
the stream's own mbstate_t object. The byte input functions
read characters from the stream as if by successive calls to
the fgetc function.
[#12] The wide-character output functions convert wide
characters to multibyte characters and write them to the
stream as if they were written by successive calls to the
fputwc function. Each conversion occurs as if by a call to
the wcrtomb function, with the conversion state described by
__________
199. Setting the file position indicator to end-of-file, as
with fseek(file, 0, SEEK_END), has undefined behavior
for a binary stream (because of possible trailing null
characters) or for any stream with state-dependent
encoding that does not assuredly end in the initial
shift state.
page 319 Library
page 320
the stream's own mbstate_t object. The byte output
functions write characters to the stream as if by successive
calls to the fputc function.
[#13] An encoding error occurs if the character sequence
presented to the underlying mbrtowc function does not form a
valid (generalized) multibyte character, or if the code
value passed to the underlying wcrtomb does not correspond
to a valid (generalized) multibyte character. The wide-
character input/output functions and the byte input/output
functions store the value of the macro EILSEQ in errno if
and only if an encoding error occurs.
Environmental limits
[#14] The value of FOPEN_MAX shall be at least eight,
including the three standard text streams.
Forward references: the exit function (7.14.4.3), the fgetc
function (7.13.7.1), the fopen function (7.13.5.3), the
fputc function (7.13.7.3), the setbuf function (7.13.5.5),
the setvbuf function (7.13.5.6), the fgetwc function
(7.19.3.1), the fputwc function (7.19.3.3), conversion state
(7.19.7), the mbrtowc function (7.19.7.3.2), the wcrtomb
function (7.19.7.3.3).
7.13.4 Operations on files
7.13.4.1 The remove function
Synopsis
[#1]
#include <stdio.h>
int remove(const char *filename);
Description
[#2] The remove function causes the file whose name is the
string pointed to by filename to be no longer accessible by
that name. A subsequent attempt to open that file using
that name will fail, unless it is created anew. If the file
is open, the behavior of the remove function is
implementation-defined.
page 320 Library
page 321
Returns
[#3] The remove function returns zero if the operation
succeeds, nonzero if it fails.
7.13.4.2 The rename function
Synopsis
[#1]
#include <stdio.h>
int rename(const char *old, const char *new);
Description
[#2] The rename function causes the file whose name is the
string pointed to by old to be henceforth known by the name
given by the string pointed to by new. The file named old
is no longer accessible by that name. If a file named by
the string pointed to by new exists prior to the call to the
rename function, the behavior is implementation-defined.
Returns
[#3] The rename function returns zero if the operation
succeeds, nonzero if it fails,200 in which case if the file
existed previously it is still known by its original name.
7.13.4.3 The tmpfile function
Synopsis
[#1]
#include <stdio.h>
FILE *tmpfile(void);
__________
200. Among the reasons the implementation may cause the
rename function to fail are that the file is open or
that it is necessary to copy its contents to effectuate
its renaming.
page 321 Library
page 322
Description
[#2] The tmpfile function creates a temporary binary file
that will automatically be removed when it is closed or at
program termination. If the program terminates abnormally,
whether an open temporary file is removed is
implementation-defined. The file is opened for update with
"wb+" mode.
Returns
[#3] The tmpfile function returns a pointer to the stream of
the file that it created. If the file cannot be created,
the tmpfile function returns a null pointer.
Forward references: the fopen function (7.13.5.3).
7.13.4.4 The tmpnam function
Synopsis
[#1]
#include <stdio.h>
char *tmpnam(char *s);
Description
[#2] The tmpnam function generates a string that is a valid
file name and that is not the same as the name of an
existing file.201
[#3] The tmpnam function generates a different string each
time it is called, up to TMP_MAX times. If it is called
more than TMP_MAX times, the behavior is implementation-
defined.
[#4] The implementation shall behave as if no library
function calls the tmpnam function.
__________
201. Files created using strings generated by the tmpnam
function are temporary only in the sense that their
names should not collide with those generated by
conventional naming rules for the implementation. It is
still necessary to use the remove function to remove
such files when their use is ended, and before program
termination.
page 322 Library
page 323
Returns
[#5] If the argument is a null pointer, the tmpnam function
leaves its result in an internal static object and returns a
pointer to that object. Subsequent calls to the tmpnam
function may modify the same object. If the argument is not
a null pointer, it is assumed to point to an array of at
least L_tmpnam chars; the tmpnam function writes its result
in that array and returns the argument as its value.
Environmental limits
[#6] The value of the macro TMP_MAX shall be at least 25.
7.13.5 File access functions
7.13.5.1 The fclose function
Synopsis
[#1]
#include <stdio.h>
int fclose(FILE *stream);
Description
[#2] The fclose function causes the stream pointed to by
stream to be flushed and the associated file to be closed.
Any unwritten buffered data for the stream are delivered to
the host environment to be written to the file; any unread
buffered data are discarded. The stream is disassociated
from the file. If the associated buffer was automatically
allocated, it is deallocated.
Returns
[#3] The fclose function returns zero if the stream was
successfully closed, or EOF if any errors were detected.
7.13.5.2 The fflush function
Synopsis
[#1]
#include <stdio.h>
int fflush(FILE *stream);
page 323 Library
page 324
Description
[#2] If stream points to an output stream or an update
stream in which the most recent operation was not input, the
fflush function causes any unwritten data for that stream to
be delivered to the host environment to be written to the
file; otherwise, the behavior is undefined.
[#3] If stream is a null pointer, the fflush function
performs this flushing action on all streams for which the
behavior is defined above.
Returns
[#4] The fflush function sets the error indicator for the
stream and returns EOF if a write error occurs, otherwise it
returns zero.
Forward references: the fopen function (7.13.5.3), the
ungetc function (7.13.7.11).
7.13.5.3 The fopen function
Synopsis
[#1]
#include <stdio.h>
FILE *fopen(const char * restrict filename,
const char * restrict mode);
Description
[#2] The fopen function opens the file whose name is the
string pointed to by filename, and associates a stream with
it.
[#3] The argument mode points to a string. If the string is
one of the following, the file is open in the indicated
mode. Otherwise, the behavior is undefined.202
__________
202. If the string begins with one of the above sequences,
the implementation might choose to ignore the remaining
characters, or it might use them to select different
kinds of a file (some of which might not conform to the
properties in 7.13.2).
page 324 Library
page 325
r open text file for reading
w truncate to zero length or create text file for writing
a append; open or create text file for writing at end-of-file
rb open binary file for reading
wb truncate to zero length or create binary file for writing
ab append; open or create binary file for writing at end-of-file
r+ open text file for update (reading and writing)
w+ truncate to zero length or create text file for update
a+ append; open or create text file for update, writing at end-of-file
r+b or rb+ open binary file for update (reading and writing)
w+b or wb+ truncate to zero length or create binary file for update
a+b or ab+ append; open or create binary file for update, writing at end-of-file
[#4] Opening a file with read mode ('r' as the first
character in the mode argument) fails if the file does not
exist or cannot be read.
[#5] Opening a file with append mode ('a' as the first
character in the mode argument) causes all subsequent writes
to the file to be forced to the then current end-of-file,
regardless of intervening calls to the fseek function. In
some implementations, opening a binary file with append mode
('b' as the second or third character in the above list of
mode argument values) may initially position the file
position indicator for the stream beyond the last data
written, because of null character padding.
[#6] When a file is opened with update mode ('+' as the
second or third character in the above list of mode argument
values), both input and output may be performed on the
associated stream. However, output shall not be directly
followed by input without an intervening call to the fflush
function or to a file positioning function (fseek, fsetpos,
or rewind), and input shall not be directly followed by
output without an intervening call to a file positioning
function, unless the input operation encounters end-of-file.
Opening (or creating) a text file with update mode may
instead open (or create) a binary stream in some
implementations.
[#7] When opened, a stream is fully buffered if and only if
it can be determined not to refer to an interactive device.
The error and end-of-file indicators for the stream are
cleared.
Returns
[#8] The fopen function returns a pointer to the object
controlling the stream. If the open operation fails, fopen
returns a null pointer.
page 325 Library
page 326
Forward references: file positioning functions (7.13.9).
7.13.5.4 The freopen function
Synopsis
[#1]
#include <stdio.h>
FILE *freopen(const char * restrict filename,
const char * restrict mode,
FILE * restrict stream);
Description
[#2] The freopen function opens the file whose name is the
string pointed to by filename and associates the stream
pointed to by stream with it. The mode argument is used
just as in the fopen function.203
[#3] The freopen function first attempts to close any file
that is associated with the specified stream. Failure to
close the file successfully is ignored. The error and end-
of-file indicators for the stream are cleared.
Returns
[#4] The freopen function returns a null pointer if the open
operation fails. Otherwise, freopen returns the value of
stream.
7.13.5.5 The setbuf function
Synopsis
[#1]
#include <stdio.h>
void setbuf(FILE * restrict stream,
char * restrict buf);
__________
203. The primary use of the freopen function is to change
the file associated with a standard text stream (stderr,
stdin, or stdout), as those identifiers need not be
modifiable lvalues to which the value returned by the
fopen function may be assigned.
page 326 Library
page 327
Description
[#2] Except that it returns no value, the setbuf function is
equivalent to the setvbuf function invoked with the values
_IOFBF for mode and BUFSIZ for size, or (if buf is a null
pointer), with the value _IONBF for mode.
Returns
[#3] The setbuf function returns no value.
Forward references: the setvbuf function (7.13.5.6).
7.13.5.6 The setvbuf function
Synopsis
[#1]
#include <stdio.h>
int setvbuf(FILE * restrict stream,
char * restrict buf,
int mode, size_t size);
Description
[#2] The setvbuf function may be used only after the stream
pointed to by stream has been associated with an open file
and before any other operation (other than an unsuccessful
call to setvbuf) is performed on the stream. The argument
mode determines how stream will be buffered, as follows:
_IOFBF causes input/output to be fully buffered; _IOLBF
causes input/output to be line buffered; _IONBF causes
input/output to be unbuffered. If buf is not a null
pointer, the array it points to may be used instead of a
buffer allocated by the setvbuf function204 and the
argument size specifies the size of the array; otherwise,
size may determine the size of a buffer allocated by the
setvbuf function. The contents of the array at any time are
indeterminate.
__________
204. The buffer must have a lifetime at least as great as
the open stream, so the stream should be closed before a
buffer that has automatic storage duration is
deallocated upon block exit.
page 327 Library
page 328
Returns
[#3] The setvbuf function returns zero on success, or
nonzero if an invalid value is given for mode or if the
request cannot be honored.
7.13.6 Formatted input/output functions
[#1] The formatted input/output functions205 shall behave
as if there is a sequence point after the actions associated
with each specifier.
7.13.6.1 The fprintf function
Synopsis
[#1]
#include <stdio.h>
int fprintf(FILE * restrict stream,
const char * restrict format, ...);
Description
[#2] The fprintf function writes output to the stream
pointed to by stream, under control of the string pointed to
by format that specifies how subsequent arguments are
converted for output. If there are insufficient arguments
for the format, the behavior is undefined. If the format is
exhausted while arguments remain, the excess arguments are
evaluated (as always) but are otherwise ignored. The
fprintf function returns when the end of the format string
is encountered.
[#3] The format shall be a multibyte character sequence,
beginning and ending in its initial shift state. The format
is composed of zero or more directives: ordinary multibyte
characters (not %), which are copied unchanged to the output
stream; and conversion specifications, each of which results
in fetching zero or more subsequent arguments. Each
conversion specification is introduced by the character %.
After the %, the following appear in sequence:
__________
205. The printf functions perform writes to memory for the
%n specifier.
page 328 Library
page 329
- Zero or more flags (in any order) that modify the
meaning of the conversion specification.
- An optional minimum field width. If the converted
value has fewer characters than the field width, it
will be padded with spaces (by default) on the left (or
right, if the left adjustment flag, described later,
has been given) to the field width. The field width
takes the form of an asterisk * (described later) or a
decimal integer.206
- An optional precision that gives the minimum number of
digits to appear for the d, i, o, u, x, and X
conversions, the number of digits to appear after the
decimal-point character for a, A, e, E, f, and F
conversions, the maximum number of significant digits
for the g and G conversions, or the maximum number of
characters to be written from a string in s
conversions. The precision takes the form of a period
(.) followed either by an asterisk * (described later)
or by an optional decimal integer; if only the period
is specified, the precision is taken as zero. If a
precision appears with any other conversion specifier,
the behavior is undefined.
- An optional hh specifying that a following d, i, o, u,
x, or X conversion specifier applies to a signed char
or unsigned char argument (the argument will have been
promoted according to the integer promotions, and its
value shall be converted to signed char or unsigned
char before printing); an optional h specifying that a
following d, i, o, u, x, or X conversion specifier
applies to a short int or unsigned short int argument
(the argument will have been promoted according to the
integer promotions, and its value shall be converted to
short int or unsigned short int before printing); an
optional h specifying that a following n conversion
specifier applies to a pointer to a short int argument;
an optional l (ell) specifying that a following d, i,
o, u, x, or X conversion specifier applies to a long
int or unsigned long int argument; an optional ll
(ell-ell) specifying that a following d, i, o, u, x, or
X conversion specifier applies to a long long int or
unsigned long long int argument; an optional l
__________
206. Note that 0 is taken as a flag, not as the beginning of
a field width.
page 329 Library
page 330
specifying that a following n conversion specifier
applies to a pointer to a long int argument; an
optional ll specifying that a following n conversion
specifier applies to a pointer to a long long int
argument; an optional l specifying that a following c
conversion specifier applies to a wint_t argument; an
optional l specifying that a following s conversion
specifier applies to a pointer to a wchar_t argument;
an optional l which has no effect on a following a, A,
e, E, f, F, g, or G conversion specifier; or an
optional L specifying that a following a, A, e, E, f,
F, g, or G conversion specifier applies to a long
double argument. If an hh, h, l, ll, or L appears with
any other conversion specifier, the behavior is
undefined.
- A character that specifies the type of conversion to be
applied.
[#4] As noted above, a field width, or precision, or both,
may be indicated by an asterisk. In this case, an int
argument supplies the field width or precision. The
arguments specifying field width, or precision, or both,
shall appear (in that order) before the argument (if any) to
be converted. A negative field width argument is taken as a
- flag followed by a positive field width. A negative
precision argument is taken as if the precision were
omitted.
[#5] The flag characters and their meanings are
- The result of the conversion will be left-justified
within the field. (It will be right-justified if this
flag is not specified.)
+ The result of a signed conversion will always begin
with a plus or minus sign. (It will begin with a sign
only when a negative value is converted if this flag
is not specified.)207
space If the first character of a signed conversion is not a
sign, or if a signed conversion results in no
characters, a space will be prefixed to the result.
__________
207. The results of all floating conversions of a negative
zero, and of negative values that round to zero, include
a minus sign.
page 330 Library
page 331
If the space and + flags both appear, the space flag
will be ignored.
# The result is to be converted to an ``alternate
form.'' For o conversion, it increases the precision,
if and only if necessary, to force the first digit of
the result to be a zero (if the value and precision
are both 0, a single 0 is printed). For x (or X)
conversion, a nonzero result will have 0x (or 0X)
prefixed to it. For a, A, e, E, f, F, g, and G
conversions, the result will always contain a
decimal-point character, even if no digits follow it.
(Normally, a decimal-point character appears in the
result of these conversions only if a digit follows
it.) For g and G conversions, trailing zeros are not
removed from the result. For other conversions, the
behavior is undefined.
0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G
conversions, leading zeros (following any indication
of sign or base) are used to pad to the field width;
no space padding is performed. If the 0 and - flags
both appear, the 0 flag will be ignored. For d, i, o,
u, x, and X conversions, if a precision is specified,
the 0 flag will be ignored. For other conversions,
the behavior is undefined.
[#6] The conversion specifiers and their meanings are
d,i The int argument is converted to signed decimal in
the style [ - ]dddd. The precision specifies the
minimum number of digits to appear; if the value
being converted can be represented in fewer digits,
it will be expanded with leading zeros. The default
precision is 1. The result of converting a zero
value with a precision of zero is no characters.
o,u,x,X The unsigned int argument is converted to unsigned
octal (o), unsigned decimal (u), or unsigned
hexadecimal notation (x or X) in the style dddd; the
letters abcdef are used for x conversion and the
letters ABCDEF for X conversion. The precision
specifies the minimum number of digits to appear; if
the value being converted can be represented in
fewer digits, it will be expanded with leading
zeros. The default precision is 1. The result of
converting a zero value with a precision of zero is
no characters.
f,F A double argument representing a floating-point
number is converted to decimal notation in the style
page 331 Library
page 332
[-]ddd.ddd, where the number of digits after the
decimal-point character is equal to the precision
specification. If the precision is missing, it is
taken as 6; if the precision is zero and the # flag
is not specified, no decimal-point character
appears. If a decimal-point character appears, at
least one digit appears before it. The value is
rounded to the appropriate number of digits.
A double argument representing an infinity is
converted to one of the styles [-]inf or [-]infinity
- which style is implementation-defined. A double
argument representing a NaN is converted in one of
the styles [-]nan or [-]nan(n-char-sequence) - which
style, and the meaning of any n-char-sequence, is
implementation-defined. The F conversion specifier
produces INF, INFINITY, or NAN instead of inf,
infinity, or nan, respectively.208
e,E A double argument representing a floating-point
number is converted in the style [-]d.ddde_dd, where
there is one digit before the decimal-point
character (which is nonzero if the argument is
nonzero) and the number of digits after it is equal
to the precision; if the precision is missing, it is
taken as 6; if the precision is zero and the # flag
is not specified, no decimal-point character
appears. The value is rounded to the appropriate
number of digits. The E conversion specifier will
produce a number with E instead of e introducing the
exponent. The exponent always contains at least two
digits, and only as many more digits as necessary to
represent the exponent. If the value is zero, the
exponent is zero.
A double argument representing an infinity or a NaN
is converted in the style of an f or F conversion
specifier.
g,G A double argument representing a floating-point
number is converted in style f or e (or in style F
or E in the case of a G conversion specifier), with
the precision specifying the number of significant
__________
208. When applied to infinite and NaN values, the -, +, and
space flag characters have their usual meaning; the #
and 0 flag characters have no effect.
page 332 Library
page 333
digits. If the precision is zero, it is taken as 1.
The style used depends on the value converted; style
e (or E) will be used only if the exponent resulting
from such a conversion is less than -4 or greater
than or equal to the precision. Trailing zeros are
removed from the fractional portion of the result; a
decimal-point character appears only if it is
followed by a digit. A double argument representing
an infinity or NaN is converted in the style of an f
or F conversion specifier.
a,A A double argument representing a floating-point
number is converted in the style [-]0xh.hhhhp_d.
The number of hexadecimal digits h after the
decimal-point character is equal to the precision;
if the precision is missing and FLT_RADIX is a power
of 2, then the precision is sufficient for an exact
representation of the value; if the precision is
missing and FLT_RADIX is not a power of 2, then the
precision is sufficient to distinguish209 values of
type double, except that trailing zeros may be
omitted. The hexadecimal digit to the left of the
decimal-point character is nonzero for normalized
floating-point numbers and is otherwise
unspecified;210 if the precision is zero and the #
flag is not specified, no decimal-point character
appears. The letters abcdef are used for a
conversion and the letters ABCDEF for A conversion.
The a conversion specifier will produce a number
with x and p and the A conversion specifier will
produce a number with X and P. The exponent always
contains at least one digit, and only as many more
digits as necessary to represent the decimal
exponent of 2. If the value is zero, the exponent
__________
209. The precision p is sufficient to distinguish values of
the source type if
16p-1 > bn
where b is FLT_RADIX and n is the number of base-b
digits in the significand of the source type. A smaller
p might suffice depending on the implementation's scheme
for determining the digit to the left of the decimal-
point character.
210. Binary implementations can choose the hexadecimal digit
to the left of the decimal-point character so that
subsequent digits align to nibble (4-bit) boundaries.
page 333 Library
page 334
is zero. A double argument representing an infinity
or a NaN is converted in the style of an f or F
conversion specifier.
c If no l qualifier is present, the int argument is
converted to an unsigned char, and the resulting
character is written. Otherwise, the wint_t
argument is converted as if by an ls conversion
specification with no precision and an argument that
points to the initial element of a two-element array
of wchar_t, the first element containing the wint_t
argument to the lc conversion specification and the
second a null wide character.
s If no l qualifier is present, the argument shall be
a pointer to the initial element of an array of
character type.211 Characters from the array are
written up to (but not including) a terminating null
character. If the precision is specified, no more
than that many characters are written. If the
precision is not specified or is greater than the
size of the array, the array shall contain a null
character.
If an l qualifier is present, the argument shall be
a pointer to the initial element of an array of
wchar_t type. Wide characters from the array are
converted to multibyte characters (each as if by a
call to the wcrtomb function, with the conversion
state described by an mbstate_t object initialized
to zero before the first wide character is
converted) up to and including a terminating null
wide character. The resulting multibyte characters
are written up to (but not including) the
terminating null character (byte). If no precision
is specified, the array shall contain a null wide
character. If a precision is specified, no more than
that many characters (bytes) are written (including
shift sequences, if any), and the array shall
contain a null wide character if, to equal the
multibyte character sequence length given by the
precision, the function would need to access a wide
character one past the end of the array. In no case
is a partial multibyte character written.212
__________
211. No special provisions are made for multibyte
characters.
page 334 Library
page 335
p The argument shall be a pointer to void. The value
of the pointer is converted to a sequence of
printable characters, in an implementation-defined
manner.
n The argument shall be a pointer to signed integer
into which is written the number of characters
written to the output stream so far by this call to
fprintf. No argument is converted, but one is
consumed. If the conversion specification with this
conversion specifier is not one of %n, %ln, %lln,
%hn, or %hhn, the behavior is undefined.
% A % is written. No argument is converted. The
complete conversion specification shall be %%.
[#7] If a conversion specification is invalid, the behavior
is undefined.213
[#8] If any argument is, or points to, a union or an
aggregate (except for an array of char type using %s
conversion, an array of wchar_t type using %ls conversion,
or a pointer using %p conversion), the behavior is
undefined.
[#9] In no case does a nonexistent or small field width
cause truncation of a field; if the result of a conversion
is wider than the field width, the field is expanded to
contain the conversion result.
[#10] For a and A conversions, if FLT_RADIX is a power of 2,
the value is correctly rounded to a hexadecimal floating
number with the given precision.
Recommended practice
[#11] If FLT_RADIX is not a power of 2, the result is one of
the two adjacent numbers in hexadecimal floating style with
the given precision, with the extra stipulation that the
error have a correct sign for the current rounding
direction.
____________________________________________________________
212. Redundant shift sequences may result if multibyte
characters have a state-dependent encoding.
213. See ``future library directions'' (7.20.5).
page 335 Library
page 336
[#12] For e, E, f, F, g, and G conversions, if the number of
significant decimal digits is at most DECIMAL_DIG, then the
result is correctly rounded.214 If the number of
significant decimal digits is more than DECIMAL_DIG but the
source value is exactly representable with DECIMAL_DIG
digits, then the result is an exact representation with
trailing zeros. Otherwise, the source value is bounded by
two adjacent decimal strings L < U, both having DECIMAL_DIG
significant digits; the value of the resultant decimal
string D satisfies L < D < U, with the extra stipulation
that the error have a correct sign for the current rounding
direction.
Returns
[#13] The fprintf function returns the number of characters
transmitted, or a negative value if an output error
occurred.
Environmental limit
[#14] The minimum value for the maximum number of characters
produced by any single conversion shall be 4095.
Examples
[#15] To print a date and time in the form ``Sunday, July 3,
10:02'' followed by pi to five decimal places:
#include <math.h>
#include <stdio.h>
/* ... */
char *weekday, *month; // pointers to strings
int day, hour, min;
fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
weekday, month, day, hour, min);
fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
[#16] In this example, multibyte characters do not have a
state-dependent encoding, and the multibyte members of the
extended character set each consist of two bytes, the first
__________
214. For binary-to-decimal conversion, the result format's
values are the numbers representable with the given
format specifier. The number of significant digits is
determined by the format specifier, and in the case of
fixed-point conversion by the source value as well.
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of which is denoted here by a $0 and the second by an
uppercase letter.
[#17] Given the following wide string with length seven,
static wchar_t wstr[] = L"$0X$0Yabc$0Z$0W";
[#18] the seven calls
fprintf(stdout, "|1234567890123|\n");
fprintf(stdout, "|%13ls|\n", wstr);
fprintf(stdout, "|%-13.9ls|\n", wstr);
fprintf(stdout, "|%13.10ls|\n", wstr);
fprintf(stdout, "|%13.1ls|\n", wstr);
fprintf(stdout, "|%13.15ls|\n", &wstr[2]);
fprintf(stdout, "|%13lc|\n", wstr[5]);
[#19] will print the following seven lines:
|1234567890123|
| $0X$0Yabc$0Z$0W|
|$0X$0Yabc$0Z |
| $0X$0Yabc$0Z|
| $0X$0Yabc$0Z$0W|
| abc$0Z$0W|
| $0Z|
[#20]
Forward references: conversion state (7.19.7), the wcrtomb
function (7.19.7.3.3).
7.13.6.2 The fscanf function
Synopsis
[#1]
#include <stdio.h>
int fscanf(FILE * restrict stream,
const char * restrict format, ...);
Description
[#2] The fscanf function reads input from the stream pointed
to by stream, under control of the string pointed to by
format that specifies the admissible input sequences and how
they are to be converted for assignment, using subsequent
arguments as pointers to the objects to receive the
converted input. If there are insufficient arguments for
the format, the behavior is undefined. If the format is
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exhausted while arguments remain, the excess arguments are
evaluated (as always) but are otherwise ignored.
[#3] The format shall be a multibyte character sequence,
beginning and ending in its initial shift state. The format
is composed of zero or more directives: one or more white-
space characters; an ordinary multibyte character (neither %
nor a white-space character); or a conversion specification.
Each conversion specification is introduced by the character
%. After the %, the following appear in sequence:
- An optional assignment-suppressing character *.
- An optional nonzero decimal integer that specifies the
maximum field width.
- An optional hh, h, l (ell), or ll (ell-ell), or L
indicating the size of the receiving object. The
conversion specifiers d, i, and n shall be preceded by
hh if the corresponding argument is a pointer to signed
char rather than a pointer to int, by h if it is a
pointer to short int rather than a pointer to int, by l
if it is a pointer to long int, or by ll if it is a
pointer to long long int. Similarly, the conversion
specifiers o, u, and x shall be preceded by hh if the
corresponding argument is a pointer to unsigned char
rather than a pointer to unsigned int, by h if it is a
pointer to unsigned short int rather than a pointer to
unsigned int, by l if it is a pointer to unsigned long
int, or by ll if it is a pointer to unsigned long long
int. The conversion specifiers a, e, f, and g shall be
preceded by l if the corresponding argument is a
pointer to double rather than a pointer to float, or by
L if it is a pointer to long double. Finally, the
conversion specifiers c, s, and [ shall be preceded by
l if the corresponding argument is a pointer to wchar_t
rather than a pointer to a character type. If an hh,
h, l, ll, or L appears with any other conversion
specifier, the behavior is undefined.
- A character that specifies the type of conversion to be
applied. The valid conversion specifiers are described
below.
[#4] The fscanf function executes each directive of the
format in turn. If a directive fails, as detailed below,
the fscanf function returns. Failures are described as
input failures (if an encoding error occurs or due to the
unavailability of input characters), or matching failures
(due to inappropriate input).
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[#5] A directive composed of white-space character(s) is
executed by reading input up to the first non-white-space
character (which remains unread), or until no more
characters can be read.
[#6] A directive that is an ordinary multibyte character is
executed by reading the next characters of the stream. If
one of the characters differs from one comprising the
directive, the directive fails, and the differing and
subsequent characters remain unread.
[#7] A directive that is a conversion specification defines
a set of matching input sequences, as described below for
each specifier. A conversion specification is executed in
the following steps:
[#8] Input white-space characters (as specified by the
isspace function) are skipped, unless the specification
includes a [, c, or n specifier.215
[#9] An input item is read from the stream, unless the
specification includes an n specifier. An input item is
defined as the longest sequence of input characters which
does not exceed any specified field width and which is, or
is a prefix of, a matching input sequence. The first
character, if any, after the input item remains unread. If
the length of the input item is zero, the execution of the
directive fails; this condition is a matching failure unless
end-of-file, an encoding error, or a read error prevented
input from the stream, in which case it is an input failure.
[#10] Except in the case of a % specifier, the input item
(or, in the case of a %n directive, the count of input
characters) is converted to a type appropriate to the
conversion specifier. If the input item is not a matching
sequence, the execution of the directive fails: this
condition is a matching failure. Unless assignment
suppression was indicated by a *, the result of the
conversion is placed in the object pointed to by the first
argument following the format argument that has not already
received a conversion result. If this object does not have
an appropriate type, or if the result of the conversion
cannot be represented in the object, the behavior is
undefined.
__________
215. These white-space characters are not counted against a
specified field width.
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[#11] The conversion specifiers and their meanings are:
d Matches an optionally signed decimal integer, whose
format is the same as expected for the subject
sequence of the strtol function with the value 10
for the base argument. The corresponding argument
shall be a pointer to signed integer.
i Matches an optionally signed integer, whose format
is the same as expected for the subject sequence of
the strtol function with the value 0 for the base
argument. The corresponding argument shall be a
pointer to signed integer.
o Matches an optionally signed octal integer, whose
format is the same as expected for the subject
sequence of the strtoul function with the value 8
for the base argument. The corresponding argument
shall be a pointer to unsigned integer.
u Matches an optionally signed decimal integer, whose
format is the same as expected for the subject
sequence of the strtoul function with the value 10
for the base argument. The corresponding argument
shall be a pointer to unsigned integer.
x Matches an optionally signed hexadecimal integer,
whose format is the same as expected for the subject
sequence of the strtoul function with the value 16
for the base argument. The corresponding argument
shall be a pointer to unsigned integer.
a,e,f,g Matches an optionally signed floating-point
constant, whose format is the same as expected for
the subject string of the strtod function. The
corresponding argument shall be a pointer to
floating.
s Matches a sequence of non-white-space characters.216
If no l qualifier is present, the corresponding
__________
216. No special provisions are made for multibyte characters
in the matching rules used by any of the conversion
specifiers s, [, c - the extent of the input field is
still determined on a byte-by-byte basis. The resulting
field must nevertheless be a sequence of multibyte
characters that begins in the initial shift state.
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argument shall be a pointer to the initial element
of a character array large enough to accept the
sequence and a terminating null character, which
will be added automatically.
If an l qualifier is present, the input shall be a
sequence of multibyte characters that begins in the
initial shift state. Each multibyte character is
converted to a wide character as if by a call to the
mbrtowc function, with the conversion state
described by an mbstate_t object initialized to zero
before the first multibyte character is converted.
The corresponding argument shall be a pointer to the
initial element of an array of wchar_t large enough
to accept the sequence and the terminating null wide
character, which will be added automatically.
[ Matches a nonempty sequence of characters from a set
of expected characters (the scanset). If no l
qualifier is present, the corresponding argument
shall be a pointer to the initial element of a
character array large enough to accept the sequence
and a terminating null character, which will be
added automatically.
If an l qualifier is present, the input shall be a
sequence of multibyte characters that begins in the
initial shift state. Each multibyte character is
converted to a wide character as if by a call to the
mbrtowc function, with the conversion state
described by an mbstate_t object initialized to zero
before the first multibyte character is converted.
The corresponding argument shall be a pointer to the
initial element of an array of wchar_t large enough
to accept the sequence and the terminating null wide
character, which will be added automatically. The
conversion specifier includes all subsequent
characters in the format string, up to and including
the matching right bracket (]). The characters
between the brackets (the scanlist) comprise the
scanset, unless the character after the left bracket
is a circumflex (^), in which case the scanset
contains all characters that do not appear in the
scanlist between the circumflex and the right
bracket. If the conversion specifier begins with []
or [^], the right bracket character is in the
scanlist and the next right bracket character is the
matching right bracket that ends the specification;
otherwise the first right bracket character is the
one that ends the specification. If a - character
is in the scanlist and is not the first, nor the
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second where the first character is a ^, nor the
last character, the behavior is implementation-
defined.
c Matches a sequence of characters of exactly the
number specified by the field width (1 if no field
width is present in the directive). If no l
qualifier is present, the corresponding argument
shall be a pointer to the initial element of a
character array large enough to accept the sequence.
No null character is added.
If an l qualifier is present, the input shall be a
sequence of multibyte characters that begins in the
initial shift state. Each multibyte character in the
sequence is converted to a wide character as if by a
call to the mbrtowc function, with the conversion
state described by an mbstate_t object initialized
to zero before the first multibyte character is
converted. The corresponding argument shall be a
pointer to the initial element of an array of
wchar_t large enough to accept the resulting
sequence of wide characters. No null wide character
is added.
p Matches an implementation-defined set of sequences,
which should be the same as the set of sequences
that may be produced by the %p conversion of the
fprintf function. The corresponding argument shall
be a pointer to a pointer to void. The
interpretation of the input item is implementation-
defined. If the input item is a value converted
earlier during the same program execution, the
pointer that results shall compare equal to that
value; otherwise the behavior of the %p conversion
is undefined.
n No input is consumed. The corresponding argument
shall be a pointer to signed integer into which is
to be written the number of characters read from the
input stream so far by this call to the fscanf
function. Execution of a %n directive does not
increment the assignment count returned at the
completion of execution of the fscanf function. No
argument is converted, but one is consumed. If the
conversion specification with this conversion
specifier is not one of %n, %ln, %lln, %hn, or %hhn,
the behavior is undefined.
% Matches a single %; no conversion or assignment
occurs. The complete conversion specification shall
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be %%.
[#12] If a conversion specification is invalid, the behavior
is undefined.217
[#13] The conversion specifiers A, E, G, and X are also
valid and behave the same as, respectively, a, e, g, and x.
[#14] If end-of-file is encountered during input, conversion
is terminated. If end-of-file occurs before any characters
matching the current directive have been read (other than
leading white space, where permitted), execution of the
current directive terminates with an input failure;
otherwise, unless execution of the current directive is
terminated with a matching failure, execution of the
following directive (if any) is terminated with an input
failure.
[#15] Trailing white space (including new-line characters)
is left unread unless matched by a directive. The success
of literal matches and suppressed assignments is not
directly determinable other than via the %n directive.
[#16] If conversion terminates on a conflicting input
character, the offending input character is left unread in
the input stream.218
Returns
[#17] The fscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the fscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
__________
217. See ``future library directions'' (7.20.5).
218. fscanf pushes back at most one input character onto the
input stream. Therefore, some sequences that are
acceptable to strtod, strtol, etc., are unacceptable to
fscanf.
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Examples
1. The call:
#include <stdio.h>
/* ... */
int n, i; float x; char name[50];
n = fscanf(stdin, "%d%f%s", &i, &x, name);
with the input line:
25 54.32E-1 thompson
will assign to n the value 3, to i the value 25, to x
the value 5.432, and name will contain thompson\0.
2. The call:
#include <stdio.h>
/* ... */
int i; float x; char name[50];
fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
with input:
56789 0123 56a72
will assign to i the value 56 and to x the value
789.0, will skip 0123, and name will contain 56\0.
The next character read from the input stream will be
a.
3. To accept repeatedly from stdin a quantity, a unit of
measure, and an item name:
#include <stdio.h>
/* ... */
int count; float quant; char units[21], item[21];
while (!feof(stdin) && !ferror(stdin)) {
count = fscanf(stdin, "%f%20s of %20s",
&quant, units, item);
fscanf(stdin,"%*[^\n]");
}
If the stdin stream contains the following lines:
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2 quarts of oil
-12.8degrees Celsius
lots of luck
10.0LBS of
dirt
100ergs of energy
the execution of the above example will be analogous
to the following assignments:
quant = 2; strcpy(units, "quarts"); strcpy(item, "oil");
count = 3;
quant = -12.8; strcpy(units, "degrees");
count = 2; // "C" fails to match "o"
count = 0; // "l" fails to match "%f"
quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt");
count = 3;
count = 0; // "100e" fails to match "%f"
count = EOF;
4. In:
#include <stdio.h>
/* ... */
int d1, d2, n1, n2, i;
i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
the value 123 is assigned to d1 and the value 3 to n1.
Because %n can never get an input failure the value of
3 is also assigned to n2. The value of d2 is not
affected. The value 1 is assigned to i.
[#18] In these examples, multibyte characters do have a
state-dependent encoding, and multibyte members of the
extended character set consist of two bytes, the first of
which is denoted here by a $0 and the second by an uppercase
letter, but are only recognized as such when in the
alternate shift state. The shift sequences are denoted by ^
and v, in which the first causes entry into the alternate
shift state.
1. After the call:
#include <stdio.h>
/* ... */
char str[50];
fscanf(stdin, "a%s", str);
with the input line:
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a^$0X$0Yv bc
str will contain ^$0X$0Yv\0 assuming that none of the
bytes of the shift sequences (or of the multibyte
characters, in the more general case) appears to be a
single-byte white-space character.
2. In contrast, after the call:
#include <stdio.h>
#include <stddef.h>
/* ... */
wchar_t wstr[50];
fscanf(stdin, "a%ls", wstr);
with the same input line, wstr will contain the two
wide characters that correspond to $0X and $0Y and a
terminating null wide character.
3. However, the call:
#include <stdio.h>
#include <stddef.h>
/* ... */
wchar_t wstr[50];
fscanf(stdin, "a^$0Xv%ls", wstr);
with the same input line will return zero due to a
matching failure against the v sequence in the format
string.
4. Assuming that the first byte of the multibyte
character $0X is the same as the first byte of the
multibyte character $0Y, after the call:
#include <stdio.h>
#include <stddef.h>
/* ... */
wchar_t wstr[50];
fscanf(stdin, "a^$0Yv%ls", wstr);
with the same input line, zero will again be returned,
but stdin will be left with a partially consumed
multibyte character.
Forward references: the strtod function (7.14.1.4), the
strtol function (7.14.1.5), the strtoul function (7.14.1.6),
conversion state (7.19.7), the wcrtomb function
(7.19.7.3.3).
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7.13.6.3 The printf function
Synopsis
[#1]
#include <stdio.h>
int printf(const char * restrict format, ...);
Description
[#2] The printf function is equivalent to fprintf with the
argument stdout interposed before the arguments to printf.
Returns
[#3] The printf function returns the number of characters
transmitted, or a negative value if an output error
occurred.
7.13.6.4 The scanf function
Synopsis
[#1]
#include <stdio.h>
int scanf(const char * restrict format, ...);
Description
[#2] The scanf function is equivalent to fscanf with the
argument stdin interposed before the arguments to scanf.
Returns
[#3] The scanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the scanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
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7.13.6.5 The sprintf function
Synopsis
[#1]
#include <stdio.h>
int sprintf(char * restrict s,
const char * restrict format, ...);
Description
[#2] The sprintf function is equivalent to fprintf, except
that the argument s specifies an array into which the
generated output is to be written, rather than to a stream.
A null character is written at the end of the characters
written; it is not counted as part of the returned sum. If
copying takes place between objects that overlap, the
behavior is undefined.
Returns
[#3] The sprintf function returns the number of characters
written in the array, not counting the terminating null
character.
7.13.6.6 The snprintf function
Synopsis
[#1]
#include <stdio.h>
int snprintf(char * restrict s, size_t n,
const char * restrict format, ...);
Description
[#2] The snprintf function is equivalent to fprintf, except
that the argument s specifies an array into which the
generated output is to be written, rather than to a stream.
If n is zero, nothing is written, and s may be a null
pointer. Otherwise, output characters beyond the n-1st are
discarded rather than being written to the array, and a null
character is written at the end of the characters actually
written into the array. If copying takes place between
objects that overlap, the behavior is undefined.
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Returns
[#3] The snprintf function returns the number of characters
that would have been written had n been sufficiently large,
not counting the terminating null character. Thus, the
null-terminated output has been completely written if and
only if the returned value is less than n.
7.13.6.7 The sscanf function
Synopsis
[#1]
#include <stdio.h>
int sscanf(const char * restrict s,
const char * restrict format, ...);
Description
[#2] The sscanf function is equivalent to fscanf, except
that the argument s specifies a string from which the input
is to be obtained, rather than from a stream. Reaching the
end of the string is equivalent to encountering end-of-file
for the fscanf function. If copying takes place between
objects that overlap, the behavior is undefined.
Returns
[#3] The sscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the sscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.13.6.8 The vfprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vfprintf(FILE * restrict stream,
const char * restrict format,
va_list arg);
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Description
[#2] The vfprintf function is equivalent to fprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vfprintf function does not
invoke the va_end macro.219
Returns
[#3] The vfprintf function returns the number of characters
transmitted, or a negative value if an output error
occurred.
Examples
[#4] The following shows the use of the vfprintf function in
a general error-reporting routine.
#include <stdarg.h>
#include <stdio.h>
void error(char *function_name, char *format, ...)
{
va_list args;
va_start(args, format);
// print out name of function causing error
fprintf(stderr, "ERROR in %s: ", function_name);
// print out remainder of message
vfprintf(stderr, format, args);
va_end(args);
}
__________
219. As the functions vfprintf, vfscanf, vprintf, vscanf,
vsnprintf, vsprintf, and vsscanf invoke the va_arg
macro, the value of arg after the return is
indeterminate.
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7.13.6.9 The vprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vprintf(const char * restrict format,
va_list arg);
Description
[#2] The vprintf function is equivalent to printf, with the
variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vprintf function does not
invoke the va_end macro.219
Returns
[#3] The vprintf function returns the number of characters
transmitted, or a negative value if an output error
occurred.
7.13.6.10 The vsprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vsprintf(char * restrict s,
const char * restrict format,
va_list arg);
Description
[#2] The vsprintf function is equivalent to sprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vsprintf function does not
invoke the va_end macro.219 If copying takes place between
objects that overlap, the behavior is undefined.
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Returns
[#3] The vsprintf function returns the number of characters
written in the array, not counting the terminating null
character.
7.13.6.11 The vsnprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vsprintf(char * restrict s, size_t n,
const char * restrict format,
va_list arg);
Description
[#2] The vsnprintf function is equivalent to snprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vsnprintf function does not
invoke the va_end macro.219 If copying takes place between
objects that overlap, the behavior is undefined.
Returns
[#3] The vsnprintf function returns the number of characters
that would have been written had n been sufficiently large,
not counting the terminating null character. Thus, the
null-terminated output has been completely written if and
only if the returned value is less than n.
7.13.6.12 The vfscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vfscanf(FILE * restrict stream,
const char * restrict format,
va_list arg);
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Description
[#2] The vfscanf function is equivalent to fscanf, with the
variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vfscanf does not invoke the
va_end macro.219
Returns
[#3] The vfscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the vfscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.13.6.13 The vscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vscanf(const char * restrict format,
va_list arg);
Description
[#2] The vscanf function is equivalent to scanf, with the
variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vscanf does not invoke the
va_end macro.219
Returns
[#3] The vscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the vscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
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7.13.6.14 The vsscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vsscanf(const char * restrict s,
const char * restrict format,
va_list arg);
Description
[#2] The vsscanf function is equivalent to sscanf, with the
variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vsscanf does not invoke the
va_end macro.219
Returns
[#3] The vsscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the vscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.13.7 Character input/output functions
7.13.7.1 The fgetc function
Synopsis
[#1]
#include <stdio.h>
int fgetc(FILE *stream);
Description
[#2] If a next character is present from the input stream
pointed to by stream, the fgetc function obtains that
character as an unsigned char converted to an int and
advances the associated file position indicator for the
stream (if defined).
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Returns
[#3] The fgetc function returns the next character from the
input stream pointed to by stream. If the stream is at
end-of-file, the end-of-file indicator for the stream is set
and fgetc returns EOF. If a read error occurs, the error
indicator for the stream is set and fgetc returns EOF.220
7.13.7.2 The fgets function
Synopsis
[#1]
#include <stdio.h>
char *fgets(char * restrict s, int n,
FILE * restrict stream);
Description
[#2] The fgets function reads at most one less than the
number of characters specified by n from the stream pointed
to by stream into the array pointed to by s. No additional
characters are read after a new-line character (which is
retained) or after end-of-file. A null character is written
immediately after the last character read into the array.
Returns
[#3] The fgets function returns s if successful. If end-
of-file is encountered and no characters have been read into
the array, the contents of the array remain unchanged and a
null pointer is returned. If a read error occurs during the
operation, the array contents are indeterminate and a null
pointer is returned.
__________
220. An end-of-file and a read error can be distinguished by
use of the feof and ferror functions.
page 355 Library
page 356
7.13.7.3 The fputc function
Synopsis
[#1]
#include <stdio.h>
int fputc(int c, FILE *stream);
Description
[#2] The fputc function writes the character specified by c
(converted to an unsigned char) to the output stream pointed
to by stream, at the position indicated by the associated
file position indicator for the stream (if defined), and
advances the indicator appropriately. If the file cannot
support positioning requests, or if the stream was opened
with append mode, the character is appended to the output
stream.
Returns
[#3] The fputc function returns the character written. If a
write error occurs, the error indicator for the stream is
set and fputc returns EOF.
7.13.7.4 The fputs function
Synopsis
[#1]
#include <stdio.h>
int fputs(const char * restrict s,
FILE * restrict stream);
Description
[#2] The fputs function writes the string pointed to by s to
the stream pointed to by stream. The terminating null
character is not written.
Returns
[#3] The fputs function returns EOF if a write error occurs;
otherwise it returns a nonnegative value.
page 356 Library
page 357
7.13.7.5 The getc function
Synopsis
[#1]
#include <stdio.h>
int getc(FILE *stream);
Description
[#2] The getc function is equivalent to fgetc, except that
if it is implemented as a macro, it may evaluate stream more
than once, so the argument should never be an expression
with side effects.
Returns
[#3] The getc function returns the next character from the
input stream pointed to by stream. If the stream is at
end-of-file, the end-of-file indicator for the stream is set
and getc returns EOF. If a read error occurs, the error
indicator for the stream is set and getc returns EOF.
7.13.7.6 The getchar function
Synopsis
[#1]
#include <stdio.h>
int getchar(void);
Description
[#2] The getchar function is equivalent to getc with the
argument stdin.
Returns
[#3] The getchar function returns the next character from
the input stream pointed to by stdin. If the stream is at
end-of-file, the end-of-file indicator for the stream is set
and getchar returns EOF. If a read error occurs, the error
indicator for the stream is set and getchar returns EOF.
page 357 Library
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7.13.7.7 The gets function
Synopsis
[#1]
#include <stdio.h>
char *gets(char *s);
Description
[#2] The gets function reads characters from the input
stream pointed to by stdin, into the array pointed to by s,
until end-of-file is encountered or a new-line character is
read. Any new-line character is discarded, and a null
character is written immediately after the last character
read into the array.
Returns
[#3] The gets function returns s if successful. If end-of-
file is encountered and no characters have been read into
the array, the contents of the array remain unchanged and a
null pointer is returned. If a read error occurs during the
operation, the array contents are indeterminate and a null
pointer is returned.
7.13.7.8 The putc function
Synopsis
[#1]
#include <stdio.h>
int putc(int c, FILE *stream);
Description
[#2] The putc function is equivalent to fputc, except that
if it is implemented as a macro, it may evaluate stream more
than once, so the argument should never be an expression
with side effects.
Returns
[#3] The putc function returns the character written. If a
write error occurs, the error indicator for the stream is
set and putc returns EOF.
page 358 Library
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7.13.7.9 The putchar function
Synopsis
[#1]
#include <stdio.h>
int putchar(int c);
Description
[#2] The putchar function is equivalent to putc with the
second argument stdout.
Returns
[#3] The putchar function returns the character written. If
a write error occurs, the error indicator for the stream is
set and putchar returns EOF.
7.13.7.10 The puts function
Synopsis
[#1]
#include <stdio.h>
int puts(const char *s);
Description
[#2] The puts function writes the string pointed to by s to
the stream pointed to by stdout, and appends a new-line
character to the output. The terminating null character is
not written.
Returns
[#3] The puts function returns EOF if a write error occurs;
otherwise it returns a nonnegative value.
7.13.7.11 The ungetc function
Synopsis
[#1]
#include <stdio.h>
int ungetc(int c, FILE *stream);
page 359 Library
page 360
Description
[#2] The ungetc function pushes the character specified by c
(converted to an unsigned char) back onto the input stream
pointed to by stream. The pushed-back characters will be
returned by subsequent reads on that stream in the reverse
order of their pushing. A successful intervening call (with
the stream pointed to by stream) to a file positioning
function (fseek, fsetpos, or rewind) discards any pushed-
back characters for the stream. The external storage
corresponding to the stream is unchanged.
[#3] One character of pushback is guaranteed. If the ungetc
function is called too many times on the same stream without
an intervening read or file positioning operation on that
stream, the operation may fail.
[#4] If the value of c equals that of the macro EOF, the
operation fails and the input stream is unchanged.
[#5] A successful call to the ungetc function clears the
end-of-file indicator for the stream. The value of the file
position indicator for the stream after reading or
discarding all pushed-back characters shall be the same as
it was before the characters were pushed back. For a text
stream, the value of its file position indicator after a
successful call to the ungetc function is unspecified until
all pushed-back characters are read or discarded. For a
binary stream, its file position indicator is decremented by
each successful call to the ungetc function; if its value
was zero before a call, it is indeterminate after the call.
Returns
[#6] The ungetc function returns the character pushed back
after conversion, or EOF if the operation fails.
Forward references: file positioning functions (7.13.9).
page 360 Library
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7.13.8 Direct input/output functions
7.13.8.1 The fread function
Synopsis
[#1]
#include <stdio.h>
size_t fread(void * restrict ptr,
size_t size, size_t nmemb,
FILE * restrict stream);
Description
[#2] The fread function reads, into the array pointed to by
ptr, up to nmemb elements whose size is specified by size,
from the stream pointed to by stream. The file position
indicator for the stream (if defined) is advanced by the
number of characters successfully read. If an error occurs,
the resulting value of the file position indicator for the
stream is indeterminate. If a partial element is read, its
value is indeterminate.
Returns
[#3] The fread function returns the number of elements
successfully read, which may be less than nmemb if a read
error or end-of-file is encountered. If size or nmemb is
zero, fread returns zero and the contents of the array and
the state of the stream remain unchanged.
7.13.8.2 The fwrite function
Synopsis
[#1]
#include <stdio.h>
size_t fwrite(const void * restrict ptr,
size_t size, size_t nmemb,
FILE * restrict stream);
Description
[#2] The fwrite function writes, from the array pointed to
by ptr, up to nmemb elements whose size is specified by
size, to the stream pointed to by stream. The file position
indicator for the stream (if defined) is advanced by the
number of characters successfully written. If an error
occurs, the resulting value of the file position indicator
page 361 Library
page 362
for the stream is indeterminate.
Returns
[#3] The fwrite function returns the number of elements
successfully written, which will be less than nmemb only if
a write error is encountered.
7.13.9 File positioning functions
7.13.9.1 The fgetpos function
Synopsis
[#1]
#include <stdio.h>
int fgetpos(FILE * restrict stream,
fpos_t * restrict pos);
Description
[#2] The fgetpos function stores the current value of the
file position indicator for the stream pointed to by stream
in the object pointed to by pos. The value stored contains
unspecified information usable by the fsetpos function for
repositioning the stream to its position at the time of the
call to the fgetpos function.
Returns
[#3] If successful, the fgetpos function returns zero; on
failure, the fgetpos function returns nonzero and stores an
implementation-defined positive value in errno.
Forward references: the fsetpos function (7.13.9.3).
7.13.9.2 The fseek function
Synopsis
[#1]
#include <stdio.h>
int fseek(FILE *stream, long int offset, int whence);
page 362 Library
page 363
Description
[#2] The fseek function sets the file position indicator for
the stream pointed to by stream. If a read or write error
occurs, the error indicator for the stream is set and fseek
fails.
[#3] For a binary stream, the new position, measured in
characters from the beginning of the file, is obtained by
adding offset to the position specified by whence. The
specified position is the beginning of the file if whence is
SEEK_SET, the current value of the file position indicator
if SEEK_CUR, or end-of-file if SEEK_END. A binary stream
need not meaningfully support fseek calls with a whence
value of SEEK_END.
[#4] For a text stream, either offset shall be zero, or
offset shall be a value returned by an earlier successful
call to the ftell function on a stream associated with the
same file and whence shall be SEEK_SET.
[#5] After determining the new position, a successful call
to the fseek function undoes any effects of the ungetc
function on the stream, clears the end-of-file indicator for
the stream, and then establishes the new position.
Returns
[#6] The fseek function returns nonzero only for a request
that cannot be satisfied.
Forward references: the ftell function (7.13.9.4).
7.13.9.3 The fsetpos function
Synopsis
[#1]
#include <stdio.h>
int fsetpos(FILE *stream, const fpos_t *pos);
Description
[#2] The fsetpos function sets the file position indicator
for the stream pointed to by stream according to the value
of the object pointed to by pos, which shall be a value
obtained from an earlier successful call to the fgetpos
function on a stream associated with the same file. If a
read or write error occurs, the error indicator for the
stream is set and fsetpos fails.
page 363 Library
page 364
[#3] A successful call to the fsetpos function clears the
end-of-file indicator for the stream and undoes any effects
of the ungetc function on the same stream. After an fsetpos
call, the next operation on an update stream may be either
input or output.
Returns
[#4] If successful, the fsetpos function returns zero; on
failure, the fsetpos function returns nonzero and stores an
implementation-defined positive value in errno.
7.13.9.4 The ftell function
Synopsis
[#1]
#include <stdio.h>
long int ftell(FILE *stream);
Description
[#2] The ftell function obtains the current value of the
file position indicator for the stream pointed to by stream.
For a binary stream, the value is the number of characters
from the beginning of the file. For a text stream, its file
position indicator contains unspecified information, usable
by the fseek function for returning the file position
indicator for the stream to its position at the time of the
ftell call; the difference between two such return values is
not necessarily a meaningful measure of the number of
characters written or read.
Returns
[#3] If successful, the ftell function returns the current
value of the file position indicator for the stream. On
failure, the ftell function returns - 1L and stores an
implementation-defined positive value in errno.
7.13.9.5 The rewind function
Synopsis
[#1]
#include <stdio.h>
void rewind(FILE *stream);
page 364 Library
page 365
Description
[#2] The rewind function sets the file position indicator
for the stream pointed to by stream to the beginning of the
file. It is equivalent to
(void)fseek(stream, 0L, SEEK_SET)
except that the error indicator for the stream is also
cleared.
Returns
[#3] The rewind function returns no value.
7.13.10 Error-handling functions
7.13.10.1 The clearerr function
Synopsis
[#1]
#include <stdio.h>
void clearerr(FILE *stream);
Description
[#2] The clearerr function clears the end-of-file and error
indicators for the stream pointed to by stream.
Returns
[#3] The clearerr function returns no value.
7.13.10.2 The feof function
Synopsis
[#1]
#include <stdio.h>
int feof(FILE *stream);
Description
[#2] The feof function tests the end-of-file indicator for
the stream pointed to by stream.
page 365 Library
page 366
Returns
[#3] The feof function returns nonzero if and only if the
end-of-file indicator is set for stream.
7.13.10.3 The ferror function
Synopsis
[#1]
#include <stdio.h>
int ferror(FILE *stream);
Description
[#2] The ferror function tests the error indicator for the
stream pointed to by stream.
Returns
[#3] The ferror function returns nonzero if and only if the
error indicator is set for stream.
7.13.10.4 The perror function
Synopsis
[#1]
#include <stdio.h>
void perror(const char *s);
Description
[#2] The perror function maps the error number in the
integer expression errno to an error message. It writes a
sequence of characters to the standard error stream thus:
first (if s is not a null pointer and the character pointed
to by s is not the null character), the string pointed to by
s followed by a colon (:) and a space; then an appropriate
error message string followed by a new-line character. The
contents of the error message strings are the same as those
returned by the strerror function with argument errno.
Returns
[#3] The perror function returns no value.
page 366 Library
page 367
Forward references: the strerror function (7.15.6.2).
page 367 Library
page 368
7.14 General utilities <stdlib.h>
[#1] The header <stdlib.h> declares five types and several
functions of general utility, and defines several macros.221
[#2] The types declared are size_t and wchar_t (both
described in 7.1.6),
div_t
which is a structure type that is the type of the value
returned by the div function,
ldiv_t
which is a structure type that is the type of the value
returned by the ldiv function, and
lldiv_t
which is a structure type that is the type of the value
returned by the lldiv function.
[#3] The macros defined are NULL (described in 7.1.6);
EXIT_FAILURE
and
EXIT_SUCCESS
which expand to integer expressions that may be used as the
argument to the exit function to return unsuccessful or
successful termination status, respectively, to the host
environment;
RAND_MAX
which expands to an integer constant expression, the value
of which is the maximum value returned by the rand function;
and
MB_CUR_MAX
which expands to a positive integer expression whose value
__________
221. See ``future library directions'' (7.20.6).
page 368 Library
page 369
is the maximum number of bytes in a multibyte character for
the extended character set specified by the current locale
(category LC_CTYPE), and whose value is never greater than
MB_LEN_MAX.
7.14.1 String conversion functions
[#1] The functions atof, atoi, atol, and atoll need not
affect the value of the integer expression errno on an
error. If the value of the result cannot be represented,
the behavior is undefined.
7.14.1.1 The atof function
Synopsis
[#1]
#include <stdlib.h>
double atof(const char *nptr);
Description
[#2] The atof function converts the initial portion of the
string pointed to by nptr to double representation. Except
for the behavior on error, it is equivalent to
strtod(nptr, (char **)NULL)
Returns
[#3] The atof function returns the converted value.
Forward references: the strtod function (7.14.1.5).
7.14.1.2 The atoi function
Synopsis
[#1]
#include <stdlib.h>
int atoi(const char *nptr);
Description
[#2] The atoi function converts the initial portion of the
string pointed to by nptr to int representation. Except for
the behavior on error, it is equivalent to
page 369 Library
page 370
(int)strtol(nptr, (char **)NULL, 10)
Returns
[#3] The atoi function returns the converted value.
Forward references: the strtol function (7.14.1.8).
7.14.1.3 The atol function
Synopsis
[#1]
#include <stdlib.h>
long int atol(const char *nptr);
Description
[#2] The atol function converts the initial portion of the
string pointed to by nptr to long int representation.
Except for the behavior on error, it is equivalent to
strtol(nptr, (char **)NULL, 10)
Returns
[#3] The atol function returns the converted value.
Forward references: the strtol function (7.14.1.8).
7.14.1.4 The atoll function
Synopsis
[#1]
#include <stdlib.h>
long long int atoll(const char *nptr);
Description
[#2] The atoll function is equivalent to the atol function,
except that it converts the initial portion of the string
pointed to by nptr to long long int representation. Except
for the behavior on error, it is equivalent to
strtoll(nptr, (char **)NULL, 10)
page 370 Library
page 371
Returns
[#3] The atoll function returns the converted value.
Forward references: the strtoll function (7.14.1.9).
7.14.1.5 The strtod function
Synopsis
[#1]
#include <stdlib.h>
double strtod(const char * restrict nptr,
char ** restrict endptr);
Description
[#2] The strtod function converts the initial portion of the
string pointed to by nptr to double representation. First,
it decomposes the input string into three parts: an
initial, possibly empty, sequence of white-space characters
(as specified by the isspace function), a subject sequence
resembling a floating-point constant; and a final string of
one or more unrecognized characters, including the
terminating null character of the input string. Then, it
attempts to convert the subject sequence to a floating-point
number, and returns the result.
[#3] The expected form of the subject sequence is an
optional plus or minus sign, then one of the following:
- a nonempty sequence of decimal digits optionally
containing a decimal-point character, then an optional
exponent part as defined in 6.1.3.1;
- a 0x or 0X, then a nonempty sequence of hexadecimal
digits optionally containing a decimal-point character,
then an optional binary-exponent part as defined in
6.1.3.1, where either the decimal-point character or
the binary-exponent part is present;
- one of INF or INFINITY, ignoring case
- one of NAN or NAN(n-char-sequence-opt), ignoring case
in the NAN part, where:
page 371 Library
page 372
n-char-sequence:
digit
nondigit
n-char-sequence digit
n-char-sequence nondigit
but no floating suffix. The subject sequence is defined as
the longest initial subsequence of the input string,
starting with the first non-white-space character, that is
of the expected form. The subject sequence contains no
characters if the input string is not of the expected form.
[#4] If the subject sequence has the expected form for a
floating-point number, the sequence of characters starting
with the first digit or the decimal-point character
(whichever occurs first) is interpreted as a floating
constant according to the rules of 6.1.3.1, except that the
decimal-point character is used in place of a period, and
that if neither an exponent part, a binary-exponent part,
nor a decimal-point character appears, a decimal point is
assumed to follow the last digit in the string. A character
sequence INF or INFINITY is interpreted as an infinity, if
representable in the double type, else like a floating
constant that is too large for the range of double. A
character sequence NAN or NAN(n-char-sequence-opt), is
interpreted as a quiet NaN, if supported in the double type,
else like a subject sequence part that does not have the
expected form; the meaning of the n-char sequences is
implementation-defined.222 If the subject sequence begins
with a minus sign, the value resulting from the conversion
is negated.223 A pointer to the final string is stored in
the object pointed to by endptr, provided that endptr is not
a null pointer.
[#5] In other than the "C" locale, additional locale-
specific subject sequence forms may be accepted.
[#6] If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of nptr
is stored in the object pointed to by endptr, provided that
__________
222. An implementation may use the n-char-sequence to
determine extra information to be represented in the
NaN's significand.
223. The strtod function honors the sign of zero if the
arithmetic supports signed zeros.
page 372 Library
page 373
endptr is not a null pointer.
[#7] If the subject sequence has the hexadecimal form and
FLT_RADIX is a power of 2, then the value resulting from the
conversion is correctly rounded.
Recommended practice
[#8] If the subject sequence has the hexadecimal form and
FLT_RADIX is not a power of 2, then the result is one of the
two numbers in the appropriate internal format that are
adjacent to the hexadecimal floating source value, with the
extra stipulation that the error have a correct sign for the
current rounding direction.
[#9] If the subject sequence has the decimal form and at
most DECIMAL_DIG (defined in <math.h>) significant digits,
then the value resulting from the conversion is correctly
rounded. If the subject sequence D has the decimal form and
more than DECIMAL_DIG significant digits, consider the two
bounding, adjacent decimal strings L and U, both having
DECIMAL_DIG significant digits, such that the values of L,
D, and U satisfy L < D < U. The result of conversion is one
of the (equal or adjacent) values that would be obtained by
correctly rounding L and U according to the current rounding
direction, with the extra stipulation that the error with
respect to D has a correct sign for the current rounding
direction.224
Returns
[#10] The strtod function returns the converted value, if
any. If no conversion could be performed, zero is returned.
If the correct value is outside the range of representable
values, plus or minus HUGE_VAL is returned (according to the
sign of the value), and the value of the macro ERANGE is
stored in errno. If the result underflows (7.7.1), the
function returns a value whose magnitude is no greater than
the smallest normalized positive number in the result type;
whether errno acquires the value ERANGE is implementation-
defined.
__________
224. DECIMAL_DIG, defined in <math.h>, is recommended to be
sufficiently large that L and U will usually round to
the same internal floating value, but if not will round
to adjacent values.
page 373 Library
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7.14.1.6 The strtof function
Synopsis
[#1]
#include <stdlib.h>
float strtof(const char * restrict nptr,
char ** restrict endptr);
Description
[#2] The strtof function is similar to the strtod function,
expect the returned value has type float and plus or minus
HUGE_VALF is returned for values outside the range.
7.14.1.7 The strtold function
Synopsis
[#1]
#include <stdlib.h>
long double strtold(const char * restrict nptr,
char ** restrict endptr);
Description
[#2] The strtold function is similar to the strtod function,
expect the returned value has type long double and plus or
minus HUGE_VALL is returned for values outside the range.
7.14.1.8 The strtol function
Synopsis
[#1]
#include <stdlib.h>
long int strtol(const char * restrict nptr,
char ** restrict endptr, int base);
Description
[#2] The strtol function converts the initial portion of the
string pointed to by nptr to long int representation.
First, it decomposes the input string into three parts: an
initial, possibly empty, sequence of white-space characters
(as specified by the isspace function), a subject sequence
resembling an integer represented in some radix determined
by the value of base, and a final string of one or more
page 374 Library
page 375
unrecognized characters, including the terminating null
character of the input string. Then, it attempts to convert
the subject sequence to an integer, and returns the result.
[#3] If the value of base is zero, the expected form of the
subject sequence is that of an integer constant as described
in 6.1.3.2, optionally preceded by a plus or minus sign, but
not including an integer suffix. If the value of base is
between 2 and 36, the expected form of the subject sequence
is a sequence of letters and digits representing an integer
with the radix specified by base, optionally preceded by a
plus or minus sign, but not including an integer suffix.
The letters from a (or A) through z (or Z) are ascribed the
values 10 to 35; only letters whose ascribed values are less
than that of base are permitted. If the value of base is
16, the characters 0x or 0X may optionally precede the
sequence of letters and digits, following the sign if
present.
[#4] The subject sequence is defined as the longest initial
subsequence of the input string, starting with the first
non-white-space character, that is of the expected form.
The subject sequence contains no characters if the input
string is empty or consists entirely of white space, or if
the first non-white-space character is other than a sign or
a permissible letter or digit.
[#5] If the subject sequence has the expected form and the
value of base is zero, the sequence of characters starting
with the first digit is interpreted as an integer constant
according to the rules of 6.1.3.2. If the subject sequence
has the expected form and the value of base is between 2 and
36, it is used as the base for conversion, ascribing to each
letter its value as given above. If the subject sequence
begins with a minus sign, the value resulting from the
conversion is negated. A pointer to the final string is
stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
[#6] In other than the "C" locale, additional locale-
specific subject sequence forms may be accepted.
[#7] If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of nptr
is stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
page 375 Library
page 376
Returns
[#8] The strtol function returns the converted value, if
any. If no conversion could be performed, zero is returned.
If the correct value is outside the range of representable
values, LONG_MAX or LONG_MIN is returned (according to the
sign of the value), and the value of the macro ERANGE is
stored in errno.
7.14.1.9 The strtoll function
Synopsis
[#1]
#include <stdlib.h>
long long int strtoll(const char * restrict nptr,
char ** restrict endptr, int base);
Description
[#2] The strtoll is equivalent to the strtol function,
except that it converts the initial portion of the string
pointed to by nptr to long long int representation.
Returns
[#3] The strtoll function returns the converted value, if
any. If no conversion could be performed, zero is returned.
If the correct value is outside the range of representable
values, LLONG_MAX or LLONG_MIN is returned (according to the
sign of the value), and the value of the macro ERANGE is
stored in errno.
7.14.1.10 The strtoul function
Synopsis
[#1]
#include <stdlib.h>
unsigned long int strtoul(
const char * restrict nptr,
char ** restrict endptr,
int base);
page 376 Library
page 377
Description
[#2] The strtoul function converts the initial portion of
the string pointed to by nptr to unsigned long int
representation. First, it decomposes the input string into
three parts: an initial, possibly empty, sequence of
white-space characters (as specified by the isspace
function), a subject sequence resembling an unsigned integer
represented in some radix determined by the value of base,
and a final string of one or more unrecognized characters,
including the terminating null character of the input
string. Then, it attempts to convert the subject sequence
to an unsigned integer, and returns the result.
[#3] If the value of base is zero, the expected form of the
subject sequence is that of an integer constant as described
in 6.1.3.2, optionally preceded by a plus or minus sign, but
not including an integer suffix. If the value of base is
between 2 and 36, the expected form of the subject sequence
is a sequence of letters and digits representing an integer
with the radix specified by base, optionally preceded by a
plus or minus sign, but not including an integer suffix.
The letters from a (or A) through z (or Z) are ascribed the
values 10 to 35; only letters whose ascribed values are less
than that of base are permitted. If the value of base is
16, the characters 0x or 0X may optionally precede the
sequence of letters and digits, following the sign if
present.
[#4] The subject sequence is defined as the longest initial
subsequence of the input string, starting with the first
non-white-space character, that is of the expected form.
The subject sequence contains no characters if the input
string is empty or consists entirely of white space, or if
the first non-white-space character is other than a sign or
a permissible letter or digit.
[#5] If the subject sequence has the expected form and the
value of base is zero, the sequence of characters starting
with the first digit is interpreted as an integer constant
according to the rules of 6.1.3.2. If the subject sequence
has the expected form and the value of base is between 2 and
36, it is used as the base for conversion, ascribing to each
letter its value as given above. If the subject sequence
begins with a minus sign, the value resulting from the
conversion is negated. A pointer to the final string is
stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
[#6] In other than the "C" locale, additional locale-
specific subject sequence forms may be accepted.
page 377 Library
page 378
[#7] If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of nptr
is stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
Returns
[#8] The strtoul function returns the converted value, if
any. If no conversion could be performed, zero is returned.
If the correct value is outside the range of representable
values, ULONG_MAX is returned, and the value of the macro
ERANGE is stored in errno.
7.14.1.11 The strtoull function
Synopsis
[#1]
#include <stdlib.h>
unsigned long long int strtoull(
const char * restrict nptr,
char ** restrict endptr,
int base);
Description
[#2] The strtoull is equivalent to the strtoul function,
except that it converts the initial portion of the string
pointed to by nptr to unsigned long long int representation.
Returns
[#3] The strtoull function returns the converted value, if
any. If no conversion could be performed, zero is returned.
If the correct value is outside the range of representable
values, ULLONG_MAX is returned, and the value of the macro
ERANGE is stored in errno.
page 378 Library
page 379
7.14.2 Pseudo-random sequence generation functions
7.14.2.1 The rand function
Synopsis
[#1]
#include <stdlib.h>
int rand(void);
Description
[#2] The rand function computes a sequence of pseudo-random
integers in the range 0 to RAND_MAX.
[#3] The implementation shall behave as if no library
function calls the rand function.
Returns
[#4] The rand function returns a pseudo-random integer.
Environmental limit
[#5] The value of the RAND_MAX macro shall be at least
32767.
7.14.2.2 The srand function
Synopsis
[#1]
#include <stdlib.h>
void srand(unsigned int seed);
Description
[#2] The srand function uses the argument as a seed for a
new sequence of pseudo-random numbers to be returned by
subsequent calls to rand. If srand is then called with the
same seed value, the sequence of pseudo-random numbers shall
be repeated. If rand is called before any calls to srand
have been made, the same sequence shall be generated as when
srand is first called with a seed value of 1.
[#3] The implementation shall behave as if no library
function calls the srand function.
page 379 Library
page 380
Returns
[#4] The srand function returns no value.
Examples
[#5] The following functions define a portable
implementation of rand and srand.
static unsigned long int next = 1;
int rand(void) // RAND_MAX assumed to be 32767
{
next = next * 1103515245 + 12345;
return (unsigned int)(next/65536) % 32768;
}
void srand(unsigned int seed)
{
next = seed;
}
7.14.3 Memory management functions
[#1] The order and contiguity of storage allocated by
successive calls to the calloc, malloc, and realloc
functions is unspecified. The pointer returned if the
allocation succeeds is suitably aligned so that it may be
assigned to a pointer to any type of object and then used to
access such an object or an array of such objects in the
space allocated (until the space is explicitly freed or
reallocated). Each such allocation shall yield a pointer to
an object disjoint from any other object. The pointer
returned points to the start (lowest byte address) of the
allocated space. If the space cannot be allocated, a null
pointer is returned. If the size of the space requested is
zero, the behavior is implementation-defined: either a null
pointer is returned, or the behavior is as if the size were
some nonzero value, except that the returned pointer shall
not be used to access an object. The value of a pointer
that refers to freed space is indeterminate.
page 380 Library
page 381
7.14.3.1 The calloc function
Synopsis
[#1]
#include <stdlib.h>
void *calloc(size_t nmemb, size_t size);
Description
[#2] The calloc function allocates space for an array of
nmemb objects, each of whose size is size. The space is
initialized to all bits zero.225
Returns
[#3] The calloc function returns either a null pointer or a
pointer to the allocated space.
7.14.3.2 The free function
Synopsis
[#1]
#include <stdlib.h>
void free(void *ptr);
Description
[#2] The free function causes the space pointed to by ptr to
be deallocated, that is, made available for further
allocation. If ptr is a null pointer, no action occurs.
Otherwise, if the argument does not match a pointer earlier
returned by the calloc, malloc, or realloc function, or if
the space has been deallocated by a call to free or realloc,
the behavior is undefined.
__________
225. Note that this need not be the same as the
representation of floating-point zero or a null pointer
constant.
page 381 Library
page 382
Returns
[#3] The free function returns no value.
7.14.3.3 The malloc function
Synopsis
[#1]
#include <stdlib.h>
void *malloc(size_t size);
Description
[#2] The malloc function allocates space for an object whose
size is specified by size and whose value is indeterminate.
Returns
[#3] The malloc function returns either a null pointer or a
pointer to the allocated space.
7.14.3.4 The realloc function
Synopsis
[#1]
#include <stdlib.h>
void *realloc(void *ptr, size_t size);
Description
[#2] The realloc function changes the size of the object
pointed to by ptr to the size specified by size. The
contents of the object shall be unchanged up to the lesser
of the new and old sizes. If the new size is larger, the
value of the newly allocated portion of the object is
indeterminate. If ptr is a null pointer, the realloc
function behaves like the malloc function for the specified
size. Otherwise, if ptr does not match a pointer earlier
returned by the calloc, malloc, or realloc function, or if
the space has been deallocated by a call to the free or
realloc function, the behavior is undefined. If the space
cannot be allocated, the object pointed to by ptr is
unchanged. If size is zero and ptr is not a null pointer,
the object it points to is freed.
page 382 Library
page 383
Returns
[#3] The realloc function returns either a null pointer or a
pointer to the possibly moved allocated space. If a pointer
is returned which does not compare equal to ptr, then the
object has moved and ptr is a pointer that refers to freed
space.
7.14.4 Communication with the environment
7.14.4.1 The abort function
Synopsis
[#1]
#include <stdlib.h>
void abort(void);
Description
[#2] The abort function causes abnormal program termination
to occur, unless the signal SIGABRT is being caught and the
signal handler does not return. Whether open output streams
are flushed or open streams closed or temporary files
removed is implementation-defined. An implementation-
defined form of the status unsuccessful termination is
returned to the host environment by means of the function
call raise(SIGABRT).
Returns
[#3] The abort function cannot return to its caller.
7.14.4.2 The atexit function
Synopsis
[#1]
#include <stdlib.h>
int atexit(void (*func)(void));
Description
[#2] The atexit function registers the function pointed to
by func, to be called without arguments at normal program
termination.
page 383 Library
page 384
Implementation limits
[#3] The implementation shall support the registration of at
least 32 functions.
Returns
[#4] The atexit function returns zero if the registration
succeeds, nonzero if it fails.
Forward references: the exit function (7.14.4.3).
7.14.4.3 The exit function
Synopsis
[#1]
#include <stdlib.h>
void exit(int status);
Description
[#2] The exit function causes normal program termination to
occur. If more than one call to the exit function is
executed by a program, the behavior is undefined.
[#3] First, all functions registered by the atexit function
are called, in the reverse order of their registration.226
[#4] Next, all open streams with unwritten buffered data are
flushed, all open streams are closed, and all files created
by the tmpfile function are removed.
[#5] Finally, control is returned to the host environment.
If the value of status is zero or EXIT_SUCCESS, an
implementation-defined form of the status successful
termination is returned. If the value of status is
EXIT_FAILURE, an implementation-defined form of the status
unsuccessful termination is returned. Otherwise the status
returned is implementation-defined.
__________
226. Each function is called as many times as it was
registered.
page 384 Library
page 385
Returns
[#6] The exit function cannot return to its caller.
7.14.4.4 The getenv function
Synopsis
[#1]
#include <stdlib.h>
char *getenv(const char *name);
Description
[#2] The getenv function searches an environment list,
provided by the host environment, for a string that matches
the string pointed to by name. The set of environment names
and the method for altering the environment list are
implementation-defined.
[#3] The implementation shall behave as if no library
function calls the getenv function.
Returns
[#4] The getenv function returns a pointer to a string
associated with the matched list member. The string pointed
to shall not be modified by the program, but may be
overwritten by a subsequent call to the getenv function. If
the specified name cannot be found, a null pointer is
returned.
7.14.4.5 The system function
Synopsis
[#1]
#include <stdlib.h>
int system(const char *string);
Description
[#2] If string is a null pointer, the system function
determines whether the host environment has a command
processor. If string is not a null pointer, the system
function passes the string pointed to by string to that
command processor to be executed in a manner which the
implementation shall document; this might then cause the
program calling system to behave in a non-conforming manner
page 385 Library
page 386
or to terminate.
Returns
[#3] If the argument is a null pointer, the system function
returns nonzero only if a command processor is available.
If the argument is not a null pointer, and the system
function does return, it returns an implementation-defined
value.
7.14.5 Searching and sorting utilities
[#1] These utilities make use of a comparison function.
[#2] The implementation shall ensure that the second
argument of the comparison function (when called from
bsearch), or both arguments (when called from qsort), shall
be pointers to elements of the array.227 The first argument
when called from bsearch shall equal key.
[#3] The comparison function shall not alter the contents of
the array. The implementation may reorder elements of the
array between calls to the comparison function, but shall
not alter the contents of any individual element.
[#4] When the same object (consisting of size bytes,
irrespective of its current position in the array) is passed
more than once to the comparison function, the results shall
be consistent with one another. That is, for qsort they
shall define a total ordering on the array, and for bsearch
the same object shall always compare the same way with the
key.
[#5] A sequence point occurs immediately before and
immediately after each call to the comparison function, and
also between any call to the comparison function and any
movement of the objects passed as arguments to that call.
__________
227. That is, if the value passed is p, then the following
expressions are always non-zero:
((char *p)p - (char *)base) % size == 0
(char *)p >= (char *)base
page 386 Library
page 387
7.14.5.1 The bsearch function
Synopsis
[#1]
#include <stdlib.h>
void *bsearch(const void *key, const void *base,
size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
Description
[#2] The bsearch function searches an array of nmemb
objects, the initial element of which is pointed to by base,
for an element that matches the object pointed to by key.
The size of each element of the array is specified by size.
[#3] The comparison function pointed to by compar is called
with two arguments that point to the key object and to an
array element, in that order. The function shall return an
integer less than, equal to, or greater than zero if the key
object is considered, respectively, to be less than, to
match, or to be greater than the array element. The array
shall consist of: all the elements that compare less than,
all the elements that compare equal to, and all the elements
that compare greater than the key object, in that order.228
Returns
[#4] The bsearch function returns a pointer to a matching
element of the array, or a null pointer if no match is
found. If two elements compare as equal, which element is
matched is unspecified.
__________
228. In practice, the entire array is sorted according to
the comparison function.
page 387 Library
page 388
7.14.5.2 The qsort function
Synopsis
[#1]
#include <stdlib.h>
void qsort(void *base, size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
Description
[#2] The qsort function sorts an array of nmemb objects, the
initial element of which is pointed to by base. The size of
each object is specified by size.
[#3] The contents of the array are sorted into ascending
order according to a comparison function pointed to by
compar, which is called with two arguments that point to the
objects being compared. The function shall return an
integer less than, equal to, or greater than zero if the
first argument is considered to be respectively less than,
equal to, or greater than the second.
[#4] If two elements compare as equal, their order in the
sorted array is unspecified.
Returns
[#5] The qsort function returns no value.
7.14.6 Integer arithmetic functions
7.14.6.1 The abs function
Synopsis
[#1]
#include <stdlib.h>
int abs(int j);
Description
[#2] The abs function computes the absolute value of an
integer j. If the result cannot be represented, the
behavior is undefined.229
page 388 Library
page 389
Returns
[#3] The abs function returns the absolute value.
7.14.6.2 The div function
Synopsis
[#1]
#include <stdlib.h>
div_t div(int numer, int denom);
Description
[#2] The div function computes the quotient and remainder of
the division of the numerator numer by the denominator
denom. The returned quotient is the algebraic quotient with
any fractional part discarded. If the result cannot be
represented, the behavior is undefined; otherwise, quot *
denom + rem shall equal numer.
Returns
[#3] The div function returns a structure of type div_t,
comprising both the quotient and the remainder. The
structure shall contain the following members, in either
order:
int quot; // quotient
int rem; // remainder
7.14.6.3 The labs function
Synopsis
[#1]
#include <stdlib.h>
long int labs(long int j);
__________
229. The absolute value of the most negative number cannot
be represented in two's complement.
page 389 Library
page 390
Description
[#2] The labs function is equivalent to the abs function,
except that the argument and the returned value each have
type long int.
7.14.6.4 The llabs function
Synopsis
[#1]
#include <stdlib.h>
long long int llabs(long long int j);
Description
[#2] The llabs function is equivalent to the abs function,
except that the argument and the returned value each have
type long long int.
7.14.6.5 The ldiv function
Synopsis
[#1]
#include <stdlib.h>
ldiv_t ldiv(long int numer, long int denom);
Description
[#2] The ldiv function is equivalent to the div function,
except that the arguments and the members of the returned
structure (which has type ldiv_t) all have type long int.
7.14.6.6 The lldiv function
Synopsis
[#1]
#include <stdlib.h>
lldiv_t lldiv(long long int numer,
long long int denom);
page 390 Library
page 391
Description
[#2] The lldiv function is equivalent to the div function,
except that the arguments and the members of the returned
structure (which has type lldiv_t) all have type long long
int.
7.14.7 Multibyte character functions
[#1] The behavior of the multibyte character functions is
affected by the LC_CTYPE category of the current locale.
For a state-dependent encoding, each function is placed into
its initial state by a call for which its character pointer
argument, s, is a null pointer. Subsequent calls with s as
other than a null pointer cause the internal state of the
function to be altered as necessary. A call with s as a
null pointer causes these functions to return a nonzero
value if encodings have state dependency, and zero
otherwise.230 Changing the LC_CTYPE category causes the
shift state of these functions to be indeterminate.
7.14.7.1 The mblen function
Synopsis
[#1]
#include <stdlib.h>
int mblen(const char *s, size_t n);
Description
[#2] If s is not a null pointer, the mblen function
determines the number of bytes contained in the multibyte
character pointed to by s. Except that the shift state of
the mbtowc function is not affected, it is equivalent to
mbtowc((wchar_t *)0, s, n);
[#3] The implementation shall behave as if no library
function calls the mblen function.
__________
230. If the locale employs special bytes to change the shift
state, these bytes do not produce separate wide
character codes, but are grouped with an adjacent
multibyte character.
page 391 Library
page 392
Returns
[#4] If s is a null pointer, the mblen function returns a
nonzero or zero value, if multibyte character encodings,
respectively, do or do not have state-dependent encodings.
If s is not a null pointer, the mblen function either
returns 0 (if s points to the null character), or returns
the number of bytes that are contained in the multibyte
character (if the next n or fewer bytes form a valid
multibyte character), or returns -1 (if they do not form a
valid multibyte character).
Forward references: the mbtowc function (7.14.7.2).
7.14.7.2 The mbtowc function
Synopsis
[#1]
#include <stdlib.h>
int mbtowc(wchar_t * restrict pwc,
const char * restrict s,
size_t n);
Description
[#2] If s is not a null pointer, the mbtowc function
determines the number of bytes that are contained in the
multibyte character pointed to by s. It then determines the
code for the value of type wchar_t that corresponds to that
multibyte character. (The value of the code corresponding
to the null character is zero.) If the multibyte character
is valid and pwc is not a null pointer, the mbtowc function
stores the code in the object pointed to by pwc. At most n
bytes of the array pointed to by s will be examined.
[#3] The implementation shall behave as if no library
function calls the mbtowc function.
Returns
If s is a null pointer, the mbtowc function returns a
nonzero or zero value, if multibyte character encodings,
respectively, do or do not have state-dependent encodings.
If s is not a null pointer, the mbtowc function either
returns 0 (if s points to the null character), or returns
the number of bytes that are contained in the converted
multibyte character (if the next n or fewer bytes form a
valid multibyte character), or returns -1 (if they do not
form a valid multibyte character).
page 392 Library
page 393
[#4] In no case will the value returned be greater than n or
the value of the MB_CUR_MAX macro.
7.14.7.3 The wctomb function
Synopsis
[#1]
#include <stdlib.h>
int wctomb(char *s, wchar_t wchar);
Description
[#2] The wctomb function determines the number of bytes
needed to represent the multibyte character corresponding to
the code whose value is wchar (including any change in shift
state). It stores the multibyte character representation in
the array object pointed to by s (if s is not a null
pointer). At most MB_CUR_MAX characters are stored. If the
value of wchar is zero, the wctomb function is left in the
initial shift state.
[#3] The implementation shall behave as if no library
function calls the wctomb function.
Returns
[#4] If s is a null pointer, the wctomb function returns a
nonzero or zero value, if multibyte character encodings,
respectively, do or do not have state-dependent encodings.
If s is not a null pointer, the wctomb function returns -1
if the value of wchar does not correspond to a valid
multibyte character, or returns the number of bytes that are
contained in the multibyte character corresponding to the
value of wchar.
[#5] In no case will the value returned be greater than the
value of the MB_CUR_MAX macro.
page 393 Library
page 394
7.14.8 Multibyte string functions
[#1] The behavior of the multibyte string functions is
affected by the LC_CTYPE category of the current locale.
7.14.8.1 The mbstowcs function
Synopsis
[#1]
#include <stdlib.h>
size_t mbstowcs(wchar_t * restrict pwcs,
const char * restrict s,
size_t n);
Description
[#2] The mbstowcs function converts a sequence of multibyte
characters that begins in the initial shift state from the
array pointed to by s into a sequence of corresponding codes
and stores not more than n codes into the array pointed to
by pwcs. No multibyte characters that follow a null
character (which is converted into a code with value zero)
will be examined or converted. Each multibyte character is
converted as if by a call to the mbtowc function, except
that the shift state of the mbtowc function is not affected.
[#3] No more than n elements will be modified in the array
pointed to by pwcs. If copying takes place between objects
that overlap, the behavior is undefined.
Returns
[#4] If an invalid multibyte character is encountered, the
mbstowcs function returns (size_t)-1. Otherwise, the
mbstowcs function returns the number of array elements
modified, not including a terminating zero code, if any.231
__________
231. The array will not be null- or zero-terminated if the
value returned is n.
page 394 Library
page 395
7.14.8.2 The wcstombs function
Synopsis
[#1]
#include <stdlib.h>
size_t wcstombs(char * restrict s,
const wchar_t * restrict pwcs,
size_t n);
Description
[#2] The wcstombs function converts a sequence of codes that
correspond to multibyte characters from the array pointed to
by pwcs into a sequence of multibyte characters that begins
in the initial shift state and stores these multibyte
characters into the array pointed to by s, stopping if a
multibyte character would exceed the limit of n total bytes
or if a null character is stored. Each code is converted as
if by a call to the wctomb function, except that the shift
state of the wctomb function is not affected.
[#3] No more than n bytes will be modified in the array
pointed to by s. If copying takes place between objects
that overlap, the behavior is undefined.
Returns
[#4] If a code is encountered that does not correspond to a
valid multibyte character, the wcstombs function returns
(size_t)-1. Otherwise, the wcstombs function returns the
number of bytes modified, not including a terminating null
character, if any.231
page 395 Library
page 396
7.15 String handling <string.h>
7.15.1 String function conventions
[#1] The header <string.h> declares one type and several
functions, and defines one macro useful for manipulating
arrays of character type and other objects treated as arrays
of character type.232 The type is size_t and the macro is
NULL (both described in 7.1.6). Various methods are used
for determining the lengths of the arrays, but in all cases
a char * or void * argument points to the initial (lowest
addressed) character of the array. If an array is accessed
beyond the end of an object, the behavior is undefined.
[#2] Where an argument declared as size_t n specifies the
length of the array for a function, n can have the value
zero on a call to that function. Unless explicitly stated
otherwise in the description of a particular function in
this subclause, pointer arguments on such a call must still
have valid values, as described in subclause 7.1.8. On such
a call, a function that locates a character finds no
occurrence, a function that compares two character sequences
returns zero, and a function that copies characters copies
zero characters.
7.15.2 Copying functions
7.15.2.1 The memcpy function
Synopsis
[#1]
#include <string.h>
void *memcpy(void * restrict s1,
const void * restrict s2,
size_t n);
Description
[#2] The memcpy function copies n characters from the object
pointed to by s2 into the object pointed to by s1. If
copying takes place between objects that overlap, the
behavior is undefined.
__________
232. See ``future library directions'' (7.20.7).
page 396 Library
page 397
Returns
[#3] The memcpy function returns the value of s1.
7.15.2.2 The memmove function
Synopsis
[#1]
#include <string.h>
void *memmove(void *s1, const void *s2, size_t n);
Description
[#2] The memmove function copies n characters from the
object pointed to by s2 into the object pointed to by s1.
Copying takes place as if the n characters from the object
pointed to by s2 are first copied into a temporary array of
n characters that does not overlap the objects pointed to by
s1 and s2, and then the n characters from the temporary
array are copied into the object pointed to by s1.
Returns
[#3] The memmove function returns the value of s1.
7.15.2.3 The strcpy function
Synopsis
[#1]
#include <string.h>
char *strcpy(char * restrict s1,
const char * restrict s2);
Description
[#2] The strcpy function copies the string pointed to by s2
(including the terminating null character) into the array
pointed to by s1. If copying takes place between objects
that overlap, the behavior is undefined.
Returns
[#3] The strcpy function returns the value of s1.
page 397 Library
page 398
7.15.2.4 The strncpy function
Synopsis
[#1]
#include <string.h>
char *strncpy(char * restrict s1,
const char * restrict s2,
size_t n);
Description
[#2] The strncpy function copies not more than n characters
(characters that follow a null character are not copied)
from the array pointed to by s2 to the array pointed to by
s1.233 If copying takes place between objects that overlap,
the behavior is undefined.
[#3] If the array pointed to by s2 is a string that is
shorter than n characters, null characters are appended to
the copy in the array pointed to by s1, until n characters
in all have been written.
Returns
[#4] The strncpy function returns the value of s1.
7.15.3 Concatenation functions
7.15.3.1 The strcat function
Synopsis
[#1]
#include <string.h>
char *strcat(char * restrict s1,
const char * restrict s2);
__________
233. Thus, if there is no null character in the first n
characters of the array pointed to by s2, the result
will not be null-terminated.
page 398 Library
page 399
Description
[#2] The strcat function appends a copy of the string
pointed to by s2 (including the terminating null character)
to the end of the string pointed to by s1. The initial
character of s2 overwrites the null character at the end of
s1. If copying takes place between objects that overlap,
the behavior is undefined.
Returns
[#3] The strcat function returns the value of s1.
7.15.3.2 The strncat function
Synopsis
[#1]
#include <string.h>
char *strncat(char * restrict s1,
const char * restrict s2,
size_t n);
Description
[#2] The strncat function appends not more than n characters
(a null character and characters that follow it are not
appended) from the array pointed to by s2 to the end of the
string pointed to by s1. The initial character of s2
overwrites the null character at the end of s1. A
terminating null character is always appended to the
result.234 If copying takes place between objects that
overlap, the behavior is undefined.
Returns
[#3] The strncat function returns the value of s1.
__________
234. Thus, the maximum number of characters that can end up
in the array pointed to by s1 is strlen(s1)+n+1.
page 399 Library
page 400
Forward references: the strlen function (7.15.6.3).
7.15.4 Comparison functions
[#1] The sign of a nonzero value returned by the comparison
functions memcmp, strcmp, and strncmp is determined by the
sign of the difference between the values of the first pair
of characters (both interpreted as unsigned char) that
differ in the objects being compared.
7.15.4.1 The memcmp function
Synopsis
[#1]
#include <string.h>
int memcmp(const void *s1, const void *s2, size_t n);
Description
[#2] The memcmp function compares the first n characters of
the object pointed to by s1 to the first n characters of the
object pointed to by s2.235
Returns
[#3] The memcmp function returns an integer greater than,
equal to, or less than zero, accordingly as the object
pointed to by s1 is greater than, equal to, or less than the
object pointed to by s2.
7.15.4.2 The strcmp function
Synopsis
[#1]
#include <string.h>
int strcmp(const char *s1, const char *s2);
__________
235. The contents of ``holes'' used as padding for purposes
of alignment within structure objects are indeterminate.
Strings shorter than their allocated space and unions
may also cause problems in comparison.
page 400 Library
page 401
Description
[#2] The strcmp function compares the string pointed to by
s1 to the string pointed to by s2.
Returns
[#3] The strcmp function returns an integer greater than,
equal to, or less than zero, accordingly as the string
pointed to by s1 is greater than, equal to, or less than the
string pointed to by s2.
7.15.4.3 The strcoll function
Synopsis
[#1]
#include <string.h>
int strcoll(const char *s1, const char *s2);
Description
The strcoll function compares the string pointed to by s1 to
the string pointed to by s2, both interpreted as appropriate
to the LC_COLLATE category of the current locale.
Returns
[#2] The strcoll function returns an integer greater than,
equal to, or less than zero, accordingly as the string
pointed to by s1 is greater than, equal to, or less than the
string pointed to by s2 when both are interpreted as
appropriate to the current locale.
7.15.4.4 The strncmp function
Synopsis
[#1]
#include <string.h>
int strncmp(const char *s1, const char *s2, size_t n);
Description
[#2] The strncmp function compares not more than n
characters (characters that follow a null character are not
compared) from the array pointed to by s1 to the array
pointed to by s2.
page 401 Library
page 402
Returns
[#3] The strncmp function returns an integer greater than,
equal to, or less than zero, accordingly as the possibly
null-terminated array pointed to by s1 is greater than,
equal to, or less than the possibly null-terminated array
pointed to by s2.
7.15.4.5 The strxfrm function
Synopsis
[#1]
#include <string.h>
size_t strxfrm(char * restrict s1,
const char * restrict s2,
size_t n);
Description
[#2] The strxfrm function transforms the string pointed to
by s2 and places the resulting string into the array pointed
to by s1. The transformation is such that if the strcmp
function is applied to two transformed strings, it returns a
value greater than, equal to, or less than zero,
corresponding to the result of the strcoll function applied
to the same two original strings. No more than n characters
are placed into the resulting array pointed to by s1,
including the terminating null character. If n is zero, s1
is permitted to be a null pointer. If copying takes place
between objects that overlap, the behavior is undefined.
Returns
[#3] The strxfrm function returns the length of the
transformed string (not including the terminating null
character). If the value returned is n or more, the
contents of the array pointed to by s1 are indeterminate.
Examples
[#4] The value of the following expression is the size of
the array needed to hold the transformation of the string
pointed to by s.
1 + strxfrm(NULL, s, 0)
page 402 Library
page 403
7.15.5 Search functions
7.15.5.1 The memchr function
Synopsis
[#1]
#include <string.h>
void *memchr(const void *s, int c, size_t n);
Description
[#2] The memchr function locates the first occurrence of c
(converted to an unsigned char) in the initial n characters
(each interpreted as unsigned char) of the object pointed to
by s.
Returns
[#3] The memchr function returns a pointer to the located
character, or a null pointer if the character does not occur
in the object.
7.15.5.2 The strchr function
Synopsis
[#1]
#include <string.h>
char *strchr(const char *s, int c);
Description
[#2] The strchr function locates the first occurrence of c
(converted to a char) in the string pointed to by s. The
terminating null character is considered to be part of the
string.
Returns
[#3] The strchr function returns a pointer to the located
character, or a null pointer if the character does not occur
in the string.
page 403 Library
page 404
7.15.5.3 The strcspn function
Synopsis
[#1]
#include <string.h>
size_t strcspn(const char *s1, const char *s2);
Description
[#2] The strcspn function computes the length of the maximum
initial segment of the string pointed to by s1 which
consists entirely of characters not from the string pointed
to by s2.
Returns
[#3] The strcspn function returns the length of the segment.
7.15.5.4 The strpbrk function
Synopsis
[#1]
#include <string.h>
char *strpbrk(const char *s1, const char *s2);
Description
[#2] The strpbrk function locates the first occurrence in
the string pointed to by s1 of any character from the string
pointed to by s2.
Returns
[#3] The strpbrk function returns a pointer to the
character, or a null pointer if no character from s2 occurs
in s1.
7.15.5.5 The strrchr function
Synopsis
[#1]
#include <string.h>
char *strrchr(const char *s, int c);
page 404 Library
page 405
Description
[#2] The strrchr function locates the last occurrence of c
(converted to a char) in the string pointed to by s. The
terminating null character is considered to be part of the
string.
Returns
[#3] The strrchr function returns a pointer to the
character, or a null pointer if c does not occur in the
string.
7.15.5.6 The strspn function
Synopsis
[#1]
#include <string.h>
size_t strspn(const char *s1, const char *s2);
Description
[#2] The strspn function computes the length of the maximum
initial segment of the string pointed to by s1 which
consists entirely of characters from the string pointed to
by s2.
Returns
[#3] The strspn function returns the length of the segment.
7.15.5.7 The strstr function
Synopsis
[#1]
#include <string.h>
char *strstr(const char *s1, const char *s2);
Description
[#2] The strstr function locates the first occurrence in the
string pointed to by s1 of the sequence of characters
(excluding the terminating null character) in the string
pointed to by s2
page 405 Library
page 406
Returns
[#3] The strstr function returns a pointer to the located
string, or a null pointer if the string is not found. If s2
points to a string with zero length, the function returns
s1.
7.15.5.8 The strtok function
Synopsis
[#1]
#include <string.h>
char *strtok(char * restrict s1,
const char * restrict s2);
Description
[#2] A sequence of calls to the strtok function breaks the
string pointed to by s1 into a sequence of tokens, each of
which is delimited by a character from the string pointed to
by s2. The first call in the sequence has s1 as its first
argument, and is followed by calls with a null pointer as
their first argument. The separator string pointed to by s2
may be different from call to call.
[#3] The first call in the sequence searches the string
pointed to by s1 for the first character that is not
contained in the current separator string pointed to by s2.
If no such character is found, then there are no tokens in
the string pointed to by s1 and the strtok function returns
a null pointer. If such a character is found, it is the
start of the first token.
[#4] The strtok function then searches from there for a
character that is contained in the current separator string.
If no such character is found, the current token extends to
the end of the string pointed to by s1, and subsequent
searches for a token will return a null pointer. If such a
character is found, it is overwritten by a null character,
which terminates the current token. The strtok function
saves a pointer to the following character, from which the
next search for a token will start.
[#5] Each subsequent call, with a null pointer as the value
of the first argument, starts searching from the saved
pointer and behaves as described above.
[#6] The implementation shall behave as if no library
function calls the strtok function.
page 406 Library
page 407
Returns
[#7] The strtok function returns a pointer to the first
character of a token, or a null pointer if there is no
token.
Examples
#include <string.h>
static char str[] = "?a???b,,,#c";
char *t;
t = strtok(str, "?"); // t points to the token "a"
t = strtok(NULL, ","); // t points to the token "??b"
t = strtok(NULL, "#,"); // t points to the token "c"
t = strtok(NULL, "?"); // t is a null pointer
7.15.6 Miscellaneous functions
7.15.6.1 The memset function
Synopsis
[#1]
#include <string.h>
void *memset(void *s, int c, size_t n);
Description
[#2] The memset function copies the value of c (converted to
an unsigned char) into each of the first n characters of the
object pointed to by s.
Returns
[#3] The memset function returns the value of s.
7.15.6.2 The strerror function
Synopsis
[#1]
#include <string.h>
char *strerror(int errnum);
page 407 Library
page 408
Description
[#2] The strerror function maps the number in errnum to a
message string. Typically, the values for errnum come from
errno, but strerror shall map any value of type int to a
message.
[#3] The implementation shall behave as if no library
function calls the strerror function.
Returns
[#4] The strerror function returns a pointer to the string,
the contents of which are locale-specific. The array
pointed to shall not be modified by the program, but may be
overwritten by a subsequent call to the strerror function.
7.15.6.3 The strlen function
Synopsis
[#1]
#include <string.h>
size_t strlen(const char *s);
Description
[#2] The strlen function computes the length of the string
pointed to by s.
Returns
[#3] The strlen function returns the number of characters
that precede the terminating null character.
page 408 Library
page 409
7.16 Date and time <time.h>
7.16.1 Components of time
[#1] The header <time.h> defines four macros, and declares
four types and several functions for manipulating time.
Many functions deal with a calendar time that represents the
current date (according to the Gregorian calendar) and time.
Some functions deal with local time, which is the calendar
time expressed for some specific time zone, and with
Daylight Saving Time, which is a temporary change in the
algorithm for determining local time. The local time zone
and Daylight Saving Time are implementation-defined.
[#2] The macros defined are NULL (described in 7.1.6);
CLOCKS_PER_SEC
which expands to a constant expression with the type clock_t
described below, and which is the number per second of the
value returned by the clock function;
_NO_LEAP_SECONDS
(described in 7.16.2.4); and
_LOCALTIME // must be outside the range [-14400, +14400]
(described in 7.16.2.4).
[#3] The types declared are size_t (described in 7.1.6);
clock_t
and
time_t
which are arithmetic types capable of representing times;
struct tm
which holds the components of a calendar time, called the
broken-down time; and
struct tmx
which is an extended version of struct tm.
[#4] The tm structure shall contain at least the following
members, in any order. The semantics of the members and
page 409 Library
page 410
their normal ranges are expressed in the comments.236
int tm_sec; // seconds after the minute - [0, 60]
int tm_min; // minutes after the hour - [0, 59]
int tm_hour; // hours since midnight - [0, 23]
int tm_mday; // day of the month - [1, 31]
int tm_mon; // months since January - [0, 11]
int tm_year; // years since 1900
int tm_wday; // days since Sunday - [0, 6]
int tm_yday; // days since January 1 - [0, 365]
int tm_isdst; // Daylight Saving Time flag
The value of tm_isdst is positive if Daylight Saving Time is
in effect, zero if Daylight Saving Time is not in effect,
and negative if the information is not available.
[#5] The tmx structure shall contain all the members of
struct tm in a manner such that all these members are part
of a common initial subsequence. In addition, it contains
the members:
int tm_version; // version number
int tm_zone; // time zone offset in minutes
// from UTC [-1439, +1439]
int tm_leapsecs; // number of leap seconds applied
void *tm_ext; // extension block
size_t tm_extlen; // size of the extension block
The meaning of tm_isdst is also different: it is the
positive number of minutes of offset if Daylight Saving Time
is in effect, zero if Daylight Saving Time is not in effect,
and - 1 if the information is not available. A positive
value for tm_zone indicates a time that is ahead of
Coordinated Universal Time (UTC). The implementation or a
future version of this International Standard may include
further members in a separate object. If so, the tm_ext
member shall point to this object and the tm_extlen object
shall be its size. Otherwise, the tm_ext member shall be a
null pointer and the value of the tm_extlen object is
unspecified.
__________
236. The range [0, 60] for tm_sec allows for a positive leap
second.
page 410 Library
page 411
7.16.2 Time manipulation functions
7.16.2.1 The clock function
Synopsis
[#1]
#include <time.h>
clock_t clock(void);
Description
[#2] The clock function determines the processor time used.
Returns
[#3] The clock function returns the implementation's best
approximation to the processor time used by the program
since the beginning of an implementation-defined era related
only to the program invocation. To determine the time in
seconds, the value returned by the clock function should be
divided by the value of the macro CLOCKS_PER_SEC. If the
processor time used is not available or its value cannot be
represented, the function returns the value (clock_t)-1.237
7.16.2.2 The difftime function
Synopsis
[#1]
#include <time.h>
double difftime(time_t time1, time_t time0);
Description
[#2] The difftime function computes the difference between
two calendar times: time1 - time0.
__________
237. In order to measure the time spent in a program, the
clock function should be called at the start of the
program and its return value subtracted from the value
returned by subsequent calls.
page 411 Library
page 412
Returns
[#3] The difftime function returns the difference expressed
in seconds as a double.
7.16.2.3 The mktime function
Synopsis
[#1]
#include <time.h>
time_t mktime(struct tm *timeptr);
Description
[#2] The mktime function converts the broken-down time,
expressed as local time, in the structure pointed to by
timeptr into a calendar time value with the same encoding as
that of the values returned by the time function. The
original values of the tm_wday and tm_yday components of the
structure are ignored, and the original values of the other
components are not restricted to the ranges indicated
above.238 On successful completion, the values of the
tm_wday and tm_yday components of the structure are set
appropriately, and the other components are set to represent
the specified calendar time, but with their values forced to
the ranges indicated above; the final value of tm_mday is
not set until tm_mon and tm_year are determined.
[#3] The normalization process shall be as described in
subclause 7.16.2.6.
[#4] If the call is successful, a second call to the mktime
function with the resulting struct tm value shall always
leave it unchanged and return the same value as the first
call. Furthermore, if the normalized time is exactly
representable as a time_t value, then the normalized
broken-down time and the broken-down time generated by
converting the result of the mktime function by a call to
__________
238. Thus, a positive or zero value for tm_isdst causes the
mktime function to presume initially that Daylight
Saving Time, respectively, is or is not in effect for
the specified time. A negative value causes it to
attempt to determine whether Daylight Saving Time is in
effect for the specified time.
page 412 Library
page 413
localtime shall be identical.
Returns
[#5] The mktime function returns the specified calendar time
encoded as a value of type time_t. If the calendar time
cannot be represented, the function returns the value
(time_t)-1. The normalization process shall be as described
in subclause 7.16.2.6.
[#6] If the call is successful, a second call to the mktime
function with the resulting struct tm value shall always
leave it unchanged and return the same value as the first
call. Furthermore, if the normalized time is exactly
representable as a time_t value, then the normalized
broken-down time and the broken-down time generated by
converting the result of the mktime function by a call to
localtime shall be identical.
Examples
[#7] What day of the week is July 4, 2001?
[#8]
#include <stdio.h>
#include <time.h>
static const char *const wday[] = {
"Sunday", "Monday", "Tuesday", "Wednesday",
"Thursday", "Friday", "Saturday", "-unknown-"
};
struct tm time_str;
/* ... */
time_str.tm_year = 2001 - 1900;
time_str.tm_mon = 7 - 1;
time_str.tm_mday = 4;
time_str.tm_hour = 0;
time_str.tm_min = 0;
time_str.tm_sec = 1;
time_str.tm_isdst = -1;
if (mktime(&time_str) == (time_t)-1)
time_str.tm_wday = 7;
printf("%s\n", wday[time_str.tm_wday]);
page 413 Library
page 414
7.16.2.4 The mkxtime function
Synopsis
[#1]
#include <time.h>
time_t mkxtime(struct tmx *timeptr);
Description
[#2] The mkxtime function has the same behavior and result
as the mktime function except that it takes into account of
the additional members.
[#3] If the value of the tm_version member is not 1, the
behavior is undefined. If the implementation cannot
determine the relationship between local time and UTC, it
shall set the tm_zone member of the pointed-to structure to
_LOCALTIME. Otherwise, if the tm_zone member was
_LOCALTIME, it shall be set to the offset of local time from
UTC, include the effects of the value of the tm_isdst
member; otherwise, the original value of the tm_isdst member
does not affect the result.
[#4] If the tm_leapsecs member is equal to _NO_LEAP_SECONDS,
then the implementation shall determine the number of leap
seconds that apply and set the member accordingly (or use 0
if it cannot determine it); otherwise, it shall use the
number of leap seconds given. The tm_leapsecs member shall
then be set to the number of leap seconds actually applied
to produce the value represented by the structure, or to
_NO_LEAP_SECONDS if it was not possible to determine it.
[#5] If the call is successful, a second call to the mkxtime
function with the resulting struct tmx value shall always
leave it unchanged and return the same value as the first
call. Furthermore, if the normalized time is exactly
representable as a time_t value, then the normalized
broken-down time and the broken-down time generated by
converting the result of the mkxtime function by a call to
zonetime (with zone set to the value of the tm_zone member)
shall be identical.
page 414 Library
page 415
7.16.2.5 The time function
Synopsis
[#1]
#include <time.h>
time_t time(time_t *timer);
Description
[#2] The time function determines the current calendar time.
The encoding of the value is unspecified.
Returns
[#3] The time function returns the implementation's best
approximation to the current calendar time. The value
(time_t)-1 is returned if the calendar time is not
available. If timer is not a null pointer, the return value
is also assigned to the object it points to.
7.16.2.6 Normalization of broken-down times
[#1] A broken-down time is normalized by the mkxtime
function in the following manner. A broken-down time is
normalized by the mktime function in the same manner, but as
if the struct tm structure had been replaced by a struct tmx
structure containing the same values except:
tm_version is 1
tm_zone is _LOCALTIME
tm_leapsecs is _NO_LEAP_SECONDS
tm_isdst is - 1, 0, or an implementation-defined
positive value according to whether the
original member is less than, equal to, or
greater than zero
[#2] If any of the following members is outside the
indicated range (where L is LONG_MAX/8), the behavior is
undefined:
tm_year [-L/366, +L/366]
tm_mon [-L/31, +L/31]
tm_mday [-L, +L]
page 415 Library
page 416
tm_hour [-L/3600, +L/3600]
tm_min [-L/60, +L/60]
tm_sec [-L, +L]
tm_leapsecs [-L, +L] or _NO_LEAP_SECONDS
tm_zone [-L/60, +L/60]
tm_isdst [-L/60, +L/60] or _LOCALTIME
The tm_version member shall be 1.
[#3] Values S and D shall be determined as follows:
#define QUOT(a,b) ((a)>0 ? (a)/(b) : -(((b)-(a)-1)/(b)))
#define REM(a,b) ((a)-(b)*QUOT(a,b))
SS = tm_hour*3600 + tm_min*60 +tm_sec +
(tm_leapsecs == _NO_LEAP_SECONDS ? X1 :
tm_leapsecs) -
(tm_zone == _LOCALTIME ? X2 : tm_zone) * 60;
// X1 is the appropriate number of leap seconds, determined by
// the implementation, or 0 if it cannot be determined.
// X2 is the appropriate offset from local time to UTC,
// determined by the implementation, or
// (tm_isdst >= 0 ? tm_isdst : 0)
M = REM(tm_mon, 12);
Y = tm_year + 1900 + QUOT(tm_mon, 12);
Z = Y - (M < 2 ? 1 : 0);
D = Y*365 + (Z/400)*97 + (Z%400)/4 +
M[(int []){0,31,59,90,120,151,181,212,243,273,
304,335}] +
tm_mday + QUOT(SS, 86400);
S = REM(SS, 86400);
[#4] The normalized broken-down time shall produce the same
values of S and D (though possibly different values of M, Y,
and Z) as the original broken-down time.239
__________
239. The effect of the above rules is to consistently use
the Gregorian calendar, regardless of which calendar was
in use in which year. In particular, the years 1100 and
- 300 are not leap years, while the years 1200 and -400
are (these 4 years correspond to tm_year values of -800,
page 416 Library
page 417
7.16.3 Time conversion functions
[#1] Except for the strftime and strfxtime functions, these
functions each return a pointer to one of two types of
static objects: a broken-down time structure or an array of
char. Execution of any of the functions that return a
pointer to one of these object types may overwrite the
information in any object of the same type pointed to by the
value returned from any previous call to any of them. The
implementation shall behave as if no other library functions
call these functions.
7.16.3.1 The asctime function
Synopsis
[#1]
#include <time.h>
char *asctime(const struct tm *timeptr);
Description
[#2] The asctime function converts the broken-down time in
the structure pointed to by timeptr into a string in the
form
Sun Sep 16 01:03:52 1973\n\0
using the equivalent of the following algorithm.
char *asctime(const struct tm *timeptr)
{
static const char wday_name[7][3] = {
"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
};
static const char mon_name[12][3] = {
"Jan", "Feb", "Mar", "Apr", "May", "Jun",
"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};
static char result[26];
____________________________________________________________
- 2200, - 700, and -2300 respectively, and the last of
these is 401 B.C.E.). In the normalized broken-down
time, tm_wday is equal to QUOT(D-2,7).
page 417 Library
page 418
sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
wday_name[timeptr->tm_wday],
mon_name[timeptr->tm_mon],
timeptr->tm_mday, timeptr->tm_hour,
timeptr->tm_min, timeptr->tm_sec,
1900 + timeptr->tm_year);
return result;
}
Returns
[#3] The asctime function returns a pointer to the string.
7.16.3.2 The ctime function
Synopsis
[#1]
#include <time.h>
char *ctime(const time_t *timer);
Description
[#2] The ctime function converts the calendar time pointed
to by timer to local time in the form of a string. It is
equivalent to
asctime(localtime(timer))
Returns
[#3] The ctime function returns the pointer returned by the
asctime function with that broken-down time as argument.
Forward references: the localtime function (7.16.3.4).
7.16.3.3 The gmtime function
Synopsis
[#1]
#include <time.h>
struct tm *gmtime(const time_t *timer);
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Description
[#2] The gmtime function converts the calendar time pointed
to by timer into a broken-down time, expressed as UTC.
Returns
[#3] The gmtime function returns a pointer to that object,
or a null pointer if UTC is not available.
7.16.3.4 The localtime function
Synopsis
[#1]
#include <time.h>
struct tm *localtime(const time_t *timer);
Description
[#2] The localtime function converts the calendar time
pointed to by timer into a broken-down time, expressed as
local time.
Returns
[#3] The localtime function returns a pointer to that
object.
7.16.3.5 The zonetime function
Synopsis
[#1]
#include <time.h>
struct tmx *zonetime(const time_t *timer, int zone);
Description
[#2] The zonetime function converts the calendar time
pointed to by timer into a broken-down time as represented
in the specified time zone. The tm_version member is set to
1. If the implementation cannot determine the relationship
between local time and UTC, it shall set the tm_zone member
to _LOCALTIME; otherwise, it shall set the tm_zone member to
the value of zone unless the latter is _LOCALTIME, in which
case it shall set it to the offset of local time from UTC.
The value shall include the effect of Daylight Saving Time,
if in effect. The tm_leapsecs member shall be set to the
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number of leap seconds (the UTC-UT1 offset) applied in the
result240 if it can be determined, or to the value
_NO_LEAP_SECONDS if it cannot (and so none were applied).
Returns
[#3] The zonetime function returns a pointer to that object.
7.16.3.6 The strftime function
Synopsis
[#1]
#include <time.h>
size_t strftime(char * restrict s,
size_t maxsize,
const char * restrict format,
const struct tm * restrict timeptr);
Description
[#2] The strftime function places characters into the array
pointed to by s as controlled by the string pointed to by
format. The format shall be a multibyte character sequence,
beginning and ending in its initial shift state. The format
string consists of zero or more conversion specifiers and
ordinary multibyte characters. A conversion specifier
consists of a % character followed by a character that
determines the behavior of the conversion specifier. All
ordinary multibyte characters (including the terminating
null character) are copied unchanged into the array. If
copying takes place between objects that overlap, the
behavior is undefined. No more than maxsize characters are
placed into the array. Each conversion specifier is
replaced by appropriate characters as described in the
following list. The appropriate characters are determined
by the LC_TIME category of the current locale and by the
values contained in the structure pointed to by timeptr.
%a is replaced by the locale's abbreviated weekday name.
[tm_wday]
%A is replaced by the locale's full weekday name.
[tm_wday]
__________
240. If the tm_sec member is set to 60, that leap second
shall not be included in the value of tm_leapsecs.
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%b is replaced by the locale's abbreviated month name.
[tm_mon]
%B is replaced by the locale's full month name. [tm_mon]
%c is replaced by the locale's appropriate date and time
representation. [all specified in 7.16.1]
%d is replaced by the day of the month as a decimal
number (01-31). [tm_mday]
%F is equivalent to "%Y-%m-%d" (the ISO 8601 date
format). [tm_year, tm_mon, tm_mday]
%g is replaced by the last 2 digits of the week-based
year (see below) as a decimal number (00-99).
[tm_year, tm_wday, tm_yday]
%G is replaced by the week-based year (see below) as a
decimal number (e.g., 1997). [tm_year, tm_wday,
tm_yday]
%H is replaced by the hour (24-hour clock) as a decimal
number (00-23). [tm_hour]
%I is replaced by the hour (12-hour clock) as a decimal
number (01-12). [tm_hour]
%j is replaced by the day of the year as a decimal number
(001-366). [tm_yday]
%m is replaced by the month as a decimal number (01-12).
[tm_mon]
%M is replaced by the minute as a decimal number (00-59).
[tm_min]
%p is replaced by the locale's equivalent of the AM/PM
designations associated with a 12-hour clock.
[tm_hour]
%S is replaced by the second as a decimal number (00-60).
[tm_sec]
%T is equivalent to "%H:%M:%S" (the ISO 8601 time
format). [tm_hour, tm_min, tm_sec]
%u is replaced by the weekday as a decimal number (1-7),
where Monday is 1 (the ISO 8601 weekday number).
[tm_wday]
%U is replaced by the week number of the year (the first
Sunday as the first day of week 1) as a decimal number
(00-53). [tm_year, tm_wday, tm_yday]
%V is replaced by the ISO 8601 week number (see below) as
a decimal number (01-53). [tm_year, tm_wday, tm_yday]
%w is replaced by the weekday as a decimal number (0-6),
where Sunday is 0. [tm_wday]
%W is replaced by the week number of the year (the first
Monday as the first day of week 1) as a decimal number
(00-53). [tm_year, tm_wday, tm_yday]
%x is replaced by the locale's appropriate date
representation. [all specified in 7.16.1]
%X is replaced by the locale's appropriate time
representation. [all specified in 7.16.1]
%y is replaced by the last 2 digits of the year as a
decimal number (00-99). [tm_year]
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%Y is replaced by the whole year as a decimal number
(e.g., 1997). [tm_year]
%z is replaced by the offset from UTC in the form "-0430"
(meaning 4 hours 30 minutes behind UTC, west of
Greenwich). This is the ISO 8601 format. [tm_isdst]
%Z is replaced by the time zone name or abbreviation, or
by no characters if no time zone is determinable.
[tm_isdst]
%% is replaced by %.
[#3] %g, %G, and %V give values according to the ISO 8601
week-based year. In this system, weeks begin on a Monday
and week 1 of the year is the week that includes both
January 4th and the first Thursday of the year. If the
first Monday of January is the 2nd, 3rd, or 4th, the
preceding days are part of the last week of the preceding
year; thus Saturday 2nd January 1999 has %G == 1998 and %V
== 53. If December 29th, 30th, or 31st is a Monday, it and
any following days are part of week 1 of the following year.
Thus, Tuesday 30th December 1997 has %G == 1998 and %V == 1.
[#4] If a conversion specifier is not one of the above, the
behavior is undefined.
[#5] The characters placed in the array by each conversion
specifier depend on one or more members of the structure
pointed to by timeptr, as specified in brackets in the
description. If this value is outside the normal range, the
characters stored are unspecified.
[#6] In the "C" locale the replacement strings for the
following specifiers are:
%a the first three characters of %A.
%A one of "Sunday", "Monday", ..., "Saturday".
%b the first three characters of %B.
%B one of "January", "February", ..., "December".
%c equivalent to "%A %B %d %T %Y".
%P one of "am" or "pm".
%x equivalent to "%A %B %d %Y".
%X equivalent to %T.
%Z implementation-defined.
Returns
[#7] If the total number of resulting characters including
the terminating null character is not more than maxsize, the
strftime function returns the number of characters placed
into the array pointed to by s not including the terminating
null character. Otherwise, zero is returned and the
contents of the array are indeterminate.
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7.16.3.7 The strfxtime function
Synopsis
[#1]
#include <time.h>
size_t strfxtime(char * restrict s,
size_t maxsize,
const char * restrict format,
const struct tmx * restrict timeptr);
Description
[#2] The behavior and result of the strfxtime is identical
to that of the strftime function, except that the timeptr
parameter has a different type, and the %z and %Z conversion
specifiers depend on both the tm_zone and tm_isdst members.
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7.17 Alternative spellings <iso646.h>
[#1] The header <iso646.h> defines the following eleven
macros (on the left) that expand to the corresponding tokens
(on the right):
and &&
and_eq &=
bitand &
bitor |
compl ~
not !
not_eq !=
or ||
or_eq |=
xor ^
xor_eq ^=
page 424 Library
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7.18 Wide-character classification and mapping utilities <wctype.h>
7.18.1 Introduction
[#1] The header <wctype.h> declares three data types, one
macro, and many functions.241
[#2] The types declared are
wint_t
which is an integer type unchanged by default argument
promotions that can hold any value corresponding to members
of the extended character set, as well as at least one value
that does not correspond to any member of the extended
character set. (See WEOF below.)242
wctrans_t
which is a scalar type that can hold values which represent
locale-specific character mappings, and
wctype_t
which is a scalar type that can hold values which represent
locale-specific character classifications.
[#3] The macro defined is
WEOF
which expands to a constant expression of type wint_t whose
value does not correspond to any member of the extended
character set.243 It is accepted (and returned) by several
functions in this subclause to indicate end-of-file, that
is, no more input from a stream. It is also used as a wide-
character value that does not correspond to any member of
the extended character set.
__________
241. See ``future library directions'' (7.20).
242. wchar_t and wint_t can be the same integer type.
243. The value of the macro WEOF may differ from that of EOF
and need not be negative.
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[#4] The functions declared are grouped as follows:
- Functions that provide wide-character classification;
- Extensible functions that provide wide-character
classification;
- Functions that provide wide-character case mapping;
- Extensible functions that provide wide-character
mapping.
[#5] For all functions described in this subclause that
accept an argument of type wint_t, the value shall be
representable as a wchar_t or shall equal the value of the
macro WEOF. If this argument has any other value, the
behavior is undefined.
[#6] The behavior of these functions is affected by the
LC_CTYPE category of the current locale.
7.18.2 Wide-character classification utilities
[#1] The header <wctype.h> declares several functions useful
for classifying wide characters.
[#2] The term printing wide character refers to a member of
a locale-specific set of wide characters, each of which
occupies at least one printing position on a display device.
The term control wide character refers to a member of a
locale-specific set of wide characters that are not printing
wide characters.
7.18.2.1 Wide-character classification functions
[#1] The functions in this subclause return nonzero (true)
if and only if the value of the argument wc conforms to that
in the description of the function.
[#2] Except for the iswgraph and iswpunct functions with
respect to printing, white-space, wide characters other than
L' ', each of the following eleven functions returns true
for each wide character that corresponds (as if by a call to
the wctob function) to a character (byte) for which the
respectively matching character testing function from
subclause 7.3.1 returns true.244
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[#3] Forward References: the wctob function (7.19.7.1.2).
7.18.2.1.1 The iswalnum function
Synopsis
[#1]
#include <wctype.h>
int iswalnum(wint_t wc);
Description
[#2] Th iswalnum function tests for any wide character for
which iswalpha or iswdigit is true.
7.18.2.1.2 The iswalpha function
Synopsis
[#1]
#include <wctype.h>
int iswalpha(wint_t wc);
Description
[#2] The iswalpha function tests for any wide character for
which iswupper or iswlower is true, or any wide character
that is one of a locale-specific set of wide characters for
which none of iswcntrl, iswdigit, iswpunct, or iswspace is
true.245
__________
244. For example, if the expression isalpha(wctob(wc))
evaluates to true, then the call iswalpha(wc) must also
return true. But, if the expression isgraph(wctob(wc))
evaluates to true (which cannot occur for wc == L' ' of
course), then either iswgraph(wc) or iswprint(wc) &&
iswspace(wc) must be true, but not both.
245. The functions iswlower and iswupper test true or false
separately for each of these additional wide characters;
all four combinations are possible.
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7.18.2.1.3 The iswblank function
Synopsis
[#1]
#include <ctype.h>
int iswblank(int c);
Description
[#2] The iswblank function tests for any wide character for
that is a standard blank wide character or is one of a
locale-specific set of wide characters, for which iswalnum
is false. The standard blank wide characters are the
following: space (L' '), and horizontal tab (L'\t'). In the
"C" locale, iswblank returns true only for the standard
blank characters.
7.18.2.1.4 The iswcntrl function
Synopsis
[#1]
#include <wctype.h>
int iswcntrl(wint_t wc);
Description
[#2] The iswcntrl function tests for any control wide
character.
7.18.2.1.5 The iswdigit function
Synopsis
[#1]
#include <wctype.h>
int iswdigit(wint_t wc);
Description
[#2] The iswdigit function tests for any wide character that
corresponds to a decimal-digit character (as defined in
subclause 5.2.1).
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7.18.2.1.6 The iswgraph function
Synopsis
[#1]
#include <wctype.h>
int iswgraph(wint_t wc);
Description
[#2] The iswgraph function tests for any wide character for
which iswprint is true and iswspace is false.246
7.18.2.1.7 The iswlower function
Synopsis
[#1]
#include <wctype.h>
int iswlower(wint_t wc);
Description
[#2] The iswlower function tests for any wide character that
corresponds to a lowercase letter or is one of a locale-
specific set of wide characters for which none of iswcntrl,
iswdigit, iswpunct, or iswspace is true.
7.18.2.1.8 The iswprint function
Synopsis
[#1]
#include <wctype.h>
int iswprint(wint_t wc);
__________
246. Note that the behavior of the iswgraph and iswpunct
functions may differ from their matching functions in
subclause 7.3.1 with respect to printing, white-space,
basic execution characters other than ' '.
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Description
[#2] The iswprint function tests for any printing wide
character.
7.18.2.1.9 The iswpunct function
Synopsis
[#1]
#include <wctype.h>
int iswpunct(wint_t wc);
Description
[#2] The iswpunct function tests for any printing wide
character that is one of a locale-specific set of wide
characters for which neither iswspace nor iswalnum is
true.246
7.18.2.1.10 The iswspace function
Synopsis
[#1]
#include <wctype.h>
int iswspace(wint_t wc);
Description
[#2] The iswspace function tests for any wide character that
corresponds to a locale-specific set of wide characters for
which none of iswalnum, iswgraph, or iswpunct is true.
7.18.2.1.11 The iswupper function
Synopsis
[#1]
#include <wctype.h>
int iswupper(wint_t wc);
Description
[#2] The iswupper function tests for any wide character that
corresponds to an uppercase letter or is one of a locale-
specific set of wide characters for which none of iswcntrl,
iswdigit, iswpunct, or iswspace is true.
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7.18.2.1.12 The iswxdigit function
Synopsis
[#1]
#include <wctype.h>
int iswxdigit(wint_t wc);
Description
[#2] The iswxdigit function tests for any wide character
that corresponds to a hexadecimal-digit character (as
defined in subclause 6.1.3.2).
7.18.2.2 Extensible wide-character classification functions
[#1] The functions wctype and iswctype provide extensible
wide-character classification as well as testing equivalent
to that performed by the functions described in the previous
subclause (4.5.2.1).
7.18.2.2.1 The wctype function
Synopsis
[#1]
#include <wctype.h>
wctype_t wctype(const char *property);
Description
[#2] The wctype function constructs a value with type
wctype_t that describes a class of wide characters
identified by the string argument property.
[#3] The eleven strings listed in the description of the
iswctype function shall be valid in all locales as property
arguments to the wctype function.
Returns
[#4] If property identifies a valid class of wide characters
according to the LC_CTYPE category of the current locale,
the wctype function returns a nonzero value that is valid as
the second argument to the iswctype function; otherwise, it
returns zero.
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7.18.2.2.2 The iswctype function
Synopsis
[#1]
#include <wctype.h>
int iswctype(wint_t wc, wctype_t desc);
Description
[#2] The iswctype function determines whether the wide
character wc has the property described by desc. The
current setting of the LC_CTYPE category shall be the same
as during the call to wctype that returned the value desc.
[#3] Each of the following eleven expressions has a truth-
value equivalent to the call to the wide-character testing
function (4.5.2.1) in the comment that follows the
expression:
iswctype(wc, wctype("alnum")) // iswalnum(wc)
iswctype(wc, wctype("alpha")) // iswalpha(wc)
iswctype(wc, wctype("cntrl")) // iswcntrl(wc)
iswctype(wc, wctype("digit")) // iswdigit(wc)
iswctype(wc, wctype("graph")) // iswgraph(wc)
iswctype(wc, wctype("lower")) // iswlower(wc)
iswctype(wc, wctype("print")) // iswprint(wc)
iswctype(wc, wctype("punct")) // iswpunct(wc)
iswctype(wc, wctype("space")) // iswspace(wc)
iswctype(wc, wctype("upper")) // iswupper(wc)
iswctype(wc, wctype("xdigit")) // iswxdigit(wc)
Returns
[#4] The iswctype function returns nonzero (true) if and
only if the value of the wide character wc has the property
described by desc.
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7.18.3 Wide-character mapping utilities
[#1] The header <wctype.h> declares several functions useful
for mapping wide characters.
7.18.3.1 Wide-character case-mapping functions
7.18.3.1.1 The towlower function
Synopsis
[#1]
#include <wctype.h>
wint_t towlower(wint_t wc);
Description
[#2] The towlower function converts an uppercase letter to a
corresponding lowercase letter.
Returns
[#3] If the argument is a wide character for which iswupper
is true and there are one or more corresponding wide
characters, as specified by the current locale, for which
iswlower is true, the towlower function returns one of the
corresponding wide characters (always the same one for any
given locale); otherwise, the argument is returned
unchanged.
7.18.3.1.2 The towupper function
Synopsis
[#1]
#include <wctype.h>
wint_t towupper(wint_t wc);
Description
[#2] The towupper function converts a lowercase letter to a
corresponding uppercase letter.
Returns
[#3] If the argument is a wide character for which iswlower
is true and there are one or more corresponding characters,
as specified by the current locale, for which iswupper is
true, the towupper function returns one of the corresponding
page 433 Library
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characters (always the same one for any given locale);
otherwise, the argument is returned unchanged.
7.18.3.2 Extensible wide-character mapping functions
[#1] The functions wctrans and towctrans provide extensible
wide-character mapping as well as case mapping equivalent to
that performed by the functions described in the previous
subclause (7.18.3.1).
7.18.3.2.1 The wctrans function
Synopsis
[#1]
#include <wctype.h>
wctrans_t wctrans(const char *property);
Description
[#2] The wctrans function constructs a value with type
wctrans_t that describes a mapping between wide characters
identified by the string argument property.
[#3] The two strings listed in the description of the
towctrans function shall be valid in all locales as property
arguments to the wctrans function.
Returns
[#4] If property identifies a valid mapping of wide
characters according to the LC_CTYPE category of the current
locale, the wctrans function returns a nonzero value that is
valid as the second argument to the towctrans function;
otherwise, it returns zero.
7.18.3.2.2 The towctrans function
Synopsis
[#1]
#include <wctype.h>
wint_t towctrans(wint_t wc, wctrans_t desc);
page 434 Library
page 435
Description
[#2] The towctrans function maps the wide character wc using
the mapping described by desc. The current setting of the
LC_CTYPE category shall be the same as during the call to
wctrans that returned the value desc.
[#3] Each of the following two expressions behaves the same
as the call to the wide-character case-mapping function
(7.18.3.1) in the comment that follows the expression:
towctrans(wc, wctrans("tolower")) /* towlower(wc) */
towctrans(wc, wctrans("toupper")) /* towupper(wc) */
Returns
[#4] The towctrans function returns the mapped value of wc
using the mapping described by desc.
page 435 Library
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7.19 Extended multibyte and wide-character utilities <wchar.h>
7.19.1 Introduction
[#1] The header <wchar.h> declares four data types, one tag,
four macros, and many functions.247
[#2] The types declared are wchar_t and size_t (both
described in subclause 7.1.6),
mbstate_t
[#3] which is an object type other than an array type that
can hold the conversion state information necessary to
convert between sequences of multibyte characters and wide
characters, and
wint_t
[#4] described in subclause 7.18.1.
[#5] The tag tm is declared as naming an incomplete
structure type, the contents of which are described in
subclause 7.15.1.
[#6] The macros defined are NULL (described in subclause
7.1.6),
WCHAR_MAX
[#7] which is the maximum value representable by an object
of type wchar_t,248
WCHAR_MIN
[#8] which is the minimum value representable by an object
of type wchar_t, and
WEOF
__________
247. See ``future library directions'' (7.20).
248. The values WCHAR_MAX and WCHAR_MIN do not necessarily
correspond to members of the extended character set.
page 436 Library
page 437
[#9] described in subclause 7.18.1.
[#10] The functions declared are grouped as follows:
- Functions that perform input and output of wide
characters, or multibyte characters, or both;
- Functions that provide wide-string numeric conversion;
- Functions that perform general wide-string
manipulation;
- A function for wide-string date and time conversion;
and
- Functions that provide extended capabilities for
conversion between multibyte and wide-character
sequences.
[#11] Unless explicitly stated otherwise, if the execution
of a function described in this subclause causes copying to
take place between objects that overlap, the behavior is
undefined.
7.19.2 Formatted wide-character input/output functions
[#1] The formatted wide-character input/output functions249
shall behave as if there is a sequence point after the
actions associated with each specifier.
7.19.2.1 The fwprintf function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
int fwprintf(FILE * restrict stream,
const wchar_t * restrict format, ...);
__________
249. The fwprintf functions perform writes to memory for the
%n specifier.
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Description
[#2] The fwprintf function writes output to the stream
pointed to by stream, under control of the wide string
pointed to by format that specifies how subsequent arguments
are converted for output. If there are insufficient
arguments for the format, the behavior is undefined. If the
format is exhausted while arguments remain, the excess
arguments are evaluated (as always) but are otherwise
ignored. The fwprintf function returns when the end of the
format string is encountered. The fwprintf function returns
when the end of the format string is encountered.
[#3] The format is composed of zero or more directives:
ordinary wide characters (not %), and conversion
specifications. The processing of conversion specifications
is as if they were replaced in the format string by wide-
character strings that are each the result of fetching zero
or more subsequent arguments and converting them, if
applicable, according to the corresponding conversion
specifier. The expanded wide-character format string is
then written to the output stream.
[#4] Each conversion specification is introduced by the wide
character %. After the %, the following appear in sequence:
- Zero or more flags (in any order) that modify the
meaning of the conversion specification.
- An optional minimum field width. If the converted value
has fewer wide characters than the field width, it is
padded with spaces (by default) on the left (or right,
if the left adjustment flag, described later, has been
given) to the field width. The field width takes the
form of an asterisk * (described later) or a decimal
integer.250
- An optional precision that gives the minimum number of
digits to appear for the d, i, o, u, x, and X
conversions, the number of digits to appear after the
decimal-point character for a, A, e, E, f, and F
conversions, the maximum number of significant digits
for the g and G conversions, or the maximum number of
wide characters to be written from a string in s
__________
250. Note that 0 is taken as a flag, not as the beginning of
a field width.
page 438 Library
page 439
conversions. The precision takes the form of a period
(.) followed either by an asterisk * (described later)
or by an optional decimal integer; if only the period
is specified, the precision is taken as zero. If a
precision appears with any other conversion specifier,
the behavior is undefined.
- An optional hh specifying that a following d, i, o, u,
x, or X conversion specifier applies to a signed char
or unsigned char argument (the argument will have been
promoted according to the integer promotions, and its
value shall be converted to signed char or unsigned
char before printing); an optional h specifying that a
following d, i, o, u, x, or X conversion specifier
applies to a short int or unsigned short int argument
(the argument will have been promoted according to the
integer promotions, and its value shall be converted to
short int or unsigned short int before printing); an
optional h specifying that a following n conversion
specifier applies to a pointer to a short int argument;
an optional l (ell) specifying that a following d, i,
o, u, x, or X conversion specifier applies to a long
int or unsigned long int argument; an optional ll
(ell-ell) specifying that a following d, i, o, u, x, or
X conversion specifier applies to a long long int or
unsigned long long int argument; an optional l
specifying that a following n conversion specifier
applies to a pointer to a long int argument; an
optional ll specifying that a following n conversion
specifier applies to a pointer to a long long int
argument; an optional l specifying that a following c
conversion specifier applies to a wint_t argument; an
optional l specifying that a following s conversion
specifier applies to a pointer to a wchar_t argument;
an optional l which has no effect on a following a, A,
e, E, f, F, g, or G conversion specifier; or an
optional L specifying that a following a, A, e, E, f,
F, g, or G conversion specifier applies to a long
double argument. If an hh, h, l, ll, or L appears with
any other conversion specifier, the behavior is
undefined.
- A wide character that specifies the type of conversion
to be applied.
[#5] As noted above, a field width, or precision, or both,
may be indicated by an asterisk. In this case, an int
argument supplies the field width or precision. The
arguments specifying field width, or precision, or both,
shall appear (in that order) before the argument (if any) to
be converted. A negative field width argument is taken as a
page 439 Library
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- flag followed by a positive field width. A negative
precision argument is taken as if the precision were
omitted.
[#6] The flag wide characters and their meanings are
- The result of the conversion is left-justified
within the field. (It is right-justified if this
flag is not specified.)
+ The result of a signed conversion always begins
with a plus or minus sign. (It begins with a sign
only when a negative value is converted if this
flag is not specified.)251
space If the first wide character of a signed conversion
is not a sign, or if a signed conversion results
in no wide characters, a space is prefixed to the
result. If the space and + flags both appear, the
space flag is ignored.
# The result is to be converted to an ``alternate
form''. For o conversion, it increases the
precision, if and only if necessary, to force the
first digit of the result to be a zero (if the
value and precision are both 0, a single 0 is
printed). For x (or X) conversion, a nonzero
result has 0x (or 0X) prefixed to it. For a, A, e,
E, f, F, g, and G conversions, the result always
contains a decimal-point wide character, even if
no digits follow it. (Normally, a decimal-point
wide character appears in the result of these
conversions only if a digit follows it.) For g and
G conversions, trailing zeros are not removed from
the result. For other conversions, the behavior
is undefined.
0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G
conversions, leading zeros (following any
indication of sign or base) are used to pad to the
field width; no space padding is performed. If the
0 and - flags both appear, the 0 flag is ignored.
For d, i, o, u, x, and X conversions, if a
__________
251. The results of all floating conversions of a negative
zero, and of negative values that round to zero, include
a minus sign.
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precision is specified, the 0 flag is ignored. For
other conversions, the behavior is undefined.
[#7] The conversion specifiers and their meanings are
d,i The int argument is converted to signed decimal in
the style [ - ]dddd. The precision specifies the
minimum number of digits to appear; if the value
being converted can be represented in fewer
digits, it is expanded with leading zeros. The
default precision is 1. The result of converting a
zero value with a precision of zero is no wide
characters.
o,u,x,X The unsigned int argument is converted to unsigned
octal (o), unsigned decimal (u), or unsigned
hexadecimal notation (x or X) in the style dddd;
the letters abcdef are used for x conversion and
the letters ABCDEF for X conversion. The precision
specifies the minimum number of digits to appear;
if the value being converted can be represented in
fewer digits, it is expanded with leading zeros.
The default precision is 1. The result of
converting a zero value with a precision of zero
is no wide characters.
f,F A double argument representing a floating-point
number is converted to decimal notation in the
style [-]ddd.ddd, where the number of digits after
the decimal-point wide character is equal to the
precision specification. If the precision is
missing, it is taken as 6; if the precision is
zero and the # flag is not specified, no decimal-
point wide character appears. If a decimal-point
wide character appears, at least one digit appears
before it. The value is rounded to the appropriate
number of digits.
A double argument representing an infinity is
converted to one of the styles [-]inf or [-
]infinity - which style is implementation-defined.
A double argument representing a NaN is converted
to one of the styles [-]nan or [-]nan(n-wchar-
sequence) - which style, and the meaning of any
n-wchar-sequence, is implementation-defined. The
F conversion specifier produces INF, INFINITY, or
NAN instead of inf, infinity, or nan,
respectively.252
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e,E A double argument representing a floating-point
number is converted in the style [-]d.ddde_dd,
where there is one digit before the decimal-point
wide character (which is nonzero if the argument
is nonzero) and the number of digits after it is
equal to the precision; if the precision is
missing, it is taken as 6; if the precision is
zero and the # flag is not specified, no decimal-
point wide character appears. The value is rounded
to the appropriate number of digits. The E
conversion specifier produces a number with E
instead of e introducing the exponent. The
exponent always contains at least two digits, and
only as many more digits as necessary to represent
the exponent. If the value is zero, the exponent
is zero.
A double argument representing an infinity or a
NaN is converted in the style of an f or F
conversion specifier.
g,G A double argument representing a floating-point
number is converted in style f or e (or in style F
or E in the case of a G conversion specifier),
with the precision specifying the number of
significant digits. If the precision is zero, it
is taken as 1. The style used depends on the value
converted; style e (or E) is used only if the
exponent resulting from such a conversion is less
than -4 or greater than or equal to the precision.
Trailing zeros are removed from the fractional
portion of the result; a decimal-point wide
character appears only if it is followed by a
digit. A double argument representing an infinity
or a NaN is converted in the style of an f or F
conversion specifier.
a,A A double argument representing a floating-point
number is converted in the style [-]0xh.hhhhp_d.
The number of hexadecimal digits h after the
decimal-point wide character is equal to the
precision; if the precision is missing and
FLT_RADIX is a power of 2, then the precision is
__________
252. When applied to infinite and NaN values, the -, +, and
space flag wide characters have their usual meaning; the
# and 0 flag wide characters have no effect.
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sufficient for an exact representation of the
value; if the precision is missing and FLT_RADIX
is not a power of 2, then the precision is
sufficient to distinguish253 values of type
double, except that trailing zeros may be omitted.
The hexadecimal digit to the left of the decimal-
point wide character is nonzero for normalized
floating-point numbers and is otherwise
unspecified;254 if the precision is zero and the
# flag is not specified, no decimal-point wide
character appears. The letters abcdef are used
for a conversion and the letters ABCDEF for A
conversion. The a conversion specifier will
produce a number with x and p and the A conversion
specifier will produce a number with X and P. The
exponent always contains at least one digit, and
only as many more digits as necessary to represent
the decimal exponent of 2. If the value is zero,
the exponent is zero.
A double argument representing an infinity or a
NaN is converted in the style of an f or F
conversion specifier.
c If no l qualifier is present, the int argument is
converted to a wide character as if by calling
btowc and the resulting wide character is written.
Otherwise, the wint_t argument is converted to
wchar_t and written.
s If no l qualifier is present, the argument shall
be a pointer to the initial element of a character
array containing a multibyte sequence beginning in
the initial shift state. Characters from the array
__________
253. The precision p is sufficient to distinguish values of
the source type if
16p-1 > bn
where b is FLT_RADIX and n is the number of base-b
digits in the significand of the source type. A smaller
p might suffice depending on the implementation's scheme
for determining the digit to the left of the decimal-
point wide character.
254. Binary implementations can choose the hexadecimal digit
to the left of the decimal-point wide character so that
subsequent digits align to nibble (4-bit) boundaries.
page 443 Library
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are converted as if by repeated calls to the
mbrtowc function, with the conversion state
described by an mbstate_t object initialized to
zero before the first multibyte character is
converted, and written up to (but not including)
the terminating null wide character. If the
precision is specified, no more than that many
wide characters are written. If the precision is
not specified or is greater than the size of the
converted array, the converted array shall contain
a null wide character.
If an l qualifier is present, the argument shall
be a pointer to the initial element of an array of
wchar_t type. Wide characters from the array are
written up to (but not including) a terminating
null wide character. If the precision is
specified, no more than that many wide characters
are written. If the precision is not specified or
is greater than the size of the array, the array
shall contain a null wide character.
p The argument shall be a pointer to void. The
value of the pointer is converted to a sequence of
printable wide characters, in an implementation-
defined manner.
n The argument shall be a pointer to signed integer
into which is written the number of wide
characters written to the output stream so far by
this call to fwprintf. No argument is converted,
but one is consumed. If the conversion
specification with this conversion specifier is
not one of %n, %ln, %lln, %hn, or %hhn, the
behavior is undefined.
% A % wide character is written. No argument is
converted. The complete conversion specification
shall be %%.
[#8] If a conversion specification is invalid, the behavior
is undefined.255
[#9] If any argument is, or points to, a union or an
aggregate (except for an array of char type using %s
__________
255. See ``future library directions'' (7.20).
page 444 Library
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conversion, an array of wchar_t type using %ls conversion,
or a pointer using %p conversion), the behavior is
undefined.
[#10] In no case does a nonexistent or small field width
cause truncation of a field; if the result of a conversion
is wider than the field width, the field is expanded to
contain the conversion result.
[#11] For a and A conversions, if FLT_RADIX is a power of 2,
the value is correctly rounded to a hexadecimal floating
number with the given precision.
Recommended practice
If FLT_RADIX is not a power of 2, the result is one of the
two adjacent numbers in hexadecimal floating style with the
given precision, with the extra stipulation that the error
have a correct sign for the current rounding direction.
[#12] For e, E, f, F, g, and G conversions, if the number of
significant decimal digits is at most DECIMAL_DIG, then the
result is correctly rounded.256 If the number of
significant decimal digits is more than DECIMAL_DIG but the
source value is exactly representable with DECIMAL_DIG
digits, then the result is an exact representation with
trailing zeros. Otherwise, the source value is bounded by
two adjacent decimal strings L < U, both having DECIMAL_DIG
significant digits; the value of the resultant decimal
string D satisfies L < D < U, with the extra stipulation
that the error have a correct sign for the current rounding
direction.
Returns
[#13] The fwprintf function returns the number of wide
characters transmitted, or a negative value if an output
error occurred.
__________
256. For binary-to-decimal conversion, the result format's
values are the numbers representable with the given
format specifier. The number of significant digits is
determined by the format specifier, and in the case of
fixed-point conversion by the source value as well.
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Environmental limit
[#14] The minimum value for the maximum number of wide
characters produced by any single conversion shall be 4095.
Examples
[#15] To print a date and time in the form ``Sunday, July 3,
10:02'' followed by pi to five decimal places:
#include <math.h>
#include <stdio.h>
#include <wchar.h>
/* ... */
wchar_t *weekday, *month; // pointers to wide strings
int day, hour, min;
fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",
weekday, month, day, hour, min);
fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));
[#16] Forward References: the btowc function (7.19.7.1.1),
the mbrtowc function (7.19.7.3.2).
7.19.2.2 The fwscanf function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
int fwscanf(FILE * restrict stream,
const wchar_t * restrict format, ...);
Description
[#2] The fwscanf function reads input from the stream
pointed to by stream, under control of the wide string
pointed to by format that specifies the admissible input
sequences and how they are to be converted for assignment,
using subsequent arguments as pointers to the objects to
receive the converted input. If there are insufficient
arguments for the format, the behavior is undefined. If the
format is exhausted while arguments remain, the excess
arguments are evaluated (as always) but are otherwise
ignored.
[#3] The format is composed of zero or more directives: one
or more white-space wide characters; an ordinary wide
character (neither % nor a white-space wide character); or a
conversion specification. Each conversion specification is
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introduced by the wide character %. After the %, the
following appear in sequence:
- An optional assignment-suppressing wide character *.
- An optional nonzero decimal integer that specifies the
maximum field width (in wide characters).
- An optional hh, h, l (ell), or ll (ell-ell), or L
indicating the size of the receiving object. The
conversion specifiers d, i, and n shall be preceded by
hh if the corresponding argument is a pointer to signed
char rather than a pointer to int, by h if it is a
pointer to short int rather than a pointer to int, by l
if it is a pointer to long int, or by ll if it is a
pointer to long long int. Similarly, the conversion
specifiers o, u, and x shall be preceded by hh if the
corresponding argument is a pointer to unsigned char
rather than a pointer to unsigned int, by h if it is a
pointer to unsigned short int rather than a pointer to
unsigned int, by l if it is a pointer to unsigned long
int, or by ll if it is a pointer to unsigned long long
int. The conversion specifiers a, e, f, and g shall be
preceded by l if the corresponding argument is a
pointer to double rather than a pointer to float, or by
L if it is a pointer to long double. Finally, the
conversion specifiers c, s, and [ shall be preceded by
l if the corresponding argument is a pointer to wchar_t
rather than a pointer to a character type. If an hh,
h, l, ll, or L appears with any other conversion
specifier, the behavior is undefined.
- A wide character that specifies the type of conversion
to be applied. The valid conversion specifiers are
described below.
[#4] The fwscanf function executes each directive of the
format in turn. If a directive fails, as detailed below,
the fwscanf function returns. Failures are described as
input failures (if an encoding error occurs or due to the
unavailability of input characters), or matching failures
(due to inappropriate input).
[#5] A directive composed of white-space wide character(s)
is executed by reading input up to the first non-white-space
wide character (which remains unread), or until no more wide
characters can be read.
[#6] A directive that is an ordinary wide character is
executed by reading the next wide character of the stream.
If the wide character differs from the directive, the
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page 448
directive fails, and the differing and subsequent wide
characters remain unread.
[#7] A directive that is a conversion specification defines
a set of matching input sequences, as described below for
each specifier. A conversion specification is executed in
the following steps:
[#8] Input white-space wide characters (as specified by the
iswspace function) are skipped, unless the specification
includes a [, c, or n specifier.257
[#9] An input item is read from the stream, unless the
specification includes an n specifier. An input item is
defined as the longest sequence of input wide characters
which does not exceed any specified field width and which
is, or is a prefix of, a matching input sequence. The first
wide character, if any, after the input item remains unread.
If the length of the input item is zero, the execution of
the directive fails: this condition is a matching failure,
unless end-of-file, an encoding error, or a read error
prevented input from the stream, in which case it is an
input failure.
[#10] Except in the case of a % specifier, the input item
(or, in the case of a %n directive, the count of input wide
characters) is converted to a type appropriate to the
conversion specifier. If the input item is not a matching
sequence, the execution of the directive fails: this
condition is a matching failure. Unless assignment
suppression was indicated by a *, the result of the
conversion is placed in the object pointed to by the first
argument following the format argument that has not already
received a conversion result. If this object does not have
an appropriate type, or if the result of the conversion
cannot be represented in the object, the behavior is
undefined.
[#11] The conversion specifiers and their meanings are:
d Matches an optionally signed decimal integer,
whose format is the same as expected for the
subject sequence of the wcstol function with the
value 10 for the base argument. The corresponding
__________
257. These white-space wide characters are not counted
against a specified field width.
page 448 Library
page 449
argument shall be a pointer to signed integer.
i Matches an optionally signed integer, whose format
is the same as expected for the subject sequence
of the wcstol function with the value 0 for the
base argument. The corresponding argument shall be
a pointer to signed integer.
o Matches an optionally signed octal integer, whose
format is the same as expected for the subject
sequence of the wcstoul function with the value 8
for the base argument. The corresponding argument
shall be a pointer to unsigned integer.
u Matches an optionally signed decimal integer,
whose format is the same as expected for the
subject sequence of the wcstoul function with the
value 10 for the base argument. The corresponding
argument shall be a pointer to unsigned integer.
x Matches an optionally signed hexadecimal integer,
whose format is the same as expected for the
subject sequence of the wcstoul function with the
value 16 for the base argument. The corresponding
argument shall be a pointer to unsigned integer.
a,e,f,g Matches an optionally signed floating-point
number, whose format is the same as expected for
the subject sequence of the wcstod function. The
corresponding argument shall be a pointer to
floating.
s Matches a sequence of non-white-space wide
characters. If no l qualifier is present,
characters from the input field are converted as
if by repeated calls to the wcrtomb function, with
the conversion state described by an mbstate_t
object initialized to zero before the first wide
character is converted. The corresponding argument
shall be a pointer to the initial element of a
character array large enough to accept the
sequence and a terminating null character, which
will be added automatically.
Otherwise, the corresponding argument shall be a
pointer to the initial element of an array of
wchar_t type large enough to accept the sequence
and a terminating null wide character, which will
be added automatically.
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[ Matches a nonempty sequence of wide characters
from a set of expected characters (the scanset).
f no l qualifier is present, characters from the
input field are converted as if by repeated calls
to the wcrtomb function, with the conversion state
described by an mbstate_t object initialized to
zero before the first wide character is converted.
The corresponding argument shall be a pointer to
the initial element of a character array large
enough to accept the sequence and a terminating
null character, which will be added automatically.
If an l qualifier is present, the corresponding
argument shall be a pointer to the initial element
of an array of wchar_t type large enough to accept
the sequence and a terminating null wide
character, which will be added automatically.
The conversion specifier includes all subsequent
wide characters in the format string, up to and
including the matching right bracket wide
character (]). The wide characters between the
brackets (the scanlist) comprise the scanset,
unless the wide character after the left bracket
is a circumflex (^), in which case the scanset
contains all wide characters that do not appear in
the scanlist between the circumflex and the right
bracket. If the conversion specifier begins with
[] or [^], the right bracket wide character is in
the scanlist and the next right bracket wide
character is the matching right bracket that ends
the specification; otherwise the first right
bracket wide character is the one that ends the
specification. If a - wide character is in the
scanlist and is not the first, nor the second
where the first wide character is a ^, nor the
last character, the behavior is implementation-
defined.
c Matches a sequence of wide characters of exactly
the number specified by the field width (1 if no
field width is present in the directive). If no l
qualifier is present, characters from the input
field are converted as if by repeated calls to the
wcrtomb function, with the conversion state
described by an mbstate_t object initialized to
zero before the first wide character is converted.
The corresponding argument shall be a pointer to
the initial element of a character array large
enough to accept the sequence. No null character
is added.
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If an l qualifier is present, the corresponding
argument shall be a pointer to the initial element
of an array of wchar_t type large enough to accept
the sequence. No null wide character is added.
p Matches an implementation-defined set of
sequences, which should be the same as the set of
sequences that may be produced by the %p
conversion of the fwprintf function. The
corresponding argument shall be a pointer to a
pointer to void. The interpretation of the input
item is implementation-defined. If the input item
is a value converted earlier during the same
program execution, the pointer that results shall
compare equal to that value; otherwise the
behavior of the %p conversion is undefined.
n No input is consumed. The corresponding argument
shall be a pointer to signed integer into which is
to be written the number of wide characters read
from the input stream so far by this call to the
fwscanf function. Execution of a %n directive does
not increment the assignment count returned at the
completion of execution of the fwscanf function.
No argument is converted, but one is consumed. If
the conversion specification with this conversion
specifier is not one of %n, %ln, %lln, %hn, or
%hhn, the behavior is undefined.
% Matches a single %; no conversion or assignment
occurs. The complete conversion specification
shall be %%
[#12] If a conversion specification is invalid, the behavior
is undefined.258
[#13] The conversion specifiers A, E, G, and X are also
valid and behave the same as, respectively, a, e, g, and x.
[#14] If end-of-file is encountered during input, conversion
is terminated. If end-of-file occurs before any wide
characters matching the current directive have been read
(other than leading white space, where permitted), execution
of the current directive terminates with an input failure;
otherwise, unless execution of the current directive is
__________
258. See ``future library directions'' (7.20).
page 451 Library
page 452
terminated with a matching failure, execution of the
following directive (other than %n, if any) is terminated
with an input failure.
[#15] Trailing white space (including new-line wide
characters) is left unread unless matched by a directive.
The success of literal matches and suppressed assignments is
not directly determinable other than via the %n directive.
[#16] If conversion terminates on a conflicting input wide
character, the offending input wide character is left unread
in the input stream.259
Returns
[#17] The fwscanf function returns the value of the macro
EOF if an input failure occurs before any conversion.
Otherwise, the fwscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
Examples
1. The call:
#include <stdio.h>
#include <wchar.h>
/* ... */
int n, i; float x; wchar_t name[50];
n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);
[#18] with the input line:
25 54.32E-1 thompson
[#19] will assign to n the value 3, to i the value 25,
to x the value 5.432, and to name the sequence
thompson\0.
2. The call:
__________
259. fwscanf pushes back at most one input wide character
onto the input stream. Therefore, some sequences that
are acceptable to wcstod, wcstol, etc., are unacceptable
to fwscanf.
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page 453
#include <stdio.h>
#include <wchar.h>
/* ... */
int i; float x; double y;
fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);
[#20] with input:
56789 0123 56a72
[#21] will assign to i the value 56 and to x the value
789.0, will skip past 0123, and will assign to y the
value 56.0. The next wide character read from the
input stream will be a.
[#22] Forward References: the wcstod function (7.19.4.1.1),
the wcstol function (7.19.4.1.4), the wcstoul function
(7.19.4.1.6), the wcrtomb function (7.19.7.3.3).
7.19.2.3 The wprintf function
Synopsis
[#1]
#include <wchar.h>
int wprintf(const wchar_t * restrict format, ...);
Description
[#2] The wprintf function is equivalent to fwprintf with the
argument stdout interposed before the arguments to wprintf.
Returns
[#3] The wprintf function returns the number of wide
characters transmitted, or a negative value if an output
error occurred.
7.19.2.4 The wscanf function
Synopsis
[#1]
#include <wchar.h>
int wscanf(const wchar_t * restrict format, ...);
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page 454
Description
[#2] The wscanf function is equivalent to fwscanf with the
argument stdin interposed before the arguments to wscanf.
Returns
[#3] The wscanf function returns the value of the macro EOF
if an input failure occurs before any conversion. Otherwise,
the wscanf function returns the number of input items
assigned, which can be fewer than provided for, or even
zero, in the event of an early matching failure.
7.19.2.5 The swprintf function
Synopsis
[#1]
#include <wchar.h>
int swprintf(wchar_t * restrict s,
size_t n,
const wchar_t * restrict format, ...);
Description
[#2] The swprintf function is equivalent to fwprintf, except
that the argument s specifies an array of wide characters
into which the generated output is to be written, rather
than written to a stream. No more than n wide characters are
written, including a terminating null wide character, which
is always added (unless n is zero).
Returns
[#3] The swprintf function returns the number of wide
characters written in the array, not counting the
terminating null wide character, or a negative value if n or
more wide characters were requested to be written.
7.19.2.6 The swscanf function
Synopsis
[#1]
#include <wchar.h>
int swscanf(const wchar_t * restrict s,
const wchar_t * restrict format, ...);
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Description
[#2] The swscanf function is equivalent to fwscanf, except
that the argument s specifies a wide string from which the
input is to be obtained, rather than from a stream. Reaching
the end of the wide string is equivalent to encountering
end-of-file for the fwscanf function.
Returns
[#3] The swscanf function returns the value of the macro EOF
if an input failure occurs before any conversion. Otherwise,
the swscanf function returns the number of input items
assigned, which can be fewer than provided for, or even
zero, in the event of an early matching failure.
7.19.2.7 The vfwprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
#include <wchar.h>
int vfwprintf(FILE * restrict stream,
const wchar_t * restrict format,
va_list arg);
Description
[#2] The vfwprintf function is equivalent to fwprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vfwprintf function does not
invoke the va_end macro.260
Returns
[#3] The vfwprintf function returns the number of wide
characters transmitted, or a negative value if an output
error occurred.
__________
260. As the functions vfwprintf, vswprintf, vfwscanf,
vwprintf, vwscanf, and vswscanf invoke the va_arg macro,
the value of arg after the return is indeterminate.
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page 456
Examples
[#4] The following shows the use of the vfwprintf function
in a general error-reporting routine.
#include <stdarg.h>
#include <stdio.h>
#include <wchar.h>
void error(char *function_name, wchar_t *format, ...)
{
va_list args;
va_start(args, format);
// print out name of function causing error
fwprintf(stderr, L"ERROR in %s: ", function_name);
// print out remainder of message
vfwprintf(stderr, format, args);
va_end(args);
}
7.19.2.8 The vwprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <wchar.h>
int vwprintf(const wchar_t * restrict format,
va_list arg);
Description
[#2] The vwprintf function is equivalent to wprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vwprintf function does not
invoke the va_end macro.260
Returns
[#3] The vwprintf function returns the number of wide
characters transmitted, or a negative value if an output
error occurred.
page 456 Library
page 457
7.19.2.9 The vswprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <wchar.h>
int vswprintf(wchar_t * restrict s,
size_t n,
const wchar_t * restrict format,
va_list arg);
Description
[#2] The vswprintf function is equivalent to swprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vswprintf function does not
invoke the va_end macro.260
Returns
[#3] The vswprintf function returns the number of wide
characters written in the array, not counting the
terminating null wide character, or a negative value if n or
more wide characters were requested to be generated.
7.19.2.10 The vfwscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
#include <wchar.h>
int vfwscanf(FILE * restrict stream,
const wchar_t * restrict format,
va_list arg);
Description
[#2] The vfwscanf function is equivalent to fwscanf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vfwscanf function does not
invoke the va_end macro.260
page 457 Library
page 458
Returns
[#3] The vfwscanf function returns the value of the macro
EOF if an input failure occurs before any conversion.
Otherwise, the vfwscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.19.2.11 The vwscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
#include <wchar.h>
int vwscanf(FILE * restrict stream,
const wchar_t * restrict format,
va_list arg);
Description
[#2] The vwscanf function is equivalent to wscanf, with the
variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vwscanf function does not
invoke the va_end macro.260
Returns
[#3] The vwscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the vwscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.19.2.12 The vswscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
#include <wchar.h>
int vswscanf(const wchar_t * restrict s,
const wchar_t * restrict format,
va_list arg);
page 458 Library
page 459
Description
[#2] The vswscanf function is equivalent to swscanf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vswscanf function does not
invoke the va_end macro.260
Returns
[#3] The vswscanf function returns the value of the macro
EOF if an input failure occurs before any conversion.
Otherwise, the vswscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.19.3 Wide-character input/output functions
7.19.3.1 The fgetwc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t fgetwc(FILE *stream);
Description
[#2] If a next wide character is present from the input
stream pointed to by stream, the fgetwc function obtains
that wide character and advances the associated file
position indicator for the stream (if defined).
Returns
[#3] The fgetwc function returns the next wide character
from the input stream pointed to by stream. If the stream
is at end-of-file, the end-of-file indicator for the stream
is set and fgetwc returns WEOF. If a read error occurs, the
error indicator for the stream is set and fgetwc returns
WEOF. If an encoding error occurs (including too few
bytes), the value of the macro EILSEQ is stored in errno and
fgetwc returns WEOF.261
__________
261. An end-of-file and a read error can be distinguished by
use of the feof and ferror functions. Also, errno will
page 459 Library
page 460
7.19.3.2 The fgetws function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wchar_t *fgetws(wchar_t * restrict s,
int n, FILE * restrict stream);
Description
[#2] The fgetws function reads at most one less than the
number of wide characters specified by n from the stream
pointed to by stream into the array pointed to by s. No
additional wide characters are read after a new-line wide
character (which is retained) or after end-of-file. A null
wide character is written immediately after the last wide
character read into the array.
Returns
[#3] The fgetws function returns s if successful. If end-
of-file is encountered and no characters have been read into
the array, the contents of the array remain unchanged and a
null pointer is returned. If a read or encoding error occurs
during the operation, the array contents are indeterminate
and a null pointer is returned.
7.19.3.3 The fputwc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t fputwc(wchar_t c, FILE *stream);
____________________________________________________________
be set to EILSEQ by input/output functions only if an
encoding error occurs.
page 460 Library
page 461
Description
[#2] The fputwc function writes the wide character specified
by c to the output stream pointed to by stream, at the
position indicated by the associated file position indicator
for the stream (if defined), and advances the indicator
appropriately. If the file cannot support positioning
requests, or if the stream was opened with append mode, the
character is appended to the output stream.
Returns
[#3] The fputwc function returns the wide character written.
If a write error occurs, the error indicator for the stream
is set and fputwc returns WEOF. If an encoding error
occurs, the value of the macro EILSEQ is stored in errno and
fputwc returns WEOF.
7.19.3.4 The fputws function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
int fputws(const wchar_t * restrict s,
FILE * restrict stream);
Description
[#2] The fputws function writes the wide string pointed to
by s to the stream pointed to by stream. The terminating
null wide character is not written.
Returns
[#3] The fputws function returns EOF if a write or encoding
error occurs; otherwise, it returns a nonnegative value.
7.19.3.5 The getwc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t getwc(FILE *stream);
page 461 Library
page 462
Description
[#2] The getwc function is equivalent to fgetwc, except that
if it is implemented as a macro, it may evaluate stream more
than once, so the argument should never be an expression
with side effects.
Returns
[#3] The getwc function returns the next wide character from
the input stream pointed to by stream, or WEOF.
7.19.3.6 The getwchar function
Synopsis
[#1]
#include <wchar.h>
wint_t getwchar(void);
Description
[#2] The getwchar function is equivalent to getwc with the
argument stdin.
Returns
[#3] The getwchar function returns the next wide character
from the input stream pointed to by stdin, or WEOF.
7.19.3.7 The putwc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t putwc(wchar_t c, FILE *stream);
Description
[#2] The putwc function is equivalent to fputwc, except that
if it is implemented as a macro, it may evaluate stream more
than once, so the argument should never be an expression
with side effects.
page 462 Library
page 463
Returns
[#3] The putwc function returns the wide character written,
or WEOF.
7.19.3.8 The putwchar function
Synopsis
[#1]
#include <wchar.h>
wint_t putwchar(wchar_t c);
Description
[#2] The putwchar function is equivalent to putwc with the
second argument stdout.
Returns
[#3] The putwchar function returns the character written, or
WEOF.
7.19.3.9 The ungetwc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t ungetwc(wint_t c, FILE *stream);
Description
[#2] The ungetwc function pushes the wide character
specified by c back onto the input stream pointed to by
stream. The pushed-back wide characters will be returned by
subsequent reads on that stream in the reverse order of
their pushing. A successful intervening call (with the
stream pointed to by stream to a file positioning function
(fseek, fsetpos, or rewind) discards any pushed-back wide
characters for the stream. The external storage
corresponding to the stream is unchanged.
[#3] One wide character of pushback is guaranteed, even if
the call to the ungetwc function follows just after a call
to a formatted wide character input function fwscanf,
vfwscanf, vwscanf, or wscanf. If the ungetwc function is
called too many times on the same stream without an
page 463 Library
page 464
intervening read or file positioning operation on that
stream, the operation may fail.
[#4] If the value of c equals that of the macro WEOF, the
operation fails and the input stream is unchanged.
[#5] A successful call to the ungetwc function clears the
end-of-file indicator for the stream. The value of the file
position indicator for the stream after reading or
discarding all pushed-back wide characters is the same as it
was before the wide characters were pushed back. For a text
or binary stream, the value of its file position indicator
after a successful call to the ungetwc function is
unspecified until all pushed-back wide characters are read
or discarded.
Returns
[#6] The ungetwc function returns the wide character pushed
back, or WEOF if the operation fails.
7.19.3.10 The fwide function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
int fwide(FILE *stream, int mode);
Description
[#2] The fwide function determines the orientation of the
stream pointed to by stream. If mode is greater than zero,
the function first attempts to make the stream wide
oriented. If mode is less than zero, the function first
attempts to make the stream byte oriented.262 Otherwise,
mode is zero and the function does not alter the orientation
of the stream.
__________
262. If the orientation of the stream has already been
determined, fwide does not change it.
page 464 Library
page 465
Returns
[#3] The fwide function returns a value greater than zero
if, after the call, the stream has wide orientation, a value
less than zero if the stream has byte orientation, or zero
if the stream has no orientation.
7.19.4 General wide-string utilities
[#1] The header <wchar.h> declares a number of functions
useful for wide-string manipulation. Various methods are
used for determining the lengths of the arrays, but in all
cases a wchar_t * argument points to the initial (lowest
addressed) element of the array. If an array is accessed
beyond the end of an object, the behavior is undefined.
7.19.4.1 Wide-string numeric conversion functions
7.19.4.1.1 The wcstod function
Synopsis
[#1]
#include <wchar.h>
double wcstod(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
Description
[#2] The wcstod function converts the initial portion of the
wide string pointed to by nptr to double representation.
First, it decomposes the input string into three parts: an
initial, possibly empty, sequence of white-space wide
characters (as specified by the iswspace function), a
subject sequence resembling a floating-point constant; and a
final wide string of one or more unrecognized wide
characters, including the terminating null wide character of
the input wide string. Then, it attempts to convert the
subject sequence to a floating-point number, and returns the
result.
[#3] The expected form of the subject sequence is an
optional plus or minus sign, then one of the following:
- a nonempty sequence of decimal digits optionally
containing a decimal-point wide character, then an
optional exponent part as defined for the corresponding
single-byte characters in subclause 6.1.3.1;
page 465 Library
page 466
- a 0x or 0X, then a nonempty sequence of hexadecimal
digits optionally containing a decimal-point wide
character, then an optional binary-exponent part, where
either the decimal-point character or the binary-
exponent part is present;
- one of INF or INFINITY, or any other wide string
equivalent except for case
- one of NAN or NAN(n-wchar-sequence-opt), or any other
wide string equivalent except for case in the NAN part,
where:
n-wchar-sequence:
digit
nondigit
n-wchar-sequence digit
n-wchar-sequence nondigit
but no floating suffix. The subject sequence is defined as
the longest initial subsequence of the input wide string,
starting with the first non-white-space wide character, that
is of the expected form. The subject sequence contains no
wide characters if the input wide string is not of the
expected form.
[#4] If the subject sequence has the expected form for a
floating-point number, the sequence of wide characters
starting with the first digit or the decimal-point wide
character (whichever occurs first) is interpreted as a
floating constant according to the rules of subclause
6.1.3.1, except that the decimal-point wide character is
used in place of a period, and that if neither an exponent
part, a binary-exponent part, nor a decimal-point wide
character appears, a decimal point is assumed to follow the
last digit in the wide string. A wide character sequence
INF or INFINITY is interpreted as an infinity, if
representable in the double type, else like a floating
constant that is too large for the range of double. A wide
character sequence NAN or NAN(n-wchar-sequence-opt) is
interpreted as a quiet NaN, if supported in the double type,
else like a subject sequence part that does not have the
expected form; the meaning of the n-wchar sequences is
implementation-defined.263 If the subject sequence begins
__________
263. An implementation may use the n-wchar sequence to
determine extra information to be represented in the
NaN's significand.
page 466 Library
page 467
with a minus sign, the value resulting from the conversion
is negated.264 A pointer to the final wide string is stored
in the object pointed to by endptr, provided that endptr is
not a null pointer.
[#5] In other than the "C" locale, additional locale-
specific subject sequence forms may be accepted.
[#6] If the subject sequence has the hexadecimal form and
FLT_RADIX is a power of 2, then the value resulting from the
conversion is correctly rounded.
[#7] If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of nptr
is stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
Recommended practice
[#8] If the subject sequence has the hexadecimal form and
FLT_RADIX is not a power of 2, then the result is one of the
two numbers in the appropriate internal format that are
adjacent to the hexadecimal floating source value, with the
extra stipulation that the error have a correct sign for the
current rounding direction.
[#9] If the subject sequence has the decimal form and at
most DECIMAL_DIG (defined in <math.h>) significant digits,
then the value resulting from the conversion is correctly
rounded. If the subject sequence D has the decimal form and
more than DECIMAL_DIG significant digits, consider the two
bounding, adjacent decimal strings L and U, both having
DECIMAL_DIG significant digits, such that the values of L,
D, and U satisfy L < D < U. The result of conversion is one
of the (equal or adjacent) values that would be obtained by
correctly rounding L and U according to the current rounding
direction, with the extra stipulation that the error with
respect to D has a correct sign for the current rounding
direction.265
__________
264. The wcstod function honors the sign of zero if the
arithmetic supports signed zeros.
265. DECIMAL_DIG, defined in <math.h>, is recommended to be
sufficiently large that L and U will usually round to
the same internal floating value, but if not will round
to adjacent values.
page 467 Library
page 468
Returns
[#10] The wcstod function returns the converted value, if
any. If no conversion could be performed, zero is returned.
If the correct value is outside the range of representable
values, plus or minus HUGE_VAL is returned (according to the
sign of the value), and the value of the macro ERANGE is
stored in errno. If the result underflows (7.7.1), the
function returns a value whose magnitude is no greater than
the smallest normalized positive number in the result type;
whether errno acquires the value ERANGE is implementation-
defined.
7.19.4.1.2 The wcstof function
Synopsis
[#1]
#include <wchar.h>
float wcstof(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
Description
[#2] The wcstof function is similar to the wcstod function,
except the returned value has type float and plus or minus
HUGE_VALF is returned for values outside the range.
7.19.4.1.3 The wcstold function
Synopsis
[#1]
#include <wchar.h>
long double wcstold(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
Description
[#2] The wcstold function is similar to the wcstod function,
except the returned value has type long double and plus or
minus HUGE_VALL is returned for values outside the range.
page 468 Library
page 469
7.19.4.1.4 The wcstol function
Synopsis
[#1]
#include <wchar.h>
long int wcstol(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr,
int base);
Description
[#2] The wcstol function converts the initial portion of the
wide string pointed to by nptr to long int representation.
First, it decomposes the input string into three parts: an
initial, possibly empty, sequence of white-space wide
characters (as specified by the iswspace function), a
subject sequence resembling an integer represented in some
radix determined by the value of base, and a final wide
string of one or more unrecognized wide characters,
including the terminating null wide character of the input
wide string. Then, it attempts to convert the subject
sequence to an integer, and returns the result.
[#3] If the value of base is zero, the expected form of the
subject sequence is that of an integer constant as described
for the corresponding single-byte characters in subclause
6.1.3.2, optionally preceded by a plus or minus sign, but
not including an integer suffix. If the value of base is
between 2 and 36 (inclusive), the expected form of the
subject sequence is a sequence of letters and digits
representing an integer with the radix specified by base,
optionally preceded by a plus or minus sign, but not
including an integer suffix. The letters from a (or A)
through z (or Z) are ascribed the values 10 through 35; only
letters and digits whose ascribed values are less than that
of base are permitted. If the value of base is 16, the wide
characters 0x or 0X may optionally precede the sequence of
letters and digits, following the sign if present.
[#4] The subject sequence is defined as the longest initial
subsequence of the input wide string, starting with the
first non-white-space wide character, that is of the
expected form. The subject sequence contains no wide
characters if the input wide string is empty or consists
entirely of white space, or if the first non-white-space
wide character is other than a sign or a permissible letter
or digit.
page 469 Library
page 470
[#5] If the subject sequence has the expected form and the
value of base is zero, the sequence of wide characters
starting with the first digit is interpreted as an integer
constant according to the rules of subclause 6.1.3.2. If the
subject sequence has the expected form and the value of base
is between 2 and 36, it is used as the base for conversion,
ascribing to each letter its value as given above. If the
subject sequence begins with a minus sign, the value
resulting from the conversion is negated. A pointer to the
final wide string is stored in the object pointed to by
endptr, provided that endptr is not a null pointer.
[#6] In other than the "C" locale, additional locale-
specific subject sequence forms may be accepted.
[#7] If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of nptr
is stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
Returns
[#8] The wcstol function returns the converted value, if
any. If no conversion could be performed, zero is returned.
If the correct value is outside the range of representable
values, LONG_MAX or LONG_MIN is returned (according to the
sign of the value), and the value of the macro ERANGE is
stored in errno.
7.19.4.1.5 The wcstoll function
Synopsis
[#1]
#include <wchar.h>
long long int wcstoll(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr,
int base);
Description
[#2] The wcstoll function is equivalent to the wcstol
function, except that it converts the initial portion of the
wide string pointed to by nptr to long long int
representation.
page 470 Library
page 471
Returns
[#3] The wcstoll function returns the converted value, if
any. If no conversion could be performed, zero is returned.
If the correct value is outside the range of representable
values, LLONG_MAX or LLONG_MIN is returned (according to the
sign of the value), and the value of the macro ERANGE is
stored in errno.
7.19.4.1.6 The wcstoul function
Synopsis
[#1]
#include <wchar.h>
unsigned long int wcstoul(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr,
int base);
Description
[#2] The wcstoul function converts the initial portion of
the wide string pointed to by nptr to unsigned long int
representation. First, it decomposes the input string into
three parts: an initial, possibly empty, sequence of
white-space wide characters (as specified by the iswspace
function), a subject sequence resembling an unsigned integer
represented in some radix determined by the value of base,
and a final wide string of one or more unrecognized wide
characters, including the terminating null wide character of
the input wide string. Then, it attempts to convert the
subject sequence to an unsigned integer, and returns the
result.
[#3] If the value of base is zero, the expected form of the
subject sequence is that of an integer constant as described
for the corresponding single-byte characters in subclause
6.1.3.2, optionally preceded by a plus or minus sign, but
not including an integer suffix. If the value of base is
between 2 and 36 (inclusive), the expected form of the
subject sequence is a sequence of letters and digits
representing an integer with the radix specified by base,
optionally preceded by a plus or minus sign, but not
including an integer suffix. The letters from a (or A)
through z (or Z) are ascribed the values 10 through 35; only
letters and digits whose ascribed values are less than that
of base are permitted. If the value of base is 16, the wide
characters 0x or 0X may optionally precede the sequence of
letters and digits, following the sign if present.
page 471 Library
page 472
[#4] The subject sequence is defined as the longest initial
subsequence of the input wide string, starting with the
first non-white-space wide character, that is of the
expected form. The subject sequence contains no wide
characters if the input wide string is empty or consists
entirely of white space, or if the first non-white-space
wide character is other than a sign or a permissible letter
or digit.
[#5] If the subject sequence has the expected form and the
value of base is zero, the sequence of wide characters
starting with the first digit is interpreted as an integer
constant according to the rules of subclause 6.1.3.2. If the
subject sequence has the expected form and the value of base
is between 2 and 36, it is used as the base for conversion,
ascribing to each letter its value as given above. If the
subject sequence begins with a minus sign, the value
resulting from the conversion is negated. A pointer to the
final wide string is stored in the object pointed to by
endptr, provided that endptr is not a null pointer.
[#6] In other than the "C" locale, additional locale-
specific subject sequence forms may be accepted.
[#7] If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of nptr
is stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
Returns
[#8] The wcstoul function returns the converted value, if
any. If no conversion could be performed, zero is returned.
If the correct value is outside the range of representable
values, ULONG_MAX is returned, and the value of the macro
ERANGE is stored in errno.
7.19.4.1.7 The wcstoull function
Synopsis
[#1]
#include <wchar.h>
unsigned long long int wcstoull(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr,
int base);
page 472 Library
page 473
Description
[#2] The wcstoull function is equivalent to the wcstoul
function, except that it converts the initial portion of the
wide string pointed to by nptr to unsigned long long int
representation.
Returns
[#3] The wcstoull function returns the converted value, if
any. If no conversion could be performed, zero is returned.
If the correct value is outside the range of representable
values, ULLONG_MAX is returned, and the value of the macro
ERANGE is stored in errno.
7.19.4.2 Wide-string copying functions
7.19.4.2.1 The wcscpy function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcscpy(wchar_t * restrict s1,
const wchar_t * restrict s2);
Description
[#2] The wcscpy function copies the wide string pointed to
by s2 (including the terminating null wide character) into
the array pointed to by s1.
Returns
[#3] The wcscpy function returns the value of s1.
7.19.4.2.2 The wcsncpy function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcsncpy(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
page 473 Library
page 474
Description
[#2] The wcsncpy function copies not more than n wide
characters (those that follow a null wide character are not
copied) from the array pointed to by s2 to the array pointed
to by s1.266
[#3] If the array pointed to by s2 is a wide string that is
shorter than n wide characters, null wide characters are
appended to the copy in the array pointed to by s1, until n
wide characters in all have been written.
Returns
[#4] The wcsncpy function returns the value of s1.
7.19.4.3 Wide-string concatenation functions
7.19.4.3.1 The wcscat function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcscat(wchar_t * restrict s1,
const wchar_t * restrict s2);
Description
[#2] The wcscat function appends a copy of the wide string
pointed to by s2 (including the terminating null wide
character) to the end of the wide string pointed to by s1.
The initial wide character of s2 overwrites the null wide
character at the end of s1.
Returns
[#3] The wcscat function returns the value of s1.
__________
266. Thus, if there is no null wide character in the first n
wide characters of the array pointed to by s2, the
result will not be null-terminated.
page 474 Library
page 475
7.19.4.3.2 The wcsncat function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcsncat(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description
[#2] The wcsncat function appends not more than n wide
characters (a null wide character and those that follow it
are not appended) from the array pointed to by s2 to the end
of the wide string pointed to by s1. The initial wide
character of s2 overwrites the null wide character at the
end of s1 A terminating null wide character is always
appended to the result.267
Returns
[#3] The wcsncat function returns the value of s1.
7.19.4.4 Wide-string comparison functions
[#1] Unless explicitly stated otherwise, the functions
described in this subclause order two wide characters the
same way as two integers of the underlying integer type
designated by wchar_t.
7.19.4.4.1 The wcscmp function
Synopsis
[#1]
#include <wchar.h>
int wcscmp(const wchar_t *s1, const wchar_t *s2);
__________
267. Thus, the maximum number of wide characters that can
end up in the array pointed to by s1 is wcslen(s1)+n+1.
page 475 Library
page 476
Description
[#2] The wcscmp function compares the wide string pointed to
by s1 to the wide string pointed to by s2.
Returns
[#3] The wcscmp function returns an integer greater than,
equal to, or less than zero, accordingly as the wide string
pointed to by s1 is greater than, equal to, or less than the
wide string pointed to by s2.
7.19.4.4.2 The wcscoll function
Synopsis
[#1]
#include <wchar.h>
int wcscoll(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcscoll function compares the wide string pointed
to by s1 to the wide string pointed to by s2, both
interpreted as appropriate to the LC_COLLATE category of the
current locale.
Returns
[#3] The wcscoll function returns an integer greater than,
equal to, or less than zero, accordingly as the wide string
pointed to by s1 is greater than, equal to, or less than the
wide string pointed to by s2 when both are interpreted as
appropriate to the current locale.
7.19.4.4.3 The wcsncmp function
Synopsis
[#1]
#include <wchar.h>
int wcsncmp(const wchar_t *s1, const wchar_t *s2,
size_t n);
page 476 Library
page 477
Description
[#2] The wcsncmp function compares not more than n wide
characters (those that follow a null wide character are not
compared) from the array pointed to by s1 to the array
pointed to by s2.
Returns
[#3] The wcsncmp function returns an integer greater than,
equal to, or less than zero, accordingly as the possibly
null-terminated array pointed to by s1 is greater than,
equal to, or less than the possibly null-terminated array
pointed to by s2.
7.19.4.4.4 The wcsxfrm function
Synopsis
[#1]
#include <wchar.h>
size_t wcsxfrm(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description
[#2] The wcsxfrm function transforms the wide string pointed
to by s2 and places the resulting wide string into the array
pointed to by s1. The transformation is such that if the
wcscmp function is applied to two transformed wide strings,
it returns a value greater than, equal to, or less than
zero, corresponding to the result of the wcscoll function
applied to the same two original wide strings. No more than
n wide characters are placed into the resulting array
pointed to by s1, including the terminating null wide
character. If n is zero, s1 is permitted to be a null
pointer.
Returns
[#3] The wcsxfrm function returns the length of the
transformed wide string (not including the terminating null
wide character). If the value returned is n or greater, the
contents of the array pointed to by s1 are indeterminate.
page 477 Library
page 478
Examples
[#4] The value of the following expression is the length of
the array needed to hold the transformation of the wide
string pointed to by s:
1 + wcsxfrm(NULL, s, 0)
7.19.4.5 Wide-string search functions
7.19.4.5.1 The wcschr function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcschr(const wchar_t *s, wchar_t c);
Description
[#2] The wcschr function locates the first occurrence of c
in the wide string pointed to by s. The terminating null
wide character is considered to be part of the wide string.
Returns
[#3] The wcschr function returns a pointer to the located
wide character, or a null pointer if the wide character does
not occur in the wide string.
7.19.4.5.2 The wcscspn function
Synopsis
[#1]
#include <wchar.h>
size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcscspn function computes the length of the maximum
initial segment of the wide string pointed to by s1 which
consists entirely of wide characters not from the wide
string pointed to by s2.
page 478 Library
page 479
Returns
[#3] The wcscspn function returns the length of the segment.
7.19.4.5.3 The wcspbrk function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcspbrk function locates the first occurrence in
the wide string pointed to by s1 of any wide character from
the wide string pointed to by s2.
Returns
[#3] The wcspbrk function returns a pointer to the wide
character in s1, or a null pointer if no wide character from
s2 occurs in s1.
7.19.4.5.4 The wcsrchr function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
Description
[#2] The wcsrchr function locates the last occurrence of c
in the wide string pointed to by s. The terminating null
wide character is considered to be part of the wide string.
Returns
[#3] The wcsrchr function returns a pointer to the wide
character, or a null pointer if c does not occur in the wide
string.
page 479 Library
page 480
7.19.4.5.5 The wcsspn function
Synopsis
[#1]
#include <wchar.h>
size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcsspn function computes the length of the maximum
initial segment of the wide string pointed to by s1 which
consists entirely of wide characters from the wide string
pointed to by s2.
Returns
[#3] The wcsspn function returns the length of the segment.
7.19.4.5.6 The wcsstr function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcsstr function locates the first occurrence in the
wide string pointed to by s1 of the sequence of wide
characters (excluding the terminating null wide character)
in the wide string pointed to by s2.
Returns
[#3] The wcsstr function returns a pointer to the located
wide string, or a null pointer if the wide string is not
found. If s2 points to a wide string with zero length, the
function returns s1.
7.19.4.5.7 The wcstok function
Synopsis
[#1]
page 480 Library
page 481
#include <wchar.h>
wchar_t *wcstok(wchar_t * restrict s1,
const wchar_t * restrict s2,
wchar_t ** restrict ptr);
Description
[#2] A sequence of calls to the wcstok function breaks the
wide string pointed to by s1 into a sequence of tokens, each
of which is delimited by a wide character from the wide
string pointed to by s2. The third argument points to a
caller-provided wchar_t pointer into which the wcstok
function stores information necessary for it to continue
scanning the same wide string.
[#3] For the first call in the sequence, s1 shall point to a
wide string, while in subsequent calls for the same wide
string, s1 shall be a null pointer. If s1 is a null pointer,
the value pointed to by ptr shall match that stored by the
previous call for the same wide string; otherwise the value
pointed to by ptr is ignored. The separator wide string
pointed to by s2 may be different from call to call.
[#4] The first call in the sequence searches the wide string
pointed to by s1 for the first wide character that is not
contained in the current separator wide string pointed to by
s2. If no such wide character is found, then there are no
tokens in the wide string pointed to by s1 and the wcstok
function returns a null pointer. If such a wide character is
found, it is the start of the first token.
[#5] The wcstok function then searches from there for a wide
character that is contained in the current separator wide
string. If no such wide character is found, the current
token extends to the end of the wide string pointed to by
s1, and subsequent searches in the same wide string for a
token return a null pointer. If such a wide character is
found, it is overwritten by a null wide character, which
terminates the current token.
[#6] In all cases, the wcstok function stores sufficient
information in the pointer pointed to by ptr so that
subsequent calls, with a null pointer for s1 and the
unmodified pointer value for ptr, shall start searching just
past the element overwritten by a null wide character (if
any).
page 481 Library
page 482
Returns
[#7] The wcstok function returns a pointer to the first wide
character of a token, or a null pointer if there is no
token.
Examples
#include <wchar.h>
static wchar_t str1[] = L"?a???b,,,#c";
static wchar_t str2[] = L"\t \t";
wchar_t *t, *ptr1, *ptr2;
// t points to the token L"a"
t = wcstok(str1, L"?", &ptr1);
// t points to the token L"??b"
t = wcstok(NULL, L",", &ptr1);
// t is a null pointer
t = wcstok(str2, L" \t", &ptr2);
// t points to the token L"c"
t = wcstok(NULL, L"#,", &ptr1);
// t is a null pointer
t = wcstok(NULL, L"?", &ptr1);
7.19.4.5.8 The wcslen function
Synopsis
[#1]
#include <wchar.h>
size_t wcslen(const wchar_t *s);
Description
[#2] The wcslen function computes the length of the wide
string pointed to by s.
Returns
[#3] The wcslen function returns the number of wide
characters that precede the terminating null wide character.
page 482 Library
page 483
7.19.4.6 Wide-character array functions
[#1] These functions operate on arrays of type wchar_t whose
size is specified by a separate count argument. These
functions are not affected by locale and all wchar_t values
are treated identically. The null wide character and wchar_t
values not corresponding to valid multibyte characters are
not treated specially.
[#2] Unless explicitly stated otherwise, the functions
described in this subclause order two wide characters the
same way as two integers of the underlying integer type
designated by wchar_t.
[#3] Where an argument declared as size_t n determines the
length of the array for a function, n can have the value
zero on a call to that function. Unless stated explicitly
otherwise in the description of a particular function in
this subclause, pointer arguments on such a call must still
have valid values, as described in subclause 7.1.8. On
such a call, a function that locates a wide character finds
no occurrence, a function that compares two wide character
sequences returns zero, and a function that copies wide
characters copies zero wide characters.
7.19.4.6.1 The wmemchr function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wmemchr(const wchar_t *s, wchar_t c,
size_t n);
Description
[#2] The wmemchr function locates the first occurrence of c
in the initial n wide characters of the object pointed to by
s.
Returns
[#3] The wmemchr function returns a pointer to the located
wide character, or a null pointer if the wide character does
not occur in the object.
page 483 Library
page 484
7.19.4.6.2 The wmemcmp function
Synopsis
[#1]
#include <wchar.h>
int wmemcmp(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description
[#2] The wmemcmp function compares the first n wide
characters of the object pointed to by s1 to the first n
wide characters of the object pointed to by s2.
Returns
[#3] The wmemcmp function returns an integer greater than,
equal to, or less than zero, accordingly as the object
pointed to by s1 is greater than, equal to, or less than the
object pointed to by s2.
7.19.4.6.3 The wmemcpy function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wmemcpy(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description
[#2] The wmemcpy function copies n wide characters from the
object pointed to by s2 to the object pointed to by s1.
Returns
[#3] The wmemcpy function returns the value of s1.
7.19.4.6.4 The wmemmove function
page 484 Library
page 485
Synopsis
[#1]
#include <wchar.h>
wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
size_t n);
Description
[#2] The wmemmove function copies n wide characters from the
object pointed to by s2 to the object pointed to by s1.
Copying takes place as if the n wide characters from the
object pointed to by s2 are first copied into a temporary
array of n wide characters that does not overlap the objects
pointed to by s1 or s2, and then the n wide characters from
the temporary array are copied into the object pointed to by
s1.
Returns
[#3] The wmemmove function returns the value of s1.
7.19.4.6.5 The wmemset function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
Description
[#2] The wmemset function copies the value of c into each of
the first n wide characters of the object pointed to by s.
Returns
[#3] The wmemset function returns the value of s.
page 485 Library
page 486
7.19.5 The wcsftime function
Synopsis
[#1]
#include <time.h>
#include <wchar.h>
size_t wcsftime(wchar_t * restrict s,
size_t maxsize,
const wchar_t * restrict format,
const struct tm * restrict timeptr);
Description
[#2] The wcsftime function is equivalent to the strftime
function, except that:
- The argument s points to the initial element of an
array of wide characters into which the generated
output is to be placed.
- The argument maxsize indicates the limiting number of
wide characters.
- The argument format is a wide string and the conversion
specifiers are replaced by corresponding sequences of
wide characters.
- The return value indicates the number of wide
characters.
Returns
[#3] If the total number of resulting wide characters
including the terminating null wide character is not more
than maxsize, the wcsftime function returns the number of
wide characters placed into the array pointed to by s not
including the terminating null wide character. Otherwise,
zero is returned and the contents of the array are
indeterminate.
page 486 Library
page 487
7.19.6 The wcsfxtime function
Synopsis
[#1]
#include <time.h>
#include <wchar.h>
size_t wcsfxtime(wchar_t * restrict s,
size_t maxsize,
const wchar_t * restrict format,
const struct tmx * restrict timeptr);
Description
[#2] The wcsfxtime function is equivalent to the wcsftime
function, except that the timeptr parameter has a different
type, and the %z and %Z conversion specifiers depend on both
the tm_zone and tm_isdst members.
7.19.7 Extended multibyte and wide-character conversion
utilities
[#1] The header <wchar.h> declares an extended set of
functions useful for conversion between multibyte characters
and wide characters.
[#2] Most of the following functions - those that are listed
as ``restartable'', subclauses 7.19.7.3 and 7.19.7.4 - take
as a last argument a pointer to an object of type mbstate_t
that is used to describe the current conversion state from a
particular multibyte character sequence to a wide-character
sequence (or the reverse) under the rules of a particular
setting for the LC_CTYPE category of the current locale.
[#3] The initial conversion state corresponds, for a
conversion in either direction, to the beginning of a new
multibyte character in the initial shift state. A zero-
valued mbstate_t object is (at least) one way to describe an
initial conversion state. A zero-valued mbstate_t object can
be used to initiate conversion involving any multibyte
character sequence, in any LC_CTYPE category setting. If an
mbstate_t object has been altered by any of the functions
described in this subclause, and is then used with a
different multibyte character sequence, or in the other
conversion direction, or with a different LC_CTYPE category
setting than on earlier function calls, the behavior is
undefined.268
page 487 Library
page 488
[#4] On entry, each function takes the described conversion
state (either internal or pointed to by ps) as current. The
conversion state described by the pointed-to object is
altered as needed to track the shift state, and the position
within a multibyte character, for the associated multibyte
character sequence.
7.19.7.1 Single-byte wide-character conversion functions
7.19.7.1.1 The btowc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t btowc(int c);
Description
[#2] The btowc function determines whether c constitutes a
valid (one-byte) multibyte character in the initial shift
state.
Returns
[#3] The btowc returns WEOF if c has the value EOF or if
(unsigned char)c does not constitute a valid (one-byte)
multibyte character in the initial shift state. Otherwise,
it returns the wide-character representation of that
character.
7.19.7.1.2 The wctob function
Synopsis
[#1]
__________
268. Thus a particular mbstate_t object can be used, for
example, with both the mbrtowc and mbsrtowcs functions
as long as they are used to step sequentially through
the same multibyte character string.
page 488 Library
page 489
#include <stdio.h>
#include <wchar.h>
int wctob(wint_t c);
Description
[#2] The wctob function determines whether c corresponds to
a member of the extended character set whose multibyte
character representation is a single byte when in the
initial shift state.
Returns
[#3] The wctob returns EOF if c does not correspond to a
multibyte character with length one in the initial shift
state. Otherwise, it returns the single-byte representation
of that character.
7.19.7.2 The mbsinit function
Synopsis
[#1]
#include <wchar.h>
int mbsinit(const mbstate_t *ps);
Description
[#2] If ps is not a null pointer, the mbsinit function
determines whether the pointed-to mbstate_t object describes
an initial conversion state.
Returns
[#3] The mbsinit function returns nonzero if ps is a null
pointer or if the pointed-to object describes an initial
conversion state; otherwise, it returns zero.
7.19.7.3 Restartable multibyte/wide-character conversion
functions
[#1] These functions differ from the corresponding multibyte
character functions of subclause 7.14.7 (mblen, mbtowc, and
wctomb) in that they have an extra parameter, ps, of type
pointer to mbstate_t that points to an object that can
completely describe the current conversion state of the
associated multibyte character sequence. If ps is a null
pointer, each function uses its own internal mbstate_t
object instead, which is initialized at program startup to
the initial conversion state. The implementation behaves as
page 489 Library
page 490
if no library function calls these functions with a null
pointer for ps.
[#2] Also unlike their corresponding functions, the return
value does not represent whether the encoding is state-
dependent.
7.19.7.3.1 The mbrlen function
Synopsis
[#1]
#include <wchar.h>
size_t mbrlen(const char * restrict s,
size_t n,
mbstate_t * restrict ps);
Description
[#2] The mbrlen function is equivalent to the call:
mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)
where internal is the mbstate_t object for the mbrlen
function, except that the expression designated by ps is
evaluated only once.
Returns
[#3] The mbrlen function returns (size_t)-2, (size_t)-1, a
value between zero and n, inclusive.
[#4] Forward References: the mbrtowc function (7.19.7.3.2).
7.19.7.3.2 The mbrtowc function
Synopsis
[#1]
#include <wchar.h>
size_t mbrtowc(wchar_t * restrict pwc,
const char * restrict s,
size_t n,
mbstate_t * restrict ps);
page 490 Library
page 491
Description
[#2] If s is a null pointer, the mbrtowc function is
equivalent to the call:
mbrtowc(NULL, "", 1, ps)
In this case, the values of the parameters pwc and n are
ignored.
[#3] If s is not a null pointer, the mbrtowc function
inspects at most n bytes beginning with the byte pointed to
by s to determine the number of bytes needed to complete the
next multibyte character (including any shift sequences). If
the function determines that the next multibyte character is
completed, it determines the value of the corresponding wide
character and then, if pwc is not a null pointer, stores
that value in the object pointed to by pwc. If the
corresponding wide character is the null wide character, the
resulting state described is the initial conversion state.
Returns
[#4] The mbrtowc function returns the first of the following
that applies (given the current conversion state):
0 if the next n or fewer bytes complete the
multibyte character that corresponds to the
null wide character (which is the value
stored).
positive if the next n or fewer bytes complete a valid
multibyte character (which is the value
stored), the value returned is the number of
bytes that complete the multibyte character.
(size_t)-2 if the next n bytes contribute to an incomplete
(but potentially valid) multibyte character,
and all n bytes have been processed (no value
is stored).269
__________
269. When n has at least the value of the MB_CUR_MAX macro,
this case can only occur if s points at a sequence of
redundant shift sequences (for implementations with
state-dependent encodings).
page 491 Library
page 492
(size_t)-1 if an encoding error occurs, in which case the
next n or fewer bytes do not contribute to a
complete and valid multibyte character (no
value is stored); the value of the macro EILSEQ
is stored in errno, and the conversion state is
undefined.
7.19.7.3.3 The wcrtomb function
Synopsis
[#1]
#include <wchar.h>
size_t wcrtomb(char * restrict s,
wchar_t wc,
mbstate_t * restrict ps);
Description
[#2] If s is a null pointer, the wcrtomb function is
equivalent to the call
wcrtomb(buf, L'\0', ps)
where buf is an internal buffer.
[#3] If s is not a null pointer, the wcrtomb function
determines the number of bytes needed to represent the
multibyte character that corresponds to the wide character
given by wc (including any shift sequences), and stores the
resulting bytes in the array whose first element is pointed
to by s. At most MB_CUR_MAX bytes are stored. If wc is a
null wide character, a null byte is stored, preceded by any
shift sequence needed to restore the initial shift state;
the resulting state described is the initial conversion
state.
Returns
[#4] The wcrtomb function returns the number of bytes stored
in the array object (including any shift sequences). When wc
is not a valid wide character, an encoding error occurs: the
function stores the value of the macro EILSEQ in errno and
returns (size_t)-1; the conversion state is undefined.
page 492 Library
page 493
7.19.7.4 Restartable multibyte/wide-string conversion
functions
[#1] These functions differ from the corresponding multibyte
string functions of subclause 7.14.8 (mbstowcs and wcstombs)
in that they have an extra parameter, ps, of type pointer to
mbstate_t that points to an object that can completely
describe the current conversion state of the associated
multibyte character sequence. If ps is a null pointer, each
function uses its own internal mbstate_t object instead,
which is initialized at program startup to the initial
conversion state. The implementation behaves as if no
library function calls these functions with a null pointer
for ps.
[#2] Also unlike their corresponding functions, the
conversion source parameter, src, has a pointer-to-pointer
type. When the function is storing the results of
conversions (that is, when dst is not a null pointer), the
pointer object pointed to by this parameter is updated to
reflect the amount of the source processed by that
invocation.
7.19.7.4.1 The mbsrtowcs function
Synopsis
[#1]
#include <wchar.h>
size_t mbsrtowcs(wchar_t * restrict dst,
const char ** restrict src,
size_t len,
mbstate_t * restrict ps);
Description
[#2] The mbsrtowcs function converts a sequence of multibyte
characters, beginning in the conversion state described by
the object pointed to by ps, from the array indirectly
pointed to by src into a sequence of corresponding wide
characters. If dst is not a null pointer, the converted
characters are stored into the array pointed to by dst.
Conversion continues up to and including a terminating null
character, which is also stored. Conversion stops earlier in
two cases: when a sequence of bytes is encountered that does
not form a valid multibyte character, or (if dst is not a
null pointer) when len codes have been stored into the array
page 493 Library
page 494
pointed to by dst.270 Each conversion takes place as if by a
call to the mbrtowc function.
[#3] If dst is not a null pointer, the pointer object
pointed to by src is assigned either a null pointer (if
conversion stopped due to reaching a terminating null
character) or the address just past the last multibyte
character converted (if any). If conversion stopped due to
reaching a terminating null character and if dst is not a
null pointer, the resulting state described is the initial
conversion state.
Returns
[#4] If the input conversion encounters a sequence of bytes
that do not form a valid multibyte character, an encoding
error occurs: the mbsrtowcs function stores the value of the
macro EILSEQ in errno and returns (size_t)-1; the conversion
state is undefined. Otherwise, it returns the number of
multibyte characters successfully converted, not including
the terminating null (if any).
7.19.7.4.2 The wcsrtombs function
Synopsis
[#1]
#include <wchar.h>
size_t wcsrtombs(char * restrict dst,
const wchar_t ** restrict src,
size_t len,
mbstate_t * restrict ps);
Description
[#2] The wcsrtombs function converts a sequence of wide
characters from the array indirectly pointed to by src into
a sequence of corresponding multibyte characters, beginning
in the conversion state described by the object pointed to
by ps. If dst is not a null pointer, the converted
characters are then stored into the array pointed to by dst.
Conversion continues up to and including a terminating null
wide character, which is also stored. Conversion stops
__________
270. Thus, the value of len is ignored if dst is a null
pointer.
page 494 Library
page 495
earlier in two cases: when a code is reached that does not
correspond to a valid multibyte character, or (if dst is not
a null pointer) when the next multibyte character would
exceed the limit of len total bytes to be stored into the
array pointed to by dst. Each conversion takes place as if
by a call to the wcrtomb function.271
[#3] If dst is not a null pointer, the pointer object
pointed to by src is assigned either a null pointer (if
conversion stopped due to reaching a terminating null wide
character) or the address just past the last wide character
converted (if any). If conversion stopped due to reaching a
terminating null wide character, the resulting state
described is the initial conversion state.
Returns
[#4] If conversion stops because a code is reached that does
not correspond to a valid multibyte character, an encoding
error occurs: the wcsrtombs function stores the value of
the macro EILSEQ in errno and returns (size_t)-1; the
conversion state is undefined. Otherwise, it returns the
number of bytes in the resulting multibyte character
sequence, not including the terminating null (if any).
__________
271. If conversion stops because a terminating null wide
character has been reached, the bytes stored include
those necessary to reach the initial shift state
immediately before the null byte.
page 495 Library
page 496
7.20 Future library directions
[#1] The following names are grouped under individual
headers for convenience. All external names described below
are reserved no matter what headers are included by the
program.
7.20.1 Errors <errno.h>
[#1] Macros that begin with E and a digit or E and an
uppercase letter (possibly followed by any combination of
digits, letters, and underscore) may be added to the
declarations in the <errno.h> header.
7.20.2 Character handling <ctype.h>
[#1] Function names that begin with either is or to, and a
lowercase letter (possibly followed by any combination of
digits, letters, and underscore) may be added to the
declarations in the <ctype.h> header.
7.20.3 Integer types <inttypes.h>
[#1] Type names beginning with int or uint and ending with
_t may be added to the types defined in the <inttypes.h>
header. Macro names beginning with INT or UINT and ending
with _MAX or _MIN, or macro names beginning with PRI or SCN
followed by any lower case letter or X may be added to the
macros defined in the <inttypes.h> header.
7.20.4 Localization <locale.h>
[#1] Macros that begin with LC_ and an uppercase letter
(possibly followed by any combination of digits, letters,
and underscore) may be added to the definitions in the
<locale.h> header.
7.20.5 Signal handling <signal.h>
[#1] Macros that begin with either SIG and an uppercase
letter or SIG_ and an uppercase letter (possibly followed by
any combination of digits, letters, and underscore) may be
added to the definitions in the <signal.h> header.
page 496 Library
page 497
7.20.6 Input/output <stdio.h>
[#1] Lowercase letters may be added to the conversion
specifiers in fprintf and fscanf. Other characters may be
used in extensions.
[#2] The use of ungetc on a binary stream where the file
position indicator is zero prior to the call is an
obsolescent feature.
7.20.7 General utilities <stdlib.h>
[#1] Function names that begin with str and a lowercase
letter (possibly followed by any combination of digits,
letters, and underscore) may be added to the declarations in
the <stdlib.h> header.
7.20.8 Complex arithmetic <complex.h>
[#1] The function names
cexp2
cexpm1
clog10
clog1p
clog2
cerf
cerfc
cgamma
clgamma
and the same names suffixed with f or l are reserved for the
functions with complex arguments and return values.
7.20.9 String handling <string.h>
[#1] Function names that begin with str, mem, or wcs and a
lowercase letter (possibly followed by any combination of
digits, letters, and underscore) may be added to the
declarations in the <string.h> header.
page 497 Library
page 498
7.20.10 Wide-character classification and mapping utilities <wctype.h>
[#1] Function names that begin with is or to and a lowercase
letter (possibly followed by any combination of digits,
letters, and underscore) may be added to the declarations in
the <wctype.h> header.
7.20.11 Extended multibyte and wide-character utilities <wchar.h>
[#1] Function names that begin with wcs and a lowercase
letter (possibly followed by any combination of digits,
letters, and underscore) may be added to the declarations in
the <wchar.h> header.
[#2] Lowercase letters may be added to the conversion
specifiers in fwprintf and fwscanf.
page 498 Library
page 499
Annex A (informative)
Bibliography
1. ``The C Reference Manual'' by Dennis M. Ritchie, a version
of which was published in The C Programming Language by
Brian W. Kernighan and Dennis M. Ritchie, Prentice-Hall,
Inc., (1978). Copyright owned by AT&T.
2. 1984 /usr/group Standard by the /usr/group Standards
Committee, Santa Clara, California, USA, November 1984.
3. ANSI X3/TR-1-82 (1982), American National Dictionary for
Information Processing Systems, Information Processing
Systems Technical Report.
4. ANSI/IEEE 754-1985, American National Standard for Binary
Floating-Point Arithmetic.
5. ANSI/IEEE 854-1987, American National Standard for Radix-
Independent Floating-Point Arithmetic.
6. IEC 559:1993, Binary floating-point arithmetic for
microprocessor systems, second edition.
7. ISO 646:1983, Information processing - ISO 7-bit coded
character set for information interchange.
8. ISO/IEC 2382-1:1993, Information technology - Vocabulary -
Part 1: Fundamental terms.
9. ISO 4217:1995, Codes for the representation of currencies
and funds.
10. ISO 8601:1988, Data elements and interchange formats -
Information interchange - Representation of dates and
times.
11. ISO/IEC 9945-2:1993, Information technology - Portable
Operating System Interface (POSIX) - Part 2: Shell and
Utilities.
12. ISO/IEC 9899:1993, Programming languages - C.
13. ISO/IEC TR 10176, Information technology - Guidelines for
the preparation of programming language standards.
page 499 Bibliography
page 500
14. ISO/IEC 10646-1:1993, Information technology - Universal
Multiple-Octet Coded Character Set (UCS) - Part 1:
Architecture and Basic Multilingual Plane.
15. ISO/IEC 10967-1:1994, Information technology - Language
independent arithmetic - Part 1: Integer and floating point
arithmetic.
page 500 Bibliography
page 501
Annex B (informative)
Language syntax summary
[#1] Note - The notation is described in the introduction to
clause 6 (Language).
B.1 Lexical grammar
B.1.1 Character sets
[#1]
(5.2.1) hex-quad:
hexadecimal-digit hexadecimal-digit
hexadecimal-digit hexadecimal-digit
(5.2.1) universal-character-name:
\u hex-quad
\U hex-quad hex-quad
B.1.2 Lexical elements
[#1]
(6.1) token:
keyword
identifier
constant
string-literal
operator
punctuator
(6.1) preprocessing-token:
header-name
identifier
pp-number
character-constant
string-literal
operator
punctuator
each non-white-space character that cannot be one of the above
page 501 Language syntax summary
page 502
B.1.3 Keywords
(6.1.1) keyword: one of
auto break case char
complex const continue default
do double else enum
extern float for goto
if imaginary inline int
long register restrict return
short signed sizeof static
struct switch typedef union
unsigned void volatile while
B.1.4 Identifiers
(6.1.2) identifier:
nondigit
identifier nondigit
identifier digit
(6.1.2) nondigit: one of
universal-character-name
_ a b c d e f g h i j k l m
n o p q r s t u v w x y z
A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z
(6.1.2) digit: one of
0 1 2 3 4 5 6 7 8 9
B.1.5 Constants
(6.1.3) constant:
floating-constant
integer-constant
enumeration-constant
character-constant
(6.1.3.1) floating-constant:
decimal-floating-constant
hexadecimal-floating-constant
(6.1.3.1) decimal-floating-constant:
fractional-constant exponent-part-opt floating-suffix-opt
digit-sequence exponent-part floating-suffix-opt
page 502 Language syntax summary
page 503
(6.1.3.1) hexadecimal-floating-constant:
0x hexadecimal-fractional-constant
binary-exponent-part floating-suffix-opt
0X hexadecimal-fractional-constant
binary-exponent-part floating-suffix-opt
0x hexadecimal-digit-sequence
binary-exponent-part floating-suffix-opt
0X hexadecimal-digit-sequence
binary-exponent-part floating-suffix-opt
(6.1.3.1) fractional-constant:
digit-sequence-opt . digit-sequence
digit-sequence .
(6.1.3.1) exponent-part:
e sign-opt digit-sequence
E sign-opt digit-sequence
(6.1.3.1) sign: one of
+ -
(6.1.3.1) digit-sequence:
digit
digit-sequence digit
(6.1.3.1) hexadecimal-fractional-constant:
hexadecimal-digit-sequence-opt .
hexadecimal-digit-sequence
hexadecimal-digit-sequence .
(6.1.3.1) binary-exponent-part:
p sign-opt digit-sequence
P sign-opt digit-sequence
(6.1.3.1) hexadecimal-digit-sequence:
hexadecimal-digit
hexadecimal-digit-sequence hexadecimal-digit
(6.1.3.1) hexadecimal-digit: one of
0 1 2 3 4 5 6 7 8 9
a b c d e f
A B C D E F
(6.1.3.1) floating-suffix: one of
f l F L
(6.1.3.2) integer-constant:
decimal-constant integer-suffix-opt
octal-constant integer-suffix-opt
hexadecimal-constant integer-suffix-opt
page 503 Language syntax summary
page 504
(6.1.3.2) decimal-constant:
nonzero-digit
decimal-constant digit
(6.1.3.2) octal-constant:
0
octal-constant octal-digit
(6.1.3.2) hexadecimal-constant:
0x hexadecimal-digit
0X hexadecimal-digit
hexadecimal-constant hexadecimal-digit
(6.1.3.2) nonzero-digit: one of
1 2 3 4 5 6 7 8 9
(6.1.3.2) octal-digit: one of
0 1 2 3 4 5 6 7
(6.1.3.2) integer-suffix:
unsigned-suffix long-suffix-opt
long-suffix unsigned-suffix-opt
unsigned-suffix long-long-suffix-opt
long-long-suffix unsigned-suffix-opt
(6.1.3.2) unsigned-suffix: one of
u U
(6.1.3.2) long-suffix: one of
l L
(6.1.3.2) long-long-suffix: one of
ll LL
(6.1.3.3) enumeration-constant:
identifier
(6.1.3.4) character-constant:
'c-char-sequence'
L'c-char-sequence'
(6.1.3.4) c-char-sequence:
c-char
c-char-sequence c-char
(6.1.3.4) c-char:
any member of the source character set except
the single-quote ', backslash \, or new-line character
escape-sequence
universal-character-name
page 504 Language syntax summary
page 505
(6.1.3.4) escape-sequence:
simple-escape-sequence
octal-escape-sequence
hexadecimal-escape-sequence
(6.1.3.4) simple-escape-sequence: one of
\' \" \? \\
\a \b \f \n \r \t \v
(6.1.3.4) octal-escape-sequence:
\ octal-digit
\ octal-digit octal-digit
\ octal-digit octal-digit octal-digit
(6.1.3.4) hexadecimal-escape-sequence:
\x hexadecimal-digit
hexadecimal-escape-sequence hexadecimal-digit
B.1.6 String literals
(6.1.4) string-literal:
"s-char-sequence-opt"
L"s-char-sequence-opt"
(6.1.4) s-char-sequence:
s-char
s-char-sequence s-char
(6.1.4) s-char:
any member of the source character set except
the double-quote ", backslash \, or new-line character
escape-sequence
universal-character-name
B.1.7 Operators
(6.1.5) operator: one of
[ ] ( ) . ->
++ -- & * + - ~ ! sizeof
/ % << >> < > <= >= == != ^ | && ||
? :
= *= /= %= += -= <<= >>= &= ^= |=
, # ## <: :> %: %:%:
page 505 Language syntax summary
page 506
B.1.8 Punctuators
(6.1.6) punctuator: one of
[ ] ( ) { } * , : = ; ... #
<: :> <% %> %:
B.1.9 Header names
(6.1.7) header-name:
<h-char-sequence>
"q-char-sequence"
(6.1.7) h-char-sequence:
h-char
h-char-sequence h-char
(6.1.7) h-char:
any member of the source character set except
the new-line character and >
(6.1.7) q-char-sequence:
q-char
q-char-sequence q-char
(6.1.7) q-char:
any member of the source character set except
the new-line character and "
B.1.10 Preprocessing numbers
(6.1.8) pp-number:
digit
. digit
pp-number digit
pp-number nondigit
pp-number e sign
pp-number E sign
pp-number p sign
pp-number P sign
pp-number .
page 506 Language syntax summary
page 507
B.2 Phrase structure grammar
B.2.1 Expressions
(6.3.1) primary-expr:
identifier
constant
string-literal
( expression )
(6.3.2) postfix-expr:
primary-expr
postfix-expr [ expression ]
postfix-expr ( argument-expression-list-opt )
postfix-expr . identifier
postfix-expr -> identifier
postfix-expr ++
postfix-expr --
( type-name ) { initializer-list }
( type-name ) { initializer-list , }
(6.3.2) argument-expression-list:
assignment-expr
argument-expression-list , assignment-expr
(6.3.3) unary-expr:
postfix-expr
++ unary-expr
-- unary-expr
unary-operator cast-expr
sizeof unary-expr
sizeof ( type-name )
(6.3.3) unary-operator: one of
& * + - ~ !
(6.3.4) cast-expr:
unary-expr
( type-name ) cast-expr
(6.3.5) multiplicative-expr:
cast-expr
multiplicative-expr * cast-expr
multiplicative-expr / cast-expr
multiplicative-expr % cast-expr
(6.3.6) additive-expr:
multiplicative-expr
additive-expr + multiplicative-expr
additive-expr - multiplicative-expr
page 507 Language syntax summary
page 508
(6.3.7) shift-expr:
additive-expr
shift-expr << additive-expr
shift-expr >> additive-expr
(6.3.8) relational-expr:
shift-expr
relational-expr < shift-expr
relational-expr > shift-expr
relational-expr <= shift-expr
relational-expr >= shift-expr
(6.3.9) equality-expr:
relational-expr
equality-expr == relational-expr
equality-expr != relational-expr
(6.3.10) AND-expr:
equality-expr
AND-expr & equality-expr
(6.3.11) exclusive-OR-expr:
AND-expr
exclusive-OR-expr ^ AND-expr
(6.3.12) inclusive-OR-expr:
exclusive-OR-expr
inclusive-OR-expr | exclusive-OR-expr
(6.3.13) logical-AND-expr:
inclusive-OR-expr
logical-AND-expr && inclusive-OR-expr
(6.3.14) logical-OR-expr:
logical-AND-expr
logical-OR-expr || logical-AND-expr
(6.3.15) conditional-expr:
logical-OR-expr
logical-OR-expr ? expr : conditional-expr
(6.3.16) assignment-expr:
conditional-expr
unary-expr assignment-operator assignment-expr
(6.3.16) assignment-operator: one of
= *= /= %= += -= <<= >>= &= ^= |=
page 508 Language syntax summary
page 509
(6.3.17) expression:
assignment-expr
expression , assignment-expr
(6.4) constant-expr:
conditional-expr
B.2.2 Declarations
(6.5) declaration:
declaration-specifiers init-declarator-list-opt ;
(6.5) declaration-specifiers:
storage-class-specifier declaration-specifiers-opt
type-specifier declaration-specifiers-opt
type-qualifier declaration-specifiers-opt
function-specifiers
(6.5) init-declarator-list:
init-declarator
init-declarator-list , init-declarator
(6.5) init-declarator:
declarator
declarator = initializer
(6.5.1) storage-class-specifier:
typedef
extern
static
auto
register
(6.5.2) type-specifier:
void
char
short
int
long
float
double
complex
signed
unsigned
struct-or-union-specifier
enum-specifier
typedef-name
page 509 Language syntax summary
page 510
(6.5.2.1) struct-or-union-specifier:
struct-or-union identifier-opt { struct-declaration-list }
struct-or-union identifier
(6.5.2.1) struct-or-union:
struct
union
(6.5.2.1) struct-declaration-list:
struct-declaration
struct-declaration-list struct-declaration
(6.5.2.1) struct-declaration:
specifier-qualifier-list struct-declarator-list ;
(6.5.2.1) specifier-qualifier-list:
type-specifier specifier-qualifier-list-opt
type-qualifier specifier-qualifier-list-opt
(6.5.2.1) struct-declarator-list:
struct-declarator
struct-declarator-list , struct-declarator
(6.5.2.1) struct-declarator:
declarator
declarator-opt : constant-expr
(6.5.2.2) enum-specifier:
enum identifier-opt { enumerator-list }
enum identifier-opt { enumerator-list , }
enum identifier
(6.5.2.2) enumerator-list:
enumerator
enumerator-list , enumerator
(6.5.2.2) enumerator:
enumeration-constant
enumeration-constant = constant-expression
(6.5.3) type-qualifier:
const
restrict
volatile
(6.5.4) function-specifier:
inline
(6.5.5) declarator:
pointer-opt direct-declarator
page 510 Language syntax summary
page 511
(6.5.5) direct-declarator:
identifier
( declarator )
direct-declarator [ assignment-expr-opt ]
direct-declarator [ * ]
direct-declarator ( parameter-type-list )
direct-declarator ( identifier-list-opt )
(6.5.5) pointer:
* type-qualifier-list-opt
* type-qualifier-list-opt pointer
(6.5.5) type-qualifier-list:
type-qualifier
type-qualifier-list type-qualifier
(6.5.5) parameter-type-list:
parameter-list
parameter-list , ...
(6.5.5) parameter-list:
parameter-declaration
parameter-list , parameter-declaration
(6.5.5) parameter-declaration:
declaration-specifiers declarator
declaration-specifiers abstract-declarator-opt
(6.5.5) identifier-list:
identifier
identifier-list , identifier
(6.5.6) type-name:
specifier-qualifier-list abstract-declarator-opt
(6.5.6) abstract-declarator:
pointer
pointer-opt direct-abstract-declarator
(6.5.6) direct-abstract-declarator:
( abstract-declarator )
direct-abstract-declarator-opt [ assignment-expr-opt ]
direct-abstract-declarator [ * ]
direct-abstract-declarator-opt ( parameter-type-list-opt )
(6.5.7) typedef-name:
identifier
page 511 Language syntax summary
page 512
(6.5.8) initializer:
assignment-expr
{ initializer-list }
{ initializer-list , }
(6.5.8) initializer-list:
designation-opt initializer
initializer-list , designation-opt initializer
(6.5.8) designation:
designator-list =
(6.5.8) designator-list:
designator
designator-list designator
(6.5.8) designator:
[ constant-expression ]
. identifier
B.2.3 Statements
(6.6) statement:
labeled-statement
compound-statement
expression-statement
selection-statement
iteration-statement
jump-statement
(6.6.1) labeled-statement:
identifier : statement
case constant-expr : statement
default : statement
(6.6.2) compound-statement:
{ block-item-list-opt }
(6.6.2) block-item-list:
block-item
block-item-list block-item
(6.6.2) block-item:
declaration
statement
(6.6.3) expression-statement:
expression-opt ;
page 512 Language syntax summary
page 513
(6.6.4) selection-statement:
if ( expression ) statement
if ( expression ) statement else statement
switch ( expression ) statement
(6.6.5) iteration-statement:
while ( expression ) statement
do statement while ( expression ) ;
for ( expr-opt ; expr-opt ; expr-opt ) statement
for ( declaration ; expr-opt ; expr-opt ) statement
(6.6.6) jump-statement:
goto identifier ;
continue ;
break ;
return expression-opt ;
B.2.4 External definitions
(6.7) translation-unit:
external-declaration
translation-unit external-declaration
(6.7) external-declaration:
function-definition
declaration
(6.7.1) function-definition:
declaration-specifiers declarator declaration-list-opt compound-statement
B.3 Preprocessing directives
(6.8) preprocessing-file:
group-opt
(6.8) group:
group-part
group group-part
(6.8) group-part:
pp-tokens-opt new-line
if-section
control-line
(6.8.1) if-section:
if-group elif-groups-opt else-group-opt endif-line
page 513 Language syntax summary
page 514
(6.8.1) if-group:
# if constant-expr new-line group-opt
# ifdef identifier new-line group-opt
# ifndef identifier new-line group-opt
(6.8.1) elif-groups:
elif-group
elif-groups elif-group
(6.8.1) elif-group:
# elif constant-expr new-line group-opt
(6.8.1) else-group:
# else new-line group-opt
(6.8.1) endif-line:
# endif new-line
control-line:
(6.8.2) # include pp-tokens new-line
(6.8.3) # define identifier replacement-list new-line
(6.8.3) # define identifier lparen identifier-list-opt )
replacement-list new-line
(6.8.3) # define identifier lparen ... ) replacement-list new-line
(6.8.3) # define identifier lparen identifier-list , ... )
replacement-list new-line
(6.8.3) # undef identifier new-line
(6.8.4) # line pp-tokens new-line
(6.8.5) # error pp-tokens-opt new-line
(6.8.6) # pragma pp-tokens-opt new-line
(6.8.7) # new-line
(6.8.3) lparen:
the left-parenthesis character without preceding white space
(6.8.3) replacement-list:
pp-tokens-opt
(6.8) pp-tokens:
preprocessing-token
pp-tokens preprocessing-token
(6.8) new-line:
the new-line character
page 514 Language syntax summary
page 515
Annex C (informative)
Sequence points
[#1] The following are the sequence points described in 5.1.2.3.
[#2]
- The call to a function, after the arguments have been
evaluated (6.3.2.2).
- The end of the first operand of the following operators:
logical AND && (6.3.13); logical OR || (6.3.14); conditional
? (6.3.15); comma , (6.3.17).
- The end of a full declarator: declarators (6.5.5);
- The end of a full expression: an initializer (6.5.8); the
expression in an expression statement (6.6.3); the
controlling expression of a selection statement (if or
switch) (6.6.4); the controlling expression of a while or do
statement (6.6.5); each of the three expressions of a for
statement (6.6.5.3); the expression in a return statement
(6.6.6.4).
- Immediately before a library function return (7.1.8).
page 515 Sequence points
page 516
Annex D (informative)
Library summary
[#1]
D.1 Errors <errno.h>
EDOM
EILSEQ
ERANGE
errno
D.2 Common definitions <stddef.h>
NULL
offsetof(type, member-designator)
ptrdiff_t
size_t
wchar_t
D.3 Boolean type and values <stdbool.h>
bool
true
false
__bool_true_false_are_defined
D.4 Diagnostics <assert.h>
NDEBUG
void assert(int expression);
page 516 Library summary
page 517
D.5 Character handling <ctype.h>
int isalnum(int c);
int isalpha(int c);
int iscntrl(int c);
int isdigit(int c);
int isgraph(int c);
int islower(int c);
int isprint(int c);
int ispunct(int c);
int isspace(int c);
int isupper(int c);
int isxdigit(int c);
int tolower(int c);
int toupper(int c);
D.6 Integer types <inttypes.h>
int8_t
int16_t
int32_t
int64_t
uint8_t
uint16_t
uint32_t
uint64_t
int_least8_t
int_least16_t
int_least32_t
int_least64_t
uint_least8_t
uint_least16_t
uint_least32_t
uint_least64_t
int_fast8_t
int_fast16_t
int_fast32_t
int_fast64_t
uint_fast8_t
uint_fast16_t
uint_fast32_t
uint_fast64_t
intptr_t
uintptr_t
intmax_t
uintmax_t
INT8_MIN
INT16_MIN
INT32_MIN
INT64_MIN
INT8_MAX
page 517 Library summary
page 518
INT16_MAX
INT32_MAX
INT64_MAX
UINT8_MAX
UINT16_MAX
UINT32_MAX
UINT64_MAX
INT_LEAST8_MIN
INT_LEAST16_MIN
INT_LEAST32_MIN
INT_LEAST64_MIN
INT_LEAST8_MAX
INT_LEAST16_MAX
INT_LEAST32_MAX
INT_LEAST64_MAX
UINT_LEAST8_MAX
UINT_LEAST16_MAX
UINT_LEAST32_MAX
UINT_LEAST64_MAX
INT_FAST8_MIN
INT_FAST16_MIN
INT_FAST32_MIN
INT_FAST64_MIN
INT_FAST8_MAX
INT_FAST16_MAX
INT_FAST32_MAX
INT_FAST64_MAX
UINT_FAST8_MAX
UINT_FAST16_MAX
UINT_FAST32_MAX
UINT_FAST64_MAX
INTPTR_MIN
INTPTR_MAX
UINTPTR_MAX
INTMAX_MIN
INTMAX_MAX
UINTMAX_MAX
INT8_C(value)
INT16_C(value)
INT32_C(value)
INT64_C(value)
UINT8_C(value)
UINT16_C(value)
UINT32_C(value)
UINT64_C(value)
INTMAX_C(value)
UINTMAX_C(value)
PRId8
PRId16
PRId32
PRId64
page 518 Library summary
page 519
PRIdLEAST8
PRIdLEAST16
PRIdLEAST32
PRIdLEAST64
PRIdFAST8
PRIdFAST16
PRIdFAST32
PRIdFAST64
PRIdMAX
PRIdPTR
PRIi8
PRIi16
PRIi32
PRIi64
PRIiLEAST8
PRIiLEAST16
PRIiLEAST32
PRIiLEAST64
PRIiFAST8
PRIiFAST16
PRIiFAST32
PRIiFAST64
PRIiMAX
PRIiPTR
PRIo8
PRIo16
PRIo32
PRIo64
PRIoLEAST8
PRIoLEAST16
PRIoLEAST32
PRIoLEAST64
PRIoFAST8
PRIoFAST16
PRIoFAST32
PRIoFAST64
PRIoMAX
PRIoPTR
PRIu8
PRIu16
PRIu32
PRIu64
PRIuLEAST8
PRIuLEAST16
PRIuLEAST32
PRIuLEAST64
PRIuFAST8
PRIuFAST16
PRIuFAST32
PRIuFAST64
PRIuMAX
page 519 Library summary
page 520
PRIuPTR
PRIx8
PRIx16
PRIx32
PRIx64
PRIxLEAST8
PRIxLEAST16
PRIxLEAST32
PRIxLEAST64
PRIxFAST8
PRIxFAST16
PRIxFAST32
PRIxFAST64
PRIxMAX
PRIxPTR
PRIX8
PRIX16
PRIX32
PRIX64
PRIXLEAST8
PRIXLEAST16
PRIXLEAST32
PRIXLEAST64
PRIXFAST8
PRIXFAST16
PRIXFAST32
PRIXFAST64
PRIXMAX
PRIXPTR
SCNd8
SCNd16
SCNd32
SCNd64
SCNdLEAST8
SCNdLEAST16
SCNdLEAST32
SCNdLEAST64
SCNdFAST8
SCNdFAST16
SCNdFAST32
SCNdFAST64
SCNdMAX
SCNdPTR
SCNi8
SCNi16
SCNi32
SCNi64
SCNiLEAST8
SCNiLEAST16
SCNiLEAST32
SCNiLEAST64
page 520 Library summary
page 521
SCNiFAST8
SCNiFAST16
SCNiFAST32
SCNiFAST64
SCNiMAX
SCNiPTR
SCNo8
SCNo16
SCNo32
SCNo64
SCNoLEAST8
SCNoLEAST16
SCNoLEAST32
SCNoLEAST64
SCNoFAST8
SCNoFAST16
SCNoFAST32
SCNoFAST64
SCNoMAX
SCNoPTR
SCNu8
SCNu16
SCNu32
SCNu64
SCNuLEAST8
SCNuLEAST16
SCNuLEAST32
SCNuLEAST64
SCNuFAST8
SCNuFAST16
SCNuFAST32
SCNuFAST64
SCNuMAX
SCNuPTR
SCNx8
SCNx16
SCNx32
SCNx64
SCNxLEAST8
SCNxLEAST16
SCNxLEAST32
SCNxLEAST64
SCNxFAST8
SCNxFAST16
SCNxFAST32
SCNxFAST64
SCNxMAX
SCNxPTR
PTRDIFF_MIN
PTRDIFF_MAX
SIG_ATOMIC_MIN
page 521 Library summary
page 522
SIG_ATOMIC_MAX
SIZE_MAX
WCHAR_MIN
WCHAR_MAX
WINT_MIN
WINT_MAX
intmax_t strtoimax(const char * restrict nptr,
char ** restrict endptr, int base);
uintmax_t strtoumax(const char * restrict nptr,
char ** restrict endptr, int base);
intmax_t wcstoimax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
uintmax_t wcstoumax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
page 522 Library summary
page 523
D.7 Floating-point environment <fenv.h>
fenv_t
fexcept_t
FE_ALL_EXCEPT
FE_DFL_ENV
FE_DIVBYZERO
FE_INEXACT
FE_INVALID
FE_OVERFLOW
FE_UNDERFLOW
FE_DOWNWARD
FE_TONEAREST
FE_TOWARDZERO
FE_UPWARD
#pragma STDC FENV_ACCESS on-off-switch
void feclearexcept(int excepts);
void fegetexceptflag(fexcept_t *flagp,
int excepts);
void feraiseexcept(int excepts);
void fesetexceptflag(const fexcept_t *flagp, int excepts);
int fetestexcept(int excepts);
int fegetround(void);
int fesetround(int round);
void fegetenv(fenv_t *envp);
int feholdexcept(fenv_t *envp);
void fesetenv(const fenv_t *envp);
void feupdateenv(const fenv_t *envp);
D.8 Localization <locale.h>
LC_ALL
LC_COLLATE
LC_CTYPE
LC_MONETARY
LC_NUMERIC
LC_TIME
NULL
struct lconv
char *setlocale(int category, const char *locale);
struct lconv *localeconv(void);
page 523 Library summary
page 524
D.9 Mathematics <math.h>
float_t
double_t
INFINITY
NAN
FP_NAN
FP_INFINITE
FP_NORMAL
FP_SUBNORMAL
FP_ZERO
FP_FAST_FMA
FP_FAST_FMAF
FP_FAST_FMAL
FP_ILOGB0
FP_ILOGBNAN
DECIMAL_DIG
#pragma STDC FP_CONTRACT on-off-switch
int signbit(real-floating x);
HUGE_VAL
HUGE_VALL
HUGE_VALF
int fpclassify(real-floating x);
int isfinite(real-floating x);
int isnormal(real-floating x);
int isnan(real-floating x);
int isinf(real-floating x);
double acos(double x);
float acosf(float x);
long double acosl(long double x);
double asin(double x);
float asinf(float x);
long double asinl(long double x);
double atan(double x);
float atanf(float x);
long double atanl(long double x);
double atan2(double y, double x);
float atan2f(float y, float x);
long double atan2l(long double y, long double x);
double cos(double x);
float cosf(float x);
long double cosl(long double x);
double sin(double x);
float sinf(float x);
long double sinl(long double x);
double tan(double x);
float tanf(float x);
long double tanl(long double x);
double cosh(double x);
float coshf(float x);
long double coshl(long double x);
page 524 Library summary
page 525
double sinh(double x);
float sinhf(float x);
long double sinhl(long double x);
double tanh(double x);
float tanhf(float x);
long double tanhl(long double x);
double acosh(double x);
float acoshf(float x);
long double acoshl(long double x);
double asinh(double x);
float asinhf(float x);
long double asinhl(long double x);
double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);
double exp(double x);
float expf(float x);
long double expl(long double x);
double frexp(double value, int *exp);
float frexpf(float value, int *exp);
long double frexpl(long double value, int *exp);
double ldexp(double x, int exp);
float ldexpf(float x, int exp);
long double ldexpl(long doub