1 N1548 Committee Draft -- December 2, 2010 ISO/IEC 9899:201x
6 INTERNATIONAL STANDARD (C)ISO/IEC ISO/IEC 9899:201x
11 Programming languages -- C
18 (Cover sheet to be provided by ISO Secretariat.)
20 This International Standard specifies the form and establishes the interpretation of
21 programs expressed in the programming language C. Its purpose is to promote
22 portability, reliability, maintainability, and efficient execution of C language programs on
23 a variety of computing systems.
25 Clauses are included that detail the C language itself and the contents of the C language
26 execution library. Annexes summarize aspects of both of them, and enumerate factors
27 that influence the portability of C programs.
29 Although this International Standard is intended to guide knowledgeable C language
30 programmers as well as implementors of C language translation systems, the document
31 itself is not designed to serve as a tutorial.
33 Recipients of this draft are invited to submit, with their comments, notification of any
34 relevant patent rights of which they are aware and to provide supporting documentation.
36 Changes from the previous draft (N1256) are indicated by ''diff marks'' in the right
37 margin: deleted text is marked with ''*'', new or changed text with '' ''.
49 Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
50 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
51 1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
52 2. Normative references . . . . . . . . . . . . . . . . . . . . . . . 2
53 3. Terms, definitions, and symbols . . . . . . . . . . . . . . . . . . . 3
54 4. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . . 8
55 5. Environment . . . . . . . . . . . . . . . . . . . . . . . . . . 10
56 5.1 Conceptual models . . . . . . . . . . . . . . . . . . . . . 10
57 5.1.1 Translation environment . . . . . . . . . . . . . . . . 10
58 5.1.2 Execution environments . . . . . . . . . . . . . . . . 12
59 5.2 Environmental considerations . . . . . . . . . . . . . . . . . 22
60 5.2.1 Character sets . . . . . . . . . . . . . . . . . . . . 22
61 5.2.2 Character display semantics . . . . . . . . . . . . . . 24
62 5.2.3 Signals and interrupts . . . . . . . . . . . . . . . . . 25
63 5.2.4 Environmental limits . . . . . . . . . . . . . . . . . 25
64 6. Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
65 6.1 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . 35
66 6.2 Concepts . . . . . . . . . . . . . . . . . . . . . . . . . 35
67 6.2.1 Scopes of identifiers . . . . . . . . . . . . . . . . . 35
68 6.2.2 Linkages of identifiers . . . . . . . . . . . . . . . . . 36
69 6.2.3 Name spaces of identifiers . . . . . . . . . . . . . . . 37
70 6.2.4 Storage durations of objects . . . . . . . . . . . . . . 38
71 6.2.5 Types . . . . . . . . . . . . . . . . . . . . . . . 39
72 6.2.6 Representations of types . . . . . . . . . . . . . . . . 44
73 6.2.7 Compatible type and composite type . . . . . . . . . . . 47
74 6.2.8 Alignment of objects . . . . . . . . . . . . . . . . . 48
75 6.3 Conversions . . . . . . . . . . . . . . . . . . . . . . . . 50
76 6.3.1 Arithmetic operands . . . . . . . . . . . . . . . . . 50
77 6.3.2 Other operands . . . . . . . . . . . . . . . . . . . 54
78 6.4 Lexical elements . . . . . . . . . . . . . . . . . . . . . . 57
79 6.4.1 Keywords . . . . . . . . . . . . . . . . . . . . . . 58
80 6.4.2 Identifiers . . . . . . . . . . . . . . . . . . . . . . 59
81 6.4.3 Universal character names . . . . . . . . . . . . . . . 61
82 6.4.4 Constants . . . . . . . . . . . . . . . . . . . . . . 62
83 6.4.5 String literals . . . . . . . . . . . . . . . . . . . . 70
84 6.4.6 Punctuators . . . . . . . . . . . . . . . . . . . . . 72
85 6.4.7 Header names . . . . . . . . . . . . . . . . . . . . 73
86 6.4.8 Preprocessing numbers . . . . . . . . . . . . . . . . 74
87 6.4.9 Comments . . . . . . . . . . . . . . . . . . . . . 75
92 6.5 Expressions . . . . . . . . . . . . . . . . . . . . . . . . 76
93 6.5.1 Primary expressions . . . . . . . . . . . . . . . . . 78
94 6.5.2 Postfix operators . . . . . . . . . . . . . . . . . . . 79
95 6.5.3 Unary operators . . . . . . . . . . . . . . . . . . . 88
96 6.5.4 Cast operators . . . . . . . . . . . . . . . . . . . . 91
97 6.5.5 Multiplicative operators . . . . . . . . . . . . . . . . 92
98 6.5.6 Additive operators . . . . . . . . . . . . . . . . . . 92
99 6.5.7 Bitwise shift operators . . . . . . . . . . . . . . . . . 94
100 6.5.8 Relational operators . . . . . . . . . . . . . . . . . . 95
101 6.5.9 Equality operators . . . . . . . . . . . . . . . . . . 96
102 6.5.10 Bitwise AND operator . . . . . . . . . . . . . . . . . 97
103 6.5.11 Bitwise exclusive OR operator . . . . . . . . . . . . . 98
104 6.5.12 Bitwise inclusive OR operator . . . . . . . . . . . . . . 98
105 6.5.13 Logical AND operator . . . . . . . . . . . . . . . . . 99
106 6.5.14 Logical OR operator . . . . . . . . . . . . . . . . . 99
107 6.5.15 Conditional operator . . . . . . . . . . . . . . . . . 100
108 6.5.16 Assignment operators . . . . . . . . . . . . . . . . . 101
109 6.5.17 Comma operator . . . . . . . . . . . . . . . . . . . 104
110 6.6 Constant expressions . . . . . . . . . . . . . . . . . . . . . 105
111 6.7 Declarations . . . . . . . . . . . . . . . . . . . . . . . . 107
112 6.7.1 Storage-class specifiers . . . . . . . . . . . . . . . . 108
113 6.7.2 Type specifiers . . . . . . . . . . . . . . . . . . . . 109
114 6.7.3 Type qualifiers . . . . . . . . . . . . . . . . . . . . 120
115 6.7.4 Function specifiers . . . . . . . . . . . . . . . . . . 124
116 6.7.5 Alignment specifier . . . . . . . . . . . . . . . . . . 126
117 6.7.6 Declarators . . . . . . . . . . . . . . . . . . . . . 127
118 6.7.7 Type names . . . . . . . . . . . . . . . . . . . . . 135
119 6.7.8 Type definitions . . . . . . . . . . . . . . . . . . . 136
120 6.7.9 Initialization . . . . . . . . . . . . . . . . . . . . 138
121 6.7.10 Static assertions . . . . . . . . . . . . . . . . . . . 144
122 6.8 Statements and blocks . . . . . . . . . . . . . . . . . . . . 145
123 6.8.1 Labeled statements . . . . . . . . . . . . . . . . . . 145
124 6.8.2 Compound statement . . . . . . . . . . . . . . . . . 146
125 6.8.3 Expression and null statements . . . . . . . . . . . . . 146
126 6.8.4 Selection statements . . . . . . . . . . . . . . . . . 147
127 6.8.5 Iteration statements . . . . . . . . . . . . . . . . . . 149
128 6.8.6 Jump statements . . . . . . . . . . . . . . . . . . . 150
129 6.9 External definitions . . . . . . . . . . . . . . . . . . . . . 154
130 6.9.1 Function definitions . . . . . . . . . . . . . . . . . . 155
131 6.9.2 External object definitions . . . . . . . . . . . . . . . 157
132 6.10 Preprocessing directives . . . . . . . . . . . . . . . . . . . 159
133 6.10.1 Conditional inclusion . . . . . . . . . . . . . . . . . 161
134 6.10.2 Source file inclusion . . . . . . . . . . . . . . . . . 163
135 6.10.3 Macro replacement . . . . . . . . . . . . . . . . . . 165
140 6.10.4 Line control . . . . . . . . . . . . . . . . . . . . . 172
141 6.10.5 Error directive . . . . . . . . . . . . . . . . . . . . 173
142 6.10.6 Pragma directive . . . . . . . . . . . . . . . . . . . 173
143 6.10.7 Null directive . . . . . . . . . . . . . . . . . . . . 174
144 6.10.8 Predefined macro names . . . . . . . . . . . . . . . . 174
145 6.10.9 Pragma operator . . . . . . . . . . . . . . . . . . . 176
146 6.11 Future language directions . . . . . . . . . . . . . . . . . . 178
147 6.11.1 Floating types . . . . . . . . . . . . . . . . . . . . 178
148 6.11.2 Linkages of identifiers . . . . . . . . . . . . . . . . . 178
149 6.11.3 External names . . . . . . . . . . . . . . . . . . . 178
150 6.11.4 Character escape sequences . . . . . . . . . . . . . . 178
151 6.11.5 Storage-class specifiers . . . . . . . . . . . . . . . . 178
152 6.11.6 Function declarators . . . . . . . . . . . . . . . . . 178
153 6.11.7 Function definitions . . . . . . . . . . . . . . . . . . 178
154 6.11.8 Pragma directives . . . . . . . . . . . . . . . . . . 178
155 6.11.9 Predefined macro names . . . . . . . . . . . . . . . . 178
156 7. Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
157 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 179
158 7.1.1 Definitions of terms . . . . . . . . . . . . . . . . . . 179
159 7.1.2 Standard headers . . . . . . . . . . . . . . . . . . . 180
160 7.1.3 Reserved identifiers . . . . . . . . . . . . . . . . . . 181
161 7.1.4 Use of library functions . . . . . . . . . . . . . . . . 182
162 7.2 Diagnostics <assert.h> . . . . . . . . . . . . . . . . . . 185
163 7.2.1 Program diagnostics . . . . . . . . . . . . . . . . . 185
164 7.3 Complex arithmetic <complex.h> . . . . . . . . . . . . . . 187
165 7.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . 187
166 7.3.2 Conventions . . . . . . . . . . . . . . . . . . . . . 188
167 7.3.3 Branch cuts . . . . . . . . . . . . . . . . . . . . . 188
168 7.3.4 The CX_LIMITED_RANGE pragma . . . . . . . . . . . 188
169 7.3.5 Trigonometric functions . . . . . . . . . . . . . . . . 189
170 7.3.6 Hyperbolic functions . . . . . . . . . . . . . . . . . 191
171 7.3.7 Exponential and logarithmic functions . . . . . . . . . . 193
172 7.3.8 Power and absolute-value functions . . . . . . . . . . . 194
173 7.3.9 Manipulation functions . . . . . . . . . . . . . . . . 195
174 7.4 Character handling <ctype.h> . . . . . . . . . . . . . . . . 199
175 7.4.1 Character classification functions . . . . . . . . . . . . 199
176 7.4.2 Character case mapping functions . . . . . . . . . . . . 202
177 7.5 Errors <errno.h> . . . . . . . . . . . . . . . . . . . . . 204
178 7.6 Floating-point environment <fenv.h> . . . . . . . . . . . . . 205
179 7.6.1 The FENV_ACCESS pragma . . . . . . . . . . . . . . 207
180 7.6.2 Floating-point exceptions . . . . . . . . . . . . . . . 208
181 7.6.3 Rounding . . . . . . . . . . . . . . . . . . . . . . 211
182 7.6.4 Environment . . . . . . . . . . . . . . . . . . . . 212
183 7.7 Characteristics of floating types <float.h> . . . . . . . . . . . 215
187 7.8 Format conversion of integer types <inttypes.h> . . . . . . . . 216
188 7.8.1 Macros for format specifiers . . . . . . . . . . . . . . 216
189 7.8.2 Functions for greatest-width integer types . . . . . . . . . 217
190 7.9 Alternative spellings <iso646.h> . . . . . . . . . . . . . . . 220
191 7.10 Sizes of integer types <limits.h> . . . . . . . . . . . . . . 221
192 7.11 Localization <locale.h> . . . . . . . . . . . . . . . . . . 222
193 7.11.1 Locale control . . . . . . . . . . . . . . . . . . . . 223
194 7.11.2 Numeric formatting convention inquiry . . . . . . . . . . 224
195 7.12 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 230
196 7.12.1 Treatment of error conditions . . . . . . . . . . . . . . 232
197 7.12.2 The FP_CONTRACT pragma . . . . . . . . . . . . . . 234
198 7.12.3 Classification macros . . . . . . . . . . . . . . . . . 234
199 7.12.4 Trigonometric functions . . . . . . . . . . . . . . . . 237
200 7.12.5 Hyperbolic functions . . . . . . . . . . . . . . . . . 239
201 7.12.6 Exponential and logarithmic functions . . . . . . . . . . 241
202 7.12.7 Power and absolute-value functions . . . . . . . . . . . 246
203 7.12.8 Error and gamma functions . . . . . . . . . . . . . . . 248
204 7.12.9 Nearest integer functions . . . . . . . . . . . . . . . . 250
205 7.12.10 Remainder functions . . . . . . . . . . . . . . . . . 253
206 7.12.11 Manipulation functions . . . . . . . . . . . . . . . . 254
207 7.12.12 Maximum, minimum, and positive difference functions . . . 256
208 7.12.13 Floating multiply-add . . . . . . . . . . . . . . . . . 257
209 7.12.14 Comparison macros . . . . . . . . . . . . . . . . . . 258
210 7.13 Nonlocal jumps <setjmp.h> . . . . . . . . . . . . . . . . 261
211 7.13.1 Save calling environment . . . . . . . . . . . . . . . 261
212 7.13.2 Restore calling environment . . . . . . . . . . . . . . 262
213 7.14 Signal handling <signal.h> . . . . . . . . . . . . . . . . . 264
214 7.14.1 Specify signal handling . . . . . . . . . . . . . . . . 265
215 7.14.2 Send signal . . . . . . . . . . . . . . . . . . . . . 266
216 7.15 Alignment <stdalign.h> . . . . . . . . . . . . . . . . . 267
217 7.16 Variable arguments <stdarg.h> . . . . . . . . . . . . . . . 268
218 7.16.1 Variable argument list access macros . . . . . . . . . . . 268
219 7.17 Atomics <stdatomic.h> . . . . . . . . . . . . . . . . . . 272
220 7.17.1 Introduction . . . . . . . . . . . . . . . . . . . . . 272
221 7.17.2 Initialization . . . . . . . . . . . . . . . . . . . . 273
222 7.17.3 Order and consistency . . . . . . . . . . . . . . . . . 274
223 7.17.4 Fences . . . . . . . . . . . . . . . . . . . . . . . 277
224 7.17.5 Lock-free property . . . . . . . . . . . . . . . . . . 278
225 7.17.6 Atomic integer and address types . . . . . . . . . . . . 279
226 7.17.7 Operations on atomic types . . . . . . . . . . . . . . . 281
227 7.17.8 Atomic flag type and operations . . . . . . . . . . . . . 284
228 7.18 Boolean type and values <stdbool.h> . . . . . . . . . . . . 286
229 7.19 Common definitions <stddef.h> . . . . . . . . . . . . . . . 287
230 7.20 Integer types <stdint.h> . . . . . . . . . . . . . . . . . . 289
235 7.20.1 Integer types . . . . . . . . . . . . . . . . . . . . 289
236 7.20.2 Limits of specified-width integer types . . . . . . . . . . 291
237 7.20.3 Limits of other integer types . . . . . . . . . . . . . . 293
238 7.20.4 Macros for integer constants . . . . . . . . . . . . . . 294
239 7.21 Input/output <stdio.h> . . . . . . . . . . . . . . . . . . 296
240 7.21.1 Introduction . . . . . . . . . . . . . . . . . . . . . 296
241 7.21.2 Streams . . . . . . . . . . . . . . . . . . . . . . 298
242 7.21.3 Files . . . . . . . . . . . . . . . . . . . . . . . . 300
243 7.21.4 Operations on files . . . . . . . . . . . . . . . . . . 302
244 7.21.5 File access functions . . . . . . . . . . . . . . . . . 304
245 7.21.6 Formatted input/output functions . . . . . . . . . . . . 309
246 7.21.7 Character input/output functions . . . . . . . . . . . . . 330
247 7.21.8 Direct input/output functions . . . . . . . . . . . . . . 334
248 7.21.9 File positioning functions . . . . . . . . . . . . . . . 335
249 7.21.10 Error-handling functions . . . . . . . . . . . . . . . . 338
250 7.22 General utilities <stdlib.h> . . . . . . . . . . . . . . . . 340
251 7.22.1 Numeric conversion functions . . . . . . . . . . . . . . 341
252 7.22.2 Pseudo-random sequence generation functions . . . . . . . 346
253 7.22.3 Memory management functions . . . . . . . . . . . . . 347
254 7.22.4 Communication with the environment . . . . . . . . . . 349
255 7.22.5 Searching and sorting utilities . . . . . . . . . . . . . . 353
256 7.22.6 Integer arithmetic functions . . . . . . . . . . . . . . 355
257 7.22.7 Multibyte/wide character conversion functions . . . . . . . 356
258 7.22.8 Multibyte/wide string conversion functions . . . . . . . . 358
259 7.23 String handling <string.h> . . . . . . . . . . . . . . . . . 360
260 7.23.1 String function conventions . . . . . . . . . . . . . . . 360
261 7.23.2 Copying functions . . . . . . . . . . . . . . . . . . 360
262 7.23.3 Concatenation functions . . . . . . . . . . . . . . . . 362
263 7.23.4 Comparison functions . . . . . . . . . . . . . . . . . 363
264 7.23.5 Search functions . . . . . . . . . . . . . . . . . . . 365
265 7.23.6 Miscellaneous functions . . . . . . . . . . . . . . . . 368
266 7.24 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 370
267 7.25 Threads <threads.h> . . . . . . . . . . . . . . . . . . . 373
268 7.25.1 Introduction . . . . . . . . . . . . . . . . . . . . . 373
269 7.25.2 Initialization functions . . . . . . . . . . . . . . . . . 375
270 7.25.3 Condition variable functions . . . . . . . . . . . . . . 375
271 7.25.4 Mutex functions . . . . . . . . . . . . . . . . . . . 377
272 7.25.5 Thread functions . . . . . . . . . . . . . . . . . . . 380
273 7.25.6 Thread-specific storage functions . . . . . . . . . . . . 382
274 7.25.7 Time functions . . . . . . . . . . . . . . . . . . . . 384
275 7.26 Date and time <time.h> . . . . . . . . . . . . . . . . . . 385
276 7.26.1 Components of time . . . . . . . . . . . . . . . . . 385
277 7.26.2 Time manipulation functions . . . . . . . . . . . . . . 386
278 7.26.3 Time conversion functions . . . . . . . . . . . . . . . 388
283 7.27 Unicode utilities <uchar.h> . . . . . . . . . . . . . . . . . 395
284 7.27.1 Restartable multibyte/wide character conversion functions . . 395
285 7.28 Extended multibyte and wide character utilities <wchar.h> . . . . . 399
286 7.28.1 Introduction . . . . . . . . . . . . . . . . . . . . . 399
287 7.28.2 Formatted wide character input/output functions . . . . . . 400
288 7.28.3 Wide character input/output functions . . . . . . . . . . 418
289 7.28.4 General wide string utilities . . . . . . . . . . . . . . 422
290 7.28.4.1 Wide string numeric conversion functions . . . . . 423
291 7.28.4.2 Wide string copying functions . . . . . . . . . . 427
292 7.28.4.3 Wide string concatenation functions . . . . . . . 429
293 7.28.4.4 Wide string comparison functions . . . . . . . . 430
294 7.28.4.5 Wide string search functions . . . . . . . . . . 432
295 7.28.4.6 Miscellaneous functions . . . . . . . . . . . . 436
296 7.28.5 Wide character time conversion functions . . . . . . . . . 436
297 7.28.6 Extended multibyte/wide character conversion utilities . . . . 437
298 7.28.6.1 Single-byte/wide character conversion functions . . . 438
299 7.28.6.2 Conversion state functions . . . . . . . . . . . 438
300 7.28.6.3 Restartable multibyte/wide character conversion
301 functions . . . . . . . . . . . . . . . . . . 439
302 7.28.6.4 Restartable multibyte/wide string conversion
303 functions . . . . . . . . . . . . . . . . . . 441
304 7.29 Wide character classification and mapping utilities <wctype.h> . . . 444
305 7.29.1 Introduction . . . . . . . . . . . . . . . . . . . . . 444
306 7.29.2 Wide character classification utilities . . . . . . . . . . . 445
307 7.29.2.1 Wide character classification functions . . . . . . 445
308 7.29.2.2 Extensible wide character classification
309 functions . . . . . . . . . . . . . . . . . . 448
310 7.29.3 Wide character case mapping utilities . . . . . . . . . . . 450
311 7.29.3.1 Wide character case mapping functions . . . . . . 450
312 7.29.3.2 Extensible wide character case mapping
313 functions . . . . . . . . . . . . . . . . . . 450
314 7.30 Future library directions . . . . . . . . . . . . . . . . . . . 452
315 7.30.1 Complex arithmetic <complex.h> . . . . . . . . . . . 452
316 7.30.2 Character handling <ctype.h> . . . . . . . . . . . . 452
317 7.30.3 Errors <errno.h> . . . . . . . . . . . . . . . . . 452
318 7.30.4 Format conversion of integer types <inttypes.h> . . . . 452
319 7.30.5 Localization <locale.h> . . . . . . . . . . . . . . 452
320 7.30.6 Signal handling <signal.h> . . . . . . . . . . . . . 452
321 7.30.7 Boolean type and values <stdbool.h> . . . . . . . . . 452
322 7.30.8 Integer types <stdint.h> . . . . . . . . . . . . . . 452
323 7.30.9 Input/output <stdio.h> . . . . . . . . . . . . . . . 453
324 7.30.10 General utilities <stdlib.h> . . . . . . . . . . . . . 453
325 7.30.11 String handling <string.h> . . . . . . . . . . . . . 453
331 7.30.12 Extended multibyte and wide character utilities
332 <wchar.h> . . . . . . . . . . . . . . . . . . . . 453
333 7.30.13 Wide character classification and mapping utilities
334 <wctype.h> . . . . . . . . . . . . . . . . . . . . 453
335 Annex A (informative) Language syntax summary . . . . . . . . . . . . 454
336 A.1 Lexical grammar . . . . . . . . . . . . . . . . . . . . . . 454
337 A.2 Phrase structure grammar . . . . . . . . . . . . . . . . . . . 461
338 A.3 Preprocessing directives . . . . . . . . . . . . . . . . . . . 469
339 Annex B (informative) Library summary . . . . . . . . . . . . . . . . 471
340 B.1 Diagnostics <assert.h> . . . . . . . . . . . . . . . . . . 471
341 B.2 Complex <complex.h> . . . . . . . . . . . . . . . . . . . 471
342 B.3 Character handling <ctype.h> . . . . . . . . . . . . . . . . 473
343 B.4 Errors <errno.h> . . . . . . . . . . . . . . . . . . . . . 473
344 B.5 Floating-point environment <fenv.h> . . . . . . . . . . . . . 473
345 B.6 Characteristics of floating types <float.h> . . . . . . . . . . . 474
346 B.7 Format conversion of integer types <inttypes.h> . . . . . . . . 474
347 B.8 Alternative spellings <iso646.h> . . . . . . . . . . . . . . . 475
348 B.9 Sizes of integer types <limits.h> . . . . . . . . . . . . . . 475
349 B.10 Localization <locale.h> . . . . . . . . . . . . . . . . . . 475
350 B.11 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 475
351 B.12 Nonlocal jumps <setjmp.h> . . . . . . . . . . . . . . . . 480
352 B.13 Signal handling <signal.h> . . . . . . . . . . . . . . . . . 480
353 B.14 Alignment <stdalign.h> . . . . . . . . . . . . . . . . . 481
354 B.15 Variable arguments <stdarg.h> . . . . . . . . . . . . . . . 481
355 B.16 Atomics <stdatomic.h> . . . . . . . . . . . . . . . . . . 481
356 B.17 Boolean type and values <stdbool.h> . . . . . . . . . . . . 483
357 B.18 Common definitions <stddef.h> . . . . . . . . . . . . . . . 483
358 B.19 Integer types <stdint.h> . . . . . . . . . . . . . . . . . . 483
359 B.20 Input/output <stdio.h> . . . . . . . . . . . . . . . . . . 484
360 B.21 General utilities <stdlib.h> . . . . . . . . . . . . . . . . 487
361 B.22 String handling <string.h> . . . . . . . . . . . . . . . . . 489
362 B.23 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 491
363 B.24 Threads <threads.h> . . . . . . . . . . . . . . . . . . . 491
364 B.25 Date and time <time.h> . . . . . . . . . . . . . . . . . . 492
365 B.26 Unicode utilities <uchar.h> . . . . . . . . . . . . . . . . . 493
366 B.27 Extended multibyte/wide character utilities <wchar.h> . . . . . . 493
367 B.28 Wide character classification and mapping utilities <wctype.h> . . . 498
368 Annex C (informative) Sequence points . . . . . . . . . . . . . . . . . 499
369 Annex D (normative) Universal character names for identifiers . . . . . . . 500
370 D.1 Ranges of characters allowed . . . . . . . . . . . . . . . . . 500
371 D.2 Ranges of characters disallowed initially . . . . . . . . . . . . . 500
372 Annex E (informative) Implementation limits . . . . . . . . . . . . . . 501
376 Annex F (normative) IEC 60559 floating-point arithmetic . . . . . . . . . . 503
377 F.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 503
378 F.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
379 F.3 Operators and functions . . . . . . . . . . . . . . . . . . . 504
380 F.4 Floating to integer conversion . . . . . . . . . . . . . . . . . 506
381 F.5 Binary-decimal conversion . . . . . . . . . . . . . . . . . . 506
382 F.6 The return statement . . . . . . . . . . . . . . . . . . . . 507
383 F.7 Contracted expressions . . . . . . . . . . . . . . . . . . . . 507
384 F.8 Floating-point environment . . . . . . . . . . . . . . . . . . 507
385 F.9 Optimization . . . . . . . . . . . . . . . . . . . . . . . . 510
386 F.10 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 513
387 F.10.1 Trigonometric functions . . . . . . . . . . . . . . . . 514
388 F.10.2 Hyperbolic functions . . . . . . . . . . . . . . . . . 516
389 F.10.3 Exponential and logarithmic functions . . . . . . . . . . 516
390 F.10.4 Power and absolute value functions . . . . . . . . . . . 520
391 F.10.5 Error and gamma functions . . . . . . . . . . . . . . . 521
392 F.10.6 Nearest integer functions . . . . . . . . . . . . . . . . 522
393 F.10.7 Remainder functions . . . . . . . . . . . . . . . . . 524
394 F.10.8 Manipulation functions . . . . . . . . . . . . . . . . 525
395 F.10.9 Maximum, minimum, and positive difference functions . . . 526
396 F.10.10 Floating multiply-add . . . . . . . . . . . . . . . . . 526
397 F.10.11 Comparison macros . . . . . . . . . . . . . . . . . . 527
398 Annex G (normative) IEC 60559-compatible complex arithmetic . . . . . . . 528
399 G.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 528
400 G.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 528
401 G.3 Conventions . . . . . . . . . . . . . . . . . . . . . . . . 528
402 G.4 Conversions . . . . . . . . . . . . . . . . . . . . . . . . 529
403 G.4.1 Imaginary types . . . . . . . . . . . . . . . . . . . 529
404 G.4.2 Real and imaginary . . . . . . . . . . . . . . . . . . 529
405 G.4.3 Imaginary and complex . . . . . . . . . . . . . . . . 529
406 G.5 Binary operators . . . . . . . . . . . . . . . . . . . . . . 529
407 G.5.1 Multiplicative operators . . . . . . . . . . . . . . . . 530
408 G.5.2 Additive operators . . . . . . . . . . . . . . . . . . 533
409 G.6 Complex arithmetic <complex.h> . . . . . . . . . . . . . . 533
410 G.6.1 Trigonometric functions . . . . . . . . . . . . . . . . 535
411 G.6.2 Hyperbolic functions . . . . . . . . . . . . . . . . . 535
412 G.6.3 Exponential and logarithmic functions . . . . . . . . . . 539
413 G.6.4 Power and absolute-value functions . . . . . . . . . . . 540
414 G.7 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 541
415 Annex H (informative) Language independent arithmetic . . . . . . . . . . 542
416 H.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 542
417 H.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
418 H.3 Notification . . . . . . . . . . . . . . . . . . . . . . . . 546
423 Annex I (informative) Common warnings . . . . . . . . . . . . . . . . 548
424 Annex J (informative) Portability issues . . . . . . . . . . . . . . . . . 550
425 J.1 Unspecified behavior . . . . . . . . . . . . . . . . . . . . . 550
426 J.2 Undefined behavior . . . . . . . . . . . . . . . . . . . . . 553
427 J.3 Implementation-defined behavior . . . . . . . . . . . . . . . . 566
428 J.4 Locale-specific behavior . . . . . . . . . . . . . . . . . . . 574
429 J.5 Common extensions . . . . . . . . . . . . . . . . . . . . . 575
430 Annex K (normative) Bounds-checking interfaces . . . . . . . . . . . . . 578
431 K.1 Background . . . . . . . . . . . . . . . . . . . . . . . . 578
432 K.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 579
433 K.3 Library . . . . . . . . . . . . . . . . . . . . . . . . . . 579
434 K.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . 579
435 K.3.1.1 Standard headers . . . . . . . . . . . . . . . 579
436 K.3.1.2 Reserved identifiers . . . . . . . . . . . . . . 580
437 K.3.1.3 Use of errno . . . . . . . . . . . . . . . . . 580
438 K.3.1.4 Runtime-constraint violations . . . . . . . . . . 580
439 K.3.2 Errors <errno.h> . . . . . . . . . . . . . . . . . 581
440 K.3.3 Common definitions <stddef.h> . . . . . . . . . . . 581
441 K.3.4 Integer types <stdint.h> . . . . . . . . . . . . . . 581
442 K.3.5 Input/output <stdio.h> . . . . . . . . . . . . . . . 582
443 K.3.5.1 Operations on files . . . . . . . . . . . . . . 582
444 K.3.5.2 File access functions . . . . . . . . . . . . . . 584
445 K.3.5.3 Formatted input/output functions . . . . . . . . . 587
446 K.3.5.4 Character input/output functions . . . . . . . . . 598
447 K.3.6 General utilities <stdlib.h> . . . . . . . . . . . . . 600
448 K.3.6.1 Runtime-constraint handling . . . . . . . . . . 600
449 K.3.6.2 Communication with the environment . . . . . . . 602
450 K.3.6.3 Searching and sorting utilities . . . . . . . . . . 603
451 K.3.6.4 Multibyte/wide character conversion functions . . . 606
452 K.3.6.5 Multibyte/wide string conversion functions . . . . . 607
453 K.3.7 String handling <string.h> . . . . . . . . . . . . . 610
454 K.3.7.1 Copying functions . . . . . . . . . . . . . . 610
455 K.3.7.2 Concatenation functions . . . . . . . . . . . . 613
456 K.3.7.3 Search functions . . . . . . . . . . . . . . . 616
457 K.3.7.4 Miscellaneous functions . . . . . . . . . . . . 617
458 K.3.8 Date and time <time.h> . . . . . . . . . . . . . . . 620
459 K.3.8.1 Components of time . . . . . . . . . . . . . . 620
460 K.3.8.2 Time conversion functions . . . . . . . . . . . 620
461 K.3.9 Extended multibyte and wide character utilities
462 <wchar.h> . . . . . . . . . . . . . . . . . . . . 623
463 K.3.9.1 Formatted wide character input/output functions . . . 624
464 K.3.9.2 General wide string utilities . . . . . . . . . . . 635
470 K.3.9.3 Extended multibyte/wide character conversion
471 utilities . . . . . . . . . . . . . . . . . . . 643
472 Annex L (normative) Analyzability . . . . . . . . . . . . . . . . . . 648
473 L.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 648
474 L.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 648
475 L.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 649
476 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
477 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653
485 1 ISO (the International Organization for Standardization) and IEC (the International
486 Electrotechnical Commission) form the specialized system for worldwide
487 standardization. National bodies that are member of ISO or IEC participate in the
488 development of International Standards through technical committees established by the
489 respective organization to deal with particular fields of technical activity. ISO and IEC
490 technical committees collaborate in fields of mutual interest. Other international
491 organizations, governmental and non-governmental, in liaison with ISO and IEC, also
492 take part in the work.
493 2 International Standards are drafted in accordance with the rules given in the ISO/IEC
494 Directives, Part 2. This International Standard was drafted in accordance with the fifth
496 3 In the field of information technology, ISO and IEC have established a joint technical
497 committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical
498 committee are circulated to national bodies for voting. Publication as an International
499 Standard requires approval by at least 75% of the national bodies casting a vote.
500 4 Attention is drawn to the possibility that some of the elements of this document may be
501 the subject of patent rights. ISO and IEC shall not be held responsible for identifying any
502 or all such patent rights.
503 5 This International Standard was prepared by Joint Technical Committee ISO/IEC JTC 1,
504 Information technology, Subcommittee SC 22, Programming languages, their
505 environments and system software interfaces. The Working Group responsible for this
506 standard (WG 14) maintains a site on the World Wide Web at http://www.open-
507 std.org/JTC1/SC22/WG14/ containing additional information relevant to this
508 standard such as a Rationale for many of the decisions made during its preparation and a
509 log of Defect Reports and Responses.
510 6 This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as
511 corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and
512 ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include:
513 -- conditional (optional) features (including some that were previously mandatory)
514 -- support for multiple threads of execution including an improved memory sequencing
515 model, atomic objects, and thread-local storage (<stdatomic.h> and
517 -- additional floating-point characteristic macros (<float.h>)
518 -- querying and specifying alignment of objects (<stdalign.h>, <stdlib.h>)
519 -- Unicode characters and strings (<uchar.h>) (originally specified in
520 ISO/IEC TR 19769:2004)
521 -- type-generic expressions
527 -- anonymous structures and unions
528 -- no-return functions
529 -- macros to create complex numbers (<complex.h>)
530 -- support for opening files for exclusive access
531 -- removed the gets function (<stdio.h>)
532 -- added the aligned_alloc, at_quick_exit, and quick_exit functions
534 -- (conditional) support for bounds-checking interfaces (originally specified in
535 ISO/IEC TR 24731-1:2007)
536 -- (conditional) support for analyzability
537 7 Major changes in the second edition included:
538 -- restricted character set support via digraphs and <iso646.h> (originally specified
540 -- wide character library support in <wchar.h> and <wctype.h> (originally
542 -- more precise aliasing rules via effective type
543 -- restricted pointers
544 -- variable length arrays
545 -- flexible array members
546 -- static and type qualifiers in parameter array declarators
547 -- complex (and imaginary) support in <complex.h>
548 -- type-generic math macros in <tgmath.h>
549 -- the long long int type and library functions
550 -- increased minimum translation limits
551 -- additional floating-point characteristics in <float.h>
552 -- remove implicit int
553 -- reliable integer division
554 -- universal character names (\u and \U)
555 -- extended identifiers
556 -- hexadecimal floating-point constants and %a and %A printf/scanf conversion
564 -- designated initializers
566 -- extended integer types and library functions in <inttypes.h> and <stdint.h>
567 -- remove implicit function declaration
568 -- preprocessor arithmetic done in intmax_t/uintmax_t
569 -- mixed declarations and code
570 -- new block scopes for selection and iteration statements
571 -- integer constant type rules
572 -- integer promotion rules
573 -- macros with a variable number of arguments
574 -- the vscanf family of functions in <stdio.h> and <wchar.h>
575 -- additional math library functions in <math.h>
576 -- treatment of error conditions by math library functions (math_errhandling)
577 -- floating-point environment access in <fenv.h>
578 -- IEC 60559 (also known as IEC 559 or IEEE arithmetic) support
579 -- trailing comma allowed in enum declaration
580 -- %lf conversion specifier allowed in printf
582 -- the snprintf family of functions in <stdio.h>
583 -- boolean type in <stdbool.h>
584 -- idempotent type qualifiers
585 -- empty macro arguments
586 -- new structure type compatibility rules (tag compatibility)
587 -- additional predefined macro names
588 -- _Pragma preprocessing operator
590 -- __func__ predefined identifier
592 -- additional strftime conversion specifiers
593 -- LIA compatibility annex
598 -- deprecate ungetc at the beginning of a binary file
599 -- remove deprecation of aliased array parameters
600 -- conversion of array to pointer not limited to lvalues
601 -- relaxed constraints on aggregate and union initialization
602 -- relaxed restrictions on portable header names
603 -- return without expression not permitted in function that returns a value (and vice
605 8 Annexes D, F, G, K, and L form a normative part of this standard; annexes A, B, C, E, H, *
606 I, J, the bibliography, and the index are for information only. In accordance with Part 2 of
607 the ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples
608 are also for information only.
616 1 With the introduction of new devices and extended character sets, new features may be
617 added to this International Standard. Subclauses in the language and library clauses warn
618 implementors and programmers of usages which, though valid in themselves, may
619 conflict with future additions.
620 2 Certain features are obsolescent, which means that they may be considered for
621 withdrawal in future revisions of this International Standard. They are retained because
622 of their widespread use, but their use in new implementations (for implementation
623 features) or new programs (for language [6.11] or library features [7.30]) is discouraged.
624 3 This International Standard is divided into four major subdivisions:
625 -- preliminary elements (clauses 1-4);
626 -- the characteristics of environments that translate and execute C programs (clause 5);
627 -- the language syntax, constraints, and semantics (clause 6);
628 -- the library facilities (clause 7).
629 4 Examples are provided to illustrate possible forms of the constructions described.
630 Footnotes are provided to emphasize consequences of the rules described in that
631 subclause or elsewhere in this International Standard. References are used to refer to
632 other related subclauses. Recommendations are provided to give advice or guidance to
633 implementors. Annexes provide additional information and summarize the information
634 contained in this International Standard. A bibliography lists documents that were
635 referred to during the preparation of the standard.
636 5 The language clause (clause 6) is derived from ''The C Reference Manual''.
637 6 The library clause (clause 7) is based on the 1984 /usr/group Standard.
650 Programming languages -- C
655 1 This International Standard specifies the form and establishes the interpretation of
656 programs written in the C programming language.1) It specifies
657 -- the representation of C programs;
658 -- the syntax and constraints of the C language;
659 -- the semantic rules for interpreting C programs;
660 -- the representation of input data to be processed by C programs;
661 -- the representation of output data produced by C programs;
662 -- the restrictions and limits imposed by a conforming implementation of C.
663 2 This International Standard does not specify
664 -- the mechanism by which C programs are transformed for use by a data-processing
666 -- the mechanism by which C programs are invoked for use by a data-processing
668 -- the mechanism by which input data are transformed for use by a C program;
669 -- the mechanism by which output data are transformed after being produced by a C
671 -- the size or complexity of a program and its data that will exceed the capacity of any
672 specific data-processing system or the capacity of a particular processor;
673 -- all minimal requirements of a data-processing system that is capable of supporting a
674 conforming implementation.
677 1) This International Standard is designed to promote the portability of C programs among a variety of
678 data-processing systems. It is intended for use by implementors and programmers.
683 2. Normative references
684 1 The following referenced documents are indispensable for the application of this
685 document. For dated references, only the edition cited applies. For undated references,
686 the latest edition of the referenced document (including any amendments) applies.
687 2 ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and symbols for
688 use in the physical sciences and technology.
689 3 ISO/IEC 646, Information technology -- ISO 7-bit coded character set for information
691 4 ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: Fundamental
693 5 ISO 4217, Codes for the representation of currencies and funds.
694 6 ISO 8601, Data elements and interchange formats -- Information interchange --
695 Representation of dates and times.
696 7 ISO/IEC 10646 (all parts), Information technology -- Universal Multiple-Octet Coded
698 8 IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously
699 designated IEC 559:1989).
707 3. Terms, definitions, and symbols
708 1 For the purposes of this International Standard, the following definitions apply. Other
709 terms are defined where they appear in italic type or on the left side of a syntax rule.
710 Terms explicitly defined in this International Standard are not to be presumed to refer
711 implicitly to similar terms defined elsewhere. Terms not defined in this International
712 Standard are to be interpreted according to ISO/IEC 2382-1. Mathematical symbols not
713 defined in this International Standard are to be interpreted according to ISO 31-11.
716 <execution-time action> to read or modify the value of an object
717 2 NOTE 1 Where only one of these two actions is meant, ''read'' or ''modify'' is used.
719 3 NOTE 2 ''Modify'' includes the case where the new value being stored is the same as the previous value.
721 4 NOTE 3 Expressions that are not evaluated do not access objects.
725 requirement that objects of a particular type be located on storage boundaries with
726 addresses that are particular multiples of a byte address
730 actual parameter (deprecated)
731 expression in the comma-separated list bounded by the parentheses in a function call
732 expression, or a sequence of preprocessing tokens in the comma-separated list bounded
733 by the parentheses in a function-like macro invocation
736 external appearance or action
738 1 implementation-defined behavior
739 unspecified behavior where each implementation documents how the choice is made
740 2 EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit
741 when a signed integer is shifted right.
744 1 locale-specific behavior
745 behavior that depends on local conventions of nationality, culture, and language that each
746 implementation documents
751 2 EXAMPLE An example of locale-specific behavior is whether the islower function returns true for
752 characters other than the 26 lowercase Latin letters.
756 behavior, upon use of a nonportable or erroneous program construct or of erroneous data,
757 for which this International Standard imposes no requirements
758 2 NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable
759 results, to behaving during translation or program execution in a documented manner characteristic of the
760 environment (with or without the issuance of a diagnostic message), to terminating a translation or
761 execution (with the issuance of a diagnostic message).
763 3 EXAMPLE An example of undefined behavior is the behavior on integer overflow.
766 1 unspecified behavior
767 use of an unspecified value, or other behavior where this International Standard provides
768 two or more possibilities and imposes no further requirements on which is chosen in any
770 2 EXAMPLE An example of unspecified behavior is the order in which the arguments to a function are
775 unit of data storage in the execution environment large enough to hold an object that may
776 have one of two values
777 2 NOTE It need not be possible to express the address of each individual bit of an object.
781 addressable unit of data storage large enough to hold any member of the basic character
782 set of the execution environment
783 2 NOTE 1 It is possible to express the address of each individual byte of an object uniquely.
785 3 NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation-
786 defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order
791 <abstract> member of a set of elements used for the organization, control, or
792 representation of data
795 single-byte character
796 <C> bit representation that fits in a byte
800 1 multibyte character
801 sequence of one or more bytes representing a member of the extended character set of
802 either the source or the execution environment
803 2 NOTE The extended character set is a superset of the basic character set.
807 bit representation that fits in an object of type wchar_t, capable of representing any
808 character in the current locale
811 restriction, either syntactic or semantic, by which the exposition of language elements is
814 1 correctly rounded result
815 representation in the result format that is nearest in value, subject to the current rounding
816 mode, to what the result would be given unlimited range and precision
819 message belonging to an implementation-defined subset of the implementation's message
823 reference to a later subclause of this International Standard that contains additional
824 information relevant to this subclause
827 particular set of software, running in a particular translation environment under particular
828 control options, that performs translation of programs for, and supports execution of
829 functions in, a particular execution environment
831 1 implementation limit
832 restriction imposed upon programs by the implementation
835 either an object of scalar type, or a maximal sequence of adjacent bit-fields all having
840 2 NOTE 1 Two threads of execution can update and access separate memory locations without interfering
843 3 NOTE 2 A bit-field and an adjacent non-bit-field member are in separate memory locations. The same
844 applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the
845 two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member
846 declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all
847 members declared between them are also (non-zero-length) bit-fields, no matter what the sizes of those
848 intervening bit-fields happen to be.
850 4 EXAMPLE A structure declared as
853 int b:5, c:11, :0, d:8;
854 struct { int ee:8; } e;
856 contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate
857 memory locations, and can be modified concurrently without interfering with each other. The bit-fields b
858 and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently
859 modified, but b and a, for example, can be.
863 region of data storage in the execution environment, the contents of which can represent
865 2 NOTE When referenced, an object may be interpreted as having a particular type; see 6.3.2.1.
870 formal argument (deprecated)
871 object declared as part of a function declaration or definition that acquires a value on
872 entry to the function, or an identifier from the comma-separated list bounded by the
873 parentheses immediately following the macro name in a function-like macro definition
875 1 recommended practice
876 specification that is strongly recommended as being in keeping with the intent of the
877 standard, but that may be impractical for some implementations
880 requirement on a program when calling a library function
881 2 NOTE 1 Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and
882 need not be diagnosed at translation time.
884 3 NOTE 2 Implementations that support the extensions in annex K are required to verify that the runtime-
885 constraints for a library function are not violated by the program; see K.3.1.4.
891 precise meaning of the contents of an object when interpreted as having a specific type
893 1 implementation-defined value
894 unspecified value where each implementation documents how the choice is made
896 1 indeterminate value
897 either an unspecified value or a trap representation
900 valid value of the relevant type where this International Standard imposes no
901 requirements on which value is chosen in any instance
902 2 NOTE An unspecified value cannot be a trap representation.
905 1 trap representation
906 an object representation that need not represent a value of the object type
909 interrupt execution of the program such that no further operations are performed
910 2 NOTE In this International Standard, when the word ''trap'' is not immediately followed by
911 ''representation'', this is the intended usage.2)
915 ceiling of x: the least integer greater than or equal to x
916 2 EXAMPLE [^2.4^] is 3, [^-2.4^] is -2.
920 floor of x: the greatest integer less than or equal to x
921 2 EXAMPLE [_2.4_] is 2, [_-2.4_] is -3.
926 2) For example, ''Trapping or stopping (if supported) is disabled...'' (F.8.2). Note that fetching a trap
927 representation might perform a trap but is not required to (see 6.2.6.1).
933 1 In this International Standard, ''shall'' is to be interpreted as a requirement on an
934 implementation or on a program; conversely, ''shall not'' is to be interpreted as a
936 2 If a ''shall'' or ''shall not'' requirement that appears outside of a constraint or runtime-
937 constraint is violated, the behavior is undefined. Undefined behavior is otherwise
938 indicated in this International Standard by the words ''undefined behavior'' or by the
939 omission of any explicit definition of behavior. There is no difference in emphasis among
940 these three; they all describe ''behavior that is undefined''.
941 3 A program that is correct in all other aspects, operating on correct data, containing
942 unspecified behavior shall be a correct program and act in accordance with 5.1.2.3.
943 4 The implementation shall not successfully translate a preprocessing translation unit
944 containing a #error preprocessing directive unless it is part of a group skipped by
945 conditional inclusion.
946 5 A strictly conforming program shall use only those features of the language and library
947 specified in this International Standard.3) It shall not produce output dependent on any
948 unspecified, undefined, or implementation-defined behavior, and shall not exceed any
949 minimum implementation limit.
950 6 The two forms of conforming implementation are hosted and freestanding. A conforming
951 hosted implementation shall accept any strictly conforming program. A conforming
952 freestanding implementation shall accept any strictly conforming program that does not
953 use complex types and in which the use of the features specified in the library clause
954 (clause 7) is confined to the contents of the standard headers <float.h>,
955 <iso646.h>, <limits.h>, <stdalign.h>, <stdarg.h>, <stdbool.h>,
956 <stddef.h>, and <stdint.h>. A conforming implementation may have extensions
957 (including additional library functions), provided they do not alter the behavior of any
958 strictly conforming program.4)
962 3) A strictly conforming program can use conditional features (see 6.10.8.3) provided the use is guarded
963 by an appropriate conditional inclusion preprocessing directive using the related macro. For example:
964 #ifdef __STDC_IEC_559__ /* FE_UPWARD defined */
966 fesetround(FE_UPWARD);
970 4) This implies that a conforming implementation reserves no identifiers other than those explicitly
971 reserved in this International Standard.
975 7 A conforming program is one that is acceptable to a conforming implementation.5)
976 8 An implementation shall be accompanied by a document that defines all implementation-
977 defined and locale-specific characteristics and all extensions.
978 Forward references: conditional inclusion (6.10.1), error directive (6.10.5),
979 characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h>
980 (7.9), sizes of integer types <limits.h> (7.10), alignment <stdalign.h> (7.15),
981 variable arguments <stdarg.h> (7.16), boolean type and values <stdbool.h>
982 (7.18), common definitions <stddef.h> (7.19), integer types <stdint.h> (7.20).
987 5) Strictly conforming programs are intended to be maximally portable among conforming
988 implementations. Conforming programs may depend upon nonportable features of a conforming
995 1 An implementation translates C source files and executes C programs in two data-
996 processing-system environments, which will be called the translation environment and
997 the execution environment in this International Standard. Their characteristics define and
998 constrain the results of executing conforming C programs constructed according to the
999 syntactic and semantic rules for conforming implementations.
1000 Forward references: In this clause, only a few of many possible forward references
1002 5.1 Conceptual models
1003 5.1.1 Translation environment
1004 5.1.1.1 Program structure
1005 1 A C program need not all be translated at the same time. The text of the program is kept
1006 in units called source files, (or preprocessing files) in this International Standard. A
1007 source file together with all the headers and source files included via the preprocessing
1008 directive #include is known as a preprocessing translation unit. After preprocessing, a
1009 preprocessing translation unit is called a translation unit. Previously translated translation
1010 units may be preserved individually or in libraries. The separate translation units of a
1011 program communicate by (for example) calls to functions whose identifiers have external
1012 linkage, manipulation of objects whose identifiers have external linkage, or manipulation
1013 of data files. Translation units may be separately translated and then later linked to
1014 produce an executable program.
1015 Forward references: linkages of identifiers (6.2.2), external definitions (6.9),
1016 preprocessing directives (6.10).
1017 5.1.1.2 Translation phases
1018 1 The precedence among the syntax rules of translation is specified by the following
1020 1. Physical source file multibyte characters are mapped, in an implementation-
1021 defined manner, to the source character set (introducing new-line characters for
1022 end-of-line indicators) if necessary. Trigraph sequences are replaced by
1023 corresponding single-character internal representations.
1027 6) Implementations shall behave as if these separate phases occur, even though many are typically folded
1028 together in practice. Source files, translation units, and translated translation units need not
1029 necessarily be stored as files, nor need there be any one-to-one correspondence between these entities
1030 and any external representation. The description is conceptual only, and does not specify any
1031 particular implementation.
1035 2. Each instance of a backslash character (\) immediately followed by a new-line
1036 character is deleted, splicing physical source lines to form logical source lines.
1037 Only the last backslash on any physical source line shall be eligible for being part
1038 of such a splice. A source file that is not empty shall end in a new-line character,
1039 which shall not be immediately preceded by a backslash character before any such
1040 splicing takes place.
1041 3. The source file is decomposed into preprocessing tokens7) and sequences of
1042 white-space characters (including comments). A source file shall not end in a
1043 partial preprocessing token or in a partial comment. Each comment is replaced by
1044 one space character. New-line characters are retained. Whether each nonempty
1045 sequence of white-space characters other than new-line is retained or replaced by
1046 one space character is implementation-defined.
1047 4. Preprocessing directives are executed, macro invocations are expanded, and
1048 _Pragma unary operator expressions are executed. If a character sequence that
1049 matches the syntax of a universal character name is produced by token
1050 concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing
1051 directive causes the named header or source file to be processed from phase 1
1052 through phase 4, recursively. All preprocessing directives are then deleted.
1053 5. Each source character set member and escape sequence in character constants and
1054 string literals is converted to the corresponding member of the execution character
1055 set; if there is no corresponding member, it is converted to an implementation-
1056 defined member other than the null (wide) character.8)
1057 6. Adjacent string literal tokens are concatenated.
1058 7. White-space characters separating tokens are no longer significant. Each
1059 preprocessing token is converted into a token. The resulting tokens are
1060 syntactically and semantically analyzed and translated as a translation unit.
1061 8. All external object and function references are resolved. Library components are
1062 linked to satisfy external references to functions and objects not defined in the
1063 current translation. All such translator output is collected into a program image
1064 which contains information needed for execution in its execution environment.
1065 Forward references: universal character names (6.4.3), lexical elements (6.4),
1066 preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9).
1070 7) As described in 6.4, the process of dividing a source file's characters into preprocessing tokens is
1071 context-dependent. For example, see the handling of < within a #include preprocessing directive.
1072 8) An implementation need not convert all non-corresponding source characters to the same execution
1078 1 A conforming implementation shall produce at least one diagnostic message (identified in
1079 an implementation-defined manner) if a preprocessing translation unit or translation unit
1080 contains a violation of any syntax rule or constraint, even if the behavior is also explicitly
1081 specified as undefined or implementation-defined. Diagnostic messages need not be
1082 produced in other circumstances.9)
1083 2 EXAMPLE An implementation shall issue a diagnostic for the translation unit:
1086 because in those cases where wording in this International Standard describes the behavior for a construct
1087 as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed.
1089 5.1.2 Execution environments
1090 1 Two execution environments are defined: freestanding and hosted. In both cases,
1091 program startup occurs when a designated C function is called by the execution
1092 environment. All objects with static storage duration shall be initialized (set to their
1093 initial values) before program startup. The manner and timing of such initialization are
1094 otherwise unspecified. Program termination returns control to the execution
1096 Forward references: storage durations of objects (6.2.4), initialization (6.7.9).
1097 5.1.2.1 Freestanding environment
1098 1 In a freestanding environment (in which C program execution may take place without any
1099 benefit of an operating system), the name and type of the function called at program
1100 startup are implementation-defined. Any library facilities available to a freestanding
1101 program, other than the minimal set required by clause 4, are implementation-defined.
1102 2 The effect of program termination in a freestanding environment is implementation-
1104 5.1.2.2 Hosted environment
1105 1 A hosted environment need not be provided, but shall conform to the following
1106 specifications if present.
1111 9) The intent is that an implementation should identify the nature of, and where possible localize, each
1112 violation. Of course, an implementation is free to produce any number of diagnostics as long as a
1113 valid program is still correctly translated. It may also successfully translate an invalid program.
1117 5.1.2.2.1 Program startup
1118 1 The function called at program startup is named main. The implementation declares no
1119 prototype for this function. It shall be defined with a return type of int and with no
1121 int main(void) { /* ... */ }
1122 or with two parameters (referred to here as argc and argv, though any names may be
1123 used, as they are local to the function in which they are declared):
1124 int main(int argc, char *argv[]) { /* ... */ }
1125 or equivalent;10) or in some other implementation-defined manner.
1126 2 If they are declared, the parameters to the main function shall obey the following
1128 -- The value of argc shall be nonnegative.
1129 -- argv[argc] shall be a null pointer.
1130 -- If the value of argc is greater than zero, the array members argv[0] through
1131 argv[argc-1] inclusive shall contain pointers to strings, which are given
1132 implementation-defined values by the host environment prior to program startup. The
1133 intent is to supply to the program information determined prior to program startup
1134 from elsewhere in the hosted environment. If the host environment is not capable of
1135 supplying strings with letters in both uppercase and lowercase, the implementation
1136 shall ensure that the strings are received in lowercase.
1137 -- If the value of argc is greater than zero, the string pointed to by argv[0]
1138 represents the program name; argv[0][0] shall be the null character if the
1139 program name is not available from the host environment. If the value of argc is
1140 greater than one, the strings pointed to by argv[1] through argv[argc-1]
1141 represent the program parameters.
1142 -- The parameters argc and argv and the strings pointed to by the argv array shall
1143 be modifiable by the program, and retain their last-stored values between program
1144 startup and program termination.
1145 5.1.2.2.2 Program execution
1146 1 In a hosted environment, a program may use all the functions, macros, type definitions,
1147 and objects described in the library clause (clause 7).
1152 10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as
1153 char ** argv, and so on.
1157 5.1.2.2.3 Program termination
1158 1 If the return type of the main function is a type compatible with int, a return from the
1159 initial call to the main function is equivalent to calling the exit function with the value
1160 returned by the main function as its argument;11) reaching the } that terminates the
1161 main function returns a value of 0. If the return type is not compatible with int, the
1162 termination status returned to the host environment is unspecified.
1163 Forward references: definition of terms (7.1.1), the exit function (7.22.4.4).
1164 5.1.2.3 Program execution
1165 1 The semantic descriptions in this International Standard describe the behavior of an
1166 abstract machine in which issues of optimization are irrelevant.
1167 2 Accessing a volatile object, modifying an object, modifying a file, or calling a function
1168 that does any of those operations are all side effects,12) which are changes in the state of
1169 the execution environment. Evaluation of an expression in general includes both value
1170 computations and initiation of side effects. Value computation for an lvalue expression
1171 includes determining the identity of the designated object.
1172 3 Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations
1173 executed by a single thread, which induces a partial order among those evaluations.
1174 Given any two evaluations A and B, if A is sequenced before B, then the execution of A
1175 shall precede the execution of B. (Conversely, if A is sequenced before B, then B is
1176 sequenced after A.) If A is not sequenced before or after B, then A and B are
1177 unsequenced. Evaluations A and B are indeterminately sequenced when A is sequenced
1178 either before or after B, but it is unspecified which.13) The presence of a sequence point
1179 between the evaluation of expressions A and B implies that every value computation and
1180 side effect associated with A is sequenced before every value computation and side effect
1181 associated with B. (A summary of the sequence points is given in annex C.)
1182 4 In the abstract machine, all expressions are evaluated as specified by the semantics. An
1183 actual implementation need not evaluate part of an expression if it can deduce that its
1184 value is not used and that no needed side effects are produced (including any caused by
1186 11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main
1187 will have ended in the former case, even where they would not have in the latter.
1188 12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status
1189 flags and control modes. Floating-point operations implicitly set the status flags; modes affect result
1190 values of floating-point operations. Implementations that support such floating-point state are
1191 required to regard changes to it as side effects -- see annex F for details. The floating-point
1192 environment library <fenv.h> provides a programming facility for indicating when these side
1193 effects matter, freeing the implementations in other cases.
1194 13) The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations
1195 cannot interleave, but can be executed in any order.
1199 calling a function or accessing a volatile object).
1200 5 When the processing of the abstract machine is interrupted by receipt of a signal, the
1201 values of objects that are neither lock-free atomic objects nor of type volatile
1202 sig_atomic_t are unspecified, and the value of any object that is modified by the
1203 handler that is neither a lock-free atomic object nor of type volatile
1204 sig_atomic_t becomes undefined.
1205 6 The least requirements on a conforming implementation are:
1206 -- Accesses to volatile objects are evaluated strictly according to the rules of the abstract
1208 -- At program termination, all data written into files shall be identical to the result that
1209 execution of the program according to the abstract semantics would have produced.
1210 -- The input and output dynamics of interactive devices shall take place as specified in
1211 7.21.3. The intent of these requirements is that unbuffered or line-buffered output
1212 appear as soon as possible, to ensure that prompting messages actually appear prior to
1213 a program waiting for input.
1214 This is the observable behavior of the program.
1215 7 What constitutes an interactive device is implementation-defined.
1216 8 More stringent correspondences between abstract and actual semantics may be defined by
1217 each implementation.
1218 9 EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual
1219 semantics: at every sequence point, the values of the actual objects would agree with those specified by the
1220 abstract semantics. The keyword volatile would then be redundant.
1221 10 Alternatively, an implementation might perform various optimizations within each translation unit, such
1222 that the actual semantics would agree with the abstract semantics only when making function calls across
1223 translation unit boundaries. In such an implementation, at the time of each function entry and function
1224 return where the calling function and the called function are in different translation units, the values of all
1225 externally linked objects and of all objects accessible via pointers therein would agree with the abstract
1226 semantics. Furthermore, at the time of each such function entry the values of the parameters of the called
1227 function and of all objects accessible via pointers therein would agree with the abstract semantics. In this
1228 type of implementation, objects referred to by interrupt service routines activated by the signal function
1229 would require explicit specification of volatile storage, as well as other implementation-defined
1232 11 EXAMPLE 2 In executing the fragment
1236 the ''integer promotions'' require that the abstract machine promote the value of each variable to int size
1237 and then add the two ints and truncate the sum. Provided the addition of two chars can be done without
1238 overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only
1239 produce the same result, possibly omitting the promotions.
1243 12 EXAMPLE 3 Similarly, in the fragment
1248 the multiplication may be executed using single-precision arithmetic if the implementation can ascertain
1249 that the result would be the same as if it were executed using double-precision arithmetic (for example, if d
1250 were replaced by the constant 2.0, which has type double).
1252 13 EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate
1253 semantics. Values are independent of whether they are represented in a register or in memory. For
1254 example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load
1255 is required to round to the precision of the storage type. In particular, casts and assignments are required to
1256 perform their specified conversion. For the fragment
1259 d1 = f = expression;
1260 d2 = (float) expression;
1261 the values assigned to d1 and d2 are required to have been converted to float.
1263 14 EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in
1264 precision as well as range. The implementation cannot generally apply the mathematical associative rules
1265 for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of
1266 overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to
1267 rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real
1268 numbers are often not valid (see F.9).
1271 x = (x * y) * z; // not equivalent to x *= y * z;
1272 z = (x - y) + y ; // not equivalent to z = x;
1273 z = x + x * y; // not equivalent to z = x * (1.0 + y);
1274 y = x / 5.0; // not equivalent to y = x * 0.2;
1276 15 EXAMPLE 6 To illustrate the grouping behavior of expressions, in the following fragment
1279 a = a + 32760 + b + 5;
1280 the expression statement behaves exactly the same as
1281 a = (((a + 32760) + b) + 5);
1282 due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is
1283 next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in
1284 which overflows produce an explicit trap and in which the range of values representable by an int is
1285 [-32768, +32767], the implementation cannot rewrite this expression as
1286 a = ((a + b) + 32765);
1287 since if the values for a and b were, respectively, -32754 and -15, the sum a + b would produce a trap
1288 while the original expression would not; nor can the expression be rewritten either as
1293 a = ((a + 32765) + b);
1295 a = (a + (b + 32765));
1296 since the values for a and b might have been, respectively, 4 and -8 or -17 and 12. However, on a machine
1297 in which overflow silently generates some value and where positive and negative overflows cancel, the
1298 above expression statement can be rewritten by the implementation in any of the above ways because the
1299 same result will occur.
1301 16 EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the
1307 sum = sum * 10 - '0' + (*p++ = getchar());
1308 the expression statement is grouped as if it were written as
1309 sum = (((sum * 10) - '0') + ((*(p++)) = (getchar())));
1310 but the actual increment of p can occur at any time between the previous sequence point and the next
1311 sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned
1314 Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), the
1315 signal function (7.14), files (7.21.3).
1316 5.1.2.4 Multi-threaded executions and data races
1317 1 Under a hosted implementation, a program can have more than one thread of execution
1318 (or thread) running concurrently. The execution of each thread proceeds as defined by
1319 the remainder of this standard. The execution of the entire program consists of an
1320 execution of all of its threads.14) Under a freestanding implementation, it is
1321 implementation-defined whether a program can have more than one thread of execution.
1322 2 The value of an object visible to a thread T at a particular point is the initial value of the
1323 object, a value stored in the object by T , or a value stored in the object by another thread,
1324 according to the rules below.
1325 3 NOTE 1 In some cases, there may instead be undefined behavior. Much of this section is motivated by
1326 the desire to support atomic operations with explicit and detailed visibility constraints. However, it also
1327 implicitly supports a simpler view for more restricted programs.
1329 4 Two expression evaluations conflict if one of them modifies a memory location and the
1330 other one reads or modifies the same memory location.
1335 14) The execution can usually be viewed as an interleaving of all of the threads. However, some kinds of
1336 atomic operations, for example, allow executions inconsistent with a simple interleaving as described
1341 5 The library defines a number of atomic operations (7.17) and operations on mutexes
1342 (7.25.4) that are specially identified as synchronization operations. These operations play
1343 a special role in making assignments in one thread visible to another. A synchronization
1344 operation on one or more memory locations is either an acquire operation, a release
1345 operation, both an acquire and release operation, or a consume operation. A
1346 synchronization operation without an associated memory location is a fence and can be
1347 either an acquire fence, a release fence, or both an acquire and release fence. In addition,
1348 there are relaxed atomic operations, which are not synchronization operations, and
1349 atomic read-modify-write operations, which have special characteristics.
1350 6 NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations
1351 composing the mutex. Correspondingly, a call that releases the same mutex will perform a release
1352 operation on those same locations. Informally, performing a release operation on A forces prior side effects
1353 on other memory locations to become visible to other threads that later perform an acquire or consume
1354 operation on A. We do not include relaxed atomic operations as synchronization operations although, like
1355 synchronization operations, they cannot contribute to data races.
1357 7 All modifications to a particular atomic object M occur in some particular total order,
1358 called the modification order of M. If A and B are modifications of an atomic object M,
1359 and A happens before B, then A shall precede B in the modification order of M, which is
1361 8 NOTE 3 This states that the modification orders must respect the ''happens before'' relation.
1363 9 NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be
1364 combined into a single total order for all objects. In general this will be impossible since different threads
1365 may observe modifications to different variables in inconsistent orders.
1367 10 A release sequence on an atomic object M is a maximal contiguous sub-sequence of side
1368 effects in the modification order of M, where the first operation is a release and every
1369 subsequent operation either is performed by the same thread that performed the release or
1370 is an atomic read-modify-write operation.
1371 11 Certain library calls synchronize with other library calls performed by another thread. In
1372 particular, an atomic operation A that performs a release operation on an object M
1373 synchronizes with an atomic operation B that performs an acquire operation on M and
1374 reads a value written by any side effect in the release sequence headed by A.
1375 12 NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as
1376 described below. Such a requirement would sometimes interfere with efficient implementation.
1378 13 NOTE 6 The specifications of the synchronization operations define when one reads the value written by
1379 another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total
1380 order. Each mutex acquisition ''reads the value written'' by the last mutex release.
1382 14 An evaluation A carries a dependency 15) to an evaluation B if:
1385 15) The ''carries a dependency'' relation is a subset of the ''sequenced before'' relation, and is similarly
1386 strictly intra-thread.
1390 -- the value of A is used as an operand of B, unless:
1391 o B is an invocation of the kill_dependency macro,
1393 o A is the left operand of a && or || operator,
1395 o A is the left operand of a ? : operator, or
1397 o A is the left operand of a , operator;
1399 -- A writes a scalar object or bit-field M, B reads from M the value written by A, and A
1400 is sequenced before B, or
1401 -- for some evaluation X, A carries a dependency to X and X carries a dependency to B.
1402 15 An evaluation A is dependency-ordered before16) an evaluation B if:
1403 -- A performs a release operation on an atomic object M, and B performs a consume
1404 operation on M and reads a value written by any side effect in the release sequence
1406 -- for some evaluation X, A is dependency-ordered before X and X carries a
1408 16 An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A
1409 is dependency-ordered before B, or, for some evaluation X:
1410 -- A synchronizes with X and X is sequenced before B,
1411 -- A is sequenced before X and X inter-thread happens before B, or
1412 -- A inter-thread happens before X and X inter-thread happens before B.
1413 17 NOTE 7 The ''inter-thread happens before'' relation describes arbitrary concatenations of ''sequenced
1414 before'', ''synchronizes with'', and ''dependency-ordered before'' relationships, with two exceptions. The
1415 first exception is that a concatenation is not permitted to end with ''dependency-ordered before'' followed
1416 by ''sequenced before''. The reason for this limitation is that a consume operation participating in a
1417 ''dependency-ordered before'' relationship provides ordering only with respect to operations to which this
1418 consume operation actually carries a dependency. The reason that this limitation applies only to the end of
1419 such a concatenation is that any subsequent release operation will provide the required ordering for a prior
1420 consume operation. The second exception is that a concatenation is not permitted to consist entirely of
1421 ''sequenced before''. The reasons for this limitation are (1) to permit ''inter-thread happens before'' to be
1422 transitively closed and (2) the ''happens before'' relation, defined below, provides for relationships
1423 consisting entirely of ''sequenced before''.
1425 18 An evaluation A happens before an evaluation B if A is sequenced before B or A inter-
1426 thread happens before B.
1430 16) The ''dependency-ordered before'' relation is analogous to the ''synchronizes with'' relation, but uses
1431 release/consume in place of release/acquire.
1435 19 A visible side effect A on an object M with respect to a value computation B of M
1436 satisfies the conditions:
1437 -- A happens before B, and
1438 -- there is no other side effect X to M such that A happens before X and X happens
1440 The value of a non-atomic scalar object M, as determined by evaluation B, shall be the
1441 value stored by the visible side effect A.
1442 20 NOTE 8 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data
1443 race and the behavior is undefined.
1445 21 NOTE 9 This states that operations on ordinary variables are not visibly reordered. This is not actually
1446 detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable
1447 restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent)
1450 22 The visible sequence of side effects on an atomic object M, with respect to a value
1451 computation B of M, is a maximal contiguous sub-sequence of side effects in the
1452 modification order of M, where the first side effect is visible with respect to B, and for
1453 every subsequent side effect, it is not the case that B happens before it. The value of an
1454 atomic object M, as determined by evaluation B, shall be the value stored by some
1455 operation in the visible sequence of M with respect to B. Furthermore, if a value
1456 computation A of an atomic object M happens before a value computation B of M, and
1457 the value computed by A corresponds to the value stored by side effect X, then the value
1458 computed by B shall either equal the value computed by A, or be the value stored by side
1459 effect Y , where Y follows X in the modification order of M.
1460 23 NOTE 10 This effectively disallows compiler reordering of atomic operations to a single object, even if
1461 both operations are ''relaxed'' loads. By doing so, we effectively make the ''cache coherence'' guarantee
1462 provided by most hardware available to C atomic operations.
1464 24 NOTE 11 The visible sequence depends on the ''happens before'' relation, which in turn depends on the
1465 values observed by loads of atomics, which we are restricting here. The intended reading is that there must
1466 exist an association of atomic loads with modifications they observe that, together with suitably chosen
1467 modification orders and the ''happens before'' relation derived as described above, satisfy the resulting
1468 constraints as imposed here.
1470 25 The execution of a program contains a data race if it contains two conflicting actions in
1471 different threads, at least one of which is not atomic, and neither happens before the
1472 other. Any such data race results in undefined behavior.
1473 26 NOTE 12 It can be shown that programs that correctly use simple mutexes and
1474 memory_order_seq_cst operations to prevent all data races, and use no other synchronization
1475 operations, behave as though the operations executed by their constituent threads were simply interleaved,
1476 with each value computation of an object being the last value stored in that interleaving. This is normally
1477 referred to as ''sequential consistency''. However, this applies only to data-race-free programs, and data-
1478 race-free programs cannot observe most program transformations that do not change single-threaded
1479 program semantics. In fact, most single-threaded program transformations continue to be allowed, since
1480 any program that behaves differently as a result must contain undefined behavior.
1484 27 NOTE 13 Compiler transformations that introduce assignments to a potentially shared memory location
1485 that would not be modified by the abstract machine are generally precluded by this standard, since such an
1486 assignment might overwrite another assignment by a different thread in cases in which an abstract machine
1487 execution would not have encountered a data race. This includes implementations of data member
1488 assignment that overwrite adjacent members in separate memory locations. We also generally preclude
1489 reordering of atomic loads in cases in which the atomics in question may alias, since this may violate the
1490 "visible sequence" rules.
1492 28 NOTE 14 Transformations that introduce a speculative read of a potentially shared memory location may
1493 not preserve the semantics of the program as defined in this standard, since they potentially introduce a data
1494 race. However, they are typically valid in the context of an optimizing compiler that targets a specific
1495 machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that
1496 is not tolerant of races or provides hardware race detection.
1503 5.2 Environmental considerations
1504 5.2.1 Character sets
1505 1 Two sets of characters and their associated collating sequences shall be defined: the set in
1506 which source files are written (the source character set), and the set interpreted in the
1507 execution environment (the execution character set). Each set is further divided into a
1508 basic character set, whose contents are given by this subclause, and a set of zero or more
1509 locale-specific members (which are not members of the basic character set) called
1510 extended characters. The combined set is also called the extended character set. The
1511 values of the members of the execution character set are implementation-defined.
1512 2 In a character constant or string literal, members of the execution character set shall be
1513 represented by corresponding members of the source character set or by escape
1514 sequences consisting of the backslash \ followed by one or more characters. A byte with
1515 all bits set to 0, called the null character, shall exist in the basic execution character set; it
1516 is used to terminate a character string.
1517 3 Both the basic source and basic execution character sets shall have the following
1518 members: the 26 uppercase letters of the Latin alphabet
1519 A B C D E F G H I J K L M
1520 N O P Q R S T U V W X Y Z
1521 the 26 lowercase letters of the Latin alphabet
1522 a b c d e f g h i j k l m
1523 n o p q r s t u v w x y z
1524 the 10 decimal digits
1526 the following 29 graphic characters
1527 ! " # % & ' ( ) * + , - . / :
1528 ; < = > ? [ \ ] ^ _ { | } ~
1529 the space character, and control characters representing horizontal tab, vertical tab, and
1530 form feed. The representation of each member of the source and execution basic
1531 character sets shall fit in a byte. In both the source and execution basic character sets, the
1532 value of each character after 0 in the above list of decimal digits shall be one greater than
1533 the value of the previous. In source files, there shall be some way of indicating the end of
1534 each line of text; this International Standard treats such an end-of-line indicator as if it
1535 were a single new-line character. In the basic execution character set, there shall be
1536 control characters representing alert, backspace, carriage return, and new line. If any
1537 other characters are encountered in a source file (except in an identifier, a character
1538 constant, a string literal, a header name, a comment, or a preprocessing token that is never
1542 converted to a token), the behavior is undefined.
1543 4 A letter is an uppercase letter or a lowercase letter as defined above; in this International
1544 Standard the term does not include other characters that are letters in other alphabets.
1545 5 The universal character name construct provides a way to name other characters.
1546 Forward references: universal character names (6.4.3), character constants (6.4.4.4),
1547 preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1).
1548 5.2.1.1 Trigraph sequences
1549 1 Before any other processing takes place, each occurrence of one of the following
1550 sequences of three characters (called trigraph sequences17)) is replaced with the
1551 corresponding single character.
1555 No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed
1556 above is not changed.
1558 ??=define arraycheck(a, b) a??(b??) ??!??! b??(a??)
1560 #define arraycheck(a, b) a[b] || b[a]
1562 3 EXAMPLE 2 The following source line
1564 becomes (after replacement of the trigraph sequence ??/)
1567 5.2.1.2 Multibyte characters
1568 1 The source character set may contain multibyte characters, used to represent members of
1569 the extended character set. The execution character set may also contain multibyte
1570 characters, which need not have the same encoding as for the source character set. For
1571 both character sets, the following shall hold:
1572 -- The basic character set shall be present and each character shall be encoded as a
1574 -- The presence, meaning, and representation of any additional members is locale-
1577 17) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as
1578 described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set.
1582 -- A multibyte character set may have a state-dependent encoding, wherein each
1583 sequence of multibyte characters begins in an initial shift state and enters other
1584 locale-specific shift states when specific multibyte characters are encountered in the
1585 sequence. While in the initial shift state, all single-byte characters retain their usual
1586 interpretation and do not alter the shift state. The interpretation for subsequent bytes
1587 in the sequence is a function of the current shift state.
1588 -- A byte with all bits zero shall be interpreted as a null character independent of shift
1589 state. Such a byte shall not occur as part of any other multibyte character.
1590 2 For source files, the following shall hold:
1591 -- An identifier, comment, string literal, character constant, or header name shall begin
1592 and end in the initial shift state.
1593 -- An identifier, comment, string literal, character constant, or header name shall consist
1594 of a sequence of valid multibyte characters.
1595 5.2.2 Character display semantics
1596 1 The active position is that location on a display device where the next character output by
1597 the fputc function would appear. The intent of writing a printing character (as defined
1598 by the isprint function) to a display device is to display a graphic representation of
1599 that character at the active position and then advance the active position to the next
1600 position on the current line. The direction of writing is locale-specific. If the active
1601 position is at the final position of a line (if there is one), the behavior of the display device
1603 2 Alphabetic escape sequences representing nongraphic characters in the execution
1604 character set are intended to produce actions on display devices as follows:
1605 \a (alert) Produces an audible or visible alert without changing the active position.
1606 \b (backspace) Moves the active position to the previous position on the current line. If
1607 the active position is at the initial position of a line, the behavior of the display
1608 device is unspecified.
1609 \f ( form feed) Moves the active position to the initial position at the start of the next
1611 \n (new line) Moves the active position to the initial position of the next line.
1612 \r (carriage return) Moves the active position to the initial position of the current line.
1613 \t (horizontal tab) Moves the active position to the next horizontal tabulation position
1614 on the current line. If the active position is at or past the last defined horizontal
1615 tabulation position, the behavior of the display device is unspecified.
1616 \v (vertical tab) Moves the active position to the initial position of the next vertical
1617 tabulation position. If the active position is at or past the last defined vertical
1620 tabulation position, the behavior of the display device is unspecified.
1621 3 Each of these escape sequences shall produce a unique implementation-defined value
1622 which can be stored in a single char object. The external representations in a text file
1623 need not be identical to the internal representations, and are outside the scope of this
1624 International Standard.
1625 Forward references: the isprint function (7.4.1.8), the fputc function (7.21.7.3).
1626 5.2.3 Signals and interrupts
1627 1 Functions shall be implemented such that they may be interrupted at any time by a signal,
1628 or may be called by a signal handler, or both, with no alteration to earlier, but still active,
1629 invocations' control flow (after the interruption), function return values, or objects with
1630 automatic storage duration. All such objects shall be maintained outside the function
1631 image (the instructions that compose the executable representation of a function) on a
1632 per-invocation basis.
1633 5.2.4 Environmental limits
1634 1 Both the translation and execution environments constrain the implementation of
1635 language translators and libraries. The following summarizes the language-related
1636 environmental limits on a conforming implementation; the library-related limits are
1637 discussed in clause 7.
1638 5.2.4.1 Translation limits
1639 1 The implementation shall be able to translate and execute at least one program that
1640 contains at least one instance of every one of the following limits:18)
1641 -- 127 nesting levels of blocks
1642 -- 63 nesting levels of conditional inclusion
1643 -- 12 pointer, array, and function declarators (in any combinations) modifying an
1644 arithmetic, structure, union, or void type in a declaration
1645 -- 63 nesting levels of parenthesized declarators within a full declarator
1646 -- 63 nesting levels of parenthesized expressions within a full expression
1647 -- 63 significant initial characters in an internal identifier or a macro name (each
1648 universal character name or extended source character is considered a single
1650 -- 31 significant initial characters in an external identifier (each universal character name
1651 specifying a short identifier of 0000FFFF or less is considered 6 characters, each
1654 18) Implementations should avoid imposing fixed translation limits whenever possible.
1658 universal character name specifying a short identifier of 00010000 or more is
1659 considered 10 characters, and each extended source character is considered the same
1660 number of characters as the corresponding universal character name, if any)19)
1661 -- 4095 external identifiers in one translation unit
1662 -- 511 identifiers with block scope declared in one block
1663 -- 4095 macro identifiers simultaneously defined in one preprocessing translation unit
1664 -- 127 parameters in one function definition
1665 -- 127 arguments in one function call
1666 -- 127 parameters in one macro definition
1667 -- 127 arguments in one macro invocation
1668 -- 4095 characters in a logical source line
1669 -- 4095 characters in a string literal (after concatenation)
1670 -- 65535 bytes in an object (in a hosted environment only)
1671 -- 15 nesting levels for #included files
1672 -- 1023 case labels for a switch statement (excluding those for any nested switch
1674 -- 1023 members in a single structure or union
1675 -- 1023 enumeration constants in a single enumeration
1676 -- 63 levels of nested structure or union definitions in a single struct-declaration-list
1677 5.2.4.2 Numerical limits
1678 1 An implementation is required to document all the limits specified in this subclause,
1679 which are specified in the headers <limits.h> and <float.h>. Additional limits are
1680 specified in <stdint.h>.
1681 Forward references: integer types <stdint.h> (7.20).
1682 5.2.4.2.1 Sizes of integer types <limits.h>
1683 1 The values given below shall be replaced by constant expressions suitable for use in #if
1684 preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the
1685 following shall be replaced by expressions that have the same type as would an
1686 expression that is an object of the corresponding type converted according to the integer
1687 promotions. Their implementation-defined values shall be equal or greater in magnitude
1690 19) See ''future language directions'' (6.11.3).
1694 (absolute value) to those shown, with the same sign.
1695 -- number of bits for smallest object that is not a bit-field (byte)
1697 -- minimum value for an object of type signed char
1698 SCHAR_MIN -127 // -(27 - 1)
1699 -- maximum value for an object of type signed char
1700 SCHAR_MAX +127 // 27 - 1
1701 -- maximum value for an object of type unsigned char
1702 UCHAR_MAX 255 // 28 - 1
1703 -- minimum value for an object of type char
1705 -- maximum value for an object of type char
1707 -- maximum number of bytes in a multibyte character, for any supported locale
1709 -- minimum value for an object of type short int
1710 SHRT_MIN -32767 // -(215 - 1)
1711 -- maximum value for an object of type short int
1712 SHRT_MAX +32767 // 215 - 1
1713 -- maximum value for an object of type unsigned short int
1714 USHRT_MAX 65535 // 216 - 1
1715 -- minimum value for an object of type int
1716 INT_MIN -32767 // -(215 - 1)
1717 -- maximum value for an object of type int
1718 INT_MAX +32767 // 215 - 1
1719 -- maximum value for an object of type unsigned int
1720 UINT_MAX 65535 // 216 - 1
1721 -- minimum value for an object of type long int
1722 LONG_MIN -2147483647 // -(231 - 1)
1723 -- maximum value for an object of type long int
1724 LONG_MAX +2147483647 // 231 - 1
1725 -- maximum value for an object of type unsigned long int
1726 ULONG_MAX 4294967295 // 232 - 1
1731 -- minimum value for an object of type long long int
1732 LLONG_MIN -9223372036854775807 // -(263 - 1)
1733 -- maximum value for an object of type long long int
1734 LLONG_MAX +9223372036854775807 // 263 - 1
1735 -- maximum value for an object of type unsigned long long int
1736 ULLONG_MAX 18446744073709551615 // 264 - 1
1737 2 If the value of an object of type char is treated as a signed integer when used in an
1738 expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the
1739 value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of
1740 CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of
1741 UCHAR_MAX.20) The value UCHAR_MAX shall equal 2CHAR_BIT - 1.
1742 Forward references: representations of types (6.2.6), conditional inclusion (6.10.1).
1743 5.2.4.2.2 Characteristics of floating types <float.h>
1744 1 The characteristics of floating types are defined in terms of a model that describes a
1745 representation of floating-point numbers and values that provide information about an
1746 implementation's floating-point arithmetic.21) The following parameters are used to
1747 define the model for each floating-point type:
1749 b base or radix of exponent representation (an integer > 1)
1750 e exponent (an integer between a minimum emin and a maximum emax )
1751 p precision (the number of base-b digits in the significand)
1752 fk nonnegative integers less than b (the significand digits)
1753 2 A floating-point number (x) is defined by the following model:
1755 x = sb e (Sum) f k b-k ,
1759 3 In addition to normalized floating-point numbers ( f 1 > 0 if x != 0), floating types may be
1760 able to contain other kinds of floating-point numbers, such as subnormal floating-point
1761 numbers (x != 0, e = emin , f 1 = 0) and unnormalized floating-point numbers (x != 0,
1762 e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and
1763 NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates
1764 through almost every arithmetic operation without raising a floating-point exception; a
1765 signaling NaN generally raises a floating-point exception when occurring as an
1769 21) The floating-point model is intended to clarify the description of each floating-point characteristic and
1770 does not require the floating-point arithmetic of the implementation to be identical.
1774 arithmetic operand.22)
1775 4 An implementation may give zero and values that are not floating-point numbers (such as
1776 infinities and NaNs) a sign or may leave them unsigned. Wherever such values are
1777 unsigned, any requirement in this International Standard to retrieve the sign shall produce
1778 an unspecified sign, and any requirement to set the sign shall be ignored.
1779 5 The minimum range of representable values for a floating type is the most negative finite
1780 floating-point number representable in that type through the most positive finite floating-
1781 point number representable in that type. In addition, if negative infinity is representable
1782 in a type, the range of that type is extended to all negative real numbers; likewise, if
1783 positive infinity is representable in a type, the range of that type is extended to all positive
1785 6 The accuracy of the floating-point operations (+, -, *, /) and of the library functions in
1786 <math.h> and <complex.h> that return floating-point results is implementation-
1787 defined, as is the accuracy of the conversion between floating-point internal
1788 representations and string representations performed by the library functions in
1789 <stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that the
1790 accuracy is unknown.
1791 7 All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant
1792 expressions suitable for use in #if preprocessing directives; all floating values shall be
1793 constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX,
1794 and FLT_ROUNDS have separate names for all three floating-point types. The floating-
1795 point model representation is provided for all values except FLT_EVAL_METHOD and
1797 8 The rounding mode for floating-point addition is characterized by the implementation-
1798 defined value of FLT_ROUNDS:23)
1802 2 toward positive infinity
1803 3 toward negative infinity
1804 All other values for FLT_ROUNDS characterize implementation-defined rounding
1808 22) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support
1809 IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings with
1811 23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through
1812 the function fesetround in <fenv.h>.
1816 9 Except for assignment and cast (which remove all extra range and precision), the values
1817 yielded by operators with floating operands and values subject to the usual arithmetic
1818 conversions and of floating constants are evaluated to a format whose range and precision
1819 may be greater than required by the type. The use of evaluation formats is characterized
1820 by the implementation-defined value of FLT_EVAL_METHOD:24)
1822 0 evaluate all operations and constants just to the range and precision of the
1824 1 evaluate operations and constants of type float and double to the
1825 range and precision of the double type, evaluate long double
1826 operations and constants to the range and precision of the long double
1828 2 evaluate all operations and constants to the range and precision of the
1830 All other negative values for FLT_EVAL_METHOD characterize implementation-defined
1832 10 The presence or absence of subnormal numbers is characterized by the implementation-
1833 defined values of FLT_HAS_SUBNORM, DBL_HAS_SUBNORM, and
1835 -1 indeterminable25)
1836 0 absent26) (type does not support subnormal numbers)
1837 1 present (type does support subnormal numbers)
1838 11 The values given in the following list shall be replaced by constant expressions with
1839 implementation-defined values that are greater or equal in magnitude (absolute value) to
1840 those shown, with the same sign:
1841 -- radix of exponent representation, b
1847 24) The evaluation method determines evaluation formats of expressions involving all floating types, not
1848 just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float
1849 _Complex operands is represented in the double _Complex format, and its parts are evaluated to
1851 25) Characterization as indeterminable is intended if floating-point operations do not consistently interpret
1852 subnormal representations as zero, nor as nonzero.
1853 26) Characterization as absent is intended if no floating-point operations produce subnormal results from
1854 non-subnormal inputs, even if the type format includes representations of subnormal numbers.
1858 -- number of base-FLT_RADIX digits in the floating-point significand, p
1862 -- number of decimal digits, n, such that any floating-point number with p radix b digits
1863 can be rounded to a floating-point number with n decimal digits and back again
1864 without change to the value,
1865 { p log10 b if b is a power of 10
1867 { [^1 + p log10 b^] otherwise
1871 -- number of decimal digits, n, such that any floating-point number in the widest
1872 supported floating type with pmax radix b digits can be rounded to a floating-point
1873 number with n decimal digits and back again without change to the value,
1874 { pmax log10 b if b is a power of 10
1876 { [^1 + pmax log10 b^] otherwise
1878 -- number of decimal digits, q, such that any floating-point number with q decimal digits
1879 can be rounded into a floating-point number with p radix b digits and back again
1880 without change to the q decimal digits,
1881 { p log10 b if b is a power of 10
1883 { [_( p - 1) log10 b_] otherwise
1887 -- minimum negative integer such that FLT_RADIX raised to one less than that power is
1888 a normalized floating-point number, emin
1898 -- minimum negative integer such that 10 raised to that power is in the range of
1899 normalized floating-point numbers, [^log10 b emin -1 ^]
1904 -- maximum integer such that FLT_RADIX raised to one less than that power is a
1905 representable finite floating-point number, emax
1909 -- maximum integer such that 10 raised to that power is in the range of representable
1910 finite floating-point numbers, [_log10 ((1 - b- p )b emax )_]
1914 12 The values given in the following list shall be replaced by constant expressions with
1915 implementation-defined values that are greater than or equal to those shown:
1916 -- maximum representable finite floating-point number, (1 - b- p )b emax
1920 13 The values given in the following list shall be replaced by constant expressions with
1921 implementation-defined (positive) values that are less than or equal to those shown:
1922 -- the difference between 1 and the least value greater than 1 that is representable in the
1923 given floating point type, b1- p
1927 -- minimum normalized positive floating-point number, b emin -1
1937 -- minimum positive floating-point number27)
1941 Recommended practice
1942 14 Conversion from (at least) double to decimal with DECIMAL_DIG digits and back
1943 should be the identity function.
1944 15 EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum
1945 requirements of this International Standard, and the appropriate values in a <float.h> header for type
1948 x = s16e (Sum) f k 16-k ,
1954 FLT_EPSILON 9.53674316E-07F
1958 FLT_MIN 2.93873588E-39F
1961 FLT_MAX 3.40282347E+38F
1964 16 EXAMPLE 2 The following describes floating-point representations that also meet the requirements for
1965 single-precision and double-precision numbers in IEC 60559,28) and the appropriate values in a
1966 <float.h> header for types float and double:
1968 x f = s2e (Sum) f k 2-k ,
1973 x d = s2e (Sum) f k 2-k ,
1980 FLT_EPSILON 1.19209290E-07F // decimal constant
1981 FLT_EPSILON 0X1P-23F // hex constant
1985 27) If the presence or absence of subnormal numbers is indeterminable, then the value is intended to be a
1986 positive number no greater than the minimum normalized positive number for the type.
1987 28) The floating-point model in that standard sums powers of b from zero, so the values of the exponent
1988 limits are one less than shown here.
1994 FLT_MIN 1.17549435E-38F // decimal constant
1995 FLT_MIN 0X1P-126F // hex constant
1996 FLT_TRUE_MIN 1.40129846E-45F // decimal constant
1997 FLT_TRUE_MIN 0X1P-149F // hex constant
2001 FLT_MAX 3.40282347E+38F // decimal constant
2002 FLT_MAX 0X1.fffffeP127F // hex constant
2005 DBL_EPSILON 2.2204460492503131E-16 // decimal constant
2006 DBL_EPSILON 0X1P-52 // hex constant
2010 DBL_MIN 2.2250738585072014E-308 // decimal constant
2011 DBL_MIN 0X1P-1022 // hex constant
2012 DBL_TRUE_MIN 4.9406564584124654E-324 // decimal constant
2013 DBL_TRUE_MIN 0X1P-1074 // hex constant
2017 DBL_MAX 1.7976931348623157E+308 // decimal constant
2018 DBL_MAX 0X1.fffffffffffffP1023 // hex constant
2020 If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For
2021 example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of
2022 precision), then DECIMAL_DIG would be 21.
2024 Forward references: conditional inclusion (6.10.1), complex arithmetic
2025 <complex.h> (7.3), extended multibyte and wide character utilities <wchar.h>
2026 (7.28), floating-point environment <fenv.h> (7.6), general utilities <stdlib.h>
2027 (7.22), input/output <stdio.h> (7.21), mathematics <math.h> (7.12).
2037 1 In the syntax notation used in this clause, syntactic categories (nonterminals) are
2038 indicated by italic type, and literal words and character set members (terminals) by bold
2039 type. A colon (:) following a nonterminal introduces its definition. Alternative
2040 definitions are listed on separate lines, except when prefaced by the words ''one of''. An
2041 optional symbol is indicated by the subscript ''opt'', so that
2043 indicates an optional expression enclosed in braces.
2044 2 When syntactic categories are referred to in the main text, they are not italicized and
2045 words are separated by spaces instead of hyphens.
2046 3 A summary of the language syntax is given in annex A.
2048 6.2.1 Scopes of identifiers
2049 1 An identifier can denote an object; a function; a tag or a member of a structure, union, or
2050 enumeration; a typedef name; a label name; a macro name; or a macro parameter. The
2051 same identifier can denote different entities at different points in the program. A member
2052 of an enumeration is called an enumeration constant. Macro names and macro
2053 parameters are not considered further here, because prior to the semantic phase of
2054 program translation any occurrences of macro names in the source file are replaced by the
2055 preprocessing token sequences that constitute their macro definitions.
2056 2 For each different entity that an identifier designates, the identifier is visible (i.e., can be
2057 used) only within a region of program text called its scope. Different entities designated
2058 by the same identifier either have different scopes, or are in different name spaces. There
2059 are four kinds of scopes: function, file, block, and function prototype. (A function
2060 prototype is a declaration of a function that declares the types of its parameters.)
2061 3 A label name is the only kind of identifier that has function scope. It can be used (in a
2062 goto statement) anywhere in the function in which it appears, and is declared implicitly
2063 by its syntactic appearance (followed by a : and a statement).
2064 4 Every other identifier has scope determined by the placement of its declaration (in a
2065 declarator or type specifier). If the declarator or type specifier that declares the identifier
2066 appears outside of any block or list of parameters, the identifier has file scope, which
2067 terminates at the end of the translation unit. If the declarator or type specifier that
2068 declares the identifier appears inside a block or within the list of parameter declarations in
2069 a function definition, the identifier has block scope, which terminates at the end of the
2070 associated block. If the declarator or type specifier that declares the identifier appears
2074 within the list of parameter declarations in a function prototype (not part of a function
2075 definition), the identifier has function prototype scope, which terminates at the end of the
2076 function declarator. If an identifier designates two different entities in the same name
2077 space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end
2078 strictly before the scope of the other entity (the outer scope). Within the inner scope, the
2079 identifier designates the entity declared in the inner scope; the entity declared in the outer
2080 scope is hidden (and not visible) within the inner scope.
2081 5 Unless explicitly stated otherwise, where this International Standard uses the term
2082 ''identifier'' to refer to some entity (as opposed to the syntactic construct), it refers to the
2083 entity in the relevant name space whose declaration is visible at the point the identifier
2085 6 Two identifiers have the same scope if and only if their scopes terminate at the same
2087 7 Structure, union, and enumeration tags have scope that begins just after the appearance of
2088 the tag in a type specifier that declares the tag. Each enumeration constant has scope that
2089 begins just after the appearance of its defining enumerator in an enumerator list. Any
2090 other identifier has scope that begins just after the completion of its declarator.
2091 8 As a special case, a type name (which is not a declaration of an identifier) is considered to
2092 have a scope that begins just after the place within the type name where the omitted
2093 identifier would appear were it not omitted.
2094 Forward references: declarations (6.7), function calls (6.5.2.2), function definitions
2095 (6.9.1), identifiers (6.4.2), macro replacement (6.10.3), name spaces of identifiers (6.2.3),
2096 source file inclusion (6.10.2), statements (6.8).
2097 6.2.2 Linkages of identifiers
2098 1 An identifier declared in different scopes or in the same scope more than once can be
2099 made to refer to the same object or function by a process called linkage.29) There are
2100 three kinds of linkage: external, internal, and none.
2101 2 In the set of translation units and libraries that constitutes an entire program, each
2102 declaration of a particular identifier with external linkage denotes the same object or
2103 function. Within one translation unit, each declaration of an identifier with internal
2104 linkage denotes the same object or function. Each declaration of an identifier with no
2105 linkage denotes a unique entity.
2106 3 If the declaration of a file scope identifier for an object or a function contains the storage-
2107 class specifier static, the identifier has internal linkage.30)
2111 29) There is no linkage between different identifiers.
2115 4 For an identifier declared with the storage-class specifier extern in a scope in which a
2116 prior declaration of that identifier is visible,31) if the prior declaration specifies internal or
2117 external linkage, the linkage of the identifier at the later declaration is the same as the
2118 linkage specified at the prior declaration. If no prior declaration is visible, or if the prior
2119 declaration specifies no linkage, then the identifier has external linkage.
2120 5 If the declaration of an identifier for a function has no storage-class specifier, its linkage
2121 is determined exactly as if it were declared with the storage-class specifier extern. If
2122 the declaration of an identifier for an object has file scope and no storage-class specifier,
2123 its linkage is external.
2124 6 The following identifiers have no linkage: an identifier declared to be anything other than
2125 an object or a function; an identifier declared to be a function parameter; a block scope
2126 identifier for an object declared without the storage-class specifier extern.
2127 7 If, within a translation unit, the same identifier appears with both internal and external
2128 linkage, the behavior is undefined.
2129 Forward references: declarations (6.7), expressions (6.5), external definitions (6.9),
2131 6.2.3 Name spaces of identifiers
2132 1 If more than one declaration of a particular identifier is visible at any point in a
2133 translation unit, the syntactic context disambiguates uses that refer to different entities.
2134 Thus, there are separate name spaces for various categories of identifiers, as follows:
2135 -- label names (disambiguated by the syntax of the label declaration and use);
2136 -- the tags of structures, unions, and enumerations (disambiguated by following any32)
2137 of the keywords struct, union, or enum);
2138 -- the members of structures or unions; each structure or union has a separate name
2139 space for its members (disambiguated by the type of the expression used to access the
2140 member via the . or -> operator);
2141 -- all other identifiers, called ordinary identifiers (declared in ordinary declarators or as
2142 enumeration constants).
2143 Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1),
2144 structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags
2145 (6.7.2.3), the goto statement (6.8.6.1).
2147 30) A function declaration can contain the storage-class specifier static only if it is at file scope; see
2149 31) As specified in 6.2.1, the later declaration might hide the prior declaration.
2150 32) There is only one name space for tags even though three are possible.
2154 6.2.4 Storage durations of objects
2155 1 An object has a storage duration that determines its lifetime. There are four storage
2156 durations: static, thread, automatic, and allocated. Allocated storage is described in
2158 2 The lifetime of an object is the portion of program execution during which storage is
2159 guaranteed to be reserved for it. An object exists, has a constant address,33) and retains
2160 its last-stored value throughout its lifetime.34) If an object is referred to outside of its
2161 lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when
2162 the object it points to (or just past) reaches the end of its lifetime.
2163 3 An object whose identifier is declared without the storage-class specifier
2164 _Thread_local, and either with external or internal linkage or with the storage-class
2165 specifier static, has static storage duration. Its lifetime is the entire execution of the
2166 program and its stored value is initialized only once, prior to program startup.
2167 4 An object whose identifier is declared with the storage-class specifier _Thread_local
2168 has thread storage duration. Its lifetime is the entire execution of the thread for which it
2169 is created, and its stored value is initialized when the thread is started. There is a distinct
2170 object per thread, and use of the declared name in an expression refers to the object
2171 associated with the thread evaluating the expression. The result of attempting to
2172 indirectly access an object with thread storage duration from a thread other than the one
2173 with which the object is associated is implementation-defined.
2174 5 An object whose identifier is declared with no linkage and without the storage-class
2175 specifier static has automatic storage duration, as do some compound literals. The
2176 result of attempting to indirectly access an object with automatic storage duration from a
2177 thread other than the one with which the object is associated is implementation-defined.
2178 6 For such an object that does not have a variable length array type, its lifetime extends
2179 from entry into the block with which it is associated until execution of that block ends in
2180 any way. (Entering an enclosed block or calling a function suspends, but does not end,
2181 execution of the current block.) If the block is entered recursively, a new instance of the
2182 object is created each time. The initial value of the object is indeterminate. If an
2183 initialization is specified for the object, it is performed each time the declaration or
2184 compound literal is reached in the execution of the block; otherwise, the value becomes
2185 indeterminate each time the declaration is reached.
2189 33) The term ''constant address'' means that two pointers to the object constructed at possibly different
2190 times will compare equal. The address may be different during two different executions of the same
2192 34) In the case of a volatile object, the last store need not be explicit in the program.
2196 7 For such an object that does have a variable length array type, its lifetime extends from
2197 the declaration of the object until execution of the program leaves the scope of the
2198 declaration.35) If the scope is entered recursively, a new instance of the object is created
2199 each time. The initial value of the object is indeterminate.
2200 8 A non-lvalue expression with structure or union type, where the structure or union
2201 contains a member with array type (including, recursively, members of all contained
2202 structures and unions) refers to an object with automatic storage duration and temporary
2203 lifetime.36) Its lifetime begins when the expression is evaluated and its initial value is the
2204 value of the expression. Its lifetime ends when the evaluation of the containing full
2205 expression or full declarator ends. Any attempt to modify an object with temporary
2206 lifetime results in undefined behavior.
2207 Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators
2208 (6.7.6), function calls (6.5.2.2), initialization (6.7.9), statements (6.8).
2210 1 The meaning of a value stored in an object or returned by a function is determined by the
2211 type of the expression used to access it. (An identifier declared to be an object is the
2212 simplest such expression; the type is specified in the declaration of the identifier.) Types
2213 are partitioned into object types (types that describe objects) and function types (types
2214 that describe functions). At various points within a translation unit an object type may be
2215 incomplete (lacking sufficient information to determine the size of objects of that type) or
2216 complete (having sufficient information).37)
2217 2 An object declared as type _Bool is large enough to store the values 0 and 1.
2218 3 An object declared as type char is large enough to store any member of the basic
2219 execution character set. If a member of the basic execution character set is stored in a
2220 char object, its value is guaranteed to be nonnegative. If any other character is stored in
2221 a char object, the resulting value is implementation-defined but shall be within the range
2222 of values that can be represented in that type.
2223 4 There are five standard signed integer types, designated as signed char, short
2224 int, int, long int, and long long int. (These and other types may be
2225 designated in several additional ways, as described in 6.7.2.) There may also be
2226 implementation-defined extended signed integer types.38) The standard and extended
2227 signed integer types are collectively called signed integer types.39)
2229 35) Leaving the innermost block containing the declaration, or jumping to a point in that block or an
2230 embedded block prior to the declaration, leaves the scope of the declaration.
2231 36) The address of such an object is taken implicitly when an array member is accessed.
2232 37) A type may be incomplete or complete throughout an entire translation unit, or it may change states at
2233 different points within a translation unit.
2237 5 An object declared as type signed char occupies the same amount of storage as a
2238 ''plain'' char object. A ''plain'' int object has the natural size suggested by the
2239 architecture of the execution environment (large enough to contain any value in the range
2240 INT_MIN to INT_MAX as defined in the header <limits.h>).
2241 6 For each of the signed integer types, there is a corresponding (but different) unsigned
2242 integer type (designated with the keyword unsigned) that uses the same amount of
2243 storage (including sign information) and has the same alignment requirements. The type
2244 _Bool and the unsigned integer types that correspond to the standard signed integer
2245 types are the standard unsigned integer types. The unsigned integer types that
2246 correspond to the extended signed integer types are the extended unsigned integer types.
2247 The standard and extended unsigned integer types are collectively called unsigned integer
2249 7 The standard signed integer types and standard unsigned integer types are collectively
2250 called the standard integer types, the extended signed integer types and extended
2251 unsigned integer types are collectively called the extended integer types.
2252 8 For any two integer types with the same signedness and different integer conversion rank
2253 (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a
2254 subrange of the values of the other type.
2255 9 The range of nonnegative values of a signed integer type is a subrange of the
2256 corresponding unsigned integer type, and the representation of the same value in each
2257 type is the same.41) A computation involving unsigned operands can never overflow,
2258 because a result that cannot be represented by the resulting unsigned integer type is
2259 reduced modulo the number that is one greater than the largest value that can be
2260 represented by the resulting type.
2261 10 There are three real floating types, designated as float, double, and long
2262 double.42) The set of values of the type float is a subset of the set of values of the
2263 type double; the set of values of the type double is a subset of the set of values of the
2267 38) Implementation-defined keywords shall have the form of an identifier reserved for any use as
2269 39) Therefore, any statement in this Standard about signed integer types also applies to the extended
2270 signed integer types.
2271 40) Therefore, any statement in this Standard about unsigned integer types also applies to the extended
2272 unsigned integer types.
2273 41) The same representation and alignment requirements are meant to imply interchangeability as
2274 arguments to functions, return values from functions, and members of unions.
2275 42) See ''future language directions'' (6.11.1).
2279 11 There are three complex types, designated as float _Complex, double
2280 _Complex, and long double _Complex.43) (Complex types are a conditional
2281 feature that implementations need not support; see 6.10.8.3.) The real floating and
2282 complex types are collectively called the floating types.
2283 12 For each floating type there is a corresponding real type, which is always a real floating
2284 type. For real floating types, it is the same type. For complex types, it is the type given
2285 by deleting the keyword _Complex from the type name.
2286 13 Each complex type has the same representation and alignment requirements as an array
2287 type containing exactly two elements of the corresponding real type; the first element is
2288 equal to the real part, and the second element to the imaginary part, of the complex
2290 14 The type char, the signed and unsigned integer types, and the floating types are
2291 collectively called the basic types. The basic types are complete object types. Even if the
2292 implementation defines two or more basic types to have the same representation, they are
2293 nevertheless different types.44)
2294 15 The three types char, signed char, and unsigned char are collectively called
2295 the character types. The implementation shall define char to have the same range,
2296 representation, and behavior as either signed char or unsigned char.45)
2297 16 An enumeration comprises a set of named integer constant values. Each distinct
2298 enumeration constitutes a different enumerated type.
2299 17 The type char, the signed and unsigned integer types, and the enumerated types are
2300 collectively called integer types. The integer and real floating types are collectively called
2302 18 Integer and floating types are collectively called arithmetic types. Each arithmetic type
2303 belongs to one type domain: the real type domain comprises the real types, the complex
2304 type domain comprises the complex types.
2305 19 The void type comprises an empty set of values; it is an incomplete object type that
2306 cannot be completed.
2310 43) A specification for imaginary types is in annex G.
2311 44) An implementation may define new keywords that provide alternative ways to designate a basic (or
2312 any other) type; this does not violate the requirement that all basic types be different.
2313 Implementation-defined keywords shall have the form of an identifier reserved for any use as
2315 45) CHAR_MIN, defined in <limits.h>, will have one of the values 0 or SCHAR_MIN, and this can be
2316 used to distinguish the two options. Irrespective of the choice made, char is a separate type from the
2317 other two and is not compatible with either.
2321 20 Any number of derived types can be constructed from the object and function types, as
2323 -- An array type describes a contiguously allocated nonempty set of objects with a
2324 particular member object type, called the element type. The element type shall be
2325 complete whenever the array type is specified. Array types are characterized by their
2326 element type and by the number of elements in the array. An array type is said to be
2327 derived from its element type, and if its element type is T , the array type is sometimes
2328 called ''array of T ''. The construction of an array type from an element type is called
2329 ''array type derivation''.
2330 -- A structure type describes a sequentially allocated nonempty set of member objects
2331 (and, in certain circumstances, an incomplete array), each of which has an optionally
2332 specified name and possibly distinct type.
2333 -- A union type describes an overlapping nonempty set of member objects, each of
2334 which has an optionally specified name and possibly distinct type.
2335 -- A function type describes a function with specified return type. A function type is
2336 characterized by its return type and the number and types of its parameters. A
2337 function type is said to be derived from its return type, and if its return type is T , the
2338 function type is sometimes called ''function returning T ''. The construction of a
2339 function type from a return type is called ''function type derivation''.
2340 -- A pointer type may be derived from a function type or an object type, called the
2341 referenced type. A pointer type describes an object whose value provides a reference
2342 to an entity of the referenced type. A pointer type derived from the referenced type T
2343 is sometimes called ''pointer to T ''. The construction of a pointer type from a
2344 referenced type is called ''pointer type derivation''. A pointer type is a complete
2346 -- An atomic type describes the type designated by the construct _Atomic ( type-
2347 name ). (Atomic types are a conditional feature that implementations need not
2348 support; see 6.10.8.3.)
2349 These methods of constructing derived types can be applied recursively.
2350 21 Arithmetic types and pointer types are collectively called scalar types. Array and
2351 structure types are collectively called aggregate types.46)
2352 22 An array type of unknown size is an incomplete type. It is completed, for an identifier of
2353 that type, by specifying the size in a later declaration (with internal or external linkage).
2354 A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete
2357 46) Note that aggregate type does not include union type because an object with union type can only
2358 contain one member at a time.
2362 type. It is completed, for all declarations of that type, by declaring the same structure or
2363 union tag with its defining content later in the same scope.
2364 23 A type has known constant size if the type is not incomplete and is not a variable length
2366 24 Array, function, and pointer types are collectively called derived declarator types. A
2367 declarator type derivation from a type T is the construction of a derived declarator type
2368 from T by the application of an array-type, a function-type, or a pointer-type derivation to
2370 25 A type is characterized by its type category, which is either the outermost derivation of a
2371 derived type (as noted above in the construction of derived types), or the type itself if the
2372 type consists of no derived types.
2373 26 Any type so far mentioned is an unqualified type. Each unqualified type has several
2374 qualified versions of its type,47) corresponding to the combinations of one, two, or all
2375 three of the const, volatile, and restrict qualifiers. The qualified or unqualified
2376 versions of a type are distinct types that belong to the same type category and have the
2377 same representation and alignment requirements.48) A derived type is not qualified by the
2378 qualifiers (if any) of the type from which it is derived.
2379 27 Further, there is the _Atomic qualifier. The presence of the _Atomic qualifier
2380 designates an atomic type. The size, representation, and alignment of an atomic type
2381 need not be the same as those of the corresponding unqualified type. Therefore, this
2382 Standard explicitly uses the phrase ''atomic, qualified or unqualified type'' whenever the
2383 atomic version of a type is permitted along with the other qualified versions of a type.
2384 The phrase ''qualified or unqualified type'', without specific mention of atomic, does not
2385 include the atomic types.
2386 28 A pointer to void shall have the same representation and alignment requirements as a
2387 pointer to a character type.48) Similarly, pointers to qualified or unqualified versions of
2388 compatible types shall have the same representation and alignment requirements. All
2389 pointers to structure types shall have the same representation and alignment requirements
2390 as each other. All pointers to union types shall have the same representation and
2391 alignment requirements as each other. Pointers to other types need not have the same
2392 representation or alignment requirements.
2393 29 EXAMPLE 1 The type designated as ''float *'' has type ''pointer to float''. Its type category is
2394 pointer, not a floating type. The const-qualified version of this type is designated as ''float * const''
2395 whereas the type designated as ''const float *'' is not a qualified type -- its type is ''pointer to const-
2398 47) See 6.7.3 regarding qualified array and function types.
2399 48) The same representation and alignment requirements are meant to imply interchangeability as
2400 arguments to functions, return values from functions, and members of unions.
2404 qualified float'' and is a pointer to a qualified type.
2406 30 EXAMPLE 2 The type designated as ''struct tag (*[5])(float)'' has type ''array of pointer to
2407 function returning struct tag''. The array has length five and the function has a single parameter of type
2408 float. Its type category is array.
2410 Forward references: compatible type and composite type (6.2.7), declarations (6.7).
2411 6.2.6 Representations of types
2413 1 The representations of all types are unspecified except as stated in this subclause.
2414 2 Except for bit-fields, objects are composed of contiguous sequences of one or more bytes,
2415 the number, order, and encoding of which are either explicitly specified or
2416 implementation-defined.
2417 3 Values stored in unsigned bit-fields and objects of type unsigned char shall be
2418 represented using a pure binary notation.49)
2419 4 Values stored in non-bit-field objects of any other object type consist of n x CHAR_BIT
2420 bits, where n is the size of an object of that type, in bytes. The value may be copied into
2421 an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is
2422 called the object representation of the value. Values stored in bit-fields consist of m bits,
2423 where m is the size specified for the bit-field. The object representation is the set of m
2424 bits the bit-field comprises in the addressable storage unit holding it. Two values (other
2425 than NaNs) with the same object representation compare equal, but values that compare
2426 equal may have different object representations.
2427 5 Certain object representations need not represent a value of the object type. If the stored
2428 value of an object has such a representation and is read by an lvalue expression that does
2429 not have character type, the behavior is undefined. If such a representation is produced
2430 by a side effect that modifies all or any part of the object by an lvalue expression that
2431 does not have character type, the behavior is undefined.50) Such a representation is called
2432 a trap representation.
2433 6 When a value is stored in an object of structure or union type, including in a member
2434 object, the bytes of the object representation that correspond to any padding bytes take
2435 unspecified values.51) The value of a structure or union object is never a trap
2438 49) A positional representation for integers that uses the binary digits 0 and 1, in which the values
2439 represented by successive bits are additive, begin with 1, and are multiplied by successive integral
2440 powers of 2, except perhaps the bit with the highest position. (Adapted from the American National
2441 Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of
2442 type unsigned char range from 0 to 2
2445 50) Thus, an automatic variable can be initialized to a trap representation without causing undefined
2446 behavior, but the value of the variable cannot be used until a proper value is stored in it.
2450 representation, even though the value of a member of the structure or union object may be
2451 a trap representation.
2452 7 When a value is stored in a member of an object of union type, the bytes of the object
2453 representation that do not correspond to that member but do correspond to other members
2454 take unspecified values.
2455 8 Where an operator is applied to a value that has more than one object representation,
2456 which object representation is used shall not affect the value of the result.52) Where a
2457 value is stored in an object using a type that has more than one object representation for
2458 that value, it is unspecified which representation is used, but a trap representation shall
2460 9 Loads and stores of objects with atomic types are done with
2461 memory_order_seq_cst semantics.
2462 Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function
2463 designators (6.3.2.1), order and consistency (7.17.3).
2464 6.2.6.2 Integer types
2465 1 For unsigned integer types other than unsigned char, the bits of the object
2466 representation shall be divided into two groups: value bits and padding bits (there need
2467 not be any of the latter). If there are N value bits, each bit shall represent a different
2468 power of 2 between 1 and 2 N -1 , so that objects of that type shall be capable of
2469 representing values from 0 to 2 N - 1 using a pure binary representation; this shall be
2470 known as the value representation. The values of any padding bits are unspecified.53)
2471 2 For signed integer types, the bits of the object representation shall be divided into three
2472 groups: value bits, padding bits, and the sign bit. There need not be any padding bits;
2473 signed char shall not have any padding bits. There shall be exactly one sign bit.
2474 Each bit that is a value bit shall have the same value as the same bit in the object
2475 representation of the corresponding unsigned type (if there are M value bits in the signed
2476 type and N in the unsigned type, then M <= N ). If the sign bit is zero, it shall not affect
2478 51) Thus, for example, structure assignment need not copy any padding bits.
2479 52) It is possible for objects x and y with the same effective type T to have the same value when they are
2480 accessed as objects of type T, but to have different values in other contexts. In particular, if == is
2481 defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0.
2482 Furthermore, x == y does not necessarily imply that x and y have the same value; other operations
2483 on values of type T may distinguish between them.
2484 53) Some combinations of padding bits might generate trap representations, for example, if one padding
2485 bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
2486 representation other than as part of an exceptional condition such as an overflow, and this cannot occur
2487 with unsigned types. All other combinations of padding bits are alternative object representations of
2488 the value specified by the value bits.
2492 the resulting value. If the sign bit is one, the value shall be modified in one of the
2494 -- the corresponding value with sign bit 0 is negated (sign and magnitude);
2495 -- the sign bit has the value -(2 M ) (two's complement);
2496 -- the sign bit has the value -(2 M - 1) (ones' complement).
2497 Which of these applies is implementation-defined, as is whether the value with sign bit 1
2498 and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones'
2499 complement), is a trap representation or a normal value. In the case of sign and
2500 magnitude and ones' complement, if this representation is a normal value it is called a
2502 3 If the implementation supports negative zeros, they shall be generated only by:
2503 -- the &, |, ^, ~, <<, and >> operators with operands that produce such a value;
2504 -- the +, -, *, /, and % operators where one operand is a negative zero and the result is
2506 -- compound assignment operators based on the above cases.
2507 It is unspecified whether these cases actually generate a negative zero or a normal zero,
2508 and whether a negative zero becomes a normal zero when stored in an object.
2509 4 If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<,
2510 and >> operators with operands that would produce such a value is undefined.
2511 5 The values of any padding bits are unspecified.54) A valid (non-trap) object representation
2512 of a signed integer type where the sign bit is zero is a valid object representation of the
2513 corresponding unsigned type, and shall represent the same value. For any integer type,
2514 the object representation where all the bits are zero shall be a representation of the value
2516 6 The precision of an integer type is the number of bits it uses to represent values,
2517 excluding any sign and padding bits. The width of an integer type is the same but
2518 including any sign bit; thus for unsigned integer types the two values are the same, while
2519 for signed integer types the width is one greater than the precision.
2524 54) Some combinations of padding bits might generate trap representations, for example, if one padding
2525 bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
2526 representation other than as part of an exceptional condition such as an overflow. All other
2527 combinations of padding bits are alternative object representations of the value specified by the value
2532 6.2.7 Compatible type and composite type
2533 1 Two types have compatible type if their types are the same. Additional rules for
2534 determining whether two types are compatible are described in 6.7.2 for type specifiers,
2535 in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.55) Moreover, two structure,
2536 union, or enumerated types declared in separate translation units are compatible if their
2537 tags and members satisfy the following requirements: If one is declared with a tag, the
2538 other shall be declared with the same tag. If both are completed anywhere within their
2539 respective translation units, then the following additional requirements apply: there shall
2540 be a one-to-one correspondence between their members such that each pair of
2541 corresponding members are declared with compatible types; if one member of the pair is
2542 declared with an alignment specifier, the other is declared with an equivalent alignment
2543 specifier; and if one member of the pair is declared with a name, the other is declared
2544 with the same name. For two structures, corresponding members shall be declared in the
2545 same order. For two structures or unions, corresponding bit-fields shall have the same
2546 widths. For two enumerations, corresponding members shall have the same values.
2547 2 All declarations that refer to the same object or function shall have compatible type;
2548 otherwise, the behavior is undefined.
2549 3 A composite type can be constructed from two types that are compatible; it is a type that
2550 is compatible with both of the two types and satisfies the following conditions:
2551 -- If both types are array types, the following rules are applied:
2552 o If one type is an array of known constant size, the composite type is an array of
2554 o Otherwise, if one type is a variable length array whose size is specified by an
2555 expression that is not evaluated, the behavior is undefined.
2556 o Otherwise, if one type is a variable length array whose size is specified, the
2557 composite type is a variable length array of that size.
2558 o Otherwise, if one type is a variable length array of unspecified size, the composite
2559 type is a variable length array of unspecified size.
2560 o Otherwise, both types are arrays of unknown size and the composite type is an
2561 array of unknown size.
2562 The element type of the composite type is the composite type of the two element
2564 -- If only one type is a function type with a parameter type list (a function prototype),
2565 the composite type is a function prototype with the parameter type list.
2568 55) Two types need not be identical to be compatible.
2572 -- If both types are function types with parameter type lists, the type of each parameter
2573 in the composite parameter type list is the composite type of the corresponding
2575 These rules apply recursively to the types from which the two types are derived.
2576 4 For an identifier with internal or external linkage declared in a scope in which a prior
2577 declaration of that identifier is visible,56) if the prior declaration specifies internal or
2578 external linkage, the type of the identifier at the later declaration becomes the composite
2580 Forward references: array declarators (6.7.6.2).
2581 5 EXAMPLE Given the following two file scope declarations:
2582 int f(int (*)(), double (*)[3]);
2583 int f(int (*)(char *), double (*)[]);
2584 The resulting composite type for the function is:
2585 int f(int (*)(char *), double (*)[3]);
2587 6.2.8 Alignment of objects
2588 1 Complete object types have alignment requirements which place restrictions on the
2589 addresses at which objects of that type may be allocated. An alignment is an
2590 implementation-defined integer value representing the number of bytes between
2591 successive addresses at which a given object can be allocated. An object type imposes an
2592 alignment requirement on every object of that type: stricter alignment can be requested
2593 using the _Alignas keyword.
2594 2 A fundamental alignment is represented by an alignment less than or equal to the greatest
2595 alignment supported by the implementation in all contexts, which is equal to
2596 alignof(max_align_t).
2597 3 An extended alignment is represented by an alignment greater than
2598 alignof(max_align_t). It is implementation-defined whether any extended
2599 alignments are supported and the contexts in which they are supported. A type having an
2600 extended alignment requirement is an over-aligned type.57)
2601 4 Alignments are represented as values of the type size_t. Valid alignments include only
2602 those values returned by an alignof expression for fundamental types, plus an
2603 additional implementation-defined set of values, which may be empty. Every valid
2604 alignment value shall be a nonnegative integral power of two.
2607 56) As specified in 6.2.1, the later declaration might hide the prior declaration.
2608 57) Every over-aligned type is, or contains, a structure or union type with a member to which an extended
2609 alignment has been applied.
2613 5 Alignments have an order from weaker to stronger or stricter alignments. Stricter
2614 alignments have larger alignment values. An address that satisfies an alignment
2615 requirement also satisfies any weaker valid alignment requirement.
2616 6 The alignment requirement of a complete type can be queried using an alignof
2617 expression. The types char, signed char, and unsigned char shall have the
2618 weakest alignment requirement.
2619 7 Comparing alignments is meaningful and provides the obvious results:
2620 -- Two alignments are equal when their numeric values are equal.
2621 -- Two alignments are different when their numeric values are not equal.
2622 -- When an alignment is larger than another it represents a stricter alignment.
2630 1 Several operators convert operand values from one type to another automatically. This
2631 subclause specifies the result required from such an implicit conversion, as well as those
2632 that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes
2633 the conversions performed by most ordinary operators; it is supplemented as required by
2634 the discussion of each operator in 6.5.
2635 2 Conversion of an operand value to a compatible type causes no change to the value or the
2637 Forward references: cast operators (6.5.4).
2638 6.3.1 Arithmetic operands
2639 6.3.1.1 Boolean, characters, and integers
2640 1 Every integer type has an integer conversion rank defined as follows:
2641 -- No two signed integer types shall have the same rank, even if they have the same
2643 -- The rank of a signed integer type shall be greater than the rank of any signed integer
2644 type with less precision.
2645 -- The rank of long long int shall be greater than the rank of long int, which
2646 shall be greater than the rank of int, which shall be greater than the rank of short
2647 int, which shall be greater than the rank of signed char.
2648 -- The rank of any unsigned integer type shall equal the rank of the corresponding
2649 signed integer type, if any.
2650 -- The rank of any standard integer type shall be greater than the rank of any extended
2651 integer type with the same width.
2652 -- The rank of char shall equal the rank of signed char and unsigned char.
2653 -- The rank of _Bool shall be less than the rank of all other standard integer types.
2654 -- The rank of any enumerated type shall equal the rank of the compatible integer type
2656 -- The rank of any extended signed integer type relative to another extended signed
2657 integer type with the same precision is implementation-defined, but still subject to the
2658 other rules for determining the integer conversion rank.
2659 -- For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 has
2660 greater rank than T3, then T1 has greater rank than T3.
2661 2 The following may be used in an expression wherever an int or unsigned int may
2666 -- An object or expression with an integer type (other than int or unsigned int)
2667 whose integer conversion rank is less than or equal to the rank of int and
2669 -- A bit-field of type _Bool, int, signed int, or unsigned int.
2670 If an int can represent all values of the original type (as restricted by the width, for a
2671 bit-field), the value is converted to an int; otherwise, it is converted to an unsigned
2672 int. These are called the integer promotions.58) All other types are unchanged by the
2674 3 The integer promotions preserve value including sign. As discussed earlier, whether a
2675 ''plain'' char is treated as signed is implementation-defined.
2676 Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers
2678 6.3.1.2 Boolean type
2679 1 When any scalar value is converted to _Bool, the result is 0 if the value compares equal
2680 to 0; otherwise, the result is 1.59)
2681 6.3.1.3 Signed and unsigned integers
2682 1 When a value with integer type is converted to another integer type other than _Bool, if
2683 the value can be represented by the new type, it is unchanged.
2684 2 Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or
2685 subtracting one more than the maximum value that can be represented in the new type
2686 until the value is in the range of the new type.60)
2687 3 Otherwise, the new type is signed and the value cannot be represented in it; either the
2688 result is implementation-defined or an implementation-defined signal is raised.
2689 6.3.1.4 Real floating and integer
2690 1 When a finite value of real floating type is converted to an integer type other than _Bool,
2691 the fractional part is discarded (i.e., the value is truncated toward zero). If the value of
2692 the integral part cannot be represented by the integer type, the behavior is undefined.61)
2695 58) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain
2696 argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of the
2697 shift operators, as specified by their respective subclauses.
2698 59) NaNs do not compare equal to 0 and thus convert to 1.
2699 60) The rules describe arithmetic on the mathematical value, not the value of a given type of expression.
2700 61) The remaindering operation performed when a value of integer type is converted to unsigned type
2701 need not be performed when a value of real floating type is converted to unsigned type. Thus, the
2702 range of portable real floating values is (-1, Utype_MAX+1).
2706 2 When a value of integer type is converted to a real floating type, if the value being
2707 converted can be represented exactly in the new type, it is unchanged. If the value being
2708 converted is in the range of values that can be represented but cannot be represented
2709 exactly, the result is either the nearest higher or nearest lower representable value, chosen
2710 in an implementation-defined manner. If the value being converted is outside the range of
2711 values that can be represented, the behavior is undefined. Results of some implicit
2712 conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that
2713 required by the new type.
2714 6.3.1.5 Real floating types
2715 1 When a value of real floating type is converted to a real floating type, if the value being
2716 converted can be represented exactly in the new type, it is unchanged. If the value being
2717 converted is in the range of values that can be represented but cannot be represented
2718 exactly, the result is either the nearest higher or nearest lower representable value, chosen
2719 in an implementation-defined manner. If the value being converted is outside the range of
2720 values that can be represented, the behavior is undefined. Results of some implicit
2721 conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that
2722 required by the new type.
2723 6.3.1.6 Complex types
2724 1 When a value of complex type is converted to another complex type, both the real and
2725 imaginary parts follow the conversion rules for the corresponding real types.
2726 6.3.1.7 Real and complex
2727 1 When a value of real type is converted to a complex type, the real part of the complex
2728 result value is determined by the rules of conversion to the corresponding real type and
2729 the imaginary part of the complex result value is a positive zero or an unsigned zero.
2730 2 When a value of complex type is converted to a real type, the imaginary part of the
2731 complex value is discarded and the value of the real part is converted according to the
2732 conversion rules for the corresponding real type.
2733 6.3.1.8 Usual arithmetic conversions
2734 1 Many operators that expect operands of arithmetic type cause conversions and yield result
2735 types in a similar way. The purpose is to determine a common real type for the operands
2736 and result. For the specified operands, each operand is converted, without change of type
2737 domain, to a type whose corresponding real type is the common real type. Unless
2738 explicitly stated otherwise, the common real type is also the corresponding real type of
2739 the result, whose type domain is the type domain of the operands if they are the same,
2740 and complex otherwise. This pattern is called the usual arithmetic conversions:
2741 First, if the corresponding real type of either operand is long double, the other
2742 operand is converted, without change of type domain, to a type whose
2746 corresponding real type is long double.
2747 Otherwise, if the corresponding real type of either operand is double, the other
2748 operand is converted, without change of type domain, to a type whose
2749 corresponding real type is double.
2750 Otherwise, if the corresponding real type of either operand is float, the other
2751 operand is converted, without change of type domain, to a type whose
2752 corresponding real type is float.62)
2753 Otherwise, the integer promotions are performed on both operands. Then the
2754 following rules are applied to the promoted operands:
2755 If both operands have the same type, then no further conversion is needed.
2756 Otherwise, if both operands have signed integer types or both have unsigned
2757 integer types, the operand with the type of lesser integer conversion rank is
2758 converted to the type of the operand with greater rank.
2759 Otherwise, if the operand that has unsigned integer type has rank greater or
2760 equal to the rank of the type of the other operand, then the operand with
2761 signed integer type is converted to the type of the operand with unsigned
2763 Otherwise, if the type of the operand with signed integer type can represent
2764 all of the values of the type of the operand with unsigned integer type, then
2765 the operand with unsigned integer type is converted to the type of the
2766 operand with signed integer type.
2767 Otherwise, both operands are converted to the unsigned integer type
2768 corresponding to the type of the operand with signed integer type.
2769 2 The values of floating operands and of the results of floating expressions may be
2770 represented in greater precision and range than that required by the type; the types are not
2776 62) For example, addition of a double _Complex and a float entails just the conversion of the
2777 float operand to double (and yields a double _Complex result).
2778 63) The cast and assignment operators are still required to remove extra range and precision.
2782 6.3.2 Other operands
2783 6.3.2.1 Lvalues, arrays, and function designators
2784 1 An lvalue is an expression (with an object type other than void) that potentially
2785 designates an object;64) if an lvalue does not designate an object when it is evaluated, the
2786 behavior is undefined. When an object is said to have a particular type, the type is
2787 specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that
2788 does not have array type, does not have an incomplete type, does not have a const-
2789 qualified type, and if it is a structure or union, does not have any member (including,
2790 recursively, any member or element of all contained aggregates or unions) with a const-
2792 2 Except when it is the operand of the sizeof operator, the unary & operator, the ++
2793 operator, the -- operator, or the left operand of the . operator or an assignment operator,
2794 an lvalue that does not have array type is converted to the value stored in the designated
2795 object (and is no longer an lvalue); this is called lvalue conversion. If the lvalue has
2796 qualified type, the value has the unqualified version of the type of the lvalue; additionally,
2797 if the lvalue has atomic type, the value has the non-atomic version of the type of the
2798 lvalue; otherwise, the value has the type of the lvalue. If the lvalue has an incomplete
2799 type and does not have array type, the behavior is undefined. If the lvalue designates an
2800 object of automatic storage duration that could have been declared with the register
2801 storage class (never had its address taken), and that object is uninitialized (not declared
2802 with an initializer and no assignment to it has been performed prior to use), the behavior
2804 3 Except when it is the operand of the sizeof operator or the unary & operator, or is a
2805 string literal used to initialize an array, an expression that has type ''array of type'' is
2806 converted to an expression with type ''pointer to type'' that points to the initial element of
2807 the array object and is not an lvalue. If the array object has register storage class, the
2808 behavior is undefined.
2809 4 A function designator is an expression that has function type. Except when it is the
2810 operand of the sizeof operator65) or the unary & operator, a function designator with
2811 type ''function returning type'' is converted to an expression that has type ''pointer to
2814 64) The name ''lvalue'' comes originally from the assignment expression E1 = E2, in which the left
2815 operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an
2816 object ''locator value''. What is sometimes called ''rvalue'' is in this International Standard described
2817 as the ''value of an expression''.
2818 An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary
2819 expression that is a pointer to an object, *E is an lvalue that designates the object to which E points.
2820 65) Because this conversion does not occur, the operand of the sizeof operator remains a function
2821 designator and violates the constraint in 6.5.3.4.
2825 function returning type''.
2826 Forward references: address and indirection operators (6.5.3.2), assignment operators
2827 (6.5.16), common definitions <stddef.h> (7.19), initialization (6.7.9), postfix
2828 increment and decrement operators (6.5.2.4), prefix increment and decrement operators
2829 (6.5.3.1), the sizeof operator (6.5.3.4), structure and union members (6.5.2.3).
2831 1 The (nonexistent) value of a void expression (an expression that has type void) shall not
2832 be used in any way, and implicit or explicit conversions (except to void) shall not be
2833 applied to such an expression. If an expression of any other type is evaluated as a void
2834 expression, its value or designator is discarded. (A void expression is evaluated for its
2837 1 A pointer to void may be converted to or from a pointer to any object type. A pointer to
2838 any object type may be converted to a pointer to void and back again; the result shall
2839 compare equal to the original pointer.
2840 2 For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to
2841 the q-qualified version of the type; the values stored in the original and converted pointers
2842 shall compare equal.
2843 3 An integer constant expression with the value 0, or such an expression cast to type
2844 void *, is called a null pointer constant.66) If a null pointer constant is converted to a
2845 pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal
2846 to a pointer to any object or function.
2847 4 Conversion of a null pointer to another pointer type yields a null pointer of that type.
2848 Any two null pointers shall compare equal.
2849 5 An integer may be converted to any pointer type. Except as previously specified, the
2850 result is implementation-defined, might not be correctly aligned, might not point to an
2851 entity of the referenced type, and might be a trap representation.67)
2852 6 Any pointer type may be converted to an integer type. Except as previously specified, the
2853 result is implementation-defined. If the result cannot be represented in the integer type,
2854 the behavior is undefined. The result need not be in the range of values of any integer
2860 66) The macro NULL is defined in <stddef.h> (and other headers) as a null pointer constant; see 7.19.
2861 67) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to
2862 be consistent with the addressing structure of the execution environment.
2866 7 A pointer to an object type may be converted to a pointer to a different object type. If the
2867 resulting pointer is not correctly aligned68) for the referenced type, the behavior is
2868 undefined. Otherwise, when converted back again, the result shall compare equal to the
2869 original pointer. When a pointer to an object is converted to a pointer to a character type,
2870 the result points to the lowest addressed byte of the object. Successive increments of the
2871 result, up to the size of the object, yield pointers to the remaining bytes of the object.
2872 8 A pointer to a function of one type may be converted to a pointer to a function of another
2873 type and back again; the result shall compare equal to the original pointer. If a converted
2874 pointer is used to call a function whose type is not compatible with the referenced type,
2875 the behavior is undefined.
2876 Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types
2877 capable of holding object pointers (7.20.1.4), simple assignment (6.5.16.1).
2882 68) In general, the concept ''correctly aligned'' is transitive: if a pointer to type A is correctly aligned for a
2883 pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is
2884 correctly aligned for a pointer to type C.
2888 6.4 Lexical elements
2896 preprocessing-token:
2903 each non-white-space character that cannot be one of the above
2905 2 Each preprocessing token that is converted to a token shall have the lexical form of a
2906 keyword, an identifier, a constant, a string literal, or a punctuator.
2908 3 A token is the minimal lexical element of the language in translation phases 7 and 8. The
2909 categories of tokens are: keywords, identifiers, constants, string literals, and punctuators.
2910 A preprocessing token is the minimal lexical element of the language in translation
2911 phases 3 through 6. The categories of preprocessing tokens are: header names,
2912 identifiers, preprocessing numbers, character constants, string literals, punctuators, and
2913 single non-white-space characters that do not lexically match the other preprocessing
2914 token categories.69) If a ' or a " character matches the last category, the behavior is
2915 undefined. Preprocessing tokens can be separated by white space; this consists of
2916 comments (described later), or white-space characters (space, horizontal tab, new-line,
2917 vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances
2918 during translation phase 4, white space (or the absence thereof) serves as more than
2919 preprocessing token separation. White space may appear within a preprocessing token
2920 only as part of a header name or between the quotation characters in a character constant
2925 69) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot
2926 occur in source files.
2930 4 If the input stream has been parsed into preprocessing tokens up to a given character, the
2931 next preprocessing token is the longest sequence of characters that could constitute a
2932 preprocessing token. There is one exception to this rule: header name preprocessing
2933 tokens are recognized only within #include preprocessing directives and in
2934 implementation-defined locations within #pragma directives. In such contexts, a
2935 sequence of characters that could be either a header name or a string literal is recognized
2937 5 EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a
2938 valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex
2939 might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program
2940 fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or
2941 not E is a macro name.
2943 6 EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on
2944 increment operators, even though the parse x ++ + ++ y might yield a correct expression.
2946 Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5),
2947 floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix
2948 increment and decrement operators (6.5.2.4), prefix increment and decrement operators
2949 (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals
2959 const register _Alignas
2960 continue restrict _Atomic
2961 default return _Bool
2963 double signed _Generic
2964 else sizeof _Imaginary
2965 enum static _Noreturn
2966 extern struct _Static_assert
2967 float switch _Thread_local
2970 2 The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as
2971 keywords, and shall not be used otherwise. The keyword _Imaginary is reserved for
2974 specifying imaginary types.70)
2980 identifier identifier-nondigit
2982 identifier-nondigit:
2984 universal-character-name
2985 other implementation-defined characters
2987 _ a b c d e f g h i j k l m
2988 n o p q r s t u v w x y z
2989 A B C D E F G H I J K L M
2990 N O P Q R S T U V W X Y Z
2994 2 An identifier is a sequence of nondigit characters (including the underscore _, the
2995 lowercase and uppercase Latin letters, and other characters) and digits, which designates
2996 one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct.
2997 There is no specific limit on the maximum length of an identifier.
2998 3 Each universal character name in an identifier shall designate a character whose encoding
2999 in ISO/IEC 10646 falls into one of the ranges specified in D.1.71) The initial character
3000 shall not be a universal character name designating a character whose encoding falls into
3001 one of the ranges specified in D.2. An implementation may allow multibyte characters
3002 that are not part of the basic source character set to appear in identifiers; which characters
3003 and their correspondence to universal character names is implementation-defined.
3007 70) One possible specification for imaginary types appears in annex G.
3008 71) On systems in which linkers cannot accept extended characters, an encoding of the universal character
3009 name may be used in forming valid external identifiers. For example, some otherwise unused
3010 character or sequence of characters may be used to encode the \u in a universal character name.
3011 Extended characters may produce a long external identifier.
3015 4 When preprocessing tokens are converted to tokens during translation phase 7, if a
3016 preprocessing token could be converted to either a keyword or an identifier, it is converted
3018 Implementation limits
3019 5 As discussed in 5.2.4.1, an implementation may limit the number of significant initial
3020 characters in an identifier; the limit for an external name (an identifier that has external
3021 linkage) may be more restrictive than that for an internal name (a macro name or an
3022 identifier that does not have external linkage). The number of significant characters in an
3023 identifier is implementation-defined.
3024 6 Any identifiers that differ in a significant character are different identifiers. If two
3025 identifiers differ only in nonsignificant characters, the behavior is undefined.
3026 Forward references: universal character names (6.4.3), macro replacement (6.10.3).
3027 6.4.2.2 Predefined identifiers
3029 1 The identifier __func__ shall be implicitly declared by the translator as if,
3030 immediately following the opening brace of each function definition, the declaration
3031 static const char __func__[] = "function-name";
3032 appeared, where function-name is the name of the lexically-enclosing function.72)
3033 2 This name is encoded as if the implicit declaration had been written in the source
3034 character set and then translated into the execution character set as indicated in translation
3036 3 EXAMPLE Consider the code fragment:
3040 printf("%s\n", __func__);
3043 Each time the function is called, it will print to the standard output stream:
3046 Forward references: function definitions (6.9.1).
3051 72) Since the name __func__ is reserved for any use by the implementation (7.1.3), if any other
3052 identifier is explicitly declared using the name __func__, the behavior is undefined.
3056 6.4.3 Universal character names
3058 1 universal-character-name:
3060 \U hex-quad hex-quad
3062 hexadecimal-digit hexadecimal-digit
3063 hexadecimal-digit hexadecimal-digit
3065 2 A universal character name shall not specify a character whose short identifier is less than
3066 00A0 other than 0024 ($), 0040 (@), or 0060 ('), nor one in the range D800 through
3069 3 Universal character names may be used in identifiers, character constants, and string
3070 literals to designate characters that are not in the basic character set.
3072 4 The universal character name \Unnnnnnnn designates the character whose eight-digit
3073 short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.74) Similarly, the universal
3074 character name \unnnn designates the character whose four-digit short identifier is nnnn
3075 (and whose eight-digit short identifier is 0000nnnn).
3080 73) The disallowed characters are the characters in the basic character set and the code positions reserved
3081 by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by
3084 74) Short identifiers for characters were first specified in ISO/IEC 10646-1/AMD9:1997.
3093 enumeration-constant
3096 2 Each constant shall have a type and the value of a constant shall be in the range of
3097 representable values for its type.
3099 3 Each constant has a type, determined by its form and value, as detailed later.
3100 6.4.4.1 Integer constants
3103 decimal-constant integer-suffixopt
3104 octal-constant integer-suffixopt
3105 hexadecimal-constant integer-suffixopt
3108 decimal-constant digit
3111 octal-constant octal-digit
3112 hexadecimal-constant:
3113 hexadecimal-prefix hexadecimal-digit
3114 hexadecimal-constant hexadecimal-digit
3115 hexadecimal-prefix: one of
3117 nonzero-digit: one of
3127 hexadecimal-digit: one of
3132 unsigned-suffix long-suffixopt
3133 unsigned-suffix long-long-suffix
3134 long-suffix unsigned-suffixopt
3135 long-long-suffix unsigned-suffixopt
3136 unsigned-suffix: one of
3140 long-long-suffix: one of
3143 2 An integer constant begins with a digit, but has no period or exponent part. It may have a
3144 prefix that specifies its base and a suffix that specifies its type.
3145 3 A decimal constant begins with a nonzero digit and consists of a sequence of decimal
3146 digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the
3147 digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed
3148 by a sequence of the decimal digits and the letters a (or A) through f (or F) with values
3149 10 through 15 respectively.
3151 4 The value of a decimal constant is computed base 10; that of an octal constant, base 8;
3152 that of a hexadecimal constant, base 16. The lexically first digit is the most significant.
3153 5 The type of an integer constant is the first of the corresponding list in which its value can
3161 Octal or Hexadecimal
3162 Suffix Decimal Constant Constant
3165 long int unsigned int
3166 long long int long int
3169 unsigned long long int
3171 u or U unsigned int unsigned int
3172 unsigned long int unsigned long int
3173 unsigned long long int unsigned long long int
3175 l or L long int long int
3176 long long int unsigned long int
3178 unsigned long long int
3180 Both u or U unsigned long int unsigned long int
3181 and l or L unsigned long long int unsigned long long int
3183 ll or LL long long int long long int
3184 unsigned long long int
3186 Both u or U unsigned long long int unsigned long long int
3188 6 If an integer constant cannot be represented by any type in its list, it may have an
3189 extended integer type, if the extended integer type can represent its value. If all of the
3190 types in the list for the constant are signed, the extended integer type shall be signed. If
3191 all of the types in the list for the constant are unsigned, the extended integer type shall be
3192 unsigned. If the list contains both signed and unsigned types, the extended integer type
3193 may be signed or unsigned. If an integer constant cannot be represented by any type in
3194 its list and has no extended integer type, then the integer constant has no type.
3201 6.4.4.2 Floating constants
3203 1 floating-constant:
3204 decimal-floating-constant
3205 hexadecimal-floating-constant
3206 decimal-floating-constant:
3207 fractional-constant exponent-partopt floating-suffixopt
3208 digit-sequence exponent-part floating-suffixopt
3209 hexadecimal-floating-constant:
3210 hexadecimal-prefix hexadecimal-fractional-constant
3211 binary-exponent-part floating-suffixopt
3212 hexadecimal-prefix hexadecimal-digit-sequence
3213 binary-exponent-part floating-suffixopt
3214 fractional-constant:
3215 digit-sequenceopt . digit-sequence
3218 e signopt digit-sequence
3219 E signopt digit-sequence
3224 digit-sequence digit
3225 hexadecimal-fractional-constant:
3226 hexadecimal-digit-sequenceopt .
3227 hexadecimal-digit-sequence
3228 hexadecimal-digit-sequence .
3229 binary-exponent-part:
3230 p signopt digit-sequence
3231 P signopt digit-sequence
3232 hexadecimal-digit-sequence:
3234 hexadecimal-digit-sequence hexadecimal-digit
3235 floating-suffix: one of
3241 2 A floating constant has a significand part that may be followed by an exponent part and a
3242 suffix that specifies its type. The components of the significand part may include a digit
3243 sequence representing the whole-number part, followed by a period (.), followed by a
3244 digit sequence representing the fraction part. The components of the exponent part are an
3245 e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence.
3246 Either the whole-number part or the fraction part has to be present; for decimal floating
3247 constants, either the period or the exponent part has to be present.
3249 3 The significand part is interpreted as a (decimal or hexadecimal) rational number; the
3250 digit sequence in the exponent part is interpreted as a decimal integer. For decimal
3251 floating constants, the exponent indicates the power of 10 by which the significand part is
3252 to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2
3253 by which the significand part is to be scaled. For decimal floating constants, and also for
3254 hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either
3255 the nearest representable value, or the larger or smaller representable value immediately
3256 adjacent to the nearest representable value, chosen in an implementation-defined manner.
3257 For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is
3259 4 An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has
3260 type float. If suffixed by the letter l or L, it has type long double.
3261 5 Floating constants are converted to internal format as if at translation-time. The
3262 conversion of a floating constant shall not raise an exceptional condition or a floating-
3263 point exception at execution time. All floating constants of the same source form75) shall
3264 convert to the same internal format with the same value.
3265 Recommended practice
3266 6 The implementation should produce a diagnostic message if a hexadecimal constant
3267 cannot be represented exactly in its evaluation format; the implementation should then
3268 proceed with the translation of the program.
3269 7 The translation-time conversion of floating constants should match the execution-time
3270 conversion of character strings by library functions, such as strtod, given matching
3271 inputs suitable for both conversions, the same result format, and default execution-time
3274 75) 1.23, 1.230, 123e-2, 123e-02, and 1.23L are all different source forms and thus need not
3275 convert to the same internal format and value.
3276 76) The specification for the library functions recommends more accurate conversion than required for
3277 floating constants (see 7.22.1.3).
3281 6.4.4.3 Enumeration constants
3283 1 enumeration-constant:
3286 2 An identifier declared as an enumeration constant has type int.
3287 Forward references: enumeration specifiers (6.7.2.2).
3288 6.4.4.4 Character constants
3290 1 character-constant:
3292 L' c-char-sequence '
3293 u' c-char-sequence '
3294 U' c-char-sequence '
3297 c-char-sequence c-char
3299 any member of the source character set except
3300 the single-quote ', backslash \, or new-line character
3303 simple-escape-sequence
3304 octal-escape-sequence
3305 hexadecimal-escape-sequence
3306 universal-character-name
3307 simple-escape-sequence: one of
3309 \a \b \f \n \r \t \v
3310 octal-escape-sequence:
3312 \ octal-digit octal-digit
3313 \ octal-digit octal-digit octal-digit
3320 hexadecimal-escape-sequence:
3321 \x hexadecimal-digit
3322 hexadecimal-escape-sequence hexadecimal-digit
3324 2 An integer character constant is a sequence of one or more multibyte characters enclosed
3325 in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the
3326 letter L, u, or U. With a few exceptions detailed later, the elements of the sequence are
3327 any members of the source character set; they are mapped in an implementation-defined
3328 manner to members of the execution character set.
3329 3 The single-quote ', the double-quote ", the question-mark ?, the backslash \, and
3330 arbitrary integer values are representable according to the following table of escape
3336 octal character \octal digits
3337 hexadecimal character \x hexadecimal digits
3338 4 The double-quote " and question-mark ? are representable either by themselves or by the
3339 escape sequences \" and \?, respectively, but the single-quote ' and the backslash \
3340 shall be represented, respectively, by the escape sequences \' and \\.
3341 5 The octal digits that follow the backslash in an octal escape sequence are taken to be part
3342 of the construction of a single character for an integer character constant or of a single
3343 wide character for a wide character constant. The numerical value of the octal integer so
3344 formed specifies the value of the desired character or wide character.
3345 6 The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape
3346 sequence are taken to be part of the construction of a single character for an integer
3347 character constant or of a single wide character for a wide character constant. The
3348 numerical value of the hexadecimal integer so formed specifies the value of the desired
3349 character or wide character.
3350 7 Each octal or hexadecimal escape sequence is the longest sequence of characters that can
3351 constitute the escape sequence.
3352 8 In addition, characters not in the basic character set are representable by universal
3353 character names and certain nongraphic characters are representable by escape sequences
3354 consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t,
3362 9 The value of an octal or hexadecimal escape sequence shall be in the range of
3363 representable values for the corresponding type:
3364 Prefix Corresponding Type
3366 L the unsigned type corresponding to wchar_t
3370 10 An integer character constant has type int. The value of an integer character constant
3371 containing a single character that maps to a single-byte execution character is the
3372 numerical value of the representation of the mapped character interpreted as an integer.
3373 The value of an integer character constant containing more than one character (e.g.,
3374 'ab'), or containing a character or escape sequence that does not map to a single-byte
3375 execution character, is implementation-defined. If an integer character constant contains
3376 a single character or escape sequence, its value is the one that results when an object with
3377 type char whose value is that of the single character or escape sequence is converted to
3379 11 A wide character constant prefixed by the letter L has type wchar_t, an integer type
3380 defined in the <stddef.h> header; a wide character constant prefixed by the letter u or
3381 U has type char16_t or char32_t, respectively, unsigned integer types defined in the
3382 <uchar.h> header. The value of a wide character constant containing a single
3383 multibyte character that maps to a single member of the extended execution character set
3384 is the wide character corresponding to that multibyte character, as defined by the
3385 mbtowc, mbrtoc16, or mbrtoc32 function as appropriate for its type, with an
3386 implementation-defined current locale. The value of a wide character constant containing
3387 more than one multibyte character or a single multibyte character that maps to multiple
3388 members of the extended execution character set, or containing a multibyte character or
3389 escape sequence not represented in the extended execution character set, is
3390 implementation-defined.
3391 12 EXAMPLE 1 The construction '\0' is commonly used to represent the null character.
3393 13 EXAMPLE 2 Consider implementations that use two's complement representation for integers and eight
3394 bits for objects that have type char. In an implementation in which type char has the same range of
3395 values as signed char, the integer character constant '\xFF' has the value -1; if type char has the
3396 same range of values as unsigned char, the character constant '\xFF' has the value +255.
3401 77) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash,
3402 the result is not a token and a diagnostic is required. See ''future language directions'' (6.11.4).
3406 14 EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123'
3407 specifies an integer character constant containing only one character, since a hexadecimal escape sequence
3408 is terminated only by a non-hexadecimal character. To specify an integer character constant containing the
3409 two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal
3410 escape sequence is terminated after three octal digits. (The value of this two-character integer character
3411 constant is implementation-defined.)
3413 15 EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction
3414 L'\1234' specifies the implementation-defined value that results from the combination of the values
3417 Forward references: common definitions <stddef.h> (7.19), the mbtowc function
3418 (7.22.7.2), Unicode utilities <uchar.h> (7.27).
3419 6.4.5 String literals
3422 encoding-prefixopt " s-char-sequenceopt "
3430 s-char-sequence s-char
3432 any member of the source character set except
3433 the double-quote ", backslash \, or new-line character
3436 2 A sequence of adjacent string literal tokens shall not include both a wide string literal and
3437 a UTF-8 string literal.
3439 3 A character string literal is a sequence of zero or more multibyte characters enclosed in
3440 double-quotes, as in "xyz". A UTF-8 string literal is the same, except prefixed by u8.
3441 A wide string literal is the same, except prefixed by the letter L, u, or U.
3442 4 The same considerations apply to each element of the sequence in a string literal as if it
3443 were in an integer character constant (for a character or UTF-8 string literal) or a wide
3444 character constant (for a wide string literal), except that the single-quote ' is
3445 representable either by itself or by the escape sequence \', but the double-quote " shall
3448 be represented by the escape sequence \".
3450 5 In translation phase 6, the multibyte character sequences specified by any sequence of
3451 adjacent character and identically-prefixed string literal tokens are concatenated into a
3452 single multibyte character sequence. If any of the tokens has an encoding prefix, the
3453 resulting multibyte character sequence is treated as having the same prefix; otherwise, it
3454 is treated as a character string literal. Whether differently-prefixed wide string literal
3455 tokens can be concatenated and, if so, the treatment of the resulting multibyte character
3456 sequence are implementation-defined.
3457 6 In translation phase 7, a byte or code of value zero is appended to each multibyte
3458 character sequence that results from a string literal or literals.78) The multibyte character
3459 sequence is then used to initialize an array of static storage duration and length just
3460 sufficient to contain the sequence. For character string literals, the array elements have
3461 type char, and are initialized with the individual bytes of the multibyte character
3462 sequence. For UTF-8 string literals, the array elements have type char, and are
3463 initialized with the characters of the multibyte character sequence, as encoded in UTF-8.
3464 For wide string literals prefixed by the letter L, the array elements have type wchar_t
3465 and are initialized with the sequence of wide characters corresponding to the multibyte
3466 character sequence, as defined by the mbstowcs function with an implementation-
3467 defined current locale. For wide string literals prefixed by the letter u or U, the array
3468 elements have type char16_t or char32_t, respectively, and are initialized with the
3469 sequence of wide characters corresponding to the multibyte character sequence, as
3470 defined by successive calls to the mbrtoc16, or mbrtoc32 function as appropriate for
3471 its type, with an implementation-defined current locale. The value of a string literal
3472 containing a multibyte character or escape sequence not represented in the execution
3473 character set is implementation-defined.
3474 7 It is unspecified whether these arrays are distinct provided their elements have the
3475 appropriate values. If the program attempts to modify such an array, the behavior is
3477 8 EXAMPLE 1 This pair of adjacent character string literals
3479 produces a single character string literal containing the two characters whose values are '\x12' and '3',
3480 because escape sequences are converted into single members of the execution character set just prior to
3481 adjacent string literal concatenation.
3483 9 EXAMPLE 2 Each of the sequences of adjacent string literal tokens
3487 78) A string literal need not be a string (see 7.1.1), because a null character may be embedded in it by a
3496 is equivalent to the string literal
3498 Likewise, each of the sequences
3506 Forward references: common definitions <stddef.h> (7.19), the mbstowcs
3507 function (7.22.8.1), Unicode utilities <uchar.h> (7.27).
3510 1 punctuator: one of
3513 / % << >> < > <= >= == != ^ | && ||
3515 = *= /= %= += -= <<= >>= &= ^= |=
3519 2 A punctuator is a symbol that has independent syntactic and semantic significance.
3520 Depending on context, it may specify an operation to be performed (which in turn may
3521 yield a value or a function designator, produce a side effect, or some combination thereof)
3522 in which case it is known as an operator (other forms of operator also exist in some
3523 contexts). An operand is an entity on which an operator acts.
3530 3 In all aspects of the language, the six tokens79)
3532 behave, respectively, the same as the six tokens
3534 except for their spelling.80)
3535 Forward references: expressions (6.5), declarations (6.7), preprocessing directives
3536 (6.10), statements (6.8).
3544 h-char-sequence h-char
3546 any member of the source character set except
3547 the new-line character and >
3550 q-char-sequence q-char
3552 any member of the source character set except
3553 the new-line character and "
3555 2 The sequences in both forms of header names are mapped in an implementation-defined
3556 manner to headers or external source file names as specified in 6.10.2.
3557 3 If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters,
3558 the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the
3563 79) These tokens are sometimes called ''digraphs''.
3564 80) Thus [ and <: behave differently when ''stringized'' (see 6.10.3.2), but can otherwise be freely
3569 sequence between the " delimiters, the behavior is undefined.81) Header name
3570 preprocessing tokens are recognized only within #include preprocessing directives and
3571 in implementation-defined locations within #pragma directives.82)
3572 4 EXAMPLE The following sequence of characters:
3575 #define const.member@$
3576 forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited
3577 by a { on the left and a } on the right).
3578 {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}
3579 {#}{include} {<1/a.h>}
3580 {#}{define} {const}{.}{member}{@}{$}
3582 Forward references: source file inclusion (6.10.2).
3583 6.4.8 Preprocessing numbers
3589 pp-number identifier-nondigit
3596 2 A preprocessing number begins with a digit optionally preceded by a period (.) and may
3597 be followed by valid identifier characters and the character sequences e+, e-, E+, E-,
3599 3 Preprocessing number tokens lexically include all floating and integer constant tokens.
3601 4 A preprocessing number does not have type or a value; it acquires both after a successful
3602 conversion (as part of translation phase 7) to a floating constant token or an integer
3606 81) Thus, sequences of characters that resemble escape sequences cause undefined behavior.
3607 82) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9.
3612 1 Except within a character constant, a string literal, or a comment, the characters /*
3613 introduce a comment. The contents of such a comment are examined only to identify
3614 multibyte characters and to find the characters */ that terminate it.83)
3615 2 Except within a character constant, a string literal, or a comment, the characters //
3616 introduce a comment that includes all multibyte characters up to, but not including, the
3617 next new-line character. The contents of such a comment are examined only to identify
3618 multibyte characters and to find the terminating new-line character.
3620 "a//b" // four-character string literal
3621 #include "//e" // undefined behavior
3622 // */ // comment, not syntax error
3623 f = g/**//h; // equivalent to f = g / h;
3625 i(); // part of a two-line comment
3627 / j(); // part of a two-line comment
3628 #define glue(x,y) x##y
3629 glue(/,/) k(); // syntax error, not comment
3630 /*//*/ l(); // equivalent to l();
3632 + p; // equivalent to m = n + p;
3637 83) Thus, /* ... */ comments do not nest.
3642 1 An expression is a sequence of operators and operands that specifies computation of a
3643 value, or that designates an object or a function, or that generates side effects, or that
3644 performs a combination thereof. The value computations of the operands of an operator
3645 are sequenced before the value computation of the result of the operator.
3646 2 If a side effect on a scalar object is unsequenced relative to either a different side effect
3647 on the same scalar object or a value computation using the value of the same scalar
3648 object, the behavior is undefined. If there are multiple allowable orderings of the
3649 subexpressions of an expression, the behavior is undefined if such an unsequenced side
3650 effect occurs in any of the orderings.84)
3651 3 The grouping of operators and operands is indicated by the syntax.85) Except as specified
3652 later, side effects and value computations of subexpressions are unsequenced.86) *
3653 4 Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |,
3654 collectively described as bitwise operators) are required to have operands that have
3655 integer type. These operators yield values that depend on the internal representations of
3656 integers, and have implementation-defined and undefined aspects for signed types.
3657 5 If an exceptional condition occurs during the evaluation of an expression (that is, if the
3658 result is not mathematically defined or not in the range of representable values for its
3659 type), the behavior is undefined.
3663 84) This paragraph renders undefined statement expressions such as
3670 85) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same
3671 as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the
3672 expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in
3673 6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators
3674 (6.5.3), and an operand contained between any of the following pairs of operators: grouping
3675 parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), and
3676 the conditional operator ? : (6.5.15).
3677 Within each major subclause, the operators have the same precedence. Left- or right-associativity is
3678 indicated in each subclause by the syntax for the expressions discussed therein.
3679 86) In an expression that is evaluated more than once during the execution of a program, unsequenced and
3680 indeterminately sequenced evaluations of its subexpressions need not be performed consistently in
3681 different evaluations.
3685 6 The effective type of an object for an access to its stored value is the declared type of the
3686 object, if any.87) If a value is stored into an object having no declared type through an
3687 lvalue having a type that is not a character type, then the type of the lvalue becomes the
3688 effective type of the object for that access and for subsequent accesses that do not modify
3689 the stored value. If a value is copied into an object having no declared type using
3690 memcpy or memmove, or is copied as an array of character type, then the effective type
3691 of the modified object for that access and for subsequent accesses that do not modify the
3692 value is the effective type of the object from which the value is copied, if it has one. For
3693 all other accesses to an object having no declared type, the effective type of the object is
3694 simply the type of the lvalue used for the access.
3695 7 An object shall have its stored value accessed only by an lvalue expression that has one of
3696 the following types:88)
3697 -- a type compatible with the effective type of the object,
3698 -- a qualified version of a type compatible with the effective type of the object,
3699 -- a type that is the signed or unsigned type corresponding to the effective type of the
3701 -- a type that is the signed or unsigned type corresponding to a qualified version of the
3702 effective type of the object,
3703 -- an aggregate or union type that includes one of the aforementioned types among its
3704 members (including, recursively, a member of a subaggregate or contained union), or
3705 -- a character type.
3706 8 A floating expression may be contracted, that is, evaluated as though it were a single
3707 operation, thereby omitting rounding errors implied by the source code and the
3708 expression evaluation method.89) The FP_CONTRACT pragma in <math.h> provides a
3709 way to disallow contracted expressions. Otherwise, whether and how expressions are
3710 contracted is implementation-defined.90)
3711 Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.23.2).
3714 87) Allocated objects have no declared type.
3715 88) The intent of this list is to specify those circumstances in which an object may or may not be aliased.
3716 89) The intermediate operations in the contracted expression are evaluated as if to infinite precision and
3717 range, while the final operation is rounded to the format determined by the expression evaluation
3718 method. A contracted expression might also omit the raising of floating-point exceptions.
3719 90) This license is specifically intended to allow implementations to exploit fast machine instructions that
3720 combine multiple C operators. As contractions potentially undermine predictability, and can even
3721 decrease accuracy for containing expressions, their use needs to be well-defined and clearly
3726 6.5.1 Primary expressions
3728 1 primary-expression:
3735 2 An identifier is a primary expression, provided it has been declared as designating an
3736 object (in which case it is an lvalue) or a function (in which case it is a function
3738 3 A constant is a primary expression. Its type depends on its form and value, as detailed in
3740 4 A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5.
3741 5 A parenthesized expression is a primary expression. Its type and value are identical to
3742 those of the unparenthesized expression. It is an lvalue, a function designator, or a void
3743 expression if the unparenthesized expression is, respectively, an lvalue, a function
3744 designator, or a void expression.
3745 Forward references: declarations (6.7).
3746 6.5.1.1 Generic selection
3748 1 generic-selection:
3749 _Generic ( assignment-expression , generic-assoc-list )
3752 generic-assoc-list , generic-association
3753 generic-association:
3754 type-name : assignment-expression
3755 default : assignment-expression
3757 2 A generic selection shall have no more than one default generic association. The type
3758 name in a generic association shall specify a complete object type other than a variably
3760 91) Thus, an undeclared identifier is a violation of the syntax.
3764 modified type. No two generic associations in the same generic selection shall specify
3765 compatible types. The controlling expression of a generic selection shall have type
3766 compatible with at most one of the types named in its generic association list. If a
3767 generic selection has no default generic association, its controlling expression shall
3768 have type compatible with exactly one of the types named in its generic association list.
3770 3 The controlling expression of a generic selection is not evaluated. If a generic selection
3771 has a generic association with a type name that is compatible with the type of the
3772 controlling expression, then the result expression of the generic selection is the
3773 expression in that generic association. Otherwise, the result expression of the generic
3774 selection is the expression in the default generic association. None of the expressions
3775 from any other generic association of the generic selection is evaluated.
3776 4 The type and value of a generic selection are identical to those of its result expression. It
3777 is an lvalue, a function designator, or a void expression if its result expression is,
3778 respectively, an lvalue, a function designator, or a void expression.
3779 5 EXAMPLE The cbrt type-generic macro could be implemented as follows:
3780 #define cbrt(X) _Generic((X), \
3781 long double: cbrtl, \
3786 6.5.2 Postfix operators
3788 1 postfix-expression:
3790 postfix-expression [ expression ]
3791 postfix-expression ( argument-expression-listopt )
3792 postfix-expression . identifier
3793 postfix-expression -> identifier
3794 postfix-expression ++
3795 postfix-expression --
3796 ( type-name ) { initializer-list }
3797 ( type-name ) { initializer-list , }
3798 argument-expression-list:
3799 assignment-expression
3800 argument-expression-list , assignment-expression
3807 6.5.2.1 Array subscripting
3809 1 One of the expressions shall have type ''pointer to complete object type'', the other
3810 expression shall have integer type, and the result has type ''type''.
3812 2 A postfix expression followed by an expression in square brackets [] is a subscripted
3813 designation of an element of an array object. The definition of the subscript operator []
3814 is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that
3815 apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the
3816 initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th
3817 element of E1 (counting from zero).
3818 3 Successive subscript operators designate an element of a multidimensional array object.
3819 If E is an n-dimensional array (n >= 2) with dimensions i x j x . . . x k, then E (used as
3820 other than an lvalue) is converted to a pointer to an (n - 1)-dimensional array with
3821 dimensions j x . . . x k. If the unary * operator is applied to this pointer explicitly, or
3822 implicitly as a result of subscripting, the result is the referenced (n - 1)-dimensional
3823 array, which itself is converted into a pointer if used as other than an lvalue. It follows
3824 from this that arrays are stored in row-major order (last subscript varies fastest).
3825 4 EXAMPLE Consider the array object defined by the declaration
3827 Here x is a 3 x 5 array of ints; more precisely, x is an array of three element objects, each of which is an
3828 array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to
3829 a pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptually
3830 entails multiplying i by the size of the object to which the pointer points, namely an array of five int
3831 objects. The results are added and indirection is applied to yield an array of five ints. When used in the
3832 expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j]
3835 Forward references: additive operators (6.5.6), address and indirection operators
3836 (6.5.3.2), array declarators (6.7.6.2).
3837 6.5.2.2 Function calls
3839 1 The expression that denotes the called function92) shall have type pointer to function
3840 returning void or returning a complete object type other than an array type.
3841 2 If the expression that denotes the called function has a type that includes a prototype, the
3842 number of arguments shall agree with the number of parameters. Each argument shall
3845 92) Most often, this is the result of converting an identifier that is a function designator.
3849 have a type such that its value may be assigned to an object with the unqualified version
3850 of the type of its corresponding parameter.
3852 3 A postfix expression followed by parentheses () containing a possibly empty, comma-
3853 separated list of expressions is a function call. The postfix expression denotes the called
3854 function. The list of expressions specifies the arguments to the function.
3855 4 An argument may be an expression of any complete object type. In preparing for the call
3856 to a function, the arguments are evaluated, and each parameter is assigned the value of the
3857 corresponding argument.93)
3858 5 If the expression that denotes the called function has type pointer to function returning an
3859 object type, the function call expression has the same type as that object type, and has the
3860 value determined as specified in 6.8.6.4. Otherwise, the function call has type void. *
3861 6 If the expression that denotes the called function has a type that does not include a
3862 prototype, the integer promotions are performed on each argument, and arguments that
3863 have type float are promoted to double. These are called the default argument
3864 promotions. If the number of arguments does not equal the number of parameters, the
3865 behavior is undefined. If the function is defined with a type that includes a prototype, and
3866 either the prototype ends with an ellipsis (, ...) or the types of the arguments after
3867 promotion are not compatible with the types of the parameters, the behavior is undefined.
3868 If the function is defined with a type that does not include a prototype, and the types of
3869 the arguments after promotion are not compatible with those of the parameters after
3870 promotion, the behavior is undefined, except for the following cases:
3871 -- one promoted type is a signed integer type, the other promoted type is the
3872 corresponding unsigned integer type, and the value is representable in both types;
3873 -- both types are pointers to qualified or unqualified versions of a character type or
3875 7 If the expression that denotes the called function has a type that does include a prototype,
3876 the arguments are implicitly converted, as if by assignment, to the types of the
3877 corresponding parameters, taking the type of each parameter to be the unqualified version
3878 of its declared type. The ellipsis notation in a function prototype declarator causes
3879 argument type conversion to stop after the last declared parameter. The default argument
3880 promotions are performed on trailing arguments.
3884 93) A function may change the values of its parameters, but these changes cannot affect the values of the
3885 arguments. On the other hand, it is possible to pass a pointer to an object, and the function may
3886 change the value of the object pointed to. A parameter declared to have array or function type is
3887 adjusted to have a pointer type as described in 6.9.1.
3891 8 No other conversions are performed implicitly; in particular, the number and types of
3892 arguments are not compared with those of the parameters in a function definition that
3893 does not include a function prototype declarator.
3894 9 If the function is defined with a type that is not compatible with the type (of the
3895 expression) pointed to by the expression that denotes the called function, the behavior is
3897 10 There is a sequence point after the evaluations of the function designator and the actual
3898 arguments but before the actual call. Every evaluation in the calling function (including
3899 other function calls) that is not otherwise specifically sequenced before or after the
3900 execution of the body of the called function is indeterminately sequenced with respect to
3901 the execution of the called function.94)
3902 11 Recursive function calls shall be permitted, both directly and indirectly through any chain
3904 12 EXAMPLE In the function call
3905 (*pf[f1()]) (f2(), f3() + f4())
3906 the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before
3907 the function pointed to by pf[f1()] is called.
3909 Forward references: function declarators (including prototypes) (6.7.6.3), function
3910 definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1).
3911 6.5.2.3 Structure and union members
3913 1 The first operand of the . operator shall have an atomic, qualified, or unqualified
3914 structure or union type, and the second operand shall name a member of that type.
3915 2 The first operand of the -> operator shall have type ''pointer to atomic, qualified, or
3916 unqualified structure'' or ''pointer to atomic, qualified, or unqualified union'', and the
3917 second operand shall name a member of the type pointed to.
3919 3 A postfix expression followed by the . operator and an identifier designates a member of
3920 a structure or union object. The value is that of the named member,95) and is an lvalue if
3921 the first expression is an lvalue. If the first expression has qualified type, the result has
3922 the so-qualified version of the type of the designated member.
3924 94) In other words, function executions do not ''interleave'' with each other.
3925 95) If the member used to read the contents of a union object is not the same as the member last used to
3926 store a value in the object, the appropriate part of the object representation of the value is reinterpreted
3927 as an object representation in the new type as described in 6.2.6 (a process sometimes called ''type
3928 punning''). This might be a trap representation.
3932 4 A postfix expression followed by the -> operator and an identifier designates a member
3933 of a structure or union object. The value is that of the named member of the object to
3934 which the first expression points, and is an lvalue.96) If the first expression is a pointer to
3935 a qualified type, the result has the so-qualified version of the type of the designated
3937 5 Accessing a member of an atomic structure or union object results in undefined
3939 6 One special guarantee is made in order to simplify the use of unions: if a union contains
3940 several structures that share a common initial sequence (see below), and if the union
3941 object currently contains one of these structures, it is permitted to inspect the common
3942 initial part of any of them anywhere that a declaration of the completed type of the union
3943 is visible. Two structures share a common initial sequence if corresponding members
3944 have compatible types (and, for bit-fields, the same widths) for a sequence of one or more
3946 7 EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or
3947 union, f().x is a valid postfix expression but is not an lvalue.
3950 struct s { int i; const int ci; };
3953 volatile struct s vs;
3954 the various members have the types:
3960 vs.ci volatile const int
3965 96) If &E is a valid pointer expression (where & is the ''address-of '' operator, which generates a pointer to
3966 its operand), the expression (&E)->MOS is the same as E.MOS.
3967 97) For example, a data race would occur if access to the entire structure or union in one thread conflicts
3968 with access to a member from another thread, where at least one access is a modification. Members
3969 can be safely accessed using a non-atomic object which is assigned to or from the atomic object.
3973 9 EXAMPLE 3 The following is a valid fragment:
3988 u.nf.doublenode = 3.14;
3990 if (u.n.alltypes == 1)
3991 if (sin(u.nf.doublenode) == 0.0)
3993 The following is not a valid fragment (because the union type is not visible within function f):
3994 struct t1 { int m; };
3995 struct t2 { int m; };
3996 int f(struct t1 *p1, struct t2 *p2)
4009 return f(&u.s1, &u.s2);
4012 Forward references: address and indirection operators (6.5.3.2), structure and union
4013 specifiers (6.7.2.1).
4020 6.5.2.4 Postfix increment and decrement operators
4022 1 The operand of the postfix increment or decrement operator shall have atomic, qualified,
4023 or unqualified real or pointer type, and shall be a modifiable lvalue.
4025 2 The result of the postfix ++ operator is the value of the operand. As a side effect, the
4026 value of the operand object is incremented (that is, the value 1 of the appropriate type is
4027 added to it). See the discussions of additive operators and compound assignment for
4028 information on constraints, types, and conversions and the effects of operations on
4029 pointers. The value computation of the result is sequenced before the side effect of
4030 updating the stored value of the operand. With respect to an indeterminately-sequenced
4031 function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object
4032 with atomic type is a read-modify-write operation with memory_order_seq_cst
4033 memory order semantics.98)
4034 3 The postfix -- operator is analogous to the postfix ++ operator, except that the value of
4035 the operand is decremented (that is, the value 1 of the appropriate type is subtracted from
4037 Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
4038 6.5.2.5 Compound literals
4040 1 The type name shall specify a complete object type or an array of unknown size, but not a
4041 variable length array type.
4042 2 All the constraints for initializer lists in 6.7.9 also apply to compound literals.
4044 3 A postfix expression that consists of a parenthesized type name followed by a brace-
4045 enclosed list of initializers is a compound literal. It provides an unnamed object whose
4046 value is given by the initializer list.99)
4049 98) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence
4050 where T is the type of E:
4055 } while (!atomic_compare_exchange_strong(&E, &result, tmp));
4056 with result being the result of the operation.
4060 4 If the type name specifies an array of unknown size, the size is determined by the
4061 initializer list as specified in 6.7.9, and the type of the compound literal is that of the
4062 completed array type. Otherwise (when the type name specifies an object type), the type
4063 of the compound literal is that specified by the type name. In either case, the result is an
4065 5 The value of the compound literal is that of an unnamed object initialized by the
4066 initializer list. If the compound literal occurs outside the body of a function, the object
4067 has static storage duration; otherwise, it has automatic storage duration associated with
4068 the enclosing block.
4069 6 All the semantic rules for initializer lists in 6.7.9 also apply to compound literals.100)
4070 7 String literals, and compound literals with const-qualified types, need not designate
4071 distinct objects.101)
4072 8 EXAMPLE 1 The file scope definition
4073 int *p = (int []){2, 4};
4074 initializes p to point to the first element of an array of two ints, the first having the value two and the
4075 second, four. The expressions in this compound literal are required to be constant. The unnamed object
4076 has static storage duration.
4078 9 EXAMPLE 2 In contrast, in
4086 p is assigned the address of the first element of an array of two ints, the first having the value previously
4087 pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The
4088 unnamed object has automatic storage duration.
4090 10 EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects
4091 created using compound literals can be passed to functions without depending on member order:
4092 drawline((struct point){.x=1, .y=1},
4093 (struct point){.x=3, .y=4});
4094 Or, if drawline instead expected pointers to struct point:
4098 99) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types
4099 or void only, and the result of a cast expression is not an lvalue.
4100 100) For example, subobjects without explicit initializers are initialized to zero.
4101 101) This allows implementations to share storage for string literals and constant compound literals with
4102 the same or overlapping representations.
4106 drawline(&(struct point){.x=1, .y=1},
4107 &(struct point){.x=3, .y=4});
4109 11 EXAMPLE 4 A read-only compound literal can be specified through constructions like:
4110 (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}
4112 12 EXAMPLE 5 The following three expressions have different meanings:
4114 (char []){"/tmp/fileXXXXXX"}
4115 (const char []){"/tmp/fileXXXXXX"}
4116 The first always has static storage duration and has type array of char, but need not be modifiable; the last
4117 two have automatic storage duration when they occur within the body of a function, and the first of these
4120 13 EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory
4121 and can even be shared. For example,
4122 (const char []){"abc"} == "abc"
4123 might yield 1 if the literals' storage is shared.
4125 14 EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly
4126 linked object. For example, there is no way to write a self-referential compound literal that could be used
4127 as the function argument in place of the named object endless_zeros below:
4128 struct int_list { int car; struct int_list *cdr; };
4129 struct int_list endless_zeros = {0, &endless_zeros};
4130 eval(endless_zeros);
4132 15 EXAMPLE 8 Each compound literal creates only a single object in a given scope:
4133 struct s { int i; };
4136 struct s *p = 0, *q;
4139 q = p, p = &((struct s){ j++ });
4140 if (j < 2) goto again;
4141 return p == q && q->i == 1;
4143 The function f() always returns the value 1.
4144 16 Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the
4145 lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would
4146 have an indeterminate value, which would result in undefined behavior.
4148 Forward references: type names (6.7.7), initialization (6.7.9).
4155 6.5.3 Unary operators
4161 unary-operator cast-expression
4162 sizeof unary-expression
4163 sizeof ( type-name )
4164 alignof ( type-name )
4165 unary-operator: one of
4167 6.5.3.1 Prefix increment and decrement operators
4169 1 The operand of the prefix increment or decrement operator shall have atomic, qualified,
4170 or unqualified real or pointer type, and shall be a modifiable lvalue.
4172 2 The value of the operand of the prefix ++ operator is incremented. The result is the new
4173 value of the operand after incrementation. The expression ++E is equivalent to (E+=1).
4174 See the discussions of additive operators and compound assignment for information on
4175 constraints, types, side effects, and conversions and the effects of operations on pointers.
4176 3 The prefix -- operator is analogous to the prefix ++ operator, except that the value of the
4177 operand is decremented.
4178 Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
4179 6.5.3.2 Address and indirection operators
4181 1 The operand of the unary & operator shall be either a function designator, the result of a
4182 [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is
4183 not declared with the register storage-class specifier.
4184 2 The operand of the unary * operator shall have pointer type.
4186 3 The unary & operator yields the address of its operand. If the operand has type ''type'',
4187 the result has type ''pointer to type''. If the operand is the result of a unary * operator,
4188 neither that operator nor the & operator is evaluated and the result is as if both were
4189 omitted, except that the constraints on the operators still apply and the result is not an
4193 lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor
4194 the unary * that is implied by the [] is evaluated and the result is as if the & operator
4195 were removed and the [] operator were changed to a + operator. Otherwise, the result is
4196 a pointer to the object or function designated by its operand.
4197 4 The unary * operator denotes indirection. If the operand points to a function, the result is
4198 a function designator; if it points to an object, the result is an lvalue designating the
4199 object. If the operand has type ''pointer to type'', the result has type ''type''. If an
4200 invalid value has been assigned to the pointer, the behavior of the unary * operator is
4202 Forward references: storage-class specifiers (6.7.1), structure and union specifiers
4204 6.5.3.3 Unary arithmetic operators
4206 1 The operand of the unary + or - operator shall have arithmetic type; of the ~ operator,
4207 integer type; of the ! operator, scalar type.
4209 2 The result of the unary + operator is the value of its (promoted) operand. The integer
4210 promotions are performed on the operand, and the result has the promoted type.
4211 3 The result of the unary - operator is the negative of its (promoted) operand. The integer
4212 promotions are performed on the operand, and the result has the promoted type.
4213 4 The result of the ~ operator is the bitwise complement of its (promoted) operand (that is,
4214 each bit in the result is set if and only if the corresponding bit in the converted operand is
4215 not set). The integer promotions are performed on the operand, and the result has the
4216 promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent
4217 to the maximum value representable in that type minus E.
4218 5 The result of the logical negation operator ! is 0 if the value of its operand compares
4219 unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int.
4220 The expression !E is equivalent to (0==E).
4224 102) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is
4225 always true that if E is a function designator or an lvalue that is a valid operand of the unary &
4226 operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of
4227 an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points.
4228 Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an
4229 address inappropriately aligned for the type of object pointed to, and the address of an object after the
4230 end of its lifetime.
4234 6.5.3.4 The sizeof and alignof operators
4236 1 The sizeof operator shall not be applied to an expression that has function type or an
4237 incomplete type, to the parenthesized name of such a type, or to an expression that
4238 designates a bit-field member. The alignof operator shall not be applied to a function
4239 type or an incomplete type.
4241 2 The sizeof operator yields the size (in bytes) of its operand, which may be an
4242 expression or the parenthesized name of a type. The size is determined from the type of
4243 the operand. The result is an integer. If the type of the operand is a variable length array
4244 type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an
4246 3 The alignof operator yields the alignment requirement of its operand type. The result
4247 is an integer constant. When applied to an array type, the result is the alignment
4248 requirement of the element type.
4249 4 When sizeof is applied to an operand that has type char, unsigned char, or
4250 signed char, (or a qualified version thereof) the result is 1. When applied to an
4251 operand that has array type, the result is the total number of bytes in the array.103) When
4252 applied to an operand that has structure or union type, the result is the total number of
4253 bytes in such an object, including internal and trailing padding.
4254 5 The value of the result of both operators is implementation-defined, and its type (an
4255 unsigned integer type) is size_t, defined in <stddef.h> (and other headers).
4256 6 EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage
4257 allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to
4258 allocate and return a pointer to void. For example:
4259 extern void *alloc(size_t);
4260 double *dp = alloc(sizeof *dp);
4261 The implementation of the alloc function should ensure that its return value is aligned suitably for
4262 conversion to a pointer to double.
4264 7 EXAMPLE 2 Another use of the sizeof operator is to compute the number of elements in an array:
4265 sizeof array / sizeof array[0]
4267 8 EXAMPLE 3 In this example, the size of a variable length array is computed and returned from a
4273 103) When applied to a parameter declared to have array or function type, the sizeof operator yields the
4274 size of the adjusted (pointer) type (see 6.9.1).
4278 size_t fsize3(int n)
4280 char b[n+3]; // variable length array
4281 return sizeof b; // execution time sizeof
4286 size = fsize3(10); // fsize3 returns 13
4290 Forward references: common definitions <stddef.h> (7.19), declarations (6.7),
4291 structure and union specifiers (6.7.2.1), type names (6.7.7), array declarators (6.7.6.2).
4292 6.5.4 Cast operators
4296 ( type-name ) cast-expression
4298 2 Unless the type name specifies a void type, the type name shall specify atomic, qualified,
4299 or unqualified scalar type, and the operand shall have scalar type.
4300 3 Conversions that involve pointers, other than where permitted by the constraints of
4301 6.5.16.1, shall be specified by means of an explicit cast.
4302 4 A pointer type shall not be converted to any floating type. A floating type shall not be
4303 converted to any pointer type.
4305 5 Preceding an expression by a parenthesized type name converts the value of the
4306 expression to the named type. This construction is called a cast.104) A cast that specifies
4307 no conversion has no effect on the type or value of an expression.
4308 6 If the value of the expression is represented with greater precision or range than required
4309 by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the
4310 type of the expression is the same as the named type and removes any extra range and
4312 Forward references: equality operators (6.5.9), function declarators (including
4313 prototypes) (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7).
4315 104) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to the
4316 unqualified version of the type.
4320 6.5.5 Multiplicative operators
4322 1 multiplicative-expression:
4324 multiplicative-expression * cast-expression
4325 multiplicative-expression / cast-expression
4326 multiplicative-expression % cast-expression
4328 2 Each of the operands shall have arithmetic type. The operands of the % operator shall
4331 3 The usual arithmetic conversions are performed on the operands.
4332 4 The result of the binary * operator is the product of the operands.
4333 5 The result of the / operator is the quotient from the division of the first operand by the
4334 second; the result of the % operator is the remainder. In both operations, if the value of
4335 the second operand is zero, the behavior is undefined.
4336 6 When integers are divided, the result of the / operator is the algebraic quotient with any
4337 fractional part discarded.105) If the quotient a/b is representable, the expression
4338 (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is
4340 6.5.6 Additive operators
4342 1 additive-expression:
4343 multiplicative-expression
4344 additive-expression + multiplicative-expression
4345 additive-expression - multiplicative-expression
4347 2 For addition, either both operands shall have arithmetic type, or one operand shall be a
4348 pointer to a complete object type and the other shall have integer type. (Incrementing is
4349 equivalent to adding 1.)
4350 3 For subtraction, one of the following shall hold:
4355 105) This is often called ''truncation toward zero''.
4359 -- both operands have arithmetic type;
4360 -- both operands are pointers to qualified or unqualified versions of compatible complete
4362 -- the left operand is a pointer to a complete object type and the right operand has
4364 (Decrementing is equivalent to subtracting 1.)
4366 4 If both operands have arithmetic type, the usual arithmetic conversions are performed on
4368 5 The result of the binary + operator is the sum of the operands.
4369 6 The result of the binary - operator is the difference resulting from the subtraction of the
4370 second operand from the first.
4371 7 For the purposes of these operators, a pointer to an object that is not an element of an
4372 array behaves the same as a pointer to the first element of an array of length one with the
4373 type of the object as its element type.
4374 8 When an expression that has integer type is added to or subtracted from a pointer, the
4375 result has the type of the pointer operand. If the pointer operand points to an element of
4376 an array object, and the array is large enough, the result points to an element offset from
4377 the original element such that the difference of the subscripts of the resulting and original
4378 array elements equals the integer expression. In other words, if the expression P points to
4379 the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and
4380 (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of
4381 the array object, provided they exist. Moreover, if the expression P points to the last
4382 element of an array object, the expression (P)+1 points one past the last element of the
4383 array object, and if the expression Q points one past the last element of an array object,
4384 the expression (Q)-1 points to the last element of the array object. If both the pointer
4385 operand and the result point to elements of the same array object, or one past the last
4386 element of the array object, the evaluation shall not produce an overflow; otherwise, the
4387 behavior is undefined. If the result points one past the last element of the array object, it
4388 shall not be used as the operand of a unary * operator that is evaluated.
4389 9 When two pointers are subtracted, both shall point to elements of the same array object,
4390 or one past the last element of the array object; the result is the difference of the
4391 subscripts of the two array elements. The size of the result is implementation-defined,
4392 and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header.
4393 If the result is not representable in an object of that type, the behavior is undefined. In
4394 other words, if the expressions P and Q point to, respectively, the i-th and j-th elements of
4395 an array object, the expression (P)-(Q) has the value i-j provided the value fits in an
4399 object of type ptrdiff_t. Moreover, if the expression P points either to an element of
4400 an array object or one past the last element of an array object, and the expression Q points
4401 to the last element of the same array object, the expression ((Q)+1)-(P) has the same
4402 value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the
4403 expression P points one past the last element of the array object, even though the
4404 expression (Q)+1 does not point to an element of the array object.106)
4405 10 EXAMPLE Pointer arithmetic is well defined with pointers to variable length array types.
4409 int (*p)[m] = a; // p == &a[0]
4410 p += 1; // p == &a[1]
4411 (*p)[2] = 99; // a[1][2] == 99
4412 n = p - a; // n == 1
4414 11 If array a in the above example were declared to be an array of known constant size, and pointer p were
4415 declared to be a pointer to an array of the same known constant size (pointing to a), the results would be
4418 Forward references: array declarators (6.7.6.2), common definitions <stddef.h>
4420 6.5.7 Bitwise shift operators
4424 shift-expression << additive-expression
4425 shift-expression >> additive-expression
4427 2 Each of the operands shall have integer type.
4429 3 The integer promotions are performed on each of the operands. The type of the result is
4430 that of the promoted left operand. If the value of the right operand is negative or is
4432 106) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In
4433 this scheme the integer expression added to or subtracted from the converted pointer is first multiplied
4434 by the size of the object originally pointed to, and the resulting pointer is converted back to the
4435 original type. For pointer subtraction, the result of the difference between the character pointers is
4436 similarly divided by the size of the object originally pointed to.
4437 When viewed in this way, an implementation need only provide one extra byte (which may overlap
4438 another object in the program) just after the end of the object in order to satisfy the ''one past the last
4439 element'' requirements.
4443 greater than or equal to the width of the promoted left operand, the behavior is undefined.
4444 4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with
4445 zeros. If E1 has an unsigned type, the value of the result is E1 x 2E2 , reduced modulo
4446 one more than the maximum value representable in the result type. If E1 has a signed
4447 type and nonnegative value, and E1 x 2E2 is representable in the result type, then that is
4448 the resulting value; otherwise, the behavior is undefined.
4449 5 The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type
4450 or if E1 has a signed type and a nonnegative value, the value of the result is the integral
4451 part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the
4452 resulting value is implementation-defined.
4453 6.5.8 Relational operators
4455 1 relational-expression:
4457 relational-expression < shift-expression
4458 relational-expression > shift-expression
4459 relational-expression <= shift-expression
4460 relational-expression >= shift-expression
4462 2 One of the following shall hold:
4463 -- both operands have real type; or *
4464 -- both operands are pointers to qualified or unqualified versions of compatible object
4467 3 If both of the operands have arithmetic type, the usual arithmetic conversions are
4469 4 For the purposes of these operators, a pointer to an object that is not an element of an
4470 array behaves the same as a pointer to the first element of an array of length one with the
4471 type of the object as its element type.
4472 5 When two pointers are compared, the result depends on the relative locations in the
4473 address space of the objects pointed to. If two pointers to object types both point to the
4474 same object, or both point one past the last element of the same array object, they
4475 compare equal. If the objects pointed to are members of the same aggregate object,
4476 pointers to structure members declared later compare greater than pointers to members
4477 declared earlier in the structure, and pointers to array elements with larger subscript
4478 values compare greater than pointers to elements of the same array with lower subscript
4482 values. All pointers to members of the same union object compare equal. If the
4483 expression P points to an element of an array object and the expression Q points to the
4484 last element of the same array object, the pointer expression Q+1 compares greater than
4485 P. In all other cases, the behavior is undefined.
4486 6 Each of the operators < (less than), > (greater than), <= (less than or equal to), and >=
4487 (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is
4488 false.107) The result has type int.
4489 6.5.9 Equality operators
4491 1 equality-expression:
4492 relational-expression
4493 equality-expression == relational-expression
4494 equality-expression != relational-expression
4496 2 One of the following shall hold:
4497 -- both operands have arithmetic type;
4498 -- both operands are pointers to qualified or unqualified versions of compatible types;
4499 -- one operand is a pointer to an object type and the other is a pointer to a qualified or
4500 unqualified version of void; or
4501 -- one operand is a pointer and the other is a null pointer constant.
4503 3 The == (equal to) and != (not equal to) operators are analogous to the relational
4504 operators except for their lower precedence.108) Each of the operators yields 1 if the
4505 specified relation is true and 0 if it is false. The result has type int. For any pair of
4506 operands, exactly one of the relations is true.
4507 4 If both of the operands have arithmetic type, the usual arithmetic conversions are
4508 performed. Values of complex types are equal if and only if both their real parts are equal
4509 and also their imaginary parts are equal. Any two values of arithmetic types from
4510 different type domains are equal if and only if the results of their conversions to the
4511 (complex) result type determined by the usual arithmetic conversions are equal.
4515 107) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, it
4516 means (a<b)<c; in other words, ''if a is less than b, compare 1 to c; otherwise, compare 0 to c''.
4517 108) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value.
4521 5 Otherwise, at least one operand is a pointer. If one operand is a pointer and the other is a
4522 null pointer constant, the null pointer constant is converted to the type of the pointer. If
4523 one operand is a pointer to an object type and the other is a pointer to a qualified or
4524 unqualified version of void, the former is converted to the type of the latter.
4525 6 Two pointers compare equal if and only if both are null pointers, both are pointers to the
4526 same object (including a pointer to an object and a subobject at its beginning) or function,
4527 both are pointers to one past the last element of the same array object, or one is a pointer
4528 to one past the end of one array object and the other is a pointer to the start of a different
4529 array object that happens to immediately follow the first array object in the address
4531 7 For the purposes of these operators, a pointer to an object that is not an element of an
4532 array behaves the same as a pointer to the first element of an array of length one with the
4533 type of the object as its element type.
4534 6.5.10 Bitwise AND operator
4538 AND-expression & equality-expression
4540 2 Each of the operands shall have integer type.
4542 3 The usual arithmetic conversions are performed on the operands.
4543 4 The result of the binary & operator is the bitwise AND of the operands (that is, each bit in
4544 the result is set if and only if each of the corresponding bits in the converted operands is
4550 109) Two objects may be adjacent in memory because they are adjacent elements of a larger array or
4551 adjacent members of a structure with no padding between them, or because the implementation chose
4552 to place them so, even though they are unrelated. If prior invalid pointer operations (such as accesses
4553 outside array bounds) produced undefined behavior, subsequent comparisons also produce undefined
4558 6.5.11 Bitwise exclusive OR operator
4560 1 exclusive-OR-expression:
4562 exclusive-OR-expression ^ AND-expression
4564 2 Each of the operands shall have integer type.
4566 3 The usual arithmetic conversions are performed on the operands.
4567 4 The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit
4568 in the result is set if and only if exactly one of the corresponding bits in the converted
4570 6.5.12 Bitwise inclusive OR operator
4572 1 inclusive-OR-expression:
4573 exclusive-OR-expression
4574 inclusive-OR-expression | exclusive-OR-expression
4576 2 Each of the operands shall have integer type.
4578 3 The usual arithmetic conversions are performed on the operands.
4579 4 The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in
4580 the result is set if and only if at least one of the corresponding bits in the converted
4588 6.5.13 Logical AND operator
4590 1 logical-AND-expression:
4591 inclusive-OR-expression
4592 logical-AND-expression && inclusive-OR-expression
4594 2 Each of the operands shall have scalar type.
4596 3 The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it
4597 yields 0. The result has type int.
4598 4 Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation;
4599 if the second operand is evaluated, there is a sequence point between the evaluations of
4600 the first and second operands. If the first operand compares equal to 0, the second
4601 operand is not evaluated.
4602 6.5.14 Logical OR operator
4604 1 logical-OR-expression:
4605 logical-AND-expression
4606 logical-OR-expression || logical-AND-expression
4608 2 Each of the operands shall have scalar type.
4610 3 The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it
4611 yields 0. The result has type int.
4612 4 Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; if the
4613 second operand is evaluated, there is a sequence point between the evaluations of the first
4614 and second operands. If the first operand compares unequal to 0, the second operand is
4622 6.5.15 Conditional operator
4624 1 conditional-expression:
4625 logical-OR-expression
4626 logical-OR-expression ? expression : conditional-expression
4628 2 The first operand shall have scalar type.
4629 3 One of the following shall hold for the second and third operands:
4630 -- both operands have arithmetic type;
4631 -- both operands have the same structure or union type;
4632 -- both operands have void type;
4633 -- both operands are pointers to qualified or unqualified versions of compatible types;
4634 -- one operand is a pointer and the other is a null pointer constant; or
4635 -- one operand is a pointer to an object type and the other is a pointer to a qualified or
4636 unqualified version of void.
4638 4 The first operand is evaluated; there is a sequence point between its evaluation and the
4639 evaluation of the second or third operand (whichever is evaluated). The second operand
4640 is evaluated only if the first compares unequal to 0; the third operand is evaluated only if
4641 the first compares equal to 0; the result is the value of the second or third operand
4642 (whichever is evaluated), converted to the type described below.110) *
4643 5 If both the second and third operands have arithmetic type, the result type that would be
4644 determined by the usual arithmetic conversions, were they applied to those two operands,
4645 is the type of the result. If both the operands have structure or union type, the result has
4646 that type. If both operands have void type, the result has void type.
4647 6 If both the second and third operands are pointers or one is a null pointer constant and the
4648 other is a pointer, the result type is a pointer to a type qualified with all the type qualifiers
4649 of the types referenced by both operands. Furthermore, if both operands are pointers to
4650 compatible types or to differently qualified versions of compatible types, the result type is
4651 a pointer to an appropriately qualified version of the composite type; if one operand is a
4652 null pointer constant, the result has the type of the other operand; otherwise, one operand
4653 is a pointer to void or a qualified version of void, in which case the result type is a
4654 pointer to an appropriately qualified version of void.
4656 110) A conditional expression does not yield an lvalue.
4660 7 EXAMPLE The common type that results when the second and third operands are pointers is determined
4661 in two independent stages. The appropriate qualifiers, for example, do not depend on whether the two
4662 pointers have compatible types.
4663 8 Given the declarations
4670 the third column in the following table is the common type that is the result of a conditional expression in
4671 which the first two columns are the second and third operands (in either order):
4672 c_vp c_ip const void *
4673 v_ip 0 volatile int *
4674 c_ip v_ip const volatile int *
4675 vp c_cp const void *
4679 6.5.16 Assignment operators
4681 1 assignment-expression:
4682 conditional-expression
4683 unary-expression assignment-operator assignment-expression
4684 assignment-operator: one of
4685 = *= /= %= += -= <<= >>= &= ^= |=
4687 2 An assignment operator shall have a modifiable lvalue as its left operand.
4689 3 An assignment operator stores a value in the object designated by the left operand. An
4690 assignment expression has the value of the left operand after the assignment,111) but is not
4691 an lvalue. The type of an assignment expression is the type the left operand would have
4692 after lvalue conversion. The side effect of updating the stored value of the left operand is
4693 sequenced after the value computations of the left and right operands. The evaluations of
4694 the operands are unsequenced.
4699 111) The implementation is permitted to read the object to determine the value but is not required to, even
4700 when the object has volatile-qualified type.
4704 6.5.16.1 Simple assignment
4706 1 One of the following shall hold:112)
4707 -- the left operand has atomic, qualified, or unqualified arithmetic type, and the right has
4709 -- the left operand has an atomic, qualified, or unqualified version of a structure or union
4710 type compatible with the type of the right;
4711 -- the left operand has atomic, qualified, or unqualified pointer type, and (considering
4712 the type the left operand would have after lvalue conversion) both operands are
4713 pointers to qualified or unqualified versions of compatible types, and the type pointed
4714 to by the left has all the qualifiers of the type pointed to by the right;
4715 -- the left operand has atomic, qualified, or unqualified pointer type, and (considering
4716 the type the left operand would have after lvalue conversion) one operand is a pointer
4717 to an object type, and the other is a pointer to a qualified or unqualified version of
4718 void, and the type pointed to by the left has all the qualifiers of the type pointed to
4720 -- the left operand is an atomic, qualified, or unqualified pointer, and the right is a null
4721 pointer constant; or
4722 -- the left operand has type atomic, qualified, or unqualified _Bool, and the right is a
4725 2 In simple assignment (=), the value of the right operand is converted to the type of the
4726 assignment expression and replaces the value stored in the object designated by the left
4728 3 If the value being stored in an object is read from another object that overlaps in any way
4729 the storage of the first object, then the overlap shall be exact and the two objects shall
4730 have qualified or unqualified versions of a compatible type; otherwise, the behavior is
4732 4 EXAMPLE 1 In the program fragment
4737 112) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion
4738 (specified in 6.3.2.1) that changes lvalues to ''the value of the expression'' and thus removes any type
4739 qualifiers that were applied to the type category of the expression (for example, it removes const but
4740 not volatile from the type int volatile * const).
4747 if ((c = f()) == -1)
4749 the int value returned by the function may be truncated when stored in the char, and then converted back
4750 to int width prior to the comparison. In an implementation in which ''plain'' char has the same range of
4751 values as unsigned char (and char is narrower than int), the result of the conversion cannot be
4752 negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the
4753 variable c should be declared as int.
4755 5 EXAMPLE 2 In the fragment:
4760 the value of i is converted to the type of the assignment expression c = i, that is, char type. The value
4761 of the expression enclosed in parentheses is then converted to the type of the outer assignment expression,
4762 that is, long int type.
4764 6 EXAMPLE 3 Consider the fragment:
4768 cpp = &p; // constraint violation
4771 The first assignment is unsafe because it would allow the following valid code to attempt to change the
4772 value of the const object c.
4774 6.5.16.2 Compound assignment
4776 1 For the operators += and -= only, either the left operand shall be an atomic, qualified, or
4777 unqualified pointer to a complete object type, and the right shall have integer type; or the
4778 left operand shall have atomic, qualified, or unqualified arithmetic type, and the right
4779 shall have arithmetic type.
4780 2 For the other operators, the left operand shall have atomic, qualified, or unqualified
4781 arithmetic type, and (considering the type the left operand would have after lvalue
4782 conversion) each operand shall have arithmetic type consistent with those allowed by the
4783 corresponding binary operator.
4785 3 A compound assignment of the form E1 op = E2 is equivalent to the simple assignment
4786 expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with
4787 respect to an indeterminately-sequenced function call, the operation of a compound
4790 assignment is a single evaluation. If E1 has an atomic type, compound assignment is a
4791 read-modify-write operation with memory_order_seq_cst memory order
4793 6.5.17 Comma operator
4796 assignment-expression
4797 expression , assignment-expression
4799 2 The left operand of a comma operator is evaluated as a void expression; there is a
4800 sequence point between its evaluation and that of the right operand. Then the right
4801 operand is evaluated; the result has its type and value.114) *
4802 3 EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot
4803 appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists
4804 of initializers). On the other hand, it can be used within a parenthesized expression or within the second
4805 expression of a conditional operator in such contexts. In the function call
4807 the function has three arguments, the second of which has the value 5.
4809 Forward references: initialization (6.7.9).
4814 113) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence
4815 where T is the type of E1:
4819 result = tmp op (E2);
4820 } while (!atomic_compare_exchange_strong(&E1, &tmp, result));
4821 with result being the result of the operation.
4822 114) A comma operator does not yield an lvalue.
4826 6.6 Constant expressions
4828 1 constant-expression:
4829 conditional-expression
4831 2 A constant expression can be evaluated during translation rather than runtime, and
4832 accordingly may be used in any place that a constant may be.
4834 3 Constant expressions shall not contain assignment, increment, decrement, function-call,
4835 or comma operators, except when they are contained within a subexpression that is not
4837 4 Each constant expression shall evaluate to a constant that is in the range of representable
4838 values for its type.
4840 5 An expression that evaluates to a constant is required in several contexts. If a floating
4841 expression is evaluated in the translation environment, the arithmetic precision and range
4842 shall be at least as great as if the expression were being evaluated in the execution
4844 6 An integer constant expression117) shall have integer type and shall only have operands
4845 that are integer constants, enumeration constants, character constants, sizeof
4846 expressions whose results are integer constants, and floating constants that are the
4847 immediate operands of casts. Cast operators in an integer constant expression shall only
4848 convert arithmetic types to integer types, except as part of an operand to the sizeof
4850 7 More latitude is permitted for constant expressions in initializers. Such a constant
4851 expression shall be, or evaluate to, one of the following:
4852 -- an arithmetic constant expression,
4856 115) The operand of a sizeof operator is usually not evaluated (6.5.3.4).
4857 116) The use of evaluation formats as characterized by FLT_EVAL_METHOD also applies to evaluation in
4858 the translation environment.
4859 117) An integer constant expression is required in a number of contexts such as the size of a bit-field
4860 member of a structure, the value of an enumeration constant, and the size of a non-variable length
4861 array. Further constraints that apply to the integer constant expressions used in conditional-inclusion
4862 preprocessing directives are discussed in 6.10.1.
4866 -- a null pointer constant,
4867 -- an address constant, or
4868 -- an address constant for a complete object type plus or minus an integer constant
4870 8 An arithmetic constant expression shall have arithmetic type and shall only have
4871 operands that are integer constants, floating constants, enumeration constants, character
4872 constants, and sizeof expressions. Cast operators in an arithmetic constant expression
4873 shall only convert arithmetic types to arithmetic types, except as part of an operand to a
4874 sizeof operator whose result is an integer constant.
4875 9 An address constant is a null pointer, a pointer to an lvalue designating an object of static
4876 storage duration, or a pointer to a function designator; it shall be created explicitly using
4877 the unary & operator or an integer constant cast to pointer type, or implicitly by the use of
4878 an expression of array or function type. The array-subscript [] and member-access .
4879 and -> operators, the address & and indirection * unary operators, and pointer casts may
4880 be used in the creation of an address constant, but the value of an object shall not be
4881 accessed by use of these operators.
4882 10 An implementation may accept other forms of constant expressions.
4883 11 The semantic rules for the evaluation of a constant expression are the same as for
4884 nonconstant expressions.118)
4885 Forward references: array declarators (6.7.6.2), initialization (6.7.9).
4890 118) Thus, in the following initialization,
4891 static int i = 2 || 1 / 0;
4892 the expression is a valid integer constant expression with value one.
4899 declaration-specifiers init-declarator-listopt ;
4900 static_assert-declaration
4901 declaration-specifiers:
4902 storage-class-specifier declaration-specifiersopt
4903 type-specifier declaration-specifiersopt
4904 type-qualifier declaration-specifiersopt
4905 function-specifier declaration-specifiersopt
4906 alignment-specifier declaration-specifiersopt
4907 init-declarator-list:
4909 init-declarator-list , init-declarator
4912 declarator = initializer
4914 2 A declaration other than a static_assert declaration shall declare at least a declarator
4915 (other than the parameters of a function or the members of a structure or union), a tag, or
4916 the members of an enumeration.
4917 3 If an identifier has no linkage, there shall be no more than one declaration of the identifier
4918 (in a declarator or type specifier) with the same scope and in the same name space, except
4919 that a typedef name can be redefined to denote the same type as it currently does and tags
4920 may be redeclared as specified in 6.7.2.3.
4921 4 All declarations in the same scope that refer to the same object or function shall specify
4924 5 A declaration specifies the interpretation and attributes of a set of identifiers. A definition
4925 of an identifier is a declaration for that identifier that:
4926 -- for an object, causes storage to be reserved for that object;
4927 -- for a function, includes the function body;119)
4931 119) Function definitions have a different syntax, described in 6.9.1.
4935 -- for an enumeration constant or typedef name, is the (only) declaration of the
4937 6 The declaration specifiers consist of a sequence of specifiers that indicate the linkage,
4938 storage duration, and part of the type of the entities that the declarators denote. The init-
4939 declarator-list is a comma-separated sequence of declarators, each of which may have
4940 additional type information, or an initializer, or both. The declarators contain the
4941 identifiers (if any) being declared.
4942 7 If an identifier for an object is declared with no linkage, the type for the object shall be
4943 complete by the end of its declarator, or by the end of its init-declarator if it has an
4944 initializer; in the case of function parameters (including in prototypes), it is the adjusted
4945 type (see 6.7.6.3) that is required to be complete.
4946 Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization
4947 (6.7.9), type names (6.7.7), type qualifiers (6.7.3).
4948 6.7.1 Storage-class specifiers
4950 1 storage-class-specifier:
4958 2 At most, one storage-class specifier may be given in the declaration specifiers in a
4959 declaration, except that _Thread_local may appear with static or extern.120)
4960 3 In the declaration of an object with block scope, if the declaration specifiers include
4961 _Thread_local, they shall also include either static or extern. If
4962 _Thread_local appears in any declaration of an object, it shall be present in every
4963 declaration of that object.
4965 4 The typedef specifier is called a ''storage-class specifier'' for syntactic convenience
4966 only; it is discussed in 6.7.8. The meanings of the various linkages and storage durations
4967 were discussed in 6.2.2 and 6.2.4.
4971 120) See ''future language directions'' (6.11.5).
4975 5 A declaration of an identifier for an object with storage-class specifier register
4976 suggests that access to the object be as fast as possible. The extent to which such
4977 suggestions are effective is implementation-defined.121)
4978 6 The declaration of an identifier for a function that has block scope shall have no explicit
4979 storage-class specifier other than extern.
4980 7 If an aggregate or union object is declared with a storage-class specifier other than
4981 typedef, the properties resulting from the storage-class specifier, except with respect to
4982 linkage, also apply to the members of the object, and so on recursively for any aggregate
4983 or union member objects.
4984 Forward references: type definitions (6.7.8).
4985 6.7.2 Type specifiers
4999 atomic-type-specifier
5000 struct-or-union-specifier
5004 2 At least one type specifier shall be given in the declaration specifiers in each declaration,
5005 and in the specifier-qualifier list in each struct declaration and type name. Each list of
5008 121) The implementation may treat any register declaration simply as an auto declaration. However,
5009 whether or not addressable storage is actually used, the address of any part of an object declared with
5010 storage-class specifier register cannot be computed, either explicitly (by use of the unary &
5011 operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in
5012 6.3.2.1). Thus, the only operator that can be applied to an array declared with storage-class specifier
5017 type specifiers shall be one of the following multisets (delimited by commas, when there
5018 is more than one multiset per item); the type specifiers may occur in any order, possibly
5019 intermixed with the other declaration specifiers.
5024 -- short, signed short, short int, or signed short int
5025 -- unsigned short, or unsigned short int
5026 -- int, signed, or signed int
5027 -- unsigned, or unsigned int
5028 -- long, signed long, long int, or signed long int
5029 -- unsigned long, or unsigned long int
5030 -- long long, signed long long, long long int, or
5031 signed long long int
5032 -- unsigned long long, or unsigned long long int
5039 -- long double _Complex
5040 -- atomic type specifier
5041 -- struct or union specifier
5044 3 The type specifier _Complex shall not be used if the implementation does not support
5045 complex types (see 6.10.8.3).
5053 4 Specifiers for structures, unions, enumerations, and atomic types are discussed in 6.7.2.1
5054 through 6.7.2.4. Declarations of typedef names are discussed in 6.7.8. The
5055 characteristics of the other types are discussed in 6.2.5.
5056 5 Each of the comma-separated multisets designates the same type, except that for bit-
5057 fields, it is implementation-defined whether the specifier int designates the same type as
5058 signed int or the same type as unsigned int.
5059 Forward references: atomic type specifiers (6.7.2.4), enumeration specifiers (6.7.2.2),
5060 structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8).
5061 6.7.2.1 Structure and union specifiers
5063 1 struct-or-union-specifier:
5064 struct-or-union identifieropt { struct-declaration-list }
5065 struct-or-union identifier
5069 struct-declaration-list:
5071 struct-declaration-list struct-declaration
5073 specifier-qualifier-list struct-declarator-listopt ;
5074 static_assert-declaration
5075 specifier-qualifier-list:
5076 type-specifier specifier-qualifier-listopt
5077 type-qualifier specifier-qualifier-listopt
5078 struct-declarator-list:
5080 struct-declarator-list , struct-declarator
5083 declaratoropt : constant-expression
5085 2 A struct-declaration that does not declare an anonymous structure or anonymous union
5086 shall contain a struct-declarator-list.
5091 3 A structure or union shall not contain a member with incomplete or function type (hence,
5092 a structure shall not contain an instance of itself, but may contain a pointer to an instance
5093 of itself), except that the last member of a structure with more than one named member
5094 may have incomplete array type; such a structure (and any union containing, possibly
5095 recursively, a member that is such a structure) shall not be a member of a structure or an
5096 element of an array.
5097 4 The expression that specifies the width of a bit-field shall be an integer constant
5098 expression with a nonnegative value that does not exceed the width of an object of the
5099 type that would be specified were the colon and expression omitted.122) If the value is
5100 zero, the declaration shall have no declarator.
5101 5 A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed
5102 int, unsigned int, or some other implementation-defined type. It is
5103 implementation-defined whether atomic types are permitted.
5105 6 As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose
5106 storage is allocated in an ordered sequence, and a union is a type consisting of a sequence
5107 of members whose storage overlap.
5108 7 Structure and union specifiers have the same form. The keywords struct and union
5109 indicate that the type being specified is, respectively, a structure type or a union type.
5110 8 The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type,
5111 within a translation unit. The struct-declaration-list is a sequence of declarations for the
5112 members of the structure or union. If the struct-declaration-list contains no named
5113 members, no anonymous structures, and no anonymous unions, the behavior is undefined.
5114 The type is incomplete until immediately after the } that terminates the list, and complete
5116 9 A member of a structure or union may have any complete object type other than a
5117 variably modified type.123) In addition, a member may be declared to consist of a
5118 specified number of bits (including a sign bit, if any). Such a member is called a
5119 bit-field;124) its width is preceded by a colon.
5120 10 A bit-field is interpreted as having a signed or unsigned integer type consisting of the
5121 specified number of bits.125) If the value 0 or 1 is stored into a nonzero-width bit-field of
5123 122) While the number of bits in a _Bool object is at least CHAR_BIT, the width (number of sign and
5124 value bits) of a _Bool may be just 1 bit.
5125 123) A structure or union cannot contain a member with a variably modified type because member names
5126 are not ordinary identifiers as defined in 6.2.3.
5127 124) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers to
5128 or arrays of bit-field objects.
5132 type _Bool, the value of the bit-field shall compare equal to the value stored; a _Bool
5133 bit-field has the semantics of a _Bool.
5134 11 An implementation may allocate any addressable storage unit large enough to hold a bit-
5135 field. If enough space remains, a bit-field that immediately follows another bit-field in a
5136 structure shall be packed into adjacent bits of the same unit. If insufficient space remains,
5137 whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is
5138 implementation-defined. The order of allocation of bit-fields within a unit (high-order to
5139 low-order or low-order to high-order) is implementation-defined. The alignment of the
5140 addressable storage unit is unspecified.
5141 12 A bit-field declaration with no declarator, but only a colon and a width, indicates an
5142 unnamed bit-field.126) As a special case, a bit-field structure member with a width of 0
5143 indicates that no further bit-field is to be packed into the unit in which the previous bit-
5144 field, if any, was placed.
5145 13 An unnamed member of structure type with no tag is called an anonymous structure; an
5146 unnamed member of union type with no tag is called an anonymous union. The members
5147 of an anonymous structure or union are considered to be members of the containing
5148 structure or union. This applies recursively if the containing structure or union is also
5150 14 Each non-bit-field member of a structure or union object is aligned in an implementation-
5151 defined manner appropriate to its type.
5152 15 Within a structure object, the non-bit-field members and the units in which bit-fields
5153 reside have addresses that increase in the order in which they are declared. A pointer to a
5154 structure object, suitably converted, points to its initial member (or if that member is a
5155 bit-field, then to the unit in which it resides), and vice versa. There may be unnamed
5156 padding within a structure object, but not at its beginning.
5157 16 The size of a union is sufficient to contain the largest of its members. The value of at
5158 most one of the members can be stored in a union object at any time. A pointer to a
5159 union object, suitably converted, points to each of its members (or if a member is a bit-
5160 field, then to the unit in which it resides), and vice versa.
5161 17 There may be unnamed padding at the end of a structure or union.
5162 18 As a special case, the last element of a structure with more than one named member may
5163 have an incomplete array type; this is called a flexible array member. In most situations,
5166 125) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int,
5167 then it is implementation-defined whether the bit-field is signed or unsigned.
5168 126) An unnamed bit-field structure member is useful for padding to conform to externally imposed
5173 the flexible array member is ignored. In particular, the size of the structure is as if the
5174 flexible array member were omitted except that it may have more trailing padding than
5175 the omission would imply. However, when a . (or ->) operator has a left operand that is
5176 (a pointer to) a structure with a flexible array member and the right operand names that
5177 member, it behaves as if that member were replaced with the longest array (with the same
5178 element type) that would not make the structure larger than the object being accessed; the
5179 offset of the array shall remain that of the flexible array member, even if this would differ
5180 from that of the replacement array. If this array would have no elements, it behaves as if
5181 it had one element but the behavior is undefined if any attempt is made to access that
5182 element or to generate a pointer one past it.
5183 19 EXAMPLE 1 The following illustrates anonymous structures and unions:
5185 union { // anonymous union
5186 struct { int i, j; }; // anonymous structure
5187 struct { long k, l; } w;
5192 v1.k = 3; // invalid: inner structure is not anonymous
5193 v1.w.k = 5; // valid
5195 20 EXAMPLE 2 After the declaration:
5196 struct s { int n; double d[]; };
5197 the structure struct s has a flexible array member d. A typical way to use this is:
5198 int m = /* some value */;
5199 struct s *p = malloc(sizeof (struct s) + sizeof (double [m]));
5200 and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if
5201 p had been declared as:
5202 struct { int n; double d[m]; } *p;
5203 (there are circumstances in which this equivalence is broken; in particular, the offsets of member d might
5205 21 Following the above declaration:
5206 struct s t1 = { 0 }; // valid
5207 struct s t2 = { 1, { 4.2 }}; // invalid
5209 t1.d[0] = 4.2; // might be undefined behavior
5210 The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not
5211 contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that
5212 sizeof (struct s) >= offsetof(struct s, d) + sizeof (double)
5213 in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming
5218 22 After the further declaration:
5219 struct ss { int n; };
5221 sizeof (struct s) >= sizeof (struct ss)
5222 sizeof (struct s) >= offsetof(struct s, d)
5223 are always equal to 1.
5224 23 If sizeof (double) is 8, then after the following code is executed:
5227 s1 = malloc(sizeof (struct s) + 64);
5228 s2 = malloc(sizeof (struct s) + 46);
5229 and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most
5230 purposes, as if the identifiers had been declared as:
5231 struct { int n; double d[8]; } *s1;
5232 struct { int n; double d[5]; } *s2;
5233 24 Following the further successful assignments:
5234 s1 = malloc(sizeof (struct s) + 10);
5235 s2 = malloc(sizeof (struct s) + 6);
5236 they then behave as if the declarations were:
5237 struct { int n; double d[1]; } *s1, *s2;
5240 dp = &(s1->d[0]); // valid
5242 dp = &(s2->d[0]); // valid
5243 *dp = 42; // undefined behavior
5246 only copies the member n; if any of the array elements are within the first sizeof (struct s) bytes
5247 of the structure, they might be copied or simply overwritten with indeterminate values.
5249 Forward references: declarators (6.7.6), tags (6.7.2.3).
5256 6.7.2.2 Enumeration specifiers
5259 enum identifieropt { enumerator-list }
5260 enum identifieropt { enumerator-list , }
5264 enumerator-list , enumerator
5266 enumeration-constant
5267 enumeration-constant = constant-expression
5269 2 The expression that defines the value of an enumeration constant shall be an integer
5270 constant expression that has a value representable as an int.
5272 3 The identifiers in an enumerator list are declared as constants that have type int and
5273 may appear wherever such are permitted.127) An enumerator with = defines its
5274 enumeration constant as the value of the constant expression. If the first enumerator has
5275 no =, the value of its enumeration constant is 0. Each subsequent enumerator with no =
5276 defines its enumeration constant as the value of the constant expression obtained by
5277 adding 1 to the value of the previous enumeration constant. (The use of enumerators with
5278 = may produce enumeration constants with values that duplicate other values in the same
5279 enumeration.) The enumerators of an enumeration are also known as its members.
5280 4 Each enumerated type shall be compatible with char, a signed integer type, or an
5281 unsigned integer type. The choice of type is implementation-defined,128) but shall be
5282 capable of representing the values of all the members of the enumeration. The
5283 enumerated type is incomplete until immediately after the } that terminates the list of
5284 enumerator declarations, and complete thereafter.
5289 127) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from
5290 each other and from other identifiers declared in ordinary declarators.
5291 128) An implementation may delay the choice of which integer type until all enumeration constants have
5296 5 EXAMPLE The following fragment:
5297 enum hue { chartreuse, burgundy, claret=20, winedark };
5301 if (*cp != burgundy)
5303 makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a
5304 pointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }.
5306 Forward references: tags (6.7.2.3).
5309 1 A specific type shall have its content defined at most once.
5310 2 Where two declarations that use the same tag declare the same type, they shall both use
5311 the same choice of struct, union, or enum.
5312 3 A type specifier of the form
5314 without an enumerator list shall only appear after the type it specifies is complete.
5316 4 All declarations of structure, union, or enumerated types that have the same scope and
5317 use the same tag declare the same type. Irrespective of whether there is a tag or what
5318 other declarations of the type are in the same translation unit, the type is incomplete129)
5319 until immediately after the closing brace of the list defining the content, and complete
5321 5 Two declarations of structure, union, or enumerated types which are in different scopes or
5322 use different tags declare distinct types. Each declaration of a structure, union, or
5323 enumerated type which does not include a tag declares a distinct type.
5324 6 A type specifier of the form
5329 129) An incomplete type may only by used when the size of an object of that type is not needed. It is not
5330 needed, for example, when a typedef name is declared to be a specifier for a structure or union, or
5331 when a pointer to or a function returning a structure or union is being declared. (See incomplete types
5332 in 6.2.5.) The specification has to be complete before such a function is called or defined.
5336 struct-or-union identifieropt { struct-declaration-list }
5338 enum identifieropt { enumerator-list }
5340 enum identifieropt { enumerator-list , }
5341 declares a structure, union, or enumerated type. The list defines the structure content,
5342 union content, or enumeration content. If an identifier is provided,130) the type specifier
5343 also declares the identifier to be the tag of that type.
5344 7 A declaration of the form
5345 struct-or-union identifier ;
5346 specifies a structure or union type and declares the identifier as a tag of that type.131)
5347 8 If a type specifier of the form
5348 struct-or-union identifier
5349 occurs other than as part of one of the above forms, and no other declaration of the
5350 identifier as a tag is visible, then it declares an incomplete structure or union type, and
5351 declares the identifier as the tag of that type.131)
5352 9 If a type specifier of the form
5353 struct-or-union identifier
5356 occurs other than as part of one of the above forms, and a declaration of the identifier as a
5357 tag is visible, then it specifies the same type as that other declaration, and does not
5359 10 EXAMPLE 1 This mechanism allows declaration of a self-referential structure.
5362 struct tnode *left, *right;
5364 specifies a structure that contains an integer and two pointers to objects of the same type. Once this
5365 declaration has been given, the declaration
5370 130) If there is no identifier, the type can, within the translation unit, only be referred to by the declaration
5371 of which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations
5372 can make use of that typedef name to declare objects having the specified structure, union, or
5374 131) A similar construction with enum does not exist.
5378 struct tnode s, *sp;
5379 declares s to be an object of the given type and sp to be a pointer to an object of the given type. With
5380 these declarations, the expression sp->left refers to the left struct tnode pointer of the object to
5381 which sp points; the expression s.right->count designates the count member of the right struct
5382 tnode pointed to from s.
5383 11 The following alternative formulation uses the typedef mechanism:
5384 typedef struct tnode TNODE;
5387 TNODE *left, *right;
5391 12 EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential
5392 structures, the declarations
5393 struct s1 { struct s2 *s2p; /* ... */ }; // D1
5394 struct s2 { struct s1 *s1p; /* ... */ }; // D2
5395 specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already
5396 declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in
5397 D2. To eliminate this context sensitivity, the declaration
5399 may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then
5400 completes the specification of the new type.
5402 Forward references: declarators (6.7.6), type definitions (6.7.8).
5403 6.7.2.4 Atomic type specifiers
5405 1 atomic-type-specifier:
5406 _Atomic ( type-name )
5408 2 Atomic type specifiers shall not be used if the implementation does not support atomic
5409 types (see 6.10.8.3).
5410 3 The type name in an atomic type specifier shall not refer to an array type, a function type,
5411 an atomic type, or a qualified type.
5413 4 The properties associated with atomic types are meaningful only for expressions that are
5414 lvalues. If the _Atomic keyword is immediately followed by a left parenthesis, it is
5415 interpreted as a type specifier (with a type name), not as a type qualifier.
5422 6.7.3 Type qualifiers
5430 2 Types other than pointer types whose referenced type is an object type shall not be
5432 3 The type modified by the _Atomic qualifier shall not be an array type or a function
5435 4 The properties associated with qualified types are meaningful only for expressions that
5437 5 If the same qualifier appears more than once in the same specifier-qualifier-list, either
5438 directly or via one or more typedefs, the behavior is the same as if it appeared only
5439 once. If other qualifiers appear along with the _Atomic qualifier in a specifier-qualifier-
5440 list, the resulting type is the so-qualified atomic type.
5441 6 If an attempt is made to modify an object defined with a const-qualified type through use
5442 of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is
5443 made to refer to an object defined with a volatile-qualified type through use of an lvalue
5444 with non-volatile-qualified type, the behavior is undefined.133)
5445 7 An object that has volatile-qualified type may be modified in ways unknown to the
5446 implementation or have other unknown side effects. Therefore any expression referring
5447 to such an object shall be evaluated strictly according to the rules of the abstract machine,
5448 as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the
5449 object shall agree with that prescribed by the abstract machine, except as modified by the
5454 132) The implementation may place a const object that is not volatile in a read-only region of
5455 storage. Moreover, the implementation need not allocate storage for such an object if its address is
5457 133) This applies to those objects that behave as if they were defined with qualified types, even if they are
5458 never actually defined as objects in the program (such as an object at a memory-mapped input/output
5463 unknown factors mentioned previously.134) What constitutes an access to an object that
5464 has volatile-qualified type is implementation-defined.
5465 8 An object that is accessed through a restrict-qualified pointer has a special association
5466 with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to
5467 that object use, directly or indirectly, the value of that particular pointer.135) The intended
5468 use of the restrict qualifier (like the register storage class) is to promote
5469 optimization, and deleting all instances of the qualifier from all preprocessing translation
5470 units composing a conforming program does not change its meaning (i.e., observable
5472 9 If the specification of an array type includes any type qualifiers, the element type is so-
5473 qualified, not the array type. If the specification of a function type includes any type
5474 qualifiers, the behavior is undefined.136)
5475 10 For two qualified types to be compatible, both shall have the identically qualified version
5476 of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers
5477 does not affect the specified type.
5478 11 EXAMPLE 1 An object declared
5479 extern const volatile int real_time_clock;
5480 may be modifiable by hardware, but cannot be assigned to, incremented, or decremented.
5482 12 EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers
5483 modify an aggregate type:
5484 const struct s { int mem; } cs = { 1 };
5485 struct s ncs; // the object ncs is modifiable
5486 typedef int A[2][3];
5487 const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int
5491 cs = ncs; // violates modifiable lvalue constraint for =
5492 pi = &ncs.mem; // valid
5493 pi = &cs.mem; // violates type constraints for =
5494 pci = &cs.mem; // valid
5495 pi = a[0]; // invalid: a[0] has type ''const int *''
5499 134) A volatile declaration may be used to describe an object corresponding to a memory-mapped
5500 input/output port or an object accessed by an asynchronously interrupting function. Actions on
5501 objects so declared shall not be ''optimized out'' by an implementation or reordered except as
5502 permitted by the rules for evaluating expressions.
5503 135) For example, a statement that assigns a value returned by malloc to a single pointer establishes this
5504 association between the allocated object and the pointer.
5505 136) Both of these can occur through the use of typedefs.
5509 13 EXAMPLE 3 The declaration
5510 _Atomic volatile int *p;
5511 specifies that p has the type ''pointer to volatile atomic int'', a pointer to a volatile-qualified atomic type.
5513 6.7.3.1 Formal definition of restrict
5514 1 Let D be a declaration of an ordinary identifier that provides a means of designating an
5515 object P as a restrict-qualified pointer to type T.
5516 2 If D appears inside a block and does not have storage class extern, let B denote the
5517 block. If D appears in the list of parameter declarations of a function definition, let B
5518 denote the associated block. Otherwise, let B denote the block of main (or the block of
5519 whatever function is called at program startup in a freestanding environment).
5520 3 In what follows, a pointer expression E is said to be based on object P if (at some
5521 sequence point in the execution of B prior to the evaluation of E) modifying P to point to
5522 a copy of the array object into which it formerly pointed would change the value of E.137)
5523 Note that ''based'' is defined only for expressions with pointer types.
5524 4 During each execution of B, let L be any lvalue that has &L based on P. If L is used to
5525 access the value of the object X that it designates, and X is also modified (by any means),
5526 then the following requirements apply: T shall not be const-qualified. Every other lvalue
5527 used to access the value of X shall also have its address based on P. Every access that
5528 modifies X shall be considered also to modify P, for the purposes of this subclause. If P
5529 is assigned the value of a pointer expression E that is based on another restricted pointer
5530 object P2, associated with block B2, then either the execution of B2 shall begin before
5531 the execution of B, or the execution of B2 shall end prior to the assignment. If these
5532 requirements are not met, then the behavior is undefined.
5533 5 Here an execution of B means that portion of the execution of the program that would
5534 correspond to the lifetime of an object with scalar type and automatic storage duration
5536 6 A translator is free to ignore any or all aliasing implications of uses of restrict.
5537 7 EXAMPLE 1 The file scope declarations
5541 assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the
5542 program, then it is never accessed using either of the other two.
5545 137) In other words, E depends on the value of P itself rather than on the value of an object referenced
5546 indirectly through P. For example, if identifier p has type (int **restrict), then the pointer
5547 expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer
5548 expressions *p and p[1] are not.
5552 8 EXAMPLE 2 The function parameter declarations in the following example
5553 void f(int n, int * restrict p, int * restrict q)
5558 assert that, during each execution of the function, if an object is accessed through one of the pointer
5559 parameters, then it is not also accessed through the other.
5560 9 The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence
5561 analysis of function f without examining any of the calls of f in the program. The cost is that the
5562 programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the
5563 second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through
5568 f(50, d + 50, d); // valid
5569 f(50, d + 1, d); // undefined behavior
5572 10 EXAMPLE 3 The function parameter declarations
5573 void h(int n, int * restrict p, int * restrict q, int * restrict r)
5576 for (i = 0; i < n; i++)
5579 illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b
5580 are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not
5581 modified within function h.
5583 11 EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a
5584 function call and an equivalent nested block. With one exception, only ''outer-to-inner'' assignments
5585 between restricted pointers declared in nested blocks have defined behavior.
5589 p1 = q1; // undefined behavior
5591 int * restrict p2 = p1; // valid
5592 int * restrict q2 = q1; // valid
5593 p1 = q2; // undefined behavior
5594 p2 = q2; // undefined behavior
5603 12 The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more
5604 precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For
5605 example, this permits new_vector to return a vector.
5606 typedef struct { int n; float * restrict v; } vector;
5607 vector new_vector(int n)
5611 t.v = malloc(n * sizeof (float));
5615 6.7.4 Function specifiers
5617 1 function-specifier:
5621 2 Function specifiers shall be used only in the declaration of an identifier for a function.
5622 3 An inline definition of a function with external linkage shall not contain a definition of a
5623 modifiable object with static or thread storage duration, and shall not contain a reference
5624 to an identifier with internal linkage.
5625 4 In a hosted environment, no function specifier(s) shall appear in a declaration of main.
5627 5 A function specifier may appear more than once; the behavior is the same as if it
5629 6 A function declared with an inline function specifier is an inline function. Making a *
5630 function an inline function suggests that calls to the function be as fast as possible.138)
5631 The extent to which such suggestions are effective is implementation-defined.139)
5636 138) By using, for example, an alternative to the usual function call mechanism, such as ''inline
5637 substitution''. Inline substitution is not textual substitution, nor does it create a new function.
5638 Therefore, for example, the expansion of a macro used within the body of the function uses the
5639 definition it had at the point the function body appears, and not where the function is called; and
5640 identifiers refer to the declarations in scope where the body occurs. Likewise, the function has a
5641 single address, regardless of the number of inline definitions that occur in addition to the external
5643 139) For example, an implementation might never perform inline substitution, or might only perform inline
5644 substitutions to calls in the scope of an inline declaration.
5648 7 Any function with internal linkage can be an inline function. For a function with external
5649 linkage, the following restrictions apply: If a function is declared with an inline
5650 function specifier, then it shall also be defined in the same translation unit. If all of the
5651 file scope declarations for a function in a translation unit include the inline function
5652 specifier without extern, then the definition in that translation unit is an inline
5653 definition. An inline definition does not provide an external definition for the function,
5654 and does not forbid an external definition in another translation unit. An inline definition
5655 provides an alternative to an external definition, which a translator may use to implement
5656 any call to the function in the same translation unit. It is unspecified whether a call to the
5657 function uses the inline definition or the external definition.140)
5658 8 A function declared with a _Noreturn function specifier shall not return to its caller.
5659 Recommended practice
5660 9 The implementation should produce a diagnostic message for a function declared with a
5661 _Noreturn function specifier that appears to be capable of returning to its caller.
5662 10 EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external
5663 definition, or a definition available for use only within the translation unit. A file scope declaration with
5664 extern creates an external definition. The following example shows an entire translation unit.
5665 inline double fahr(double t)
5667 return (9.0 * t) / 5.0 + 32.0;
5669 inline double cels(double t)
5671 return (5.0 * (t - 32.0)) / 9.0;
5673 extern double fahr(double); // creates an external definition
5674 double convert(int is_fahr, double temp)
5676 /* A translator may perform inline substitutions */
5677 return is_fahr ? cels(temp) : fahr(temp);
5679 11 Note that the definition of fahr is an external definition because fahr is also declared with extern, but
5680 the definition of cels is an inline definition. Because cels has external linkage and is referenced, an
5681 external definition has to appear in another translation unit (see 6.9); the inline definition and the external
5682 definition are distinct and either may be used for the call.
5689 140) Since an inline definition is distinct from the corresponding external definition and from any other
5690 corresponding inline definitions in other translation units, all corresponding objects with static storage
5691 duration are also distinct in each of the definitions.
5695 _Noreturn void f () {
5698 _Noreturn void g (int i) { // causes undefined behavior if i <= 0
5702 Forward references: function definitions (6.9.1).
5703 6.7.5 Alignment specifier
5705 1 alignment-specifier:
5706 _Alignas ( type-name )
5707 _Alignas ( constant-expression )
5709 2 An alignment attribute shall not be specified in a declaration of a typedef, or a bit-field, or
5710 a function, or a parameter, or an object declared with the register storage-class
5712 3 The constant expression shall be an integer constant expression. It shall evaluate to a
5713 valid fundamental alignment, or to a valid extended alignment supported by the
5714 implementation in the context in which it appears, or to zero.
5715 4 The combined effect of all alignment attributes in a declaration shall not specify an
5716 alignment that is less strict than the alignment that would otherwise be required for the
5717 type of the object or member being declared.
5719 5 The first form is equivalent to _Alignas(alignof(type-name)).
5720 6 The alignment requirement of the declared object or member is taken to be the specified
5721 alignment. An alignment specification of zero has no effect.141) When multiple
5722 alignment specifiers occur in a declaration, the effective alignment requirement is the
5723 strictest specified alignment.
5724 7 If the definition of an object has an alignment specifier, any other declaration of that
5725 object shall either specify equivalent alignment or have no alignment specifier. If the
5726 definition of an object does not have an alignment specifier, any other declaration of that
5727 object shall also have no alignment specifier. If declarations of an object in different
5728 translation units have different alignment specifiers, the behavior is undefined.
5732 141) An alignment specification of zero also does not affect other alignment specifications in the same
5740 pointeropt direct-declarator
5744 direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
5745 direct-declarator [ static type-qualifier-listopt assignment-expression ]
5746 direct-declarator [ type-qualifier-list static assignment-expression ]
5747 direct-declarator [ type-qualifier-listopt * ]
5748 direct-declarator ( parameter-type-list )
5749 direct-declarator ( identifier-listopt )
5751 * type-qualifier-listopt
5752 * type-qualifier-listopt pointer
5753 type-qualifier-list:
5755 type-qualifier-list type-qualifier
5756 parameter-type-list:
5758 parameter-list , ...
5760 parameter-declaration
5761 parameter-list , parameter-declaration
5762 parameter-declaration:
5763 declaration-specifiers declarator
5764 declaration-specifiers abstract-declaratoropt
5767 identifier-list , identifier
5769 2 Each declarator declares one identifier, and asserts that when an operand of the same
5770 form as the declarator appears in an expression, it designates a function or object with the
5771 scope, storage duration, and type indicated by the declaration specifiers.
5772 3 A full declarator is a declarator that is not part of another declarator. The end of a full
5773 declarator is a sequence point. If, in the nested sequence of declarators in a full
5776 declarator, there is a declarator specifying a variable length array type, the type specified
5777 by the full declarator is said to be variably modified. Furthermore, any type derived by
5778 declarator type derivation from a variably modified type is itself variably modified.
5779 4 In the following subclauses, consider a declaration
5781 where T contains the declaration specifiers that specify a type T (such as int) and D1 is
5782 a declarator that contains an identifier ident. The type specified for the identifier ident in
5783 the various forms of declarator is described inductively using this notation.
5784 5 If, in the declaration ''T D1'', D1 has the form
5786 then the type specified for ident is T .
5787 6 If, in the declaration ''T D1'', D1 has the form
5789 then ident has the type specified by the declaration ''T D''. Thus, a declarator in
5790 parentheses is identical to the unparenthesized declarator, but the binding of complicated
5791 declarators may be altered by parentheses.
5792 Implementation limits
5793 7 As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and
5794 function declarators that modify an arithmetic, structure, union, or void type, either
5795 directly or via one or more typedefs.
5796 Forward references: array declarators (6.7.6.2), type definitions (6.7.8).
5797 6.7.6.1 Pointer declarators
5799 1 If, in the declaration ''T D1'', D1 has the form
5800 * type-qualifier-listopt D
5801 and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
5802 T '', then the type specified for ident is ''derived-declarator-type-list type-qualifier-list
5803 pointer to T ''. For each type qualifier in the list, ident is a so-qualified pointer.
5804 2 For two pointer types to be compatible, both shall be identically qualified and both shall
5805 be pointers to compatible types.
5806 3 EXAMPLE The following pair of declarations demonstrates the difference between a ''variable pointer
5807 to a constant value'' and a ''constant pointer to a variable value''.
5814 const int *ptr_to_constant;
5815 int *const constant_ptr;
5816 The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer,
5817 but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of the
5818 int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the
5820 4 The declaration of the constant pointer constant_ptr may be clarified by including a definition for the
5821 type ''pointer to int''.
5822 typedef int *int_ptr;
5823 const int_ptr constant_ptr;
5824 declares constant_ptr as an object that has type ''const-qualified pointer to int''.
5826 6.7.6.2 Array declarators
5828 1 In addition to optional type qualifiers and the keyword static, the [ and ] may delimit
5829 an expression or *. If they delimit an expression (which specifies the size of an array), the
5830 expression shall have an integer type. If the expression is a constant expression, it shall
5831 have a value greater than zero. The element type shall not be an incomplete or function
5832 type. The optional type qualifiers and the keyword static shall appear only in a
5833 declaration of a function parameter with an array type, and then only in the outermost
5834 array type derivation.
5835 2 If an identifier is declared as having a variably modified type, it shall be an ordinary
5836 identifier (as defined in 6.2.3), have no linkage, and have either block scope or function
5837 prototype scope. If an identifier is declared to be an object with static or thread storage
5838 duration, it shall not have a variable length array type.
5840 3 If, in the declaration ''T D1'', D1 has one of the forms:
5841 D[ type-qualifier-listopt assignment-expressionopt ]
5842 D[ static type-qualifier-listopt assignment-expression ]
5843 D[ type-qualifier-list static assignment-expression ]
5844 D[ type-qualifier-listopt * ]
5845 and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
5846 T '', then the type specified for ident is ''derived-declarator-type-list array of T ''.142)
5847 (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.)
5848 4 If the size is not present, the array type is an incomplete type. If the size is * instead of
5849 being an expression, the array type is a variable length array type of unspecified size,
5850 which can only be used in declarations or type names with function prototype scope;143)
5852 142) When several ''array of'' specifications are adjacent, a multidimensional array is declared.
5856 such arrays are nonetheless complete types. If the size is an integer constant expression
5857 and the element type has a known constant size, the array type is not a variable length
5858 array type; otherwise, the array type is a variable length array type. (Variable length
5859 arrays are a conditional feature that implementations need not support; see 6.10.8.3.)
5860 5 If the size is an expression that is not an integer constant expression: if it occurs in a
5861 declaration at function prototype scope, it is treated as if it were replaced by *; otherwise,
5862 each time it is evaluated it shall have a value greater than zero. The size of each instance
5863 of a variable length array type does not change during its lifetime. Where a size
5864 expression is part of the operand of a sizeof operator and changing the value of the
5865 size expression would not affect the result of the operator, it is unspecified whether or not
5866 the size expression is evaluated.
5867 6 For two array types to be compatible, both shall have compatible element types, and if
5868 both size specifiers are present, and are integer constant expressions, then both size
5869 specifiers shall have the same constant value. If the two array types are used in a context
5870 which requires them to be compatible, it is undefined behavior if the two size specifiers
5871 evaluate to unequal values.
5873 float fa[11], *afp[17];
5874 declares an array of float numbers and an array of pointers to float numbers.
5876 8 EXAMPLE 2 Note the distinction between the declarations
5879 The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size
5880 (an incomplete type), the storage for which is defined elsewhere.
5882 9 EXAMPLE 3 The following declarations demonstrate the compatibility rules for variably modified types.
5890 int (*r)[n][n][n+1];
5891 p = a; // invalid: not compatible because 4 != 6
5892 r = c; // compatible, but defined behavior only if
5893 // n == 6 and m == n+1
5899 143) Thus, * can be used only in function declarations that are not definitions (see 6.7.6.3).
5903 10 EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or
5904 function prototype scope. Array objects declared with the _Thread_local, static, or extern
5905 storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with
5906 the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all
5907 identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of
5908 structures or unions.
5910 int A[n]; // invalid: file scope VLA
5911 extern int (*p2)[n]; // invalid: file scope VM
5912 int B[100]; // valid: file scope but not VM
5913 void fvla(int m, int C[m][m]); // valid: VLA with prototype scope
5914 void fvla(int m, int C[m][m]) // valid: adjusted to auto pointer to VLA
5916 typedef int VLA[m][m]; // valid: block scope typedef VLA
5918 int (*y)[n]; // invalid: y not ordinary identifier
5919 int z[n]; // invalid: z not ordinary identifier
5921 int D[m]; // valid: auto VLA
5922 static int E[m]; // invalid: static block scope VLA
5923 extern int F[m]; // invalid: F has linkage and is VLA
5924 int (*s)[m]; // valid: auto pointer to VLA
5925 extern int (*r)[m]; // invalid: r has linkage and points to VLA
5926 static int (*q)[m] = &B; // valid: q is a static block pointer to VLA
5929 Forward references: function declarators (6.7.6.3), function definitions (6.9.1),
5930 initialization (6.7.9).
5931 6.7.6.3 Function declarators (including prototypes)
5933 1 A function declarator shall not specify a return type that is a function type or an array
5935 2 The only storage-class specifier that shall occur in a parameter declaration is register.
5936 3 An identifier list in a function declarator that is not part of a definition of that function
5938 4 After adjustment, the parameters in a parameter type list in a function declarator that is
5939 part of a definition of that function shall not have incomplete type.
5941 5 If, in the declaration ''T D1'', D1 has the form
5948 D( parameter-type-list )
5950 D( identifier-listopt )
5951 and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
5952 T '', then the type specified for ident is ''derived-declarator-type-list function returning
5954 6 A parameter type list specifies the types of, and may declare identifiers for, the
5955 parameters of the function.
5956 7 A declaration of a parameter as ''array of type'' shall be adjusted to ''qualified pointer to
5957 type'', where the type qualifiers (if any) are those specified within the [ and ] of the
5958 array type derivation. If the keyword static also appears within the [ and ] of the
5959 array type derivation, then for each call to the function, the value of the corresponding
5960 actual argument shall provide access to the first element of an array with at least as many
5961 elements as specified by the size expression.
5962 8 A declaration of a parameter as ''function returning type'' shall be adjusted to ''pointer to
5963 function returning type'', as in 6.3.2.1.
5964 9 If the list terminates with an ellipsis (, ...), no information about the number or types
5965 of the parameters after the comma is supplied.144)
5966 10 The special case of an unnamed parameter of type void as the only item in the list
5967 specifies that the function has no parameters.
5968 11 If, in a parameter declaration, an identifier can be treated either as a typedef name or as a
5969 parameter name, it shall be taken as a typedef name.
5970 12 If the function declarator is not part of a definition of that function, parameters may have
5971 incomplete type and may use the [*] notation in their sequences of declarator specifiers
5972 to specify variable length array types.
5973 13 The storage-class specifier in the declaration specifiers for a parameter declaration, if
5974 present, is ignored unless the declared parameter is one of the members of the parameter
5975 type list for a function definition.
5976 14 An identifier list declares only the identifiers of the parameters of the function. An empty
5977 list in a function declarator that is part of a definition of that function specifies that the
5978 function has no parameters. The empty list in a function declarator that is not part of a
5979 definition of that function specifies that no information about the number or types of the
5980 parameters is supplied.145)
5984 144) The macros defined in the <stdarg.h> header (7.16) may be used to access arguments that
5985 correspond to the ellipsis.
5989 15 For two function types to be compatible, both shall specify compatible return types.146)
5990 Moreover, the parameter type lists, if both are present, shall agree in the number of
5991 parameters and in use of the ellipsis terminator; corresponding parameters shall have
5992 compatible types. If one type has a parameter type list and the other type is specified by a
5993 function declarator that is not part of a function definition and that contains an empty
5994 identifier list, the parameter list shall not have an ellipsis terminator and the type of each
5995 parameter shall be compatible with the type that results from the application of the
5996 default argument promotions. If one type has a parameter type list and the other type is
5997 specified by a function definition that contains a (possibly empty) identifier list, both shall
5998 agree in the number of parameters, and the type of each prototype parameter shall be
5999 compatible with the type that results from the application of the default argument
6000 promotions to the type of the corresponding identifier. (In the determination of type
6001 compatibility and of a composite type, each parameter declared with function or array
6002 type is taken as having the adjusted type and each parameter declared with qualified type
6003 is taken as having the unqualified version of its declared type.)
6004 16 EXAMPLE 1 The declaration
6005 int f(void), *fip(), (*pfi)();
6006 declares a function f with no parameters returning an int, a function fip with no parameter specification
6007 returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an
6008 int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the
6009 declaration suggests, and the same construction in an expression requires, the calling of a function fip,
6010 and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the
6011 extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function
6012 designator, which is then used to call the function; it returns an int.
6013 17 If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the
6014 declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either
6015 internal or external linkage (depending on what file scope declarations for these identifiers are visible), and
6016 the identifier of the pointer pfi has block scope and no linkage.
6018 18 EXAMPLE 2 The declaration
6019 int (*apfi[3])(int *x, int *y);
6020 declares an array apfi of three pointers to functions returning int. Each of these functions has two
6021 parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and
6022 go out of scope at the end of the declaration of apfi.
6024 19 EXAMPLE 3 The declaration
6025 int (*fpfi(int (*)(long), int))(int, ...);
6026 declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two
6027 parameters: a pointer to a function returning an int (with one parameter of type long int), and an int.
6028 The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more
6031 145) See ''future language directions'' (6.11.6).
6032 146) If both function types are ''old style'', parameter types are not compared.
6036 additional arguments of any type.
6038 20 EXAMPLE 4 The following prototype has a variably modified parameter.
6039 void addscalar(int n, int m,
6040 double a[n][n*m+300], double x);
6044 addscalar(4, 2, b, 2.17);
6047 void addscalar(int n, int m,
6048 double a[n][n*m+300], double x)
6050 for (int i = 0; i < n; i++)
6051 for (int j = 0, k = n*m+300; j < k; j++)
6052 // a is a pointer to a VLA with n*m+300 elements
6056 21 EXAMPLE 5 The following are all compatible function prototype declarators.
6057 double maximum(int n, int m, double a[n][m]);
6058 double maximum(int n, int m, double a[*][*]);
6059 double maximum(int n, int m, double a[ ][*]);
6060 double maximum(int n, int m, double a[ ][m]);
6062 void f(double (* restrict a)[5]);
6063 void f(double a[restrict][5]);
6064 void f(double a[restrict 3][5]);
6065 void f(double a[restrict static 3][5]);
6066 (Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a
6067 non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.)
6069 Forward references: function definitions (6.9.1), type names (6.7.7).
6079 specifier-qualifier-list abstract-declaratoropt
6080 abstract-declarator:
6082 pointeropt direct-abstract-declarator
6083 direct-abstract-declarator:
6084 ( abstract-declarator )
6085 direct-abstract-declaratoropt [ type-qualifier-listopt
6086 assignment-expressionopt ]
6087 direct-abstract-declaratoropt [ static type-qualifier-listopt
6088 assignment-expression ]
6089 direct-abstract-declaratoropt [ type-qualifier-list static
6090 assignment-expression ]
6091 direct-abstract-declaratoropt [ * ]
6092 direct-abstract-declaratoropt ( parameter-type-listopt )
6094 2 In several contexts, it is necessary to specify a type. This is accomplished using a type
6095 name, which is syntactically a declaration for a function or an object of that type that
6096 omits the identifier.147)
6097 3 EXAMPLE The constructions
6105 (h) int (*const [])(unsigned int, ...)
6106 name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an
6107 array of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function
6108 with no parameter specification returning a pointer to int, (g) pointer to function with no parameters
6109 returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one
6110 parameter that has type unsigned int and an unspecified number of other parameters, returning an
6116 147) As indicated by the syntax, empty parentheses in a type name are interpreted as ''function with no
6117 parameter specification'', rather than redundant parentheses around the omitted identifier.
6121 6.7.8 Type definitions
6126 2 If a typedef name specifies a variably modified type then it shall have block scope.
6128 3 In a declaration whose storage-class specifier is typedef, each declarator defines an
6129 identifier to be a typedef name that denotes the type specified for the identifier in the way
6130 described in 6.7.6. Any array size expressions associated with variable length array
6131 declarators are evaluated each time the declaration of the typedef name is reached in the
6132 order of execution. A typedef declaration does not introduce a new type, only a
6133 synonym for the type so specified. That is, in the following declarations:
6134 typedef T type_ident;
6136 type_ident is defined as a typedef name with the type specified by the declaration
6137 specifiers in T (known as T ), and the identifier in D has the type ''derived-declarator-
6138 type-list T '' where the derived-declarator-type-list is specified by the declarators of D. A
6139 typedef name shares the same name space as other identifiers declared in ordinary
6142 typedef int MILES, KLICKSP();
6143 typedef struct { double hi, lo; } range;
6146 extern KLICKSP *metricp;
6149 are all valid declarations. The type of distance is int, that of metricp is ''pointer to function with no
6150 parameter specification returning int'', and that of x and z is the specified structure; zp is a pointer to
6151 such a structure. The object distance has a type compatible with any other int object.
6153 5 EXAMPLE 2 After the declarations
6154 typedef struct s1 { int x; } t1, *tp1;
6155 typedef struct s2 { int x; } t2, *tp2;
6156 type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct
6157 s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int.
6164 6 EXAMPLE 3 The following obscure constructions
6165 typedef signed int t;
6172 declare a typedef name t with type signed int, a typedef name plain with type int, and a structure
6173 with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const-
6174 qualified bit-field which (if it could be accessed) would contain values in either the range [-15, +15] or
6175 [-16, +15], and one named r that contains values in one of the ranges [0, 31], [-15, +15], or [-16, +15].
6176 (The choice of range is implementation-defined.) The first two bit-field declarations differ in that
6177 unsigned is a type specifier (which forces t to be the name of a structure member), while const is a
6178 type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed
6179 in an inner scope by
6182 then a function f is declared with type ''function returning signed int with one unnamed parameter
6183 with type pointer to function returning signed int with one unnamed parameter with type signed
6184 int'', and an identifier t with type long int.
6186 7 EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the
6187 following declarations of the signal function specify exactly the same type, the first without making use
6188 of any typedef names.
6189 typedef void fv(int), (*pfv)(int);
6190 void (*signal(int, void (*)(int)))(int);
6191 fv *signal(int, fv *);
6192 pfv signal(int, pfv);
6194 8 EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the
6195 time the typedef name is defined, not each time it is used:
6198 typedef int B[n]; // B is n ints, n evaluated now
6200 B a; // a is n ints, n without += 1
6201 int b[n]; // a and b are different sizes
6202 for (int i = 1; i < n; i++)
6211 6.7.9 Initialization
6214 assignment-expression
6215 { initializer-list }
6216 { initializer-list , }
6218 designationopt initializer
6219 initializer-list , designationopt initializer
6224 designator-list designator
6226 [ constant-expression ]
6229 2 No initializer shall attempt to provide a value for an object not contained within the entity
6231 3 The type of the entity to be initialized shall be an array of unknown size or a complete
6232 object type that is not a variable length array type.
6233 4 All the expressions in an initializer for an object that has static or thread storage duration
6234 shall be constant expressions or string literals.
6235 5 If the declaration of an identifier has block scope, and the identifier has external or
6236 internal linkage, the declaration shall have no initializer for the identifier.
6237 6 If a designator has the form
6238 [ constant-expression ]
6239 then the current object (defined below) shall have array type and the expression shall be
6240 an integer constant expression. If the array is of unknown size, any nonnegative value is
6242 7 If a designator has the form
6244 then the current object (defined below) shall have structure or union type and the
6245 identifier shall be the name of a member of that type.
6249 8 An initializer specifies the initial value stored in an object.
6250 9 Except where explicitly stated otherwise, for the purposes of this subclause unnamed
6251 members of objects of structure and union type do not participate in initialization.
6252 Unnamed members of structure objects have indeterminate value even after initialization.
6253 10 If an object that has automatic storage duration is not initialized explicitly, its value is
6254 indeterminate. If an object that has static or thread storage duration is not initialized
6256 -- if it has pointer type, it is initialized to a null pointer;
6257 -- if it has arithmetic type, it is initialized to (positive or unsigned) zero;
6258 -- if it is an aggregate, every member is initialized (recursively) according to these rules,
6259 and any padding is initialized to zero bits;
6260 -- if it is a union, the first named member is initialized (recursively) according to these
6261 rules, and any padding is initialized to zero bits;
6262 11 The initializer for a scalar shall be a single expression, optionally enclosed in braces. The
6263 initial value of the object is that of the expression (after conversion); the same type
6264 constraints and conversions as for simple assignment apply, taking the type of the scalar
6265 to be the unqualified version of its declared type.
6266 12 The rest of this subclause deals with initializers for objects that have aggregate or union
6268 13 The initializer for a structure or union object that has automatic storage duration shall be
6269 either an initializer list as described below, or a single expression that has compatible
6270 structure or union type. In the latter case, the initial value of the object, including
6271 unnamed members, is that of the expression.
6272 14 An array of character type may be initialized by a character string literal or UTF-8 string
6273 literal, optionally enclosed in braces. Successive bytes of the string literal (including the
6274 terminating null character if there is room or if the array is of unknown size) initialize the
6275 elements of the array.
6276 15 An array with element type compatible with a qualified or unqualified version of
6277 wchar_t may be initialized by a wide string literal, optionally enclosed in braces.
6278 Successive wide characters of the wide string literal (including the terminating null wide
6279 character if there is room or if the array is of unknown size) initialize the elements of the
6281 16 Otherwise, the initializer for an object that has aggregate or union type shall be a brace-
6282 enclosed list of initializers for the elements or named members.
6287 17 Each brace-enclosed initializer list has an associated current object. When no
6288 designations are present, subobjects of the current object are initialized in order according
6289 to the type of the current object: array elements in increasing subscript order, structure
6290 members in declaration order, and the first named member of a union.148) In contrast, a
6291 designation causes the following initializer to begin initialization of the subobject
6292 described by the designator. Initialization then continues forward in order, beginning
6293 with the next subobject after that described by the designator.149)
6294 18 Each designator list begins its description with the current object associated with the
6295 closest surrounding brace pair. Each item in the designator list (in order) specifies a
6296 particular member of its current object and changes the current object for the next
6297 designator (if any) to be that member.150) The current object that results at the end of the
6298 designator list is the subobject to be initialized by the following initializer.
6299 19 The initialization shall occur in initializer list order, each initializer provided for a
6300 particular subobject overriding any previously listed initializer for the same subobject;151)
6301 all subobjects that are not initialized explicitly shall be initialized implicitly the same as
6302 objects that have static storage duration.
6303 20 If the aggregate or union contains elements or members that are aggregates or unions,
6304 these rules apply recursively to the subaggregates or contained unions. If the initializer of
6305 a subaggregate or contained union begins with a left brace, the initializers enclosed by
6306 that brace and its matching right brace initialize the elements or members of the
6307 subaggregate or the contained union. Otherwise, only enough initializers from the list are
6308 taken to account for the elements or members of the subaggregate or the first member of
6309 the contained union; any remaining initializers are left to initialize the next element or
6310 member of the aggregate of which the current subaggregate or contained union is a part.
6311 21 If there are fewer initializers in a brace-enclosed list than there are elements or members
6312 of an aggregate, or fewer characters in a string literal used to initialize an array of known
6313 size than there are elements in the array, the remainder of the aggregate shall be
6314 initialized implicitly the same as objects that have static storage duration.
6318 148) If the initializer list for a subaggregate or contained union does not begin with a left brace, its
6319 subobjects are initialized as usual, but the subaggregate or contained union does not become the
6320 current object: current objects are associated only with brace-enclosed initializer lists.
6321 149) After a union member is initialized, the next object is not the next member of the union; instead, it is
6322 the next subobject of an object containing the union.
6323 150) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with
6324 the surrounding brace pair. Note, too, that each separate designator list is independent.
6325 151) Any initializer for the subobject which is overridden and so not used to initialize that subobject might
6326 not be evaluated at all.
6330 22 If an array of unknown size is initialized, its size is determined by the largest indexed
6331 element with an explicit initializer. The array type is completed at the end of its
6333 23 The evaluations of the initialization list expressions are indeterminately sequenced with
6334 respect to one another and thus the order in which any side effects occur is
6336 24 EXAMPLE 1 Provided that <complex.h> has been #included, the declarations
6338 double complex c = 5 + 3 * I;
6339 define and initialize i with the value 3 and c with the value 5.0 + i3.0.
6341 25 EXAMPLE 2 The declaration
6342 int x[] = { 1, 3, 5 };
6343 defines and initializes x as a one-dimensional array object that has three elements, as no size was specified
6344 and there are three initializers.
6346 26 EXAMPLE 3 The declaration
6352 is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object
6353 y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and
6354 y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have
6357 1, 3, 5, 2, 4, 6, 3, 5, 7
6359 The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the
6360 next three are taken successively for y[1] and y[2].
6362 27 EXAMPLE 4 The declaration
6364 { 1 }, { 2 }, { 3 }, { 4 }
6366 initializes the first column of z as specified and initializes the rest with zeros.
6368 28 EXAMPLE 5 The declaration
6369 struct { int a[3], b; } w[] = { { 1 }, 2 };
6370 is a definition with an inconsistently bracketed initialization. It defines an array with two element
6374 152) In particular, the evaluation order need not be the same as the order of subobject initialization.
6378 structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.
6380 29 EXAMPLE 6 The declaration
6381 short q[4][3][2] = {
6386 contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array
6387 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
6388 q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for
6389 q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is
6390 only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers
6391 for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their
6392 respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a
6393 diagnostic message would have been issued. The same initialization result could have been achieved by:
6394 short q[4][3][2] = {
6400 short q[4][3][2] = {
6412 in a fully bracketed form.
6413 30 Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to
6416 31 EXAMPLE 7 One form of initialization that completes array types involves typedef names. Given the
6418 typedef int A[]; // OK - declared with block scope
6420 A a = { 1, 2 }, b = { 3, 4, 5 };
6422 int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
6423 due to the rules for incomplete types.
6427 32 EXAMPLE 8 The declaration
6428 char s[] = "abc", t[3] = "abc";
6429 defines ''plain'' char array objects s and t whose elements are initialized with character string literals.
6430 This declaration is identical to
6431 char s[] = { 'a', 'b', 'c', '\0' },
6432 t[] = { 'a', 'b', 'c' };
6433 The contents of the arrays are modifiable. On the other hand, the declaration
6435 defines p with type ''pointer to char'' and initializes it to point to an object with type ''array of char''
6436 with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to
6437 modify the contents of the array, the behavior is undefined.
6439 33 EXAMPLE 9 Arrays can be initialized to correspond to the elements of an enumeration by using
6441 enum { member_one, member_two };
6442 const char *nm[] = {
6443 [member_two] = "member two",
6444 [member_one] = "member one",
6447 34 EXAMPLE 10 Structure members can be initialized to nonzero values without depending on their order:
6448 div_t answer = { .quot = 2, .rem = -1 };
6450 35 EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists
6451 might be misunderstood:
6452 struct { int a[3], b; } w[] =
6453 { [0].a = {1}, [1].a[0] = 2 };
6455 36 EXAMPLE 12 Space can be ''allocated'' from both ends of an array by using a single designator:
6457 1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
6459 37 In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less
6460 than ten, some of the values provided by the first five initializers will be overridden by the second five.
6462 38 EXAMPLE 13 Any member of a union can be initialized:
6463 union { /* ... */ } u = { .any_member = 42 };
6465 Forward references: common definitions <stddef.h> (7.19).
6472 6.7.10 Static assertions
6474 1 static_assert-declaration:
6475 _Static_assert ( constant-expression , string-literal ) ;
6477 2 The constant expression shall compare unequal to 0.
6479 3 The constant expression shall be an integer constant expression. If the value of the
6480 constant expression compares unequal to 0, the declaration has no effect. Otherwise, the
6481 constraint is violated and the implementation shall produce a diagnostic message that
6482 includes the text of the string literal, except that characters not in the basic source
6483 character set are not required to appear in the message.
6484 Forward references: diagnostics (7.2).
6491 6.8 Statements and blocks
6496 expression-statement
6501 2 A statement specifies an action to be performed. Except as indicated, statements are
6502 executed in sequence.
6503 3 A block allows a set of declarations and statements to be grouped into one syntactic unit.
6504 The initializers of objects that have automatic storage duration, and the variable length
6505 array declarators of ordinary identifiers with block scope, are evaluated and the values are
6506 stored in the objects (including storing an indeterminate value in objects without an
6507 initializer) each time the declaration is reached in the order of execution, as if it were a
6508 statement, and within each declaration in the order that declarators appear.
6509 4 A full expression is an expression that is not part of another expression or of a declarator.
6510 Each of the following is a full expression: an initializer that is not part of a compound
6511 literal; the expression in an expression statement; the controlling expression of a selection
6512 statement (if or switch); the controlling expression of a while or do statement; each
6513 of the (optional) expressions of a for statement; the (optional) expression in a return
6514 statement. There is a sequence point between the evaluation of a full expression and the
6515 evaluation of the next full expression to be evaluated.
6516 Forward references: expression and null statements (6.8.3), selection statements
6517 (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4).
6518 6.8.1 Labeled statements
6520 1 labeled-statement:
6521 identifier : statement
6522 case constant-expression : statement
6525 2 A case or default label shall appear only in a switch statement. Further
6526 constraints on such labels are discussed under the switch statement.
6530 3 Label names shall be unique within a function.
6532 4 Any statement may be preceded by a prefix that declares an identifier as a label name.
6533 Labels in themselves do not alter the flow of control, which continues unimpeded across
6535 Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2).
6536 6.8.2 Compound statement
6538 1 compound-statement:
6539 { block-item-listopt }
6542 block-item-list block-item
6547 2 A compound statement is a block.
6548 6.8.3 Expression and null statements
6550 1 expression-statement:
6553 2 The expression in an expression statement is evaluated as a void expression for its side
6555 3 A null statement (consisting of just a semicolon) performs no operations.
6556 4 EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the
6557 discarding of its value may be made explicit by converting the expression to a void expression by means of
6565 153) Such as assignments, and function calls which have side effects.
6569 5 EXAMPLE 2 In the program fragment
6572 while (*s++ != '\0')
6574 a null statement is used to supply an empty loop body to the iteration statement.
6576 6 EXAMPLE 3 A null statement may also be used to carry a label just before the closing } of a compound
6590 Forward references: iteration statements (6.8.5).
6591 6.8.4 Selection statements
6593 1 selection-statement:
6594 if ( expression ) statement
6595 if ( expression ) statement else statement
6596 switch ( expression ) statement
6598 2 A selection statement selects among a set of statements depending on the value of a
6599 controlling expression.
6600 3 A selection statement is a block whose scope is a strict subset of the scope of its
6601 enclosing block. Each associated substatement is also a block whose scope is a strict
6602 subset of the scope of the selection statement.
6603 6.8.4.1 The if statement
6605 1 The controlling expression of an if statement shall have scalar type.
6607 2 In both forms, the first substatement is executed if the expression compares unequal to 0.
6608 In the else form, the second substatement is executed if the expression compares equal
6613 to 0. If the first substatement is reached via a label, the second substatement is not
6615 3 An else is associated with the lexically nearest preceding if that is allowed by the
6617 6.8.4.2 The switch statement
6619 1 The controlling expression of a switch statement shall have integer type.
6620 2 If a switch statement has an associated case or default label within the scope of an
6621 identifier with a variably modified type, the entire switch statement shall be within the
6622 scope of that identifier.154)
6623 3 The expression of each case label shall be an integer constant expression and no two of
6624 the case constant expressions in the same switch statement shall have the same value
6625 after conversion. There may be at most one default label in a switch statement.
6626 (Any enclosed switch statement may have a default label or case constant
6627 expressions with values that duplicate case constant expressions in the enclosing
6630 4 A switch statement causes control to jump to, into, or past the statement that is the
6631 switch body, depending on the value of a controlling expression, and on the presence of a
6632 default label and the values of any case labels on or in the switch body. A case or
6633 default label is accessible only within the closest enclosing switch statement.
6634 5 The integer promotions are performed on the controlling expression. The constant
6635 expression in each case label is converted to the promoted type of the controlling
6636 expression. If a converted value matches that of the promoted controlling expression,
6637 control jumps to the statement following the matched case label. Otherwise, if there is
6638 a default label, control jumps to the labeled statement. If no converted case constant
6639 expression matches and there is no default label, no part of the switch body is
6641 Implementation limits
6642 6 As discussed in 5.2.4.1, the implementation may limit the number of case values in a
6648 154) That is, the declaration either precedes the switch statement, or it follows the last case or
6649 default label associated with the switch that is in the block containing the declaration.
6653 7 EXAMPLE In the artificial program fragment
6660 /* falls through into default code */
6664 the object whose identifier is i exists with automatic storage duration (within the block) but is never
6665 initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will
6666 access an indeterminate value. Similarly, the call to the function f cannot be reached.
6668 6.8.5 Iteration statements
6670 1 iteration-statement:
6671 while ( expression ) statement
6672 do statement while ( expression ) ;
6673 for ( expressionopt ; expressionopt ; expressionopt ) statement
6674 for ( declaration expressionopt ; expressionopt ) statement
6676 2 The controlling expression of an iteration statement shall have scalar type.
6677 3 The declaration part of a for statement shall only declare identifiers for objects having
6678 storage class auto or register.
6680 4 An iteration statement causes a statement called the loop body to be executed repeatedly
6681 until the controlling expression compares equal to 0. The repetition occurs regardless of
6682 whether the loop body is entered from the iteration statement or by a jump.155)
6683 5 An iteration statement is a block whose scope is a strict subset of the scope of its
6684 enclosing block. The loop body is also a block whose scope is a strict subset of the scope
6685 of the iteration statement.
6686 6 An iteration statement whose controlling expression is not a constant expression,156) that
6687 performs no input/output operations, does not access volatile objects, and performs no
6688 synchronization or atomic operations in its body, controlling expression, or (in the case of
6690 155) Code jumped over is not executed. In particular, the controlling expression of a for or while
6691 statement is not evaluated before entering the loop body, nor is clause-1 of a for statement.
6692 156) An omitted controlling expression is replaced by a nonzero constant, which is a constant expression.
6696 a for statement) its expression-3, may be assumed by the implementation to
6698 6.8.5.1 The while statement
6699 1 The evaluation of the controlling expression takes place before each execution of the loop
6701 6.8.5.2 The do statement
6702 1 The evaluation of the controlling expression takes place after each execution of the loop
6704 6.8.5.3 The for statement
6706 for ( clause-1 ; expression-2 ; expression-3 ) statement
6707 behaves as follows: The expression expression-2 is the controlling expression that is
6708 evaluated before each execution of the loop body. The expression expression-3 is
6709 evaluated as a void expression after each execution of the loop body. If clause-1 is a
6710 declaration, the scope of any identifiers it declares is the remainder of the declaration and
6711 the entire loop, including the other two expressions; it is reached in the order of execution
6712 before the first evaluation of the controlling expression. If clause-1 is an expression, it is
6713 evaluated as a void expression before the first evaluation of the controlling expression.158)
6714 2 Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a
6716 6.8.6 Jump statements
6722 return expressionopt ;
6727 157) This is intended to allow compiler transformations such as removal of empty loops even when
6728 termination cannot be proven.
6729 158) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in
6730 the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration,
6731 such that execution of the loop continues until the expression compares equal to 0; and expression-3
6732 specifies an operation (such as incrementing) that is performed after each iteration.
6737 2 A jump statement causes an unconditional jump to another place.
6738 6.8.6.1 The goto statement
6740 1 The identifier in a goto statement shall name a label located somewhere in the enclosing
6741 function. A goto statement shall not jump from outside the scope of an identifier having
6742 a variably modified type to inside the scope of that identifier.
6744 2 A goto statement causes an unconditional jump to the statement prefixed by the named
6745 label in the enclosing function.
6746 3 EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The
6747 following outline presents one possible approach to a problem based on these three assumptions:
6748 1. The general initialization code accesses objects only visible to the current function.
6749 2. The general initialization code is too large to warrant duplication.
6750 3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by
6751 continue statements, for example.)
6755 // determine next operation
6757 if (need to reinitialize) {
6758 // reinitialize-only code
6761 // general initialization code
6765 // handle other operations
6774 4 EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably
6775 modified types. A jump within the scope, however, is permitted.
6776 goto lab3; // invalid: going INTO scope of VLA.
6782 goto lab4; // valid: going WITHIN scope of VLA.
6787 goto lab4; // invalid: going INTO scope of VLA.
6789 6.8.6.2 The continue statement
6791 1 A continue statement shall appear only in or as a loop body.
6793 2 A continue statement causes a jump to the loop-continuation portion of the smallest
6794 enclosing iteration statement; that is, to the end of the loop body. More precisely, in each
6796 while (/* ... */) { do { for (/* ... */) {
6797 /* ... */ /* ... */ /* ... */
6798 continue; continue; continue;
6799 /* ... */ /* ... */ /* ... */
6800 contin: ; contin: ; contin: ;
6801 } } while (/* ... */); }
6802 unless the continue statement shown is in an enclosed iteration statement (in which
6803 case it is interpreted within that statement), it is equivalent to goto contin;.159)
6804 6.8.6.3 The break statement
6806 1 A break statement shall appear only in or as a switch body or loop body.
6808 2 A break statement terminates execution of the smallest enclosing switch or iteration
6813 159) Following the contin: label is a null statement.
6817 6.8.6.4 The return statement
6819 1 A return statement with an expression shall not appear in a function whose return type
6820 is void. A return statement without an expression shall only appear in a function
6821 whose return type is void.
6823 2 A return statement terminates execution of the current function and returns control to
6824 its caller. A function may have any number of return statements.
6825 3 If a return statement with an expression is executed, the value of the expression is
6826 returned to the caller as the value of the function call expression. If the expression has a
6827 type different from the return type of the function in which it appears, the value is
6828 converted as if by assignment to an object having the return type of the function.160)
6830 struct s { double i; } f(void);
6847 there is no undefined behavior, although there would be if the assignment were done directly (without using
6848 a function call to fetch the value).
6853 160) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not
6854 apply to the case of function return. The representation of floating-point values may have wider range
6855 or precision than implied by the type; a cast may be used to remove this extra range and precision.
6859 6.9 External definitions
6862 external-declaration
6863 translation-unit external-declaration
6864 external-declaration:
6868 2 The storage-class specifiers auto and register shall not appear in the declaration
6869 specifiers in an external declaration.
6870 3 There shall be no more than one external definition for each identifier declared with
6871 internal linkage in a translation unit. Moreover, if an identifier declared with internal
6872 linkage is used in an expression (other than as a part of the operand of a sizeof
6873 operator whose result is an integer constant), there shall be exactly one external definition
6874 for the identifier in the translation unit.
6876 4 As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit,
6877 which consists of a sequence of external declarations. These are described as ''external''
6878 because they appear outside any function (and hence have file scope). As discussed in
6879 6.7, a declaration that also causes storage to be reserved for an object or a function named
6880 by the identifier is a definition.
6881 5 An external definition is an external declaration that is also a definition of a function
6882 (other than an inline definition) or an object. If an identifier declared with external
6883 linkage is used in an expression (other than as part of the operand of a sizeof operator
6884 whose result is an integer constant), somewhere in the entire program there shall be
6885 exactly one external definition for the identifier; otherwise, there shall be no more than
6891 161) Thus, if an identifier declared with external linkage is not used in an expression, there need be no
6892 external definition for it.
6896 6.9.1 Function definitions
6898 1 function-definition:
6899 declaration-specifiers declarator declaration-listopt compound-statement
6902 declaration-list declaration
6904 2 The identifier declared in a function definition (which is the name of the function) shall
6905 have a function type, as specified by the declarator portion of the function definition.162)
6906 3 The return type of a function shall be void or a complete object type other than array
6908 4 The storage-class specifier, if any, in the declaration specifiers shall be either extern or
6910 5 If the declarator includes a parameter type list, the declaration of each parameter shall
6911 include an identifier, except for the special case of a parameter list consisting of a single
6912 parameter of type void, in which case there shall not be an identifier. No declaration list
6914 6 If the declarator includes an identifier list, each declaration in the declaration list shall
6915 have at least one declarator, those declarators shall declare only identifiers from the
6916 identifier list, and every identifier in the identifier list shall be declared. An identifier
6917 declared as a typedef name shall not be redeclared as a parameter. The declarations in the
6918 declaration list shall contain no storage-class specifier other than register and no
6923 162) The intent is that the type category in a function definition cannot be inherited from a typedef:
6924 typedef int F(void); // type F is ''function with no parameters
6926 F f, g; // f and g both have type compatible with F
6927 F f { /* ... */ } // WRONG: syntax/constraint error
6928 F g() { /* ... */ } // WRONG: declares that g returns a function
6929 int f(void) { /* ... */ } // RIGHT: f has type compatible with F
6930 int g() { /* ... */ } // RIGHT: g has type compatible with F
6931 F *e(void) { /* ... */ } // e returns a pointer to a function
6932 F *((e))(void) { /* ... */ } // same: parentheses irrelevant
6933 int (*fp)(void); // fp points to a function that has type F
6934 F *Fp; // Fp points to a function that has type F
6940 7 The declarator in a function definition specifies the name of the function being defined
6941 and the identifiers of its parameters. If the declarator includes a parameter type list, the
6942 list also specifies the types of all the parameters; such a declarator also serves as a
6943 function prototype for later calls to the same function in the same translation unit. If the
6944 declarator includes an identifier list,163) the types of the parameters shall be declared in a
6945 following declaration list. In either case, the type of each parameter is adjusted as
6946 described in 6.7.6.3 for a parameter type list; the resulting type shall be a complete object
6948 8 If a function that accepts a variable number of arguments is defined without a parameter
6949 type list that ends with the ellipsis notation, the behavior is undefined.
6950 9 Each parameter has automatic storage duration; its identifier is an lvalue.164) The layout
6951 of the storage for parameters is unspecified.
6952 10 On entry to the function, the size expressions of each variably modified parameter are
6953 evaluated and the value of each argument expression is converted to the type of the
6954 corresponding parameter as if by assignment. (Array expressions and function
6955 designators as arguments were converted to pointers before the call.)
6956 11 After all parameters have been assigned, the compound statement that constitutes the
6957 body of the function definition is executed.
6958 12 If the } that terminates a function is reached, and the value of the function call is used by
6959 the caller, the behavior is undefined.
6960 13 EXAMPLE 1 In the following:
6961 extern int max(int a, int b)
6963 return a > b ? a : b;
6965 extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the
6966 function declarator; and
6967 { return a > b ? a : b; }
6968 is the function body. The following similar definition uses the identifier-list form for the parameter
6974 163) See ''future language directions'' (6.11.7).
6975 164) A parameter identifier cannot be redeclared in the function body except in an enclosed block.
6979 extern int max(a, b)
6982 return a > b ? a : b;
6984 Here int a, b; is the declaration list for the parameters. The difference between these two definitions is
6985 that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls
6986 to the function, whereas the second form does not.
6988 14 EXAMPLE 2 To pass one function to another, one might say
6992 Then the definition of g might read
6993 void g(int (*funcp)(void))
6996 (*funcp)(); /* or funcp(); ... */
6999 void g(int func(void))
7002 func(); /* or (*func)(); ... */
7005 6.9.2 External object definitions
7007 1 If the declaration of an identifier for an object has file scope and an initializer, the
7008 declaration is an external definition for the identifier.
7009 2 A declaration of an identifier for an object that has file scope without an initializer, and
7010 without a storage-class specifier or with the storage-class specifier static, constitutes a
7011 tentative definition. If a translation unit contains one or more tentative definitions for an
7012 identifier, and the translation unit contains no external definition for that identifier, then
7013 the behavior is exactly as if the translation unit contains a file scope declaration of that
7014 identifier, with the composite type as of the end of the translation unit, with an initializer
7016 3 If the declaration of an identifier for an object is a tentative definition and has internal
7017 linkage, the declared type shall not be an incomplete type.
7025 int i1 = 1; // definition, external linkage
7026 static int i2 = 2; // definition, internal linkage
7027 extern int i3 = 3; // definition, external linkage
7028 int i4; // tentative definition, external linkage
7029 static int i5; // tentative definition, internal linkage
7030 int i1; // valid tentative definition, refers to previous
7031 int i2; // 6.2.2 renders undefined, linkage disagreement
7032 int i3; // valid tentative definition, refers to previous
7033 int i4; // valid tentative definition, refers to previous
7034 int i5; // 6.2.2 renders undefined, linkage disagreement
7035 extern int i1; // refers to previous, whose linkage is external
7036 extern int i2; // refers to previous, whose linkage is internal
7037 extern int i3; // refers to previous, whose linkage is external
7038 extern int i4; // refers to previous, whose linkage is external
7039 extern int i5; // refers to previous, whose linkage is internal
7041 5 EXAMPLE 2 If at the end of the translation unit containing
7043 the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to
7044 zero on program startup.
7051 6.10 Preprocessing directives
7053 1 preprocessing-file:
7064 if-group elif-groupsopt else-groupopt endif-line
7066 # if constant-expression new-line groupopt
7067 # ifdef identifier new-line groupopt
7068 # ifndef identifier new-line groupopt
7071 elif-groups elif-group
7073 # elif constant-expression new-line groupopt
7075 # else new-line groupopt
7085 # include pp-tokens new-line
7086 # define identifier replacement-list new-line
7087 # define identifier lparen identifier-listopt )
7088 replacement-list new-line
7089 # define identifier lparen ... ) replacement-list new-line
7090 # define identifier lparen identifier-list , ... )
7091 replacement-list new-line
7092 # undef identifier new-line
7093 # line pp-tokens new-line
7094 # error pp-tokensopt new-line
7095 # pragma pp-tokensopt new-line
7098 pp-tokensopt new-line
7102 a ( character not immediately preceded by white-space
7107 pp-tokens preprocessing-token
7109 the new-line character
7111 2 A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the
7112 following constraints: The first token in the sequence is a # preprocessing token that (at
7113 the start of translation phase 4) is either the first character in the source file (optionally
7114 after white space containing no new-line characters) or that follows white space
7115 containing at least one new-line character. The last token in the sequence is the first new-
7116 line character that follows the first token in the sequence.165) A new-line character ends
7117 the preprocessing directive even if it occurs within what would otherwise be an
7119 165) Thus, preprocessing directives are commonly called ''lines''. These ''lines'' have no other syntactic
7120 significance, as all white space is equivalent except in certain situations during preprocessing (see the
7121 # character string literal creation operator in 6.10.3.2, for example).
7125 invocation of a function-like macro.
7126 3 A text line shall not begin with a # preprocessing token. A non-directive shall not begin
7127 with any of the directive names appearing in the syntax.
7128 4 When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any
7129 sequence of preprocessing tokens to occur between the directive name and the following
7132 5 The only white-space characters that shall appear between preprocessing tokens within a
7133 preprocessing directive (from just after the introducing # preprocessing token through
7134 just before the terminating new-line character) are space and horizontal-tab (including
7135 spaces that have replaced comments or possibly other white-space characters in
7136 translation phase 3).
7138 6 The implementation can process and skip sections of source files conditionally, include
7139 other source files, and replace macros. These capabilities are called preprocessing,
7140 because conceptually they occur before translation of the resulting translation unit.
7141 7 The preprocessing tokens within a preprocessing directive are not subject to macro
7142 expansion unless otherwise stated.
7145 EMPTY # include <file.h>
7146 the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not
7147 begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been
7150 6.10.1 Conditional inclusion
7152 1 The expression that controls conditional inclusion shall be an integer constant expression
7153 except that: identifiers (including those lexically identical to keywords) are interpreted as *
7154 described below;166) and it may contain unary operator expressions of the form
7157 defined ( identifier )
7158 which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is
7161 166) Because the controlling constant expression is evaluated during translation phase 4, all identifiers
7162 either are or are not macro names -- there simply are no keywords, enumeration constants, etc.
7166 predefined or if it has been the subject of a #define preprocessing directive without an
7167 intervening #undef directive with the same subject identifier), 0 if it is not.
7168 2 Each preprocessing token that remains (in the list of preprocessing tokens that will
7169 become the controlling expression) after all macro replacements have occurred shall be in
7170 the lexical form of a token (6.4).
7172 3 Preprocessing directives of the forms
7173 # if constant-expression new-line groupopt
7174 # elif constant-expression new-line groupopt
7175 check whether the controlling constant expression evaluates to nonzero.
7176 4 Prior to evaluation, macro invocations in the list of preprocessing tokens that will become
7177 the controlling constant expression are replaced (except for those macro names modified
7178 by the defined unary operator), just as in normal text. If the token defined is
7179 generated as a result of this replacement process or use of the defined unary operator
7180 does not match one of the two specified forms prior to macro replacement, the behavior is
7181 undefined. After all replacements due to macro expansion and the defined unary
7182 operator have been performed, all remaining identifiers (including those lexically
7183 identical to keywords) are replaced with the pp-number 0, and then each preprocessing
7184 token is converted into a token. The resulting tokens compose the controlling constant
7185 expression which is evaluated according to the rules of 6.6. For the purposes of this
7186 token conversion and evaluation, all signed integer types and all unsigned integer types
7187 act as if they have the same representation as, respectively, the types intmax_t and
7188 uintmax_t defined in the header <stdint.h>.167) This includes interpreting
7189 character constants, which may involve converting escape sequences into execution
7190 character set members. Whether the numeric value for these character constants matches
7191 the value obtained when an identical character constant occurs in an expression (other
7192 than within a #if or #elif directive) is implementation-defined.168) Also, whether a
7193 single-character character constant may have a negative value is implementation-defined.
7198 167) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant
7199 0x8000 is signed and positive within a #if expression even though it would be unsigned in
7200 translation phase 7.
7201 168) Thus, the constant expression in the following #if directive and if statement is not guaranteed to
7202 evaluate to the same value in these two contexts.
7204 if ('z' - 'a' == 25)
7209 5 Preprocessing directives of the forms
7210 # ifdef identifier new-line groupopt
7211 # ifndef identifier new-line groupopt
7212 check whether the identifier is or is not currently defined as a macro name. Their
7213 conditions are equivalent to #if defined identifier and #if !defined identifier
7215 6 Each directive's condition is checked in order. If it evaluates to false (zero), the group
7216 that it controls is skipped: directives are processed only through the name that determines
7217 the directive in order to keep track of the level of nested conditionals; the rest of the
7218 directives' preprocessing tokens are ignored, as are the other preprocessing tokens in the
7219 group. Only the first group whose control condition evaluates to true (nonzero) is
7220 processed. If none of the conditions evaluates to true, and there is a #else directive, the
7221 group controlled by the #else is processed; lacking a #else directive, all the groups
7222 until the #endif are skipped.169)
7223 Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest
7224 integer types (7.20.1.5).
7225 6.10.2 Source file inclusion
7227 1 A #include directive shall identify a header or source file that can be processed by the
7230 2 A preprocessing directive of the form
7231 # include <h-char-sequence> new-line
7232 searches a sequence of implementation-defined places for a header identified uniquely by
7233 the specified sequence between the < and > delimiters, and causes the replacement of that
7234 directive by the entire contents of the header. How the places are specified or the header
7235 identified is implementation-defined.
7236 3 A preprocessing directive of the form
7237 # include "q-char-sequence" new-line
7238 causes the replacement of that directive by the entire contents of the source file identified
7239 by the specified sequence between the " delimiters. The named source file is searched
7242 169) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive
7243 before the terminating new-line character. However, comments may appear anywhere in a source file,
7244 including within a preprocessing directive.
7248 for in an implementation-defined manner. If this search is not supported, or if the search
7249 fails, the directive is reprocessed as if it read
7250 # include <h-char-sequence> new-line
7251 with the identical contained sequence (including > characters, if any) from the original
7253 4 A preprocessing directive of the form
7254 # include pp-tokens new-line
7255 (that does not match one of the two previous forms) is permitted. The preprocessing
7256 tokens after include in the directive are processed just as in normal text. (Each
7257 identifier currently defined as a macro name is replaced by its replacement list of
7258 preprocessing tokens.) The directive resulting after all replacements shall match one of
7259 the two previous forms.170) The method by which a sequence of preprocessing tokens
7260 between a < and a > preprocessing token pair or a pair of " characters is combined into a
7261 single header name preprocessing token is implementation-defined.
7262 5 The implementation shall provide unique mappings for sequences consisting of one or
7263 more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The
7264 first character shall not be a digit. The implementation may ignore distinctions of
7265 alphabetical case and restrict the mapping to eight significant characters before the
7267 6 A #include preprocessing directive may appear in a source file that has been read
7268 because of a #include directive in another file, up to an implementation-defined
7269 nesting limit (see 5.2.4.1).
7270 7 EXAMPLE 1 The most common uses of #include preprocessing directives are as in the following:
7277 170) Note that adjacent string literals are not concatenated into a single string literal (see the translation
7278 phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive.
7282 8 EXAMPLE 2 This illustrates macro-replaced #include directives:
7284 #define INCFILE "vers1.h"
7286 #define INCFILE "vers2.h" // and so on
7288 #define INCFILE "versN.h"
7292 Forward references: macro replacement (6.10.3).
7293 6.10.3 Macro replacement
7295 1 Two replacement lists are identical if and only if the preprocessing tokens in both have
7296 the same number, ordering, spelling, and white-space separation, where all white-space
7297 separations are considered identical.
7298 2 An identifier currently defined as an object-like macro shall not be redefined by another
7299 #define preprocessing directive unless the second definition is an object-like macro
7300 definition and the two replacement lists are identical. Likewise, an identifier currently
7301 defined as a function-like macro shall not be redefined by another #define
7302 preprocessing directive unless the second definition is a function-like macro definition
7303 that has the same number and spelling of parameters, and the two replacement lists are
7305 3 There shall be white-space between the identifier and the replacement list in the definition
7306 of an object-like macro.
7307 4 If the identifier-list in the macro definition does not end with an ellipsis, the number of
7308 arguments (including those arguments consisting of no preprocessing tokens) in an
7309 invocation of a function-like macro shall equal the number of parameters in the macro
7310 definition. Otherwise, there shall be more arguments in the invocation than there are
7311 parameters in the macro definition (excluding the ...). There shall exist a )
7312 preprocessing token that terminates the invocation.
7313 5 The identifier __VA_ARGS__ shall occur only in the replacement-list of a function-like
7314 macro that uses the ellipsis notation in the parameters.
7315 6 A parameter identifier in a function-like macro shall be uniquely declared within its
7318 7 The identifier immediately following the define is called the macro name. There is one
7319 name space for macro names. Any white-space characters preceding or following the
7320 replacement list of preprocessing tokens are not considered part of the replacement list
7324 for either form of macro.
7325 8 If a # preprocessing token, followed by an identifier, occurs lexically at the point at which
7326 a preprocessing directive could begin, the identifier is not subject to macro replacement.
7327 9 A preprocessing directive of the form
7328 # define identifier replacement-list new-line
7329 defines an object-like macro that causes each subsequent instance of the macro name171)
7330 to be replaced by the replacement list of preprocessing tokens that constitute the
7331 remainder of the directive. The replacement list is then rescanned for more macro names
7333 10 A preprocessing directive of the form
7334 # define identifier lparen identifier-listopt ) replacement-list new-line
7335 # define identifier lparen ... ) replacement-list new-line
7336 # define identifier lparen identifier-list , ... ) replacement-list new-line
7337 defines a function-like macro with parameters, whose use is similar syntactically to a
7338 function call. The parameters are specified by the optional list of identifiers, whose scope
7339 extends from their declaration in the identifier list until the new-line character that
7340 terminates the #define preprocessing directive. Each subsequent instance of the
7341 function-like macro name followed by a ( as the next preprocessing token introduces the
7342 sequence of preprocessing tokens that is replaced by the replacement list in the definition
7343 (an invocation of the macro). The replaced sequence of preprocessing tokens is
7344 terminated by the matching ) preprocessing token, skipping intervening matched pairs of
7345 left and right parenthesis preprocessing tokens. Within the sequence of preprocessing
7346 tokens making up an invocation of a function-like macro, new-line is considered a normal
7347 white-space character.
7348 11 The sequence of preprocessing tokens bounded by the outside-most matching parentheses
7349 forms the list of arguments for the function-like macro. The individual arguments within
7350 the list are separated by comma preprocessing tokens, but comma preprocessing tokens
7351 between matching inner parentheses do not separate arguments. If there are sequences of
7352 preprocessing tokens within the list of arguments that would otherwise act as
7353 preprocessing directives,172) the behavior is undefined.
7354 12 If there is a ... in the identifier-list in the macro definition, then the trailing arguments,
7355 including any separating comma preprocessing tokens, are merged to form a single item:
7358 171) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens,
7359 not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they
7360 are never scanned for macro names or parameters.
7361 172) Despite the name, a non-directive is a preprocessing directive.
7365 the variable arguments. The number of arguments so combined is such that, following
7366 merger, the number of arguments is one more than the number of parameters in the macro
7367 definition (excluding the ...).
7368 6.10.3.1 Argument substitution
7369 1 After the arguments for the invocation of a function-like macro have been identified,
7370 argument substitution takes place. A parameter in the replacement list, unless preceded
7371 by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is
7372 replaced by the corresponding argument after all macros contained therein have been
7373 expanded. Before being substituted, each argument's preprocessing tokens are
7374 completely macro replaced as if they formed the rest of the preprocessing file; no other
7375 preprocessing tokens are available.
7376 2 An identifier __VA_ARGS__ that occurs in the replacement list shall be treated as if it
7377 were a parameter, and the variable arguments shall form the preprocessing tokens used to
7379 6.10.3.2 The # operator
7381 1 Each # preprocessing token in the replacement list for a function-like macro shall be
7382 followed by a parameter as the next preprocessing token in the replacement list.
7384 2 If, in the replacement list, a parameter is immediately preceded by a # preprocessing
7385 token, both are replaced by a single character string literal preprocessing token that
7386 contains the spelling of the preprocessing token sequence for the corresponding
7387 argument. Each occurrence of white space between the argument's preprocessing tokens
7388 becomes a single space character in the character string literal. White space before the
7389 first preprocessing token and after the last preprocessing token composing the argument
7390 is deleted. Otherwise, the original spelling of each preprocessing token in the argument
7391 is retained in the character string literal, except for special handling for producing the
7392 spelling of string literals and character constants: a \ character is inserted before each "
7393 and \ character of a character constant or string literal (including the delimiting "
7394 characters), except that it is implementation-defined whether a \ character is inserted
7395 before the \ character beginning a universal character name. If the replacement that
7396 results is not a valid character string literal, the behavior is undefined. The character
7397 string literal corresponding to an empty argument is "". The order of evaluation of # and
7398 ## operators is unspecified.
7405 6.10.3.3 The ## operator
7407 1 A ## preprocessing token shall not occur at the beginning or at the end of a replacement
7408 list for either form of macro definition.
7410 2 If, in the replacement list of a function-like macro, a parameter is immediately preceded
7411 or followed by a ## preprocessing token, the parameter is replaced by the corresponding
7412 argument's preprocessing token sequence; however, if an argument consists of no
7413 preprocessing tokens, the parameter is replaced by a placemarker preprocessing token
7415 3 For both object-like and function-like macro invocations, before the replacement list is
7416 reexamined for more macro names to replace, each instance of a ## preprocessing token
7417 in the replacement list (not from an argument) is deleted and the preceding preprocessing
7418 token is concatenated with the following preprocessing token. Placemarker
7419 preprocessing tokens are handled specially: concatenation of two placemarkers results in
7420 a single placemarker preprocessing token, and concatenation of a placemarker with a
7421 non-placemarker preprocessing token results in the non-placemarker preprocessing token.
7422 If the result is not a valid preprocessing token, the behavior is undefined. The resulting
7423 token is available for further macro replacement. The order of evaluation of ## operators
7425 4 EXAMPLE In the following fragment:
7426 #define hash_hash # ## #
7427 #define mkstr(a) # a
7428 #define in_between(a) mkstr(a)
7429 #define join(c, d) in_between(c hash_hash d)
7430 char p[] = join(x, y); // equivalent to
7431 // char p[] = "x ## y";
7432 The expansion produces, at various stages:
7434 in_between(x hash_hash y)
7438 In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but
7439 this new token is not the ## operator.
7442 173) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that
7443 exist only within translation phase 4.
7447 6.10.3.4 Rescanning and further replacement
7448 1 After all parameters in the replacement list have been substituted and # and ##
7449 processing has taken place, all placemarker preprocessing tokens are removed. The
7450 resulting preprocessing token sequence is then rescanned, along with all subsequent
7451 preprocessing tokens of the source file, for more macro names to replace.
7452 2 If the name of the macro being replaced is found during this scan of the replacement list
7453 (not including the rest of the source file's preprocessing tokens), it is not replaced.
7454 Furthermore, if any nested replacements encounter the name of the macro being replaced,
7455 it is not replaced. These nonreplaced macro name preprocessing tokens are no longer
7456 available for further replacement even if they are later (re)examined in contexts in which
7457 that macro name preprocessing token would otherwise have been replaced.
7458 3 The resulting completely macro-replaced preprocessing token sequence is not processed
7459 as a preprocessing directive even if it resembles one, but all pragma unary operator
7460 expressions within it are then processed as specified in 6.10.9 below.
7461 6.10.3.5 Scope of macro definitions
7462 1 A macro definition lasts (independent of block structure) until a corresponding #undef
7463 directive is encountered or (if none is encountered) until the end of the preprocessing
7464 translation unit. Macro definitions have no significance after translation phase 4.
7465 2 A preprocessing directive of the form
7466 # undef identifier new-line
7467 causes the specified identifier no longer to be defined as a macro name. It is ignored if
7468 the specified identifier is not currently defined as a macro name.
7469 3 EXAMPLE 1 The simplest use of this facility is to define a ''manifest constant'', as in
7473 4 EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments.
7474 It has the advantages of working for any compatible types of the arguments and of generating in-line code
7475 without the overhead of function calling. It has the disadvantages of evaluating one or the other of its
7476 arguments a second time (including side effects) and generating more code than a function if invoked
7477 several times. It also cannot have its address taken, as it has none.
7478 #define max(a, b) ((a) > (b) ? (a) : (b))
7479 The parentheses ensure that the arguments and the resulting expression are bound properly.
7486 5 EXAMPLE 3 To illustrate the rules for redefinition and reexamination, the sequence
7488 #define f(a) f(x * (a))
7499 #define r(x,y) x ## y
7501 f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
7502 g(x+(3,4)-w) | h 5) & m
7504 p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
7505 char c[2][6] = { str(hello), str() };
7507 f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
7508 f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
7509 int i[] = { 1, 23, 4, 5, };
7510 char c[2][6] = { "hello", "" };
7512 6 EXAMPLE 4 To illustrate the rules for creating character string literals and concatenating tokens, the
7515 #define xstr(s) str(s)
7516 #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
7518 #define INCFILE(n) vers ## n
7519 #define glue(a, b) a ## b
7520 #define xglue(a, b) glue(a, b)
7521 #define HIGHLOW "hello"
7522 #define LOW LOW ", world"
7524 fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
7525 == 0) str(: @\n), s);
7526 #include xstr(INCFILE(2).h)
7536 printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
7538 "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
7540 #include "vers2.h" (after macro replacement, before file access)
7543 or, after concatenation of the character string literals,
7544 printf("x1= %d, x2= %s", x1, x2);
7546 "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
7548 #include "vers2.h" (after macro replacement, before file access)
7551 Space around the # and ## tokens in the macro definition is optional.
7553 7 EXAMPLE 5 To illustrate the rules for placemarker preprocessing tokens, the sequence
7554 #define t(x,y,z) x ## y ## z
7555 int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
7556 t(10,,), t(,11,), t(,,12), t(,,) };
7558 int j[] = { 123, 45, 67, 89,
7561 8 EXAMPLE 6 To demonstrate the redefinition rules, the following sequence is valid.
7562 #define OBJ_LIKE (1-1)
7563 #define OBJ_LIKE /* white space */ (1-1) /* other */
7564 #define FUNC_LIKE(a) ( a )
7565 #define FUNC_LIKE( a )( /* note the white space */ \
7566 a /* other stuff on this line
7568 But the following redefinitions are invalid:
7569 #define OBJ_LIKE (0) // different token sequence
7570 #define OBJ_LIKE (1 - 1) // different white space
7571 #define FUNC_LIKE(b) ( a ) // different parameter usage
7572 #define FUNC_LIKE(b) ( b ) // different parameter spelling
7574 9 EXAMPLE 7 Finally, to show the variable argument list macro facilities:
7575 #define debug(...) fprintf(stderr, __VA_ARGS__)
7576 #define showlist(...) puts(#__VA_ARGS__)
7577 #define report(test, ...) ((test)?puts(#test):\
7578 printf(__VA_ARGS__))
7580 debug("X = %d\n", x);
7581 showlist(The first, second, and third items.);
7582 report(x>y, "x is %d but y is %d", x, y);
7588 fprintf(stderr, "Flag" );
7589 fprintf(stderr, "X = %d\n", x );
7590 puts( "The first, second, and third items." );
7592 printf("x is %d but y is %d", x, y));
7596 1 The string literal of a #line directive, if present, shall be a character string literal.
7598 2 The line number of the current source line is one greater than the number of new-line
7599 characters read or introduced in translation phase 1 (5.1.1.2) while processing the source
7600 file to the current token.
7601 3 A preprocessing directive of the form
7602 # line digit-sequence new-line
7603 causes the implementation to behave as if the following sequence of source lines begins
7604 with a source line that has a line number as specified by the digit sequence (interpreted as
7605 a decimal integer). The digit sequence shall not specify zero, nor a number greater than
7607 4 A preprocessing directive of the form
7608 # line digit-sequence "s-char-sequenceopt" new-line
7609 sets the presumed line number similarly and changes the presumed name of the source
7610 file to be the contents of the character string literal.
7611 5 A preprocessing directive of the form
7612 # line pp-tokens new-line
7613 (that does not match one of the two previous forms) is permitted. The preprocessing
7614 tokens after line on the directive are processed just as in normal text (each identifier
7615 currently defined as a macro name is replaced by its replacement list of preprocessing
7616 tokens). The directive resulting after all replacements shall match one of the two
7617 previous forms and is then processed as appropriate.
7624 6.10.5 Error directive
7626 1 A preprocessing directive of the form
7627 # error pp-tokensopt new-line
7628 causes the implementation to produce a diagnostic message that includes the specified
7629 sequence of preprocessing tokens.
7630 6.10.6 Pragma directive
7632 1 A preprocessing directive of the form
7633 # pragma pp-tokensopt new-line
7634 where the preprocessing token STDC does not immediately follow pragma in the
7635 directive (prior to any macro replacement)174) causes the implementation to behave in an
7636 implementation-defined manner. The behavior might cause translation to fail or cause the
7637 translator or the resulting program to behave in a non-conforming manner. Any such
7638 pragma that is not recognized by the implementation is ignored.
7639 2 If the preprocessing token STDC does immediately follow pragma in the directive (prior
7640 to any macro replacement), then no macro replacement is performed on the directive, and
7641 the directive shall have one of the following forms175) whose meanings are described
7643 #pragma STDC FP_CONTRACT on-off-switch
7644 #pragma STDC FENV_ACCESS on-off-switch
7645 #pragma STDC CX_LIMITED_RANGE on-off-switch
7646 on-off-switch: one of
7648 Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma
7649 (7.6.1), the CX_LIMITED_RANGE pragma (7.3.4).
7654 174) An implementation is not required to perform macro replacement in pragmas, but it is permitted
7655 except for in standard pragmas (where STDC immediately follows pragma). If the result of macro
7656 replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still
7657 implementation-defined; an implementation is permitted to behave as if it were the standard pragma,
7658 but is not required to.
7659 175) See ''future language directions'' (6.11.8).
7663 6.10.7 Null directive
7665 1 A preprocessing directive of the form
7668 6.10.8 Predefined macro names
7669 1 The values of the predefined macros listed in the following subclauses176) (except for
7670 __FILE__ and __LINE__) remain constant throughout the translation unit.
7671 2 None of these macro names, nor the identifier defined, shall be the subject of a
7672 #define or a #undef preprocessing directive. Any other predefined macro names
7673 shall begin with a leading underscore followed by an uppercase letter or a second
7675 3 The implementation shall not predefine the macro __cplusplus, nor shall it define it
7676 in any standard header.
7677 Forward references: standard headers (7.1.2).
7678 6.10.8.1 Mandatory macros
7679 1 The following macro names shall be defined by the implementation:
7680 __DATE__ The date of translation of the preprocessing translation unit: a character
7681 string literal of the form "Mmm dd yyyy", where the names of the
7682 months are the same as those generated by the asctime function, and the
7683 first character of dd is a space character if the value is less than 10. If the
7684 date of translation is not available, an implementation-defined valid date
7686 __FILE__ The presumed name of the current source file (a character string literal).177)
7687 __LINE__ The presumed line number (within the current source file) of the current
7688 source line (an integer constant).177)
7689 __STDC__ The integer constant 1, intended to indicate a conforming implementation.
7690 __STDC_HOSTED__ The integer constant 1 if the implementation is a hosted
7691 implementation or the integer constant 0 if it is not.
7696 176) See ''future language directions'' (6.11.9).
7697 177) The presumed source file name and line number can be changed by the #line directive.
7701 __STDC_VERSION__ The integer constant 201ymmL.178)
7702 __TIME__ The time of translation of the preprocessing translation unit: a character
7703 string literal of the form "hh:mm:ss" as in the time generated by the
7704 asctime function. If the time of translation is not available, an
7705 implementation-defined valid time shall be supplied.
7706 Forward references: the asctime function (7.26.3.1).
7707 6.10.8.2 Environment macros
7708 1 The following macro names are conditionally defined by the implementation:
7709 __STDC_ISO_10646__ An integer constant of the form yyyymmL (for example,
7710 199712L). If this symbol is defined, then every character in the Unicode
7711 required set, when stored in an object of type wchar_t, has the same
7712 value as the short identifier of that character. The Unicode required set
7713 consists of all the characters that are defined by ISO/IEC 10646, along with
7714 all amendments and technical corrigenda, as of the specified year and
7715 month. If some other encoding is used, the macro shall not be defined and
7716 the actual encoding used is implementation-defined.
7717 __STDC_MB_MIGHT_NEQ_WC__ The integer constant 1, intended to indicate that, in
7718 the encoding for wchar_t, a member of the basic character set need not
7719 have a code value equal to its value when used as the lone character in an
7720 integer character constant.
7721 __STDC_UTF_16__ The integer constant 1, intended to indicate that values of type
7722 char16_t are UTF-16 encoded. If some other encoding is used, the
7723 macro shall not be defined and the actual encoding used is implementation-
7725 __STDC_UTF_32__ The integer constant 1, intended to indicate that values of type
7726 char32_t are UTF-32 encoded. If some other encoding is used, the
7727 macro shall not be defined and the actual encoding used is implementation-
7729 Forward references: common definitions (7.19), unicode utilities (7.27).
7734 178) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in
7735 ISO/IEC 9899/AMD1:1995 and as 199901L in ISO/IEC 9899:1999. The intention is that this will
7736 remain an integer constant of type long int that is increased with each revision of this International
7741 6.10.8.3 Conditional feature macros
7742 1 The following macro names are conditionally defined by the implementation:
7743 __STDC_ANALYZABLE__ The integer constant 1, intended to indicate conformance to
7744 the specifications in annex L (Analyzability).
7745 __STDC_IEC_559__ The integer constant 1, intended to indicate conformance to the
7746 specifications in annex F (IEC 60559 floating-point arithmetic).
7747 __STDC_IEC_559_COMPLEX__ The integer constant 1, intended to indicate
7748 adherence to the specifications in annex G (IEC 60559 compatible complex
7750 __STDC_LIB_EXT1__ The integer constant 201ymmL, intended to indicate support
7751 for the extensions defined in annex K (Bounds-checking interfaces).179)
7752 __STDC_NO_COMPLEX__ The integer constant 1, intended to indicate that the
7753 implementation does not support complex types or the <complex.h>
7755 __STDC_NO_THREADS__ The integer constant 1, intended to indicate that the
7756 implementation does not support atomic types (including the _Atomic
7757 type qualifier and the <stdatomic.h> header) or the <threads.h>
7759 __STDC_NO_VLA__ The integer constant 1, intended to indicate that the
7760 implementation does not support variable length arrays or variably
7762 2 An implementation that defines __STDC_NO_COMPLEX__ shall not define
7763 __STDC_IEC_559_COMPLEX__.
7764 6.10.9 Pragma operator
7766 1 A unary operator expression of the form:
7767 _Pragma ( string-literal )
7768 is processed as follows: The string literal is destringized by deleting the L prefix, if
7769 present, deleting the leading and trailing double-quotes, replacing each escape sequence
7770 \" by a double-quote, and replacing each escape sequence \\ by a single backslash. The
7771 resulting sequence of characters is processed through translation phase 3 to produce
7772 preprocessing tokens that are executed as if they were the pp-tokens in a pragma
7775 179) The intention is that this will remain an integer constant of type long int that is increased with
7776 each revision of this International Standard.
7780 directive. The original four preprocessing tokens in the unary operator expression are
7782 2 EXAMPLE A directive of the form:
7783 #pragma listing on "..\listing.dir"
7784 can also be expressed as:
7785 _Pragma ( "listing on \"..\\listing.dir\"" )
7786 The latter form is processed in the same way whether it appears literally as shown, or results from macro
7788 #define LISTING(x) PRAGMA(listing on #x)
7789 #define PRAGMA(x) _Pragma(#x)
7790 LISTING ( ..\listing.dir )
7797 6.11 Future language directions
7798 6.11.1 Floating types
7799 1 Future standardization may include additional floating-point types, including those with
7800 greater range, precision, or both than long double.
7801 6.11.2 Linkages of identifiers
7802 1 Declaring an identifier with internal linkage at file scope without the static storage-
7803 class specifier is an obsolescent feature.
7804 6.11.3 External names
7805 1 Restriction of the significance of an external name to fewer than 255 characters
7806 (considering each universal character name or extended source character as a single
7807 character) is an obsolescent feature that is a concession to existing implementations.
7808 6.11.4 Character escape sequences
7809 1 Lowercase letters as escape sequences are reserved for future standardization. Other
7810 characters may be used in extensions.
7811 6.11.5 Storage-class specifiers
7812 1 The placement of a storage-class specifier other than at the beginning of the declaration
7813 specifiers in a declaration is an obsolescent feature.
7814 6.11.6 Function declarators
7815 1 The use of function declarators with empty parentheses (not prototype-format parameter
7816 type declarators) is an obsolescent feature.
7817 6.11.7 Function definitions
7818 1 The use of function definitions with separate parameter identifier and declaration lists
7819 (not prototype-format parameter type and identifier declarators) is an obsolescent feature.
7820 6.11.8 Pragma directives
7821 1 Pragmas whose first preprocessing token is STDC are reserved for future standardization.
7822 6.11.9 Predefined macro names
7823 1 Macro names beginning with __STDC_ are reserved for future standardization.
7833 7.1.1 Definitions of terms
7834 1 A string is a contiguous sequence of characters terminated by and including the first null
7835 character. The term multibyte string is sometimes used instead to emphasize special
7836 processing given to multibyte characters contained in the string or to avoid confusion
7837 with a wide string. A pointer to a string is a pointer to its initial (lowest addressed)
7838 character. The length of a string is the number of bytes preceding the null character and
7839 the value of a string is the sequence of the values of the contained characters, in order.
7840 2 The decimal-point character is the character used by functions that convert floating-point
7841 numbers to or from character sequences to denote the beginning of the fractional part of
7842 such character sequences.180) It is represented in the text and examples by a period, but
7843 may be changed by the setlocale function.
7844 3 A null wide character is a wide character with code value zero.
7845 4 A wide string is a contiguous sequence of wide characters terminated by and including
7846 the first null wide character. A pointer to a wide string is a pointer to its initial (lowest
7847 addressed) wide character. The length of a wide string is the number of wide characters
7848 preceding the null wide character and the value of a wide string is the sequence of code
7849 values of the contained wide characters, in order.
7850 5 A shift sequence is a contiguous sequence of bytes within a multibyte string that
7851 (potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have a
7852 corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte
7854 Forward references: character handling (7.4), the setlocale function (7.11.1.1).
7859 180) The functions that make use of the decimal-point character are the numeric conversion functions
7860 (7.22.1, 7.28.4.1) and the formatted input/output functions (7.21.6, 7.28.2).
7861 181) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large
7862 enough to count all the bytes in any complete multibyte character plus at least one adjacent shift
7863 sequence of maximum length. Whether these counts provide for more than one shift sequence is the
7864 implementation's choice.
7868 7.1.2 Standard headers
7869 1 Each library function is declared, with a type that includes a prototype, in a header,182)
7870 whose contents are made available by the #include preprocessing directive. The
7871 header declares a set of related functions, plus any necessary types and additional macros
7872 needed to facilitate their use. Declarations of types described in this clause shall not
7873 include type qualifiers, unless explicitly stated otherwise.
7874 2 The standard headers are183)
7875 <assert.h> <iso646.h> <stdarg.h> <string.h>
7876 <complex.h> <limits.h> <stdatomic.h> <tgmath.h>
7877 <ctype.h> <locale.h> <stdbool.h> <threads.h>
7878 <errno.h> <math.h> <stddef.h> <time.h>
7879 <fenv.h> <setjmp.h> <stdint.h> <uchar.h>
7880 <float.h> <signal.h> <stdio.h> <wchar.h>
7881 <inttypes.h> <stdalign.h> <stdlib.h> <wctype.h>
7882 3 If a file with the same name as one of the above < and > delimited sequences, not
7883 provided as part of the implementation, is placed in any of the standard places that are
7884 searched for included source files, the behavior is undefined.
7885 4 Standard headers may be included in any order; each may be included more than once in
7886 a given scope, with no effect different from being included only once, except that the
7887 effect of including <assert.h> depends on the definition of NDEBUG (see 7.2). If
7888 used, a header shall be included outside of any external declaration or definition, and it
7889 shall first be included before the first reference to any of the functions or objects it
7890 declares, or to any of the types or macros it defines. However, if an identifier is declared
7891 or defined in more than one header, the second and subsequent associated headers may be
7892 included after the initial reference to the identifier. The program shall not have any
7893 macros with names lexically identical to keywords currently defined prior to the
7895 5 Any definition of an object-like macro described in this clause shall expand to code that is
7896 fully protected by parentheses where necessary, so that it groups in an arbitrary
7897 expression as if it were a single identifier.
7898 6 Any declaration of a library function shall have external linkage.
7903 182) A header is not necessarily a source file, nor are the < and > delimited sequences in header names
7904 necessarily valid source file names.
7905 183) The headers <complex.h>, <stdatomic.h>, and <threads.h> are conditional features that
7906 implementations need not support; see 6.10.8.3.
7910 7 A summary of the contents of the standard headers is given in annex B.
7911 Forward references: diagnostics (7.2).
7912 7.1.3 Reserved identifiers
7913 1 Each header declares or defines all identifiers listed in its associated subclause, and
7914 optionally declares or defines identifiers listed in its associated future library directions
7915 subclause and identifiers which are always reserved either for any use or for use as file
7917 -- All identifiers that begin with an underscore and either an uppercase letter or another
7918 underscore are always reserved for any use.
7919 -- All identifiers that begin with an underscore are always reserved for use as identifiers
7920 with file scope in both the ordinary and tag name spaces.
7921 -- Each macro name in any of the following subclauses (including the future library
7922 directions) is reserved for use as specified if any of its associated headers is included;
7923 unless explicitly stated otherwise (see 7.1.4).
7924 -- All identifiers with external linkage in any of the following subclauses (including the
7925 future library directions) and errno are always reserved for use as identifiers with
7926 external linkage.184)
7927 -- Each identifier with file scope listed in any of the following subclauses (including the
7928 future library directions) is reserved for use as a macro name and as an identifier with
7929 file scope in the same name space if any of its associated headers is included.
7930 2 No other identifiers are reserved. If the program declares or defines an identifier in a
7931 context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved
7932 identifier as a macro name, the behavior is undefined.
7933 3 If the program removes (with #undef) any macro definition of an identifier in the first
7934 group listed above, the behavior is undefined.
7939 184) The list of reserved identifiers with external linkage includes math_errhandling, setjmp,
7940 va_copy, and va_end.
7944 7.1.4 Use of library functions
7945 1 Each of the following statements applies unless explicitly stated otherwise in the detailed
7946 descriptions that follow: If an argument to a function has an invalid value (such as a value
7947 outside the domain of the function, or a pointer outside the address space of the program,
7948 or a null pointer, or a pointer to non-modifiable storage when the corresponding
7949 parameter is not const-qualified) or a type (after promotion) not expected by a function
7950 with variable number of arguments, the behavior is undefined. If a function argument is
7951 described as being an array, the pointer actually passed to the function shall have a value
7952 such that all address computations and accesses to objects (that would be valid if the
7953 pointer did point to the first element of such an array) are in fact valid. Any function
7954 declared in a header may be additionally implemented as a function-like macro defined in
7955 the header, so if a library function is declared explicitly when its header is included, one
7956 of the techniques shown below can be used to ensure the declaration is not affected by
7957 such a macro. Any macro definition of a function can be suppressed locally by enclosing
7958 the name of the function in parentheses, because the name is then not followed by the left
7959 parenthesis that indicates expansion of a macro function name. For the same syntactic
7960 reason, it is permitted to take the address of a library function even if it is also defined as
7961 a macro.185) The use of #undef to remove any macro definition will also ensure that an
7962 actual function is referred to. Any invocation of a library function that is implemented as
7963 a macro shall expand to code that evaluates each of its arguments exactly once, fully
7964 protected by parentheses where necessary, so it is generally safe to use arbitrary
7965 expressions as arguments.186) Likewise, those function-like macros described in the
7966 following subclauses may be invoked in an expression anywhere a function with a
7967 compatible return type could be called.187) All object-like macros listed as expanding to
7970 185) This means that an implementation shall provide an actual function for each library function, even if it
7971 also provides a macro for that function.
7972 186) Such macros might not contain the sequence points that the corresponding function calls do.
7973 187) Because external identifiers and some macro names beginning with an underscore are reserved,
7974 implementations may provide special semantics for such names. For example, the identifier
7975 _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the
7976 appropriate header could specify
7977 #define abs(x) _BUILTIN_abs(x)
7978 for a compiler whose code generator will accept it.
7979 In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine
7982 whether the implementation's header provides a macro implementation of abs or a built-in
7983 implementation. The prototype for the function, which precedes and is hidden by any macro
7984 definition, is thereby revealed also.
7988 integer constant expressions shall additionally be suitable for use in #if preprocessing
7990 2 Provided that a library function can be declared without reference to any type defined in a
7991 header, it is also permissible to declare the function and use it without including its
7993 3 There is a sequence point immediately before a library function returns.
7994 4 The functions in the standard library are not guaranteed to be reentrant and may modify
7995 objects with static or thread storage duration.188)
7996 5 Unless explicitly stated otherwise in the detailed descriptions that follow, library
7997 functions shall prevent data races as follows: A library function shall not directly or
7998 indirectly access objects accessible by threads other than the current thread unless the
7999 objects are accessed directly or indirectly via the function's arguments. A library
8000 function shall not directly or indirectly modify objects accessible by threads other than
8001 the current thread unless the objects are accessed directly or indirectly via the function's
8002 non-const arguments.189) Implementations may share their own internal objects between
8003 threads if the objects are not visible to users and are protected against data races.
8004 6 Unless otherwise specified, library functions shall perform all operations solely within the
8005 current thread if those operations have effects that are visible to users.190)
8006 7 EXAMPLE The function atoi may be used in any of several ways:
8007 -- by use of its associated header (possibly generating a macro expansion)
8012 -- by use of its associated header (assuredly generating a true function reference)
8017 188) Thus, a signal handler cannot, in general, call standard library functions.
8018 189) This means, for example, that an implementation is not permitted to use a static object for internal
8019 purposes without synchronization because it could cause a data race even in programs that do not
8020 explicitly share objects between threads.
8021 190) This allows implementations to parallelize operations if there are no visible side effects.
8035 -- by explicit declaration
8036 extern int atoi(const char *);
8046 7.2 Diagnostics <assert.h>
8047 1 The header <assert.h> defines the assert and static_assert macros and
8048 refers to another macro,
8050 which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the
8051 point in the source file where <assert.h> is included, the assert macro is defined
8053 #define assert(ignore) ((void)0)
8054 The assert macro is redefined according to the current state of NDEBUG each time that
8055 <assert.h> is included.
8056 2 The assert macro shall be implemented as a macro, not as an actual function. If the
8057 macro definition is suppressed in order to access an actual function, the behavior is
8061 expands to _Static_assert.
8062 7.2.1 Program diagnostics
8063 7.2.1.1 The assert macro
8065 1 #include <assert.h>
8066 void assert(scalar expression);
8068 2 The assert macro puts diagnostic tests into programs; it expands to a void expression.
8069 When it is executed, if expression (which shall have a scalar type) is false (that is,
8070 compares equal to 0), the assert macro writes information about the particular call that
8071 failed (including the text of the argument, the name of the source file, the source line
8072 number, and the name of the enclosing function -- the latter are respectively the values of
8073 the preprocessing macros __FILE__ and __LINE__ and of the identifier
8074 __func__) on the standard error stream in an implementation-defined format.191) It
8075 then calls the abort function.
8079 191) The message written might be of the form:
8080 Assertion failed: expression, function abc, file xyz, line nnn.
8086 3 The assert macro returns no value.
8087 Forward references: the abort function (7.22.4.1).
8094 7.3 Complex arithmetic <complex.h>
8096 1 The header <complex.h> defines macros and declares functions that support complex
8098 2 Implementations that define the macro __STDC_NO_COMPLEX__ need not provide
8099 this header nor support any of its facilities.
8100 3 Each synopsis specifies a family of functions consisting of a principal function with one
8101 or more double complex parameters and a double complex or double return
8102 value; and other functions with the same name but with f and l suffixes which are
8103 corresponding functions with float and long double parameters and return values.
8106 expands to _Complex; the macro
8108 expands to a constant expression of type const float _Complex, with the value of
8109 the imaginary unit.193)
8114 are defined if and only if the implementation supports imaginary types;194) if defined,
8115 they expand to _Imaginary and a constant expression of type const float
8116 _Imaginary with the value of the imaginary unit.
8119 expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not
8120 defined, I shall expand to _Complex_I.
8121 7 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
8122 redefine the macros complex, imaginary, and I.
8124 192) See ''future library directions'' (7.30.1).
8125 193) The imaginary unit is a number i such that i 2 = -1.
8126 194) A specification for imaginary types is in informative annex G.
8130 Forward references: IEC 60559-compatible complex arithmetic (annex G).
8132 1 Values are interpreted as radians, not degrees. An implementation may set errno but is
8135 1 Some of the functions below have branch cuts, across which the function is
8136 discontinuous. For implementations with a signed zero (including all IEC 60559
8137 implementations) that follow the specifications of annex G, the sign of zero distinguishes
8138 one side of a cut from another so the function is continuous (except for format
8139 limitations) as the cut is approached from either side. For example, for the square root
8140 function, which has a branch cut along the negative real axis, the top of the cut, with
8141 imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with
8142 imaginary part -0, maps to the negative imaginary axis.
8143 2 Implementations that do not support a signed zero (see annex F) cannot distinguish the
8144 sides of branch cuts. These implementations shall map a cut so the function is continuous
8145 as the cut is approached coming around the finite endpoint of the cut in a counter
8146 clockwise direction. (Branch cuts for the functions specified here have just one finite
8147 endpoint.) For example, for the square root function, coming counter clockwise around
8148 the finite endpoint of the cut along the negative real axis approaches the cut from above,
8149 so the cut maps to the positive imaginary axis.
8150 7.3.4 The CX_LIMITED_RANGE pragma
8152 1 #include <complex.h>
8153 #pragma STDC CX_LIMITED_RANGE on-off-switch
8155 2 The usual mathematical formulas for complex multiply, divide, and absolute value are
8156 problematic because of their treatment of infinities and because of undue overflow and
8157 underflow. The CX_LIMITED_RANGE pragma can be used to inform the
8158 implementation that (where the state is ''on'') the usual mathematical formulas are
8159 acceptable.195) The pragma can occur either outside external declarations or preceding all
8160 explicit declarations and statements inside a compound statement. When outside external
8161 declarations, the pragma takes effect from its occurrence until another
8162 CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit.
8163 When inside a compound statement, the pragma takes effect from its occurrence until
8164 another CX_LIMITED_RANGE pragma is encountered (including within a nested
8165 compound statement), or until the end of the compound statement; at the end of a
8166 compound statement the state for the pragma is restored to its condition just before the
8170 compound statement. If this pragma is used in any other context, the behavior is
8171 undefined. The default state for the pragma is ''off''.
8172 7.3.5 Trigonometric functions
8173 7.3.5.1 The cacos functions
8175 1 #include <complex.h>
8176 double complex cacos(double complex z);
8177 float complex cacosf(float complex z);
8178 long double complex cacosl(long double complex z);
8180 2 The cacos functions compute the complex arc cosine of z, with branch cuts outside the
8181 interval [-1, +1] along the real axis.
8183 3 The cacos functions return the complex arc cosine value, in the range of a strip
8184 mathematically unbounded along the imaginary axis and in the interval [0, pi ] along the
8186 7.3.5.2 The casin functions
8188 1 #include <complex.h>
8189 double complex casin(double complex z);
8190 float complex casinf(float complex z);
8191 long double complex casinl(long double complex z);
8193 2 The casin functions compute the complex arc sine of z, with branch cuts outside the
8194 interval [-1, +1] along the real axis.
8196 3 The casin functions return the complex arc sine value, in the range of a strip
8197 mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2]
8199 195) The purpose of the pragma is to allow the implementation to use the formulas:
8200 (x + iy) x (u + iv) = (xu - yv) + i(yu + xv)
8201 (x + iy) / (u + iv) = [(xu + yv) + i(yu - xv)]/(u2 + v 2 )
8202 | x + iy | = sqrt: x 2 + y 2
8204 where the programmer can determine they are safe.
8208 along the real axis.
8209 7.3.5.3 The catan functions
8211 1 #include <complex.h>
8212 double complex catan(double complex z);
8213 float complex catanf(float complex z);
8214 long double complex catanl(long double complex z);
8216 2 The catan functions compute the complex arc tangent of z, with branch cuts outside the
8217 interval [-i, +i] along the imaginary axis.
8219 3 The catan functions return the complex arc tangent value, in the range of a strip
8220 mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2]
8221 along the real axis.
8222 7.3.5.4 The ccos functions
8224 1 #include <complex.h>
8225 double complex ccos(double complex z);
8226 float complex ccosf(float complex z);
8227 long double complex ccosl(long double complex z);
8229 2 The ccos functions compute the complex cosine of z.
8231 3 The ccos functions return the complex cosine value.
8232 7.3.5.5 The csin functions
8234 1 #include <complex.h>
8235 double complex csin(double complex z);
8236 float complex csinf(float complex z);
8237 long double complex csinl(long double complex z);
8239 2 The csin functions compute the complex sine of z.
8246 3 The csin functions return the complex sine value.
8247 7.3.5.6 The ctan functions
8249 1 #include <complex.h>
8250 double complex ctan(double complex z);
8251 float complex ctanf(float complex z);
8252 long double complex ctanl(long double complex z);
8254 2 The ctan functions compute the complex tangent of z.
8256 3 The ctan functions return the complex tangent value.
8257 7.3.6 Hyperbolic functions
8258 7.3.6.1 The cacosh functions
8260 1 #include <complex.h>
8261 double complex cacosh(double complex z);
8262 float complex cacoshf(float complex z);
8263 long double complex cacoshl(long double complex z);
8265 2 The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch
8266 cut at values less than 1 along the real axis.
8268 3 The cacosh functions return the complex arc hyperbolic cosine value, in the range of a
8269 half-strip of nonnegative values along the real axis and in the interval [-ipi , +ipi ] along the
8271 7.3.6.2 The casinh functions
8273 1 #include <complex.h>
8274 double complex casinh(double complex z);
8275 float complex casinhf(float complex z);
8276 long double complex casinhl(long double complex z);
8283 2 The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts
8284 outside the interval [-i, +i] along the imaginary axis.
8286 3 The casinh functions return the complex arc hyperbolic sine value, in the range of a
8287 strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2]
8288 along the imaginary axis.
8289 7.3.6.3 The catanh functions
8291 1 #include <complex.h>
8292 double complex catanh(double complex z);
8293 float complex catanhf(float complex z);
8294 long double complex catanhl(long double complex z);
8296 2 The catanh functions compute the complex arc hyperbolic tangent of z, with branch
8297 cuts outside the interval [-1, +1] along the real axis.
8299 3 The catanh functions return the complex arc hyperbolic tangent value, in the range of a
8300 strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2]
8301 along the imaginary axis.
8302 7.3.6.4 The ccosh functions
8304 1 #include <complex.h>
8305 double complex ccosh(double complex z);
8306 float complex ccoshf(float complex z);
8307 long double complex ccoshl(long double complex z);
8309 2 The ccosh functions compute the complex hyperbolic cosine of z.
8311 3 The ccosh functions return the complex hyperbolic cosine value.
8318 7.3.6.5 The csinh functions
8320 1 #include <complex.h>
8321 double complex csinh(double complex z);
8322 float complex csinhf(float complex z);
8323 long double complex csinhl(long double complex z);
8325 2 The csinh functions compute the complex hyperbolic sine of z.
8327 3 The csinh functions return the complex hyperbolic sine value.
8328 7.3.6.6 The ctanh functions
8330 1 #include <complex.h>
8331 double complex ctanh(double complex z);
8332 float complex ctanhf(float complex z);
8333 long double complex ctanhl(long double complex z);
8335 2 The ctanh functions compute the complex hyperbolic tangent of z.
8337 3 The ctanh functions return the complex hyperbolic tangent value.
8338 7.3.7 Exponential and logarithmic functions
8339 7.3.7.1 The cexp functions
8341 1 #include <complex.h>
8342 double complex cexp(double complex z);
8343 float complex cexpf(float complex z);
8344 long double complex cexpl(long double complex z);
8346 2 The cexp functions compute the complex base-e exponential of z.
8348 3 The cexp functions return the complex base-e exponential value.
8354 7.3.7.2 The clog functions
8356 1 #include <complex.h>
8357 double complex clog(double complex z);
8358 float complex clogf(float complex z);
8359 long double complex clogl(long double complex z);
8361 2 The clog functions compute the complex natural (base-e) logarithm of z, with a branch
8362 cut along the negative real axis.
8364 3 The clog functions return the complex natural logarithm value, in the range of a strip
8365 mathematically unbounded along the real axis and in the interval [-ipi , +ipi ] along the
8367 7.3.8 Power and absolute-value functions
8368 7.3.8.1 The cabs functions
8370 1 #include <complex.h>
8371 double cabs(double complex z);
8372 float cabsf(float complex z);
8373 long double cabsl(long double complex z);
8375 2 The cabs functions compute the complex absolute value (also called norm, modulus, or
8378 3 The cabs functions return the complex absolute value.
8379 7.3.8.2 The cpow functions
8381 1 #include <complex.h>
8382 double complex cpow(double complex x, double complex y);
8383 float complex cpowf(float complex x, float complex y);
8384 long double complex cpowl(long double complex x,
8385 long double complex y);
8393 2 The cpow functions compute the complex power function xy , with a branch cut for the
8394 first parameter along the negative real axis.
8396 3 The cpow functions return the complex power function value.
8397 7.3.8.3 The csqrt functions
8399 1 #include <complex.h>
8400 double complex csqrt(double complex z);
8401 float complex csqrtf(float complex z);
8402 long double complex csqrtl(long double complex z);
8404 2 The csqrt functions compute the complex square root of z, with a branch cut along the
8407 3 The csqrt functions return the complex square root value, in the range of the right half-
8408 plane (including the imaginary axis).
8409 7.3.9 Manipulation functions
8410 7.3.9.1 The carg functions
8412 1 #include <complex.h>
8413 double carg(double complex z);
8414 float cargf(float complex z);
8415 long double cargl(long double complex z);
8417 2 The carg functions compute the argument (also called phase angle) of z, with a branch
8418 cut along the negative real axis.
8420 3 The carg functions return the value of the argument in the interval [-pi , +pi ].
8427 7.3.9.2 The cimag functions
8429 1 #include <complex.h>
8430 double cimag(double complex z);
8431 float cimagf(float complex z);
8432 long double cimagl(long double complex z);
8434 2 The cimag functions compute the imaginary part of z.196)
8436 3 The cimag functions return the imaginary part value (as a real).
8437 7.3.9.3 The CMPLX macros
8439 1 #include <complex.h>
8440 double complex CMPLX(double x, double y);
8441 float complex CMPLXF(float x, float y);
8442 long double complex CMPLXL(long double x, long double y);
8444 2 The CMPLX macros expand to an expression of the specified complex type, with the real
8445 part having the (converted) value of x and the imaginary part having the (converted)
8447 Recommended practice
8448 3 The resulting expression should be suitable for use as an initializer for an object with
8449 static or thread storage duration, provided both arguments are likewise suitable.
8451 4 The CMPLX macros return the complex value x + i y.
8452 5 NOTE These macros act as if the implementation supported imaginary types and the definitions were:
8453 #define CMPLX(x, y) ((double complex)((double)(x) + \
8454 _Imaginary_I * (double)(y)))
8455 #define CMPLXF(x, y) ((float complex)((float)(x) + \
8456 _Imaginary_I * (float)(y)))
8457 #define CMPLXL(x, y) ((long double complex)((long double)(x) + \
8458 _Imaginary_I * (long double)(y)))
8463 196) For a variable z of complex type, z == creal(z) + cimag(z)*I.
8467 7.3.9.4 The conj functions
8469 1 #include <complex.h>
8470 double complex conj(double complex z);
8471 float complex conjf(float complex z);
8472 long double complex conjl(long double complex z);
8474 2 The conj functions compute the complex conjugate of z, by reversing the sign of its
8477 3 The conj functions return the complex conjugate value.
8478 7.3.9.5 The cproj functions
8480 1 #include <complex.h>
8481 double complex cproj(double complex z);
8482 float complex cprojf(float complex z);
8483 long double complex cprojl(long double complex z);
8485 2 The cproj functions compute a projection of z onto the Riemann sphere: z projects to
8486 z except that all complex infinities (even those with one infinite part and one NaN part)
8487 project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is
8489 INFINITY + I * copysign(0.0, cimag(z))
8491 3 The cproj functions return the value of the projection onto the Riemann sphere.
8492 7.3.9.6 The creal functions
8494 1 #include <complex.h>
8495 double creal(double complex z);
8496 float crealf(float complex z);
8497 long double creall(long double complex z);
8499 2 The creal functions compute the real part of z.197)
8505 3 The creal functions return the real part value.
8510 197) For a variable z of complex type, z == creal(z) + cimag(z)*I.
8514 7.4 Character handling <ctype.h>
8515 1 The header <ctype.h> declares several functions useful for classifying and mapping
8516 characters.198) In all cases the argument is an int, the value of which shall be
8517 representable as an unsigned char or shall equal the value of the macro EOF. If the
8518 argument has any other value, the behavior is undefined.
8519 2 The behavior of these functions is affected by the current locale. Those functions that
8520 have locale-specific aspects only when not in the "C" locale are noted below.
8521 3 The term printing character refers to a member of a locale-specific set of characters, each
8522 of which occupies one printing position on a display device; the term control character
8523 refers to a member of a locale-specific set of characters that are not printing
8524 characters.199) All letters and digits are printing characters.
8525 Forward references: EOF (7.21.1), localization (7.11).
8526 7.4.1 Character classification functions
8527 1 The functions in this subclause return nonzero (true) if and only if the value of the
8528 argument c conforms to that in the description of the function.
8529 7.4.1.1 The isalnum function
8531 1 #include <ctype.h>
8534 2 The isalnum function tests for any character for which isalpha or isdigit is true.
8535 7.4.1.2 The isalpha function
8537 1 #include <ctype.h>
8540 2 The isalpha function tests for any character for which isupper or islower is true,
8541 or any character that is one of a locale-specific set of alphabetic characters for which
8545 198) See ''future library directions'' (7.30.2).
8546 199) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those
8547 whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose
8548 values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL).
8552 none of iscntrl, isdigit, ispunct, or isspace is true.200) In the "C" locale,
8553 isalpha returns true only for the characters for which isupper or islower is true.
8554 7.4.1.3 The isblank function
8556 1 #include <ctype.h>
8559 2 The isblank function tests for any character that is a standard blank character or is one
8560 of a locale-specific set of characters for which isspace is true and that is used to
8561 separate words within a line of text. The standard blank characters are the following:
8562 space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only
8563 for the standard blank characters.
8564 7.4.1.4 The iscntrl function
8566 1 #include <ctype.h>
8569 2 The iscntrl function tests for any control character.
8570 7.4.1.5 The isdigit function
8572 1 #include <ctype.h>
8575 2 The isdigit function tests for any decimal-digit character (as defined in 5.2.1).
8576 7.4.1.6 The isgraph function
8578 1 #include <ctype.h>
8584 200) The functions islower and isupper test true or false separately for each of these additional
8585 characters; all four combinations are possible.
8590 2 The isgraph function tests for any printing character except space (' ').
8591 7.4.1.7 The islower function
8593 1 #include <ctype.h>
8596 2 The islower function tests for any character that is a lowercase letter or is one of a
8597 locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
8598 isspace is true. In the "C" locale, islower returns true only for the lowercase
8599 letters (as defined in 5.2.1).
8600 7.4.1.8 The isprint function
8602 1 #include <ctype.h>
8605 2 The isprint function tests for any printing character including space (' ').
8606 7.4.1.9 The ispunct function
8608 1 #include <ctype.h>
8611 2 The ispunct function tests for any printing character that is one of a locale-specific set
8612 of punctuation characters for which neither isspace nor isalnum is true. In the "C"
8613 locale, ispunct returns true for every printing character for which neither isspace
8614 nor isalnum is true.
8615 7.4.1.10 The isspace function
8617 1 #include <ctype.h>
8620 2 The isspace function tests for any character that is a standard white-space character or
8621 is one of a locale-specific set of characters for which isalnum is false. The standard
8625 white-space characters are the following: space (' '), form feed ('\f'), new-line
8626 ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the
8627 "C" locale, isspace returns true only for the standard white-space characters.
8628 7.4.1.11 The isupper function
8630 1 #include <ctype.h>
8633 2 The isupper function tests for any character that is an uppercase letter or is one of a
8634 locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
8635 isspace is true. In the "C" locale, isupper returns true only for the uppercase
8636 letters (as defined in 5.2.1).
8637 7.4.1.12 The isxdigit function
8639 1 #include <ctype.h>
8640 int isxdigit(int c);
8642 2 The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1).
8643 7.4.2 Character case mapping functions
8644 7.4.2.1 The tolower function
8646 1 #include <ctype.h>
8649 2 The tolower function converts an uppercase letter to a corresponding lowercase letter.
8651 3 If the argument is a character for which isupper is true and there are one or more
8652 corresponding characters, as specified by the current locale, for which islower is true,
8653 the tolower function returns one of the corresponding characters (always the same one
8654 for any given locale); otherwise, the argument is returned unchanged.
8661 7.4.2.2 The toupper function
8663 1 #include <ctype.h>
8666 2 The toupper function converts a lowercase letter to a corresponding uppercase letter.
8668 3 If the argument is a character for which islower is true and there are one or more
8669 corresponding characters, as specified by the current locale, for which isupper is true,
8670 the toupper function returns one of the corresponding characters (always the same one
8671 for any given locale); otherwise, the argument is returned unchanged.
8678 7.5 Errors <errno.h>
8679 1 The header <errno.h> defines several macros, all relating to the reporting of error
8685 which expand to integer constant expressions with type int, distinct positive values, and
8686 which are suitable for use in #if preprocessing directives; and
8688 which expands to a modifiable lvalue201) that has type int and thread local storage
8689 duration, the value of which is set to a positive error number by several library functions.
8690 If a macro definition is suppressed in order to access an actual object, or a program
8691 defines an identifier with the name errno, the behavior is undefined.
8692 3 The value of errno in the initial thread is zero at program startup (the initial value of
8693 errno in other threads is an indeterminate value), but is never set to zero by any library
8694 function.202) The value of errno may be set to nonzero by a library function call
8695 whether or not there is an error, provided the use of errno is not documented in the
8696 description of the function in this International Standard.
8697 4 Additional macro definitions, beginning with E and a digit or E and an uppercase
8698 letter,203) may also be specified by the implementation.
8703 201) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue
8704 resulting from a function call (for example, *errno()).
8705 202) Thus, a program that uses errno for error checking should set it to zero before a library function call,
8706 then inspect it before a subsequent library function call. Of course, a library function can save the
8707 value of errno on entry and then set it to zero, as long as the original value is restored if errno's
8708 value is still zero just before the return.
8709 203) See ''future library directions'' (7.30.3).
8713 7.6 Floating-point environment <fenv.h>
8714 1 The header <fenv.h> defines several macros, and declares types and functions that
8715 provide access to the floating-point environment. The floating-point environment refers
8716 collectively to any floating-point status flags and control modes supported by the
8717 implementation.204) A floating-point status flag is a system variable whose value is set
8718 (but never cleared) when a floating-point exception is raised, which occurs as a side effect
8719 of exceptional floating-point arithmetic to provide auxiliary information.205) A floating-
8720 point control mode is a system variable whose value may be set by the user to affect the
8721 subsequent behavior of floating-point arithmetic.
8722 2 The floating-point environment has thread storage duration. The initial state for a
8723 thread's floating-point environment is the current state of the floating-point environment
8724 of the thread that creates it at the time of creation.
8725 3 Certain programming conventions support the intended model of use for the floating-
8726 point environment:206)
8727 -- a function call does not alter its caller's floating-point control modes, clear its caller's
8728 floating-point status flags, nor depend on the state of its caller's floating-point status
8729 flags unless the function is so documented;
8730 -- a function call is assumed to require default floating-point control modes, unless its
8731 documentation promises otherwise;
8732 -- a function call is assumed to have the potential for raising floating-point exceptions,
8733 unless its documentation promises otherwise.
8736 represents the entire floating-point environment.
8739 represents the floating-point status flags collectively, including any status the
8740 implementation associates with the flags.
8743 204) This header is designed to support the floating-point exception status flags and directed-rounding
8744 control modes required by IEC 60559, and other similar floating-point state information. It is also
8745 designed to facilitate code portability among all systems.
8746 205) A floating-point status flag is not an object and can be set more than once within an expression.
8747 206) With these conventions, a programmer can safely assume default floating-point control modes (or be
8748 unaware of them). The responsibilities associated with accessing the floating-point environment fall
8749 on the programmer or program that does so explicitly.
8753 6 Each of the macros
8759 is defined if and only if the implementation supports the floating-point exception by
8760 means of the functions in 7.6.2.207) Additional implementation-defined floating-point
8761 exceptions, with macro definitions beginning with FE_ and an uppercase letter, may also
8762 be specified by the implementation. The defined macros expand to integer constant
8763 expressions with values such that bitwise ORs of all combinations of the macros result in
8764 distinct values, and furthermore, bitwise ANDs of all combinations of the macros result in
8768 is simply the bitwise OR of all floating-point exception macros defined by the
8769 implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0.
8770 8 Each of the macros
8775 is defined if and only if the implementation supports getting and setting the represented
8776 rounding direction by means of the fegetround and fesetround functions.
8777 Additional implementation-defined rounding directions, with macro definitions beginning
8778 with FE_ and an uppercase letter, may also be specified by the implementation. The
8779 defined macros expand to integer constant expressions whose values are distinct
8780 nonnegative values.209)
8785 207) The implementation supports a floating-point exception if there are circumstances where a call to at
8786 least one of the functions in 7.6.2, using the macro as the appropriate argument, will succeed. It is not
8787 necessary for all the functions to succeed all the time.
8788 208) The macros should be distinct powers of two.
8789 209) Even though the rounding direction macros may expand to constants corresponding to the values of
8790 FLT_ROUNDS, they are not required to do so.
8795 represents the default floating-point environment -- the one installed at program startup
8796 -- and has type ''pointer to const-qualified fenv_t''. It can be used as an argument to
8797 <fenv.h> functions that manage the floating-point environment.
8798 10 Additional implementation-defined environments, with macro definitions beginning with
8799 FE_ and an uppercase letter, and having type ''pointer to const-qualified fenv_t'', may
8800 also be specified by the implementation.
8801 7.6.1 The FENV_ACCESS pragma
8804 #pragma STDC FENV_ACCESS on-off-switch
8806 2 The FENV_ACCESS pragma provides a means to inform the implementation when a
8807 program might access the floating-point environment to test floating-point status flags or
8808 run under non-default floating-point control modes.210) The pragma shall occur either
8809 outside external declarations or preceding all explicit declarations and statements inside a
8810 compound statement. When outside external declarations, the pragma takes effect from
8811 its occurrence until another FENV_ACCESS pragma is encountered, or until the end of
8812 the translation unit. When inside a compound statement, the pragma takes effect from its
8813 occurrence until another FENV_ACCESS pragma is encountered (including within a
8814 nested compound statement), or until the end of the compound statement; at the end of a
8815 compound statement the state for the pragma is restored to its condition just before the
8816 compound statement. If this pragma is used in any other context, the behavior is
8817 undefined. If part of a program tests floating-point status flags, sets floating-point control
8818 modes, or runs under non-default mode settings, but was translated with the state for the
8819 FENV_ACCESS pragma ''off'', the behavior is undefined. The default state (''on'' or
8820 ''off'') for the pragma is implementation-defined. (When execution passes from a part of
8821 the program translated with FENV_ACCESS ''off'' to a part translated with
8822 FENV_ACCESS ''on'', the state of the floating-point status flags is unspecified and the
8823 floating-point control modes have their default settings.)
8828 210) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag
8829 tests and mode changes (e.g., global common subexpression elimination, code motion, and constant
8830 folding). In general, if the state of FENV_ACCESS is ''off'', the translator can assume that default
8831 modes are in effect and the flags are not tested.
8839 #pragma STDC FENV_ACCESS ON
8847 4 If the function g might depend on status flags set as a side effect of the first x + 1, or if the second
8848 x + 1 might depend on control modes set as a side effect of the call to function g, then the program shall
8849 contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.211)
8851 7.6.2 Floating-point exceptions
8852 1 The following functions provide access to the floating-point status flags.212) The int
8853 input argument for the functions represents a subset of floating-point exceptions, and can
8854 be zero or the bitwise OR of one or more floating-point exception macros, for example
8855 FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of these
8856 functions is undefined.
8857 7.6.2.1 The feclearexcept function
8860 int feclearexcept(int excepts);
8862 2 The feclearexcept function attempts to clear the supported floating-point exceptions
8863 represented by its argument.
8865 3 The feclearexcept function returns zero if the excepts argument is zero or if all
8866 the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value.
8869 211) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other
8870 hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is
8871 ''off'', just one evaluation of x + 1 would suffice.
8872 212) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic
8873 abstraction of flags that are either set or clear. An implementation may endow floating-point status
8874 flags with more information -- for example, the address of the code which first raised the floating-
8875 point exception; the functions fegetexceptflag and fesetexceptflag deal with the full
8880 7.6.2.2 The fegetexceptflag function
8883 int fegetexceptflag(fexcept_t *flagp,
8886 2 The fegetexceptflag function attempts to store an implementation-defined
8887 representation of the states of the floating-point status flags indicated by the argument
8888 excepts in the object pointed to by the argument flagp.
8890 3 The fegetexceptflag function returns zero if the representation was successfully
8891 stored. Otherwise, it returns a nonzero value.
8892 7.6.2.3 The feraiseexcept function
8895 int feraiseexcept(int excepts);
8897 2 The feraiseexcept function attempts to raise the supported floating-point exceptions
8898 represented by its argument.213) The order in which these floating-point exceptions are
8899 raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function
8900 additionally raises the ''inexact'' floating-point exception whenever it raises the
8901 ''overflow'' or ''underflow'' floating-point exception is implementation-defined.
8903 3 The feraiseexcept function returns zero if the excepts argument is zero or if all
8904 the specified exceptions were successfully raised. Otherwise, it returns a nonzero value.
8909 213) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations.
8910 Hence, enabled traps for floating-point exceptions raised by this function are taken. The specification
8911 in F.8.6 is in the same spirit.
8915 7.6.2.4 The fesetexceptflag function
8918 int fesetexceptflag(const fexcept_t *flagp,
8921 2 The fesetexceptflag function attempts to set the floating-point status flags
8922 indicated by the argument excepts to the states stored in the object pointed to by
8923 flagp. The value of *flagp shall have been set by a previous call to
8924 fegetexceptflag whose second argument represented at least those floating-point
8925 exceptions represented by the argument excepts. This function does not raise floating-
8926 point exceptions, but only sets the state of the flags.
8928 3 The fesetexceptflag function returns zero if the excepts argument is zero or if
8929 all the specified flags were successfully set to the appropriate state. Otherwise, it returns
8931 7.6.2.5 The fetestexcept function
8934 int fetestexcept(int excepts);
8936 2 The fetestexcept function determines which of a specified subset of the floating-
8937 point exception flags are currently set. The excepts argument specifies the floating-
8938 point status flags to be queried.214)
8940 3 The fetestexcept function returns the value of the bitwise OR of the floating-point
8941 exception macros corresponding to the currently set floating-point exceptions included in
8943 4 EXAMPLE Call f if ''invalid'' is set, then g if ''overflow'' is set:
8948 214) This mechanism allows testing several floating-point exceptions with just one function call.
8955 #pragma STDC FENV_ACCESS ON
8957 feclearexcept(FE_INVALID | FE_OVERFLOW);
8958 // maybe raise exceptions
8959 set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW);
8960 if (set_excepts & FE_INVALID) f();
8961 if (set_excepts & FE_OVERFLOW) g();
8966 1 The fegetround and fesetround functions provide control of rounding direction
8968 7.6.3.1 The fegetround function
8971 int fegetround(void);
8973 2 The fegetround function gets the current rounding direction.
8975 3 The fegetround function returns the value of the rounding direction macro
8976 representing the current rounding direction or a negative value if there is no such
8977 rounding direction macro or the current rounding direction is not determinable.
8978 7.6.3.2 The fesetround function
8981 int fesetround(int round);
8983 2 The fesetround function establishes the rounding direction represented by its
8984 argument round. If the argument is not equal to the value of a rounding direction macro,
8985 the rounding direction is not changed.
8987 3 The fesetround function returns zero if and only if the requested rounding direction
8993 4 EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting the
8994 rounding direction fails.
8997 void f(int round_dir)
8999 #pragma STDC FENV_ACCESS ON
9002 save_round = fegetround();
9003 setround_ok = fesetround(round_dir);
9004 assert(setround_ok == 0);
9006 fesetround(save_round);
9011 1 The functions in this section manage the floating-point environment -- status flags and
9012 control modes -- as one entity.
9013 7.6.4.1 The fegetenv function
9016 int fegetenv(fenv_t *envp);
9018 2 The fegetenv function attempts to store the current floating-point environment in the
9019 object pointed to by envp.
9021 3 The fegetenv function returns zero if the environment was successfully stored.
9022 Otherwise, it returns a nonzero value.
9023 7.6.4.2 The feholdexcept function
9026 int feholdexcept(fenv_t *envp);
9028 2 The feholdexcept function saves the current floating-point environment in the object
9029 pointed to by envp, clears the floating-point status flags, and then installs a non-stop
9030 (continue on floating-point exceptions) mode, if available, for all floating-point
9036 3 The feholdexcept function returns zero if and only if non-stop floating-point
9037 exception handling was successfully installed.
9038 7.6.4.3 The fesetenv function
9041 int fesetenv(const fenv_t *envp);
9043 2 The fesetenv function attempts to establish the floating-point environment represented
9044 by the object pointed to by envp. The argument envp shall point to an object set by a
9045 call to fegetenv or feholdexcept, or equal a floating-point environment macro.
9046 Note that fesetenv merely installs the state of the floating-point status flags
9047 represented through its argument, and does not raise these floating-point exceptions.
9049 3 The fesetenv function returns zero if the environment was successfully established.
9050 Otherwise, it returns a nonzero value.
9051 7.6.4.4 The feupdateenv function
9054 int feupdateenv(const fenv_t *envp);
9056 2 The feupdateenv function attempts to save the currently raised floating-point
9057 exceptions in its automatic storage, install the floating-point environment represented by
9058 the object pointed to by envp, and then raise the saved floating-point exceptions. The
9059 argument envp shall point to an object set by a call to feholdexcept or fegetenv,
9060 or equal a floating-point environment macro.
9062 3 The feupdateenv function returns zero if all the actions were successfully carried out.
9063 Otherwise, it returns a nonzero value.
9068 215) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap
9069 handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For
9070 such systems, the feholdexcept function can be used in conjunction with the feupdateenv
9071 function to write routines that hide spurious floating-point exceptions from their callers.
9075 4 EXAMPLE Hide spurious underflow floating-point exceptions:
9079 #pragma STDC FENV_ACCESS ON
9082 if (feholdexcept(&save_env))
9083 return /* indication of an environmental problem */;
9085 if (/* test spurious underflow */)
9086 if (feclearexcept(FE_UNDERFLOW))
9087 return /* indication of an environmental problem */;
9088 if (feupdateenv(&save_env))
9089 return /* indication of an environmental problem */;
9098 7.7 Characteristics of floating types <float.h>
9099 1 The header <float.h> defines several macros that expand to various limits and
9100 parameters of the standard floating-point types.
9101 2 The macros, their meanings, and the constraints (or restrictions) on their values are listed
9109 7.8 Format conversion of integer types <inttypes.h>
9110 1 The header <inttypes.h> includes the header <stdint.h> and extends it with
9111 additional facilities provided by hosted implementations.
9112 2 It declares functions for manipulating greatest-width integers and converting numeric
9113 character strings to greatest-width integers, and it declares the type
9115 which is a structure type that is the type of the value returned by the imaxdiv function.
9116 For each type declared in <stdint.h>, it defines corresponding macros for conversion
9117 specifiers for use with the formatted input/output functions.216)
9118 Forward references: integer types <stdint.h> (7.20), formatted input/output
9119 functions (7.21.6), formatted wide character input/output functions (7.28.2).
9120 7.8.1 Macros for format specifiers
9121 1 Each of the following object-like macros expands to a character string literal containing a *
9122 conversion specifier, possibly modified by a length modifier, suitable for use within the
9123 format argument of a formatted input/output function when converting the corresponding
9124 integer type. These macro names have the general form of PRI (character string literals
9125 for the fprintf and fwprintf family) or SCN (character string literals for the
9126 fscanf and fwscanf family),217) followed by the conversion specifier, followed by a
9127 name corresponding to a similar type name in 7.20.1. In these names, N represents the
9128 width of the type as described in 7.20.1. For example, PRIdFAST32 can be used in a
9129 format string to print the value of an integer of type int_fast32_t.
9130 2 The fprintf macros for signed integers are:
9131 PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR
9132 PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR
9133 3 The fprintf macros for unsigned integers are:
9134 PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR
9135 PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR
9136 PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR
9137 PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR
9138 4 The fscanf macros for signed integers are:
9142 216) See ''future library directions'' (7.30.4).
9143 217) Separate macros are given for use with fprintf and fscanf functions because, in the general case,
9144 different format specifiers may be required for fprintf and fscanf, even when the type is the
9149 SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR
9150 SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR
9151 5 The fscanf macros for unsigned integers are:
9152 SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR
9153 SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR
9154 SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR
9155 6 For each type that the implementation provides in <stdint.h>, the corresponding
9156 fprintf macros shall be defined and the corresponding fscanf macros shall be
9157 defined unless the implementation does not have a suitable fscanf length modifier for
9160 #include <inttypes.h>
9164 uintmax_t i = UINTMAX_MAX; // this type always exists
9165 wprintf(L"The largest integer value is %020"
9170 7.8.2 Functions for greatest-width integer types
9171 7.8.2.1 The imaxabs function
9173 1 #include <inttypes.h>
9174 intmax_t imaxabs(intmax_t j);
9176 2 The imaxabs function computes the absolute value of an integer j. If the result cannot
9177 be represented, the behavior is undefined.218)
9179 3 The imaxabs function returns the absolute value.
9184 218) The absolute value of the most negative number cannot be represented in two's complement.
9188 7.8.2.2 The imaxdiv function
9190 1 #include <inttypes.h>
9191 imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
9193 2 The imaxdiv function computes numer / denom and numer % denom in a single
9196 3 The imaxdiv function returns a structure of type imaxdiv_t comprising both the
9197 quotient and the remainder. The structure shall contain (in either order) the members
9198 quot (the quotient) and rem (the remainder), each of which has type intmax_t. If
9199 either part of the result cannot be represented, the behavior is undefined.
9200 7.8.2.3 The strtoimax and strtoumax functions
9202 1 #include <inttypes.h>
9203 intmax_t strtoimax(const char * restrict nptr,
9204 char ** restrict endptr, int base);
9205 uintmax_t strtoumax(const char * restrict nptr,
9206 char ** restrict endptr, int base);
9208 2 The strtoimax and strtoumax functions are equivalent to the strtol, strtoll,
9209 strtoul, and strtoull functions, except that the initial portion of the string is
9210 converted to intmax_t and uintmax_t representation, respectively.
9212 3 The strtoimax and strtoumax functions return the converted value, if any. If no
9213 conversion could be performed, zero is returned. If the correct value is outside the range
9214 of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned
9215 (according to the return type and sign of the value, if any), and the value of the macro
9216 ERANGE is stored in errno.
9217 Forward references: the strtol, strtoll, strtoul, and strtoull functions
9225 7.8.2.4 The wcstoimax and wcstoumax functions
9227 1 #include <stddef.h> // for wchar_t
9228 #include <inttypes.h>
9229 intmax_t wcstoimax(const wchar_t * restrict nptr,
9230 wchar_t ** restrict endptr, int base);
9231 uintmax_t wcstoumax(const wchar_t * restrict nptr,
9232 wchar_t ** restrict endptr, int base);
9234 2 The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll,
9235 wcstoul, and wcstoull functions except that the initial portion of the wide string is
9236 converted to intmax_t and uintmax_t representation, respectively.
9238 3 The wcstoimax function returns the converted value, if any. If no conversion could be
9239 performed, zero is returned. If the correct value is outside the range of representable
9240 values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the
9241 return type and sign of the value, if any), and the value of the macro ERANGE is stored in
9243 Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions
9251 7.9 Alternative spellings <iso646.h>
9252 1 The header <iso646.h> defines the following eleven macros (on the left) that expand
9253 to the corresponding tokens (on the right):
9271 7.10 Sizes of integer types <limits.h>
9272 1 The header <limits.h> defines several macros that expand to various limits and
9273 parameters of the standard integer types.
9274 2 The macros, their meanings, and the constraints (or restrictions) on their values are listed
9282 7.11 Localization <locale.h>
9283 1 The header <locale.h> declares two functions, one type, and defines several macros.
9286 which contains members related to the formatting of numeric values. The structure shall
9287 contain at least the following members, in any order. The semantics of the members and
9288 their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have
9289 the values specified in the comments.
9290 char *decimal_point; // "."
9291 char *thousands_sep; // ""
9292 char *grouping; // ""
9293 char *mon_decimal_point; // ""
9294 char *mon_thousands_sep; // ""
9295 char *mon_grouping; // ""
9296 char *positive_sign; // ""
9297 char *negative_sign; // ""
9298 char *currency_symbol; // ""
9299 char frac_digits; // CHAR_MAX
9300 char p_cs_precedes; // CHAR_MAX
9301 char n_cs_precedes; // CHAR_MAX
9302 char p_sep_by_space; // CHAR_MAX
9303 char n_sep_by_space; // CHAR_MAX
9304 char p_sign_posn; // CHAR_MAX
9305 char n_sign_posn; // CHAR_MAX
9306 char *int_curr_symbol; // ""
9307 char int_frac_digits; // CHAR_MAX
9308 char int_p_cs_precedes; // CHAR_MAX
9309 char int_n_cs_precedes; // CHAR_MAX
9310 char int_p_sep_by_space; // CHAR_MAX
9311 char int_n_sep_by_space; // CHAR_MAX
9312 char int_p_sign_posn; // CHAR_MAX
9313 char int_n_sign_posn; // CHAR_MAX
9320 3 The macros defined are NULL (described in 7.19); and
9327 which expand to integer constant expressions with distinct values, suitable for use as the
9328 first argument to the setlocale function.219) Additional macro definitions, beginning
9329 with the characters LC_ and an uppercase letter,220) may also be specified by the
9331 7.11.1 Locale control
9332 7.11.1.1 The setlocale function
9334 1 #include <locale.h>
9335 char *setlocale(int category, const char *locale);
9337 2 The setlocale function selects the appropriate portion of the program's locale as
9338 specified by the category and locale arguments. The setlocale function may be
9339 used to change or query the program's entire current locale or portions thereof. The value
9340 LC_ALL for category names the program's entire locale; the other values for
9341 category name only a portion of the program's locale. LC_COLLATE affects the
9342 behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of
9343 the character handling functions221) and the multibyte and wide character functions.
9344 LC_MONETARY affects the monetary formatting information returned by the
9345 localeconv function. LC_NUMERIC affects the decimal-point character for the
9346 formatted input/output functions and the string conversion functions, as well as the
9347 nonmonetary formatting information returned by the localeconv function. LC_TIME
9348 affects the behavior of the strftime and wcsftime functions.
9349 3 A value of "C" for locale specifies the minimal environment for C translation; a value
9350 of "" for locale specifies the locale-specific native environment. Other
9351 implementation-defined strings may be passed as the second argument to setlocale.
9353 219) ISO/IEC 9945-2 specifies locale and charmap formats that may be used to specify locales for C.
9354 220) See ''future library directions'' (7.30.5).
9355 221) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and
9360 4 At program startup, the equivalent of
9361 setlocale(LC_ALL, "C");
9363 5 A call to the setlocale function may introduce a data race with other calls to the
9364 setlocale function or with calls to functions that are affected by the current locale.
9365 The implementation shall behave as if no library function calls the setlocale function.
9367 6 If a pointer to a string is given for locale and the selection can be honored, the
9368 setlocale function returns a pointer to the string associated with the specified
9369 category for the new locale. If the selection cannot be honored, the setlocale
9370 function returns a null pointer and the program's locale is not changed.
9371 7 A null pointer for locale causes the setlocale function to return a pointer to the
9372 string associated with the category for the program's current locale; the program's
9373 locale is not changed.222)
9374 8 The pointer to string returned by the setlocale function is such that a subsequent call
9375 with that string value and its associated category will restore that part of the program's
9376 locale. The string pointed to shall not be modified by the program, but may be
9377 overwritten by a subsequent call to the setlocale function.
9378 Forward references: formatted input/output functions (7.21.6), multibyte/wide
9379 character conversion functions (7.22.7), multibyte/wide string conversion functions
9380 (7.22.8), numeric conversion functions (7.22.1), the strcoll function (7.23.4.3), the
9381 strftime function (7.26.3.5), the strxfrm function (7.23.4.5).
9382 7.11.2 Numeric formatting convention inquiry
9383 7.11.2.1 The localeconv function
9385 1 #include <locale.h>
9386 struct lconv *localeconv(void);
9388 2 The localeconv function sets the components of an object with type struct lconv
9389 with values appropriate for the formatting of numeric quantities (monetary and otherwise)
9390 according to the rules of the current locale.
9394 222) The implementation shall arrange to encode in a string the various categories due to a heterogeneous
9395 locale when category has the value LC_ALL.
9399 3 The members of the structure with type char * are pointers to strings, any of which
9400 (except decimal_point) can point to "", to indicate that the value is not available in
9401 the current locale or is of zero length. Apart from grouping and mon_grouping, the
9402 strings shall start and end in the initial shift state. The members with type char are
9403 nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not
9404 available in the current locale. The members include the following:
9406 The decimal-point character used to format nonmonetary quantities.
9408 The character used to separate groups of digits before the decimal-point
9409 character in formatted nonmonetary quantities.
9411 A string whose elements indicate the size of each group of digits in
9412 formatted nonmonetary quantities.
9413 char *mon_decimal_point
9414 The decimal-point used to format monetary quantities.
9415 char *mon_thousands_sep
9416 The separator for groups of digits before the decimal-point in formatted
9417 monetary quantities.
9419 A string whose elements indicate the size of each group of digits in
9420 formatted monetary quantities.
9422 The string used to indicate a nonnegative-valued formatted monetary
9425 The string used to indicate a negative-valued formatted monetary quantity.
9426 char *currency_symbol
9427 The local currency symbol applicable to the current locale.
9429 The number of fractional digits (those after the decimal-point) to be
9430 displayed in a locally formatted monetary quantity.
9432 Set to 1 or 0 if the currency_symbol respectively precedes or
9433 succeeds the value for a nonnegative locally formatted monetary quantity.
9440 Set to 1 or 0 if the currency_symbol respectively precedes or
9441 succeeds the value for a negative locally formatted monetary quantity.
9443 Set to a value indicating the separation of the currency_symbol, the
9444 sign string, and the value for a nonnegative locally formatted monetary
9447 Set to a value indicating the separation of the currency_symbol, the
9448 sign string, and the value for a negative locally formatted monetary
9451 Set to a value indicating the positioning of the positive_sign for a
9452 nonnegative locally formatted monetary quantity.
9454 Set to a value indicating the positioning of the negative_sign for a
9455 negative locally formatted monetary quantity.
9456 char *int_curr_symbol
9457 The international currency symbol applicable to the current locale. The
9458 first three characters contain the alphabetic international currency symbol
9459 in accordance with those specified in ISO 4217. The fourth character
9460 (immediately preceding the null character) is the character used to separate
9461 the international currency symbol from the monetary quantity.
9462 char int_frac_digits
9463 The number of fractional digits (those after the decimal-point) to be
9464 displayed in an internationally formatted monetary quantity.
9465 char int_p_cs_precedes
9466 Set to 1 or 0 if the int_curr_symbol respectively precedes or
9467 succeeds the value for a nonnegative internationally formatted monetary
9469 char int_n_cs_precedes
9470 Set to 1 or 0 if the int_curr_symbol respectively precedes or
9471 succeeds the value for a negative internationally formatted monetary
9473 char int_p_sep_by_space
9474 Set to a value indicating the separation of the int_curr_symbol, the
9475 sign string, and the value for a nonnegative internationally formatted
9479 char int_n_sep_by_space
9480 Set to a value indicating the separation of the int_curr_symbol, the
9481 sign string, and the value for a negative internationally formatted monetary
9483 char int_p_sign_posn
9484 Set to a value indicating the positioning of the positive_sign for a
9485 nonnegative internationally formatted monetary quantity.
9486 char int_n_sign_posn
9487 Set to a value indicating the positioning of the negative_sign for a
9488 negative internationally formatted monetary quantity.
9489 4 The elements of grouping and mon_grouping are interpreted according to the
9491 CHAR_MAX No further grouping is to be performed.
9492 0 The previous element is to be repeatedly used for the remainder of the
9494 other The integer value is the number of digits that compose the current group.
9495 The next element is examined to determine the size of the next group of
9496 digits before the current group.
9497 5 The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space,
9498 and int_n_sep_by_space are interpreted according to the following:
9499 0 No space separates the currency symbol and value.
9500 1 If the currency symbol and sign string are adjacent, a space separates them from the
9501 value; otherwise, a space separates the currency symbol from the value.
9502 2 If the currency symbol and sign string are adjacent, a space separates them;
9503 otherwise, a space separates the sign string from the value.
9504 For int_p_sep_by_space and int_n_sep_by_space, the fourth character of
9505 int_curr_symbol is used instead of a space.
9506 6 The values of p_sign_posn, n_sign_posn, int_p_sign_posn, and
9507 int_n_sign_posn are interpreted according to the following:
9508 0 Parentheses surround the quantity and currency symbol.
9509 1 The sign string precedes the quantity and currency symbol.
9510 2 The sign string succeeds the quantity and currency symbol.
9511 3 The sign string immediately precedes the currency symbol.
9512 4 The sign string immediately succeeds the currency symbol.
9517 7 The implementation shall behave as if no library function calls the localeconv
9520 8 The localeconv function returns a pointer to the filled-in object. The structure
9521 pointed to by the return value shall not be modified by the program, but may be
9522 overwritten by a subsequent call to the localeconv function. In addition, calls to the
9523 setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may
9524 overwrite the contents of the structure.
9525 9 EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format
9526 monetary quantities.
9527 Local format International format
9529 Country Positive Negative Positive Negative
9531 Country1 1.234,56 mk -1.234,56 mk FIM 1.234,56 FIM -1.234,56
9532 Country2 L.1.234 -L.1.234 ITL 1.234 -ITL 1.234
9533 Country3 fl. 1.234,56 fl. -1.234,56 NLG 1.234,56 NLG -1.234,56
9534 Country4 SFrs.1,234.56 SFrs.1,234.56C CHF 1,234.56 CHF 1,234.56C
9535 10 For these four countries, the respective values for the monetary members of the structure returned by
9536 localeconv could be:
9537 Country1 Country2 Country3 Country4
9539 mon_decimal_point "," "" "," "."
9540 mon_thousands_sep "." "." "." ","
9541 mon_grouping "\3" "\3" "\3" "\3"
9542 positive_sign "" "" "" ""
9543 negative_sign "-" "-" "-" "C"
9544 currency_symbol "mk" "L." "\u0192" "SFrs."
9546 p_cs_precedes 0 1 1 1
9547 n_cs_precedes 0 1 1 1
9548 p_sep_by_space 1 0 1 0
9549 n_sep_by_space 1 0 2 0
9552 int_curr_symbol "FIM " "ITL " "NLG " "CHF "
9553 int_frac_digits 2 0 2 2
9554 int_p_cs_precedes 1 1 1 1
9555 int_n_cs_precedes 1 1 1 1
9556 int_p_sep_by_space 1 1 1 1
9557 int_n_sep_by_space 2 1 2 1
9558 int_p_sign_posn 1 1 1 1
9559 int_n_sign_posn 4 1 4 2
9566 11 EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members
9567 affect the formatted value.
9570 p_cs_precedes p_sign_posn 0 1 2
9572 0 0 (1.25$) (1.25 $) (1.25$)
9573 1 +1.25$ +1.25 $ + 1.25$
9574 2 1.25$+ 1.25 $+ 1.25$ +
9575 3 1.25+$ 1.25 +$ 1.25+ $
9576 4 1.25$+ 1.25 $+ 1.25$ +
9578 1 0 ($1.25) ($ 1.25) ($1.25)
9579 1 +$1.25 +$ 1.25 + $1.25
9580 2 $1.25+ $ 1.25+ $1.25 +
9581 3 +$1.25 +$ 1.25 + $1.25
9582 4 $+1.25 $+ 1.25 $ +1.25
9589 7.12 Mathematics <math.h>
9590 1 The header <math.h> declares two types and many mathematical functions and defines
9591 several macros. Most synopses specify a family of functions consisting of a principal
9592 function with one or more double parameters, a double return value, or both; and
9593 other functions with the same name but with f and l suffixes, which are corresponding
9594 functions with float and long double parameters, return values, or both.223)
9595 Integer arithmetic functions and conversion functions are discussed later.
9599 are floating types at least as wide as float and double, respectively, and such that
9600 double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0,
9601 float_t and double_t are float and double, respectively; if
9602 FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals
9603 2, they are both long double; and for other values of FLT_EVAL_METHOD, they are
9604 otherwise implementation-defined.224)
9607 expands to a positive double constant expression, not necessarily representable as a
9611 are respectively float and long double analogs of HUGE_VAL.225)
9614 expands to a constant expression of type float representing positive or unsigned
9615 infinity, if available; else to a positive constant of type float that overflows at
9619 223) Particularly on systems with wide expression evaluation, a <math.h> function might pass arguments
9620 and return values in wider format than the synopsis prototype indicates.
9621 224) The types float_t and double_t are intended to be the implementation's most efficient types at
9622 least as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, the
9623 type float_t is the narrowest type used by the implementation to evaluate floating expressions.
9624 225) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that
9625 supports infinities.
9629 translation time.226)
9632 is defined if and only if the implementation supports quiet NaNs for the float type. It
9633 expands to a constant expression of type float representing a quiet NaN.
9634 6 The number classification macros
9640 represent the mutually exclusive kinds of floating-point values. They expand to integer
9641 constant expressions with distinct values. Additional implementation-defined floating-
9642 point classifications, with macro definitions beginning with FP_ and an uppercase letter,
9643 may also be specified by the implementation.
9646 is optionally defined. If defined, it indicates that the fma function generally executes
9647 about as fast as, or faster than, a multiply and an add of double operands.227) The
9651 are, respectively, float and long double analogs of FP_FAST_FMA. If defined,
9652 these macros expand to the integer constant 1.
9656 expand to integer constant expressions whose values are returned by ilogb(x) if x is
9657 zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or
9658 -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN.
9661 226) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic.
9662 227) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented
9663 directly with a hardware multiply-add instruction. Software implementations are expected to be
9664 substantially slower.
9671 expand to the integer constants 1 and 2, respectively; the macro
9673 expands to an expression that has type int and the value MATH_ERRNO,
9674 MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling is
9675 constant for the duration of the program. It is unspecified whether
9676 math_errhandling is a macro or an identifier with external linkage. If a macro
9677 definition is suppressed or a program defines an identifier with the name
9678 math_errhandling, the behavior is undefined. If the expression
9679 math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation
9680 shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in
9682 7.12.1 Treatment of error conditions
9683 1 The behavior of each of the functions in <math.h> is specified for all representable
9684 values of its input arguments, except where stated otherwise. Each function shall execute
9685 as if it were a single operation without raising SIGFPE and without generating any of the
9686 floating-point exceptions ''invalid'', ''divide-by-zero'', or ''overflow'' except to reflect
9687 the result of the function.
9688 2 For all functions, a domain error occurs if an input argument is outside the domain over
9689 which the mathematical function is defined. The description of each function lists any
9690 required domain errors; an implementation may define additional domain errors, provided
9691 that such errors are consistent with the mathematical definition of the function.228) On a
9692 domain error, the function returns an implementation-defined value; if the integer
9693 expression math_errhandling & MATH_ERRNO is nonzero, the integer expression
9694 errno acquires the value EDOM; if the integer expression math_errhandling &
9695 MATH_ERREXCEPT is nonzero, the ''invalid'' floating-point exception is raised.
9696 3 Similarly, a pole error (also known as a singularity or infinitary) occurs if the
9697 mathematical function has an exact infinite result as the finite input argument(s) are
9698 approached in the limit (for example, log(0.0)). The description of each function lists
9699 any required pole errors; an implementation may define additional pole errors, provided
9700 that such errors are consistent with the mathematical definition of the function. On a pole
9701 error, the function returns an implementation-defined value; if the integer expression
9704 228) In an implementation that supports infinities, this allows an infinity as an argument to be a domain
9705 error if the mathematical domain of the function does not include the infinity.
9709 math_errhandling & MATH_ERRNO is nonzero, the integer expression errno
9710 acquires the value ERANGE; if the integer expression math_errhandling &
9711 MATH_ERREXCEPT is nonzero, the ''divide-by-zero'' floating-point exception is raised.
9712 4 Likewise, a range error occurs if the mathematical result of the function cannot be
9713 represented in an object of the specified type, due to extreme magnitude.
9714 5 A floating result overflows if the magnitude of the mathematical result is finite but so
9715 large that the mathematical result cannot be represented without extraordinary roundoff
9716 error in an object of the specified type. If a floating result overflows and default rounding
9717 is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or *
9718 HUGE_VALL according to the return type, with the same sign as the correct value of the
9719 function; if the integer expression math_errhandling & MATH_ERRNO is nonzero,
9720 the integer expression errno acquires the value ERANGE; if the integer expression
9721 math_errhandling & MATH_ERREXCEPT is nonzero, the ''overflow'' floating-
9722 point exception is raised.
9723 6 The result underflows if the magnitude of the mathematical result is so small that the
9724 mathematical result cannot be represented, without extraordinary roundoff error, in an
9725 object of the specified type.229) If the result underflows, the function returns an
9726 implementation-defined value whose magnitude is no greater than the smallest
9727 normalized positive number in the specified type; if the integer expression
9728 math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the
9729 value ERANGE is implementation-defined; if the integer expression
9730 math_errhandling & MATH_ERREXCEPT is nonzero, whether the ''underflow''
9731 floating-point exception is raised is implementation-defined.
9732 7 If a domain, pole, or range error occurs and the integer expression
9733 math_errhandling & MATH_ERRNO is zero,230) then errno shall either be set to
9734 the value corresponding to the error or left unmodified. If no such error occurs, errno
9735 shall be left unmodified regardless of the setting of math_errhandling.
9740 229) The term underflow here is intended to encompass both ''gradual underflow'' as in IEC 60559 and
9741 also ''flush-to-zero'' underflow.
9742 230) Math errors are being indicated by the floating-point exception flags rather than by errno.
9746 7.12.2 The FP_CONTRACT pragma
9749 #pragma STDC FP_CONTRACT on-off-switch
9751 2 The FP_CONTRACT pragma can be used to allow (if the state is ''on'') or disallow (if the
9752 state is ''off'') the implementation to contract expressions (6.5). Each pragma can occur
9753 either outside external declarations or preceding all explicit declarations and statements
9754 inside a compound statement. When outside external declarations, the pragma takes
9755 effect from its occurrence until another FP_CONTRACT pragma is encountered, or until
9756 the end of the translation unit. When inside a compound statement, the pragma takes
9757 effect from its occurrence until another FP_CONTRACT pragma is encountered
9758 (including within a nested compound statement), or until the end of the compound
9759 statement; at the end of a compound statement the state for the pragma is restored to its
9760 condition just before the compound statement. If this pragma is used in any other
9761 context, the behavior is undefined. The default state (''on'' or ''off'') for the pragma is
9762 implementation-defined.
9763 7.12.3 Classification macros
9764 1 In the synopses in this subclause, real-floating indicates that the argument shall be an
9765 expression of real floating type.
9766 7.12.3.1 The fpclassify macro
9769 int fpclassify(real-floating x);
9771 2 The fpclassify macro classifies its argument value as NaN, infinite, normal,
9772 subnormal, zero, or into another implementation-defined category. First, an argument
9773 represented in a format wider than its semantic type is converted to its semantic type.
9774 Then classification is based on the type of the argument.231)
9776 3 The fpclassify macro returns the value of the number classification macro
9777 appropriate to the value of its argument. *
9780 231) Since an expression can be evaluated with more range and precision than its type has, it is important to
9781 know the type that classification is based on. For example, a normal long double value might
9782 become subnormal when converted to double, and zero when converted to float.
9786 7.12.3.2 The isfinite macro
9789 int isfinite(real-floating x);
9791 2 The isfinite macro determines whether its argument has a finite value (zero,
9792 subnormal, or normal, and not infinite or NaN). First, an argument represented in a
9793 format wider than its semantic type is converted to its semantic type. Then determination
9794 is based on the type of the argument.
9796 3 The isfinite macro returns a nonzero value if and only if its argument has a finite
9798 7.12.3.3 The isinf macro
9801 int isinf(real-floating x);
9803 2 The isinf macro determines whether its argument value is an infinity (positive or
9804 negative). First, an argument represented in a format wider than its semantic type is
9805 converted to its semantic type. Then determination is based on the type of the argument.
9807 3 The isinf macro returns a nonzero value if and only if its argument has an infinite
9809 7.12.3.4 The isnan macro
9812 int isnan(real-floating x);
9814 2 The isnan macro determines whether its argument value is a NaN. First, an argument
9815 represented in a format wider than its semantic type is converted to its semantic type.
9816 Then determination is based on the type of the argument.232)
9819 232) For the isnan macro, the type for determination does not matter unless the implementation supports
9820 NaNs in the evaluation type but not in the semantic type.
9825 3 The isnan macro returns a nonzero value if and only if its argument has a NaN value.
9826 7.12.3.5 The isnormal macro
9829 int isnormal(real-floating x);
9831 2 The isnormal macro determines whether its argument value is normal (neither zero,
9832 subnormal, infinite, nor NaN). First, an argument represented in a format wider than its
9833 semantic type is converted to its semantic type. Then determination is based on the type
9836 3 The isnormal macro returns a nonzero value if and only if its argument has a normal
9838 7.12.3.6 The signbit macro
9841 int signbit(real-floating x);
9843 2 The signbit macro determines whether the sign of its argument value is negative.233)
9845 3 The signbit macro returns a nonzero value if and only if the sign of its argument value
9851 233) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero is
9852 unsigned, it is treated as positive.
9856 7.12.4 Trigonometric functions
9857 7.12.4.1 The acos functions
9860 double acos(double x);
9861 float acosf(float x);
9862 long double acosl(long double x);
9864 2 The acos functions compute the principal value of the arc cosine of x. A domain error
9865 occurs for arguments not in the interval [-1, +1].
9867 3 The acos functions return arccos x in the interval [0, pi ] radians.
9868 7.12.4.2 The asin functions
9871 double asin(double x);
9872 float asinf(float x);
9873 long double asinl(long double x);
9875 2 The asin functions compute the principal value of the arc sine of x. A domain error
9876 occurs for arguments not in the interval [-1, +1].
9878 3 The asin functions return arcsin x in the interval [-pi /2, +pi /2] radians.
9879 7.12.4.3 The atan functions
9882 double atan(double x);
9883 float atanf(float x);
9884 long double atanl(long double x);
9886 2 The atan functions compute the principal value of the arc tangent of x.
9894 3 The atan functions return arctan x in the interval [-pi /2, +pi /2] radians.
9895 7.12.4.4 The atan2 functions
9898 double atan2(double y, double x);
9899 float atan2f(float y, float x);
9900 long double atan2l(long double y, long double x);
9902 2 The atan2 functions compute the value of the arc tangent of y/x, using the signs of both
9903 arguments to determine the quadrant of the return value. A domain error may occur if
9904 both arguments are zero.
9906 3 The atan2 functions return arctan y/x in the interval [-pi , +pi ] radians.
9907 7.12.4.5 The cos functions
9910 double cos(double x);
9911 float cosf(float x);
9912 long double cosl(long double x);
9914 2 The cos functions compute the cosine of x (measured in radians).
9916 3 The cos functions return cos x.
9917 7.12.4.6 The sin functions
9920 double sin(double x);
9921 float sinf(float x);
9922 long double sinl(long double x);
9924 2 The sin functions compute the sine of x (measured in radians).
9931 3 The sin functions return sin x.
9932 7.12.4.7 The tan functions
9935 double tan(double x);
9936 float tanf(float x);
9937 long double tanl(long double x);
9939 2 The tan functions return the tangent of x (measured in radians).
9941 3 The tan functions return tan x.
9942 7.12.5 Hyperbolic functions
9943 7.12.5.1 The acosh functions
9946 double acosh(double x);
9947 float acoshf(float x);
9948 long double acoshl(long double x);
9950 2 The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain
9951 error occurs for arguments less than 1.
9953 3 The acosh functions return arcosh x in the interval [0, +(inf)].
9954 7.12.5.2 The asinh functions
9957 double asinh(double x);
9958 float asinhf(float x);
9959 long double asinhl(long double x);
9961 2 The asinh functions compute the arc hyperbolic sine of x.
9967 3 The asinh functions return arsinh x.
9968 7.12.5.3 The atanh functions
9971 double atanh(double x);
9972 float atanhf(float x);
9973 long double atanhl(long double x);
9975 2 The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs
9976 for arguments not in the interval [-1, +1]. A pole error may occur if the argument equals
9979 3 The atanh functions return artanh x.
9980 7.12.5.4 The cosh functions
9983 double cosh(double x);
9984 float coshf(float x);
9985 long double coshl(long double x);
9987 2 The cosh functions compute the hyperbolic cosine of x. A range error occurs if the
9988 magnitude of x is too large.
9990 3 The cosh functions return cosh x.
9991 7.12.5.5 The sinh functions
9994 double sinh(double x);
9995 float sinhf(float x);
9996 long double sinhl(long double x);
9998 2 The sinh functions compute the hyperbolic sine of x. A range error occurs if the
9999 magnitude of x is too large.
10003 3 The sinh functions return sinh x.
10004 7.12.5.6 The tanh functions
10006 1 #include <math.h>
10007 double tanh(double x);
10008 float tanhf(float x);
10009 long double tanhl(long double x);
10011 2 The tanh functions compute the hyperbolic tangent of x.
10013 3 The tanh functions return tanh x.
10014 7.12.6 Exponential and logarithmic functions
10015 7.12.6.1 The exp functions
10017 1 #include <math.h>
10018 double exp(double x);
10019 float expf(float x);
10020 long double expl(long double x);
10022 2 The exp functions compute the base-e exponential of x. A range error occurs if the
10023 magnitude of x is too large.
10025 3 The exp functions return ex .
10026 7.12.6.2 The exp2 functions
10028 1 #include <math.h>
10029 double exp2(double x);
10030 float exp2f(float x);
10031 long double exp2l(long double x);
10033 2 The exp2 functions compute the base-2 exponential of x. A range error occurs if the
10034 magnitude of x is too large.
10039 3 The exp2 functions return 2x .
10040 7.12.6.3 The expm1 functions
10042 1 #include <math.h>
10043 double expm1(double x);
10044 float expm1f(float x);
10045 long double expm1l(long double x);
10047 2 The expm1 functions compute the base-e exponential of the argument, minus 1. A range
10048 error occurs if x is too large.234)
10050 3 The expm1 functions return ex - 1.
10051 7.12.6.4 The frexp functions
10053 1 #include <math.h>
10054 double frexp(double value, int *exp);
10055 float frexpf(float value, int *exp);
10056 long double frexpl(long double value, int *exp);
10058 2 The frexp functions break a floating-point number into a normalized fraction and an
10059 integral power of 2. They store the integer in the int object pointed to by exp.
10061 3 If value is not a floating-point number or if the integral power of 2 is outside the range
10062 of int, the results are unspecified. Otherwise, the frexp functions return the value x,
10063 such that x has a magnitude in the interval [1/2, 1) or zero, and value equals x x 2*exp .
10064 If value is zero, both parts of the result are zero.
10069 234) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1.
10073 7.12.6.5 The ilogb functions
10075 1 #include <math.h>
10076 int ilogb(double x);
10077 int ilogbf(float x);
10078 int ilogbl(long double x);
10080 2 The ilogb functions extract the exponent of x as a signed int value. If x is zero they
10081 compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is
10082 a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling
10083 the corresponding logb function and casting the returned value to type int. A domain
10084 error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside
10085 the range of the return type, the numeric result is unspecified.
10087 3 The ilogb functions return the exponent of x as a signed int value.
10088 Forward references: the logb functions (7.12.6.11).
10089 7.12.6.6 The ldexp functions
10091 1 #include <math.h>
10092 double ldexp(double x, int exp);
10093 float ldexpf(float x, int exp);
10094 long double ldexpl(long double x, int exp);
10096 2 The ldexp functions multiply a floating-point number by an integral power of 2. A
10097 range error may occur.
10099 3 The ldexp functions return x x 2exp .
10100 7.12.6.7 The log functions
10102 1 #include <math.h>
10103 double log(double x);
10104 float logf(float x);
10105 long double logl(long double x);
10112 2 The log functions compute the base-e (natural) logarithm of x. A domain error occurs if
10113 the argument is negative. A pole error may occur if the argument is zero.
10115 3 The log functions return loge x.
10116 7.12.6.8 The log10 functions
10118 1 #include <math.h>
10119 double log10(double x);
10120 float log10f(float x);
10121 long double log10l(long double x);
10123 2 The log10 functions compute the base-10 (common) logarithm of x. A domain error
10124 occurs if the argument is negative. A pole error may occur if the argument is zero.
10126 3 The log10 functions return log10 x.
10127 7.12.6.9 The log1p functions
10129 1 #include <math.h>
10130 double log1p(double x);
10131 float log1pf(float x);
10132 long double log1pl(long double x);
10134 2 The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.235)
10135 A domain error occurs if the argument is less than -1. A pole error may occur if the
10136 argument equals -1.
10138 3 The log1p functions return loge (1 + x).
10143 235) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x).
10147 7.12.6.10 The log2 functions
10149 1 #include <math.h>
10150 double log2(double x);
10151 float log2f(float x);
10152 long double log2l(long double x);
10154 2 The log2 functions compute the base-2 logarithm of x. A domain error occurs if the
10155 argument is less than zero. A pole error may occur if the argument is zero.
10157 3 The log2 functions return log2 x.
10158 7.12.6.11 The logb functions
10160 1 #include <math.h>
10161 double logb(double x);
10162 float logbf(float x);
10163 long double logbl(long double x);
10165 2 The logb functions extract the exponent of x, as a signed integer value in floating-point
10166 format. If x is subnormal it is treated as though it were normalized; thus, for positive
10168 1 <= x x FLT_RADIX-logb(x) < FLT_RADIX
10169 A domain error or pole error may occur if the argument is zero.
10171 3 The logb functions return the signed exponent of x.
10172 7.12.6.12 The modf functions
10174 1 #include <math.h>
10175 double modf(double value, double *iptr);
10176 float modff(float value, float *iptr);
10177 long double modfl(long double value, long double *iptr);
10179 2 The modf functions break the argument value into integral and fractional parts, each of
10180 which has the same type and sign as the argument. They store the integral part (in
10183 floating-point format) in the object pointed to by iptr.
10185 3 The modf functions return the signed fractional part of value.
10186 7.12.6.13 The scalbn and scalbln functions
10188 1 #include <math.h>
10189 double scalbn(double x, int n);
10190 float scalbnf(float x, int n);
10191 long double scalbnl(long double x, int n);
10192 double scalbln(double x, long int n);
10193 float scalblnf(float x, long int n);
10194 long double scalblnl(long double x, long int n);
10196 2 The scalbn and scalbln functions compute x x FLT_RADIXn efficiently, not
10197 normally by computing FLT_RADIXn explicitly. A range error may occur.
10199 3 The scalbn and scalbln functions return x x FLT_RADIXn .
10200 7.12.7 Power and absolute-value functions
10201 7.12.7.1 The cbrt functions
10203 1 #include <math.h>
10204 double cbrt(double x);
10205 float cbrtf(float x);
10206 long double cbrtl(long double x);
10208 2 The cbrt functions compute the real cube root of x.
10210 3 The cbrt functions return x1/3 .
10217 7.12.7.2 The fabs functions
10219 1 #include <math.h>
10220 double fabs(double x);
10221 float fabsf(float x);
10222 long double fabsl(long double x);
10224 2 The fabs functions compute the absolute value of a floating-point number x.
10226 3 The fabs functions return | x |.
10227 7.12.7.3 The hypot functions
10229 1 #include <math.h>
10230 double hypot(double x, double y);
10231 float hypotf(float x, float y);
10232 long double hypotl(long double x, long double y);
10234 2 The hypot functions compute the square root of the sum of the squares of x and y,
10235 without undue overflow or underflow. A range error may occur.
10237 4 The hypot functions return sqrt:x2 + y2 .
10240 7.12.7.4 The pow functions
10242 1 #include <math.h>
10243 double pow(double x, double y);
10244 float powf(float x, float y);
10245 long double powl(long double x, long double y);
10247 2 The pow functions compute x raised to the power y. A domain error occurs if x is finite
10248 and negative and y is finite and not an integer value. A range error may occur. A domain
10249 error may occur if x is zero and y is zero. A domain error or pole error may occur if x is
10250 zero and y is less than zero.
10258 3 The pow functions return xy .
10259 7.12.7.5 The sqrt functions
10261 1 #include <math.h>
10262 double sqrt(double x);
10263 float sqrtf(float x);
10264 long double sqrtl(long double x);
10266 2 The sqrt functions compute the nonnegative square root of x. A domain error occurs if
10267 the argument is less than zero.
10269 3 The sqrt functions return sqrt:x.
10272 7.12.8 Error and gamma functions
10273 7.12.8.1 The erf functions
10275 1 #include <math.h>
10276 double erf(double x);
10277 float erff(float x);
10278 long double erfl(long double x);
10280 2 The erf functions compute the error function of x.
10285 The erf functions return erf x =
10290 7.12.8.2 The erfc functions
10292 1 #include <math.h>
10293 double erfc(double x);
10294 float erfcf(float x);
10295 long double erfcl(long double x);
10297 2 The erfc functions compute the complementary error function of x. A range error
10298 occurs if x is too large.
10305 The erfc functions return erfc x = 1 - erf x =
10310 7.12.8.3 The lgamma functions
10312 1 #include <math.h>
10313 double lgamma(double x);
10314 float lgammaf(float x);
10315 long double lgammal(long double x);
10317 2 The lgamma functions compute the natural logarithm of the absolute value of gamma of
10318 x. A range error occurs if x is too large. A pole error may occur if x is a negative integer
10321 3 The lgamma functions return loge | (Gamma)(x) |.
10322 7.12.8.4 The tgamma functions
10324 1 #include <math.h>
10325 double tgamma(double x);
10326 float tgammaf(float x);
10327 long double tgammal(long double x);
10329 2 The tgamma functions compute the gamma function of x. A domain error or pole error
10330 may occur if x is a negative integer or zero. A range error occurs if the magnitude of x is
10331 too large and may occur if the magnitude of x is too small.
10333 3 The tgamma functions return (Gamma)(x).
10340 7.12.9 Nearest integer functions
10341 7.12.9.1 The ceil functions
10343 1 #include <math.h>
10344 double ceil(double x);
10345 float ceilf(float x);
10346 long double ceill(long double x);
10348 2 The ceil functions compute the smallest integer value not less than x.
10350 3 The ceil functions return [^x^], expressed as a floating-point number.
10351 7.12.9.2 The floor functions
10353 1 #include <math.h>
10354 double floor(double x);
10355 float floorf(float x);
10356 long double floorl(long double x);
10358 2 The floor functions compute the largest integer value not greater than x.
10360 3 The floor functions return [_x_], expressed as a floating-point number.
10361 7.12.9.3 The nearbyint functions
10363 1 #include <math.h>
10364 double nearbyint(double x);
10365 float nearbyintf(float x);
10366 long double nearbyintl(long double x);
10368 2 The nearbyint functions round their argument to an integer value in floating-point
10369 format, using the current rounding direction and without raising the ''inexact'' floating-
10378 3 The nearbyint functions return the rounded integer value.
10379 7.12.9.4 The rint functions
10381 1 #include <math.h>
10382 double rint(double x);
10383 float rintf(float x);
10384 long double rintl(long double x);
10386 2 The rint functions differ from the nearbyint functions (7.12.9.3) only in that the
10387 rint functions may raise the ''inexact'' floating-point exception if the result differs in
10388 value from the argument.
10390 3 The rint functions return the rounded integer value.
10391 7.12.9.5 The lrint and llrint functions
10393 1 #include <math.h>
10394 long int lrint(double x);
10395 long int lrintf(float x);
10396 long int lrintl(long double x);
10397 long long int llrint(double x);
10398 long long int llrintf(float x);
10399 long long int llrintl(long double x);
10401 2 The lrint and llrint functions round their argument to the nearest integer value,
10402 rounding according to the current rounding direction. If the rounded value is outside the
10403 range of the return type, the numeric result is unspecified and a domain error or range
10406 3 The lrint and llrint functions return the rounded integer value.
10413 7.12.9.6 The round functions
10415 1 #include <math.h>
10416 double round(double x);
10417 float roundf(float x);
10418 long double roundl(long double x);
10420 2 The round functions round their argument to the nearest integer value in floating-point
10421 format, rounding halfway cases away from zero, regardless of the current rounding
10424 3 The round functions return the rounded integer value.
10425 7.12.9.7 The lround and llround functions
10427 1 #include <math.h>
10428 long int lround(double x);
10429 long int lroundf(float x);
10430 long int lroundl(long double x);
10431 long long int llround(double x);
10432 long long int llroundf(float x);
10433 long long int llroundl(long double x);
10435 2 The lround and llround functions round their argument to the nearest integer value,
10436 rounding halfway cases away from zero, regardless of the current rounding direction. If
10437 the rounded value is outside the range of the return type, the numeric result is unspecified
10438 and a domain error or range error may occur.
10440 3 The lround and llround functions return the rounded integer value.
10441 7.12.9.8 The trunc functions
10443 1 #include <math.h>
10444 double trunc(double x);
10445 float truncf(float x);
10446 long double truncl(long double x);
10452 2 The trunc functions round their argument to the integer value, in floating format,
10453 nearest to but no larger in magnitude than the argument.
10455 3 The trunc functions return the truncated integer value.
10456 7.12.10 Remainder functions
10457 7.12.10.1 The fmod functions
10459 1 #include <math.h>
10460 double fmod(double x, double y);
10461 float fmodf(float x, float y);
10462 long double fmodl(long double x, long double y);
10464 2 The fmod functions compute the floating-point remainder of x/y.
10466 3 The fmod functions return the value x - ny, for some integer n such that, if y is nonzero,
10467 the result has the same sign as x and magnitude less than the magnitude of y. If y is zero,
10468 whether a domain error occurs or the fmod functions return zero is implementation-
10470 7.12.10.2 The remainder functions
10472 1 #include <math.h>
10473 double remainder(double x, double y);
10474 float remainderf(float x, float y);
10475 long double remainderl(long double x, long double y);
10477 2 The remainder functions compute the remainder x REM y required by IEC 60559.236)
10482 236) ''When y != 0, the remainder r = x REM y is defined regardless of the rounding mode by the
10483 mathematical relation r = x - ny, where n is the integer nearest the exact value of x/y; whenever
10484 | n - x/y | = 1/2, then n is even. If r = 0, its sign shall be that of x.'' This definition is applicable for *
10485 all implementations.
10490 3 The remainder functions return x REM y. If y is zero, whether a domain error occurs
10491 or the functions return zero is implementation defined.
10492 7.12.10.3 The remquo functions
10494 1 #include <math.h>
10495 double remquo(double x, double y, int *quo);
10496 float remquof(float x, float y, int *quo);
10497 long double remquol(long double x, long double y,
10500 2 The remquo functions compute the same remainder as the remainder functions. In
10501 the object pointed to by quo they store a value whose sign is the sign of x/y and whose
10502 magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where
10503 n is an implementation-defined integer greater than or equal to 3.
10505 3 The remquo functions return x REM y. If y is zero, the value stored in the object
10506 pointed to by quo is unspecified and whether a domain error occurs or the functions
10507 return zero is implementation defined.
10508 7.12.11 Manipulation functions
10509 7.12.11.1 The copysign functions
10511 1 #include <math.h>
10512 double copysign(double x, double y);
10513 float copysignf(float x, float y);
10514 long double copysignl(long double x, long double y);
10516 2 The copysign functions produce a value with the magnitude of x and the sign of y.
10517 They produce a NaN (with the sign of y) if x is a NaN. On implementations that
10518 represent a signed zero but do not treat negative zero consistently in arithmetic
10519 operations, the copysign functions regard the sign of zero as positive.
10521 3 The copysign functions return a value with the magnitude of x and the sign of y.
10527 7.12.11.2 The nan functions
10529 1 #include <math.h>
10530 double nan(const char *tagp);
10531 float nanf(const char *tagp);
10532 long double nanl(const char *tagp);
10534 2 The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char-
10535 sequence)", (char**) NULL); the call nan("") is equivalent to
10536 strtod("NAN()", (char**) NULL). If tagp does not point to an n-char
10537 sequence or an empty string, the call is equivalent to strtod("NAN", (char**)
10538 NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof
10541 3 The nan functions return a quiet NaN, if available, with content indicated through tagp.
10542 If the implementation does not support quiet NaNs, the functions return zero.
10543 Forward references: the strtod, strtof, and strtold functions (7.22.1.3).
10544 7.12.11.3 The nextafter functions
10546 1 #include <math.h>
10547 double nextafter(double x, double y);
10548 float nextafterf(float x, float y);
10549 long double nextafterl(long double x, long double y);
10551 2 The nextafter functions determine the next representable value, in the type of the
10552 function, after x in the direction of y, where x and y are first converted to the type of the
10553 function.237) The nextafter functions return y if x equals y. A range error may occur
10554 if the magnitude of x is the largest finite value representable in the type and the result is
10555 infinite or not representable in the type.
10557 3 The nextafter functions return the next representable value in the specified format
10558 after x in the direction of y.
10561 237) The argument values are converted to the type of the function, even by a macro implementation of the
10566 7.12.11.4 The nexttoward functions
10568 1 #include <math.h>
10569 double nexttoward(double x, long double y);
10570 float nexttowardf(float x, long double y);
10571 long double nexttowardl(long double x, long double y);
10573 2 The nexttoward functions are equivalent to the nextafter functions except that the
10574 second parameter has type long double and the functions return y converted to the
10575 type of the function if x equals y.238)
10576 7.12.12 Maximum, minimum, and positive difference functions
10577 7.12.12.1 The fdim functions
10579 1 #include <math.h>
10580 double fdim(double x, double y);
10581 float fdimf(float x, float y);
10582 long double fdiml(long double x, long double y);
10584 2 The fdim functions determine the positive difference between their arguments:
10588 A range error may occur.
10590 3 The fdim functions return the positive difference value.
10591 7.12.12.2 The fmax functions
10593 1 #include <math.h>
10594 double fmax(double x, double y);
10595 float fmaxf(float x, float y);
10596 long double fmaxl(long double x, long double y);
10600 238) The result of the nexttoward functions is determined in the type of the function, without loss of
10601 range or precision in a floating second argument.
10606 2 The fmax functions determine the maximum numeric value of their arguments.239)
10608 3 The fmax functions return the maximum numeric value of their arguments.
10609 7.12.12.3 The fmin functions
10611 1 #include <math.h>
10612 double fmin(double x, double y);
10613 float fminf(float x, float y);
10614 long double fminl(long double x, long double y);
10616 2 The fmin functions determine the minimum numeric value of their arguments.240)
10618 3 The fmin functions return the minimum numeric value of their arguments.
10619 7.12.13 Floating multiply-add
10620 7.12.13.1 The fma functions
10622 1 #include <math.h>
10623 double fma(double x, double y, double z);
10624 float fmaf(float x, float y, float z);
10625 long double fmal(long double x, long double y,
10628 2 The fma functions compute (x x y) + z, rounded as one ternary operation: they compute
10629 the value (as if) to infinite precision and round once to the result format, according to the
10630 current rounding mode. A range error may occur.
10632 3 The fma functions return (x x y) + z, rounded as one ternary operation.
10637 239) NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the
10638 fmax functions choose the numeric value. See F.10.9.2.
10639 240) The fmin functions are analogous to the fmax functions in their treatment of NaNs.
10643 7.12.14 Comparison macros
10644 1 The relational and equality operators support the usual mathematical relationships
10645 between numeric values. For any ordered pair of numeric values exactly one of the
10646 relationships -- less, greater, and equal -- is true. Relational operators may raise the
10647 ''invalid'' floating-point exception when argument values are NaNs. For a NaN and a
10648 numeric value, or for two NaNs, just the unordered relationship is true.241) The following
10649 subclauses provide macros that are quiet (non floating-point exception raising) versions
10650 of the relational operators, and other comparison macros that facilitate writing efficient
10651 code that accounts for NaNs without suffering the ''invalid'' floating-point exception. In
10652 the synopses in this subclause, real-floating indicates that the argument shall be an
10653 expression of real floating type242) (both arguments need not have the same type).243)
10654 7.12.14.1 The isgreater macro
10656 1 #include <math.h>
10657 int isgreater(real-floating x, real-floating y);
10659 2 The isgreater macro determines whether its first argument is greater than its second
10660 argument. The value of isgreater(x, y) is always equal to (x) > (y); however,
10661 unlike (x) > (y), isgreater(x, y) does not raise the ''invalid'' floating-point
10662 exception when x and y are unordered.
10664 3 The isgreater macro returns the value of (x) > (y).
10665 7.12.14.2 The isgreaterequal macro
10667 1 #include <math.h>
10668 int isgreaterequal(real-floating x, real-floating y);
10673 241) IEC 60559 requires that the built-in relational operators raise the ''invalid'' floating-point exception if
10674 the operands compare unordered, as an error indicator for programs written without consideration of
10675 NaNs; the result in these cases is false.
10676 242) If any argument is of integer type, or any other type that is not a real floating type, the behavior is
10678 243) Whether an argument represented in a format wider than its semantic type is converted to the semantic
10679 type is unspecified.
10684 2 The isgreaterequal macro determines whether its first argument is greater than or
10685 equal to its second argument. The value of isgreaterequal(x, y) is always equal
10686 to (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does
10687 not raise the ''invalid'' floating-point exception when x and y are unordered.
10689 3 The isgreaterequal macro returns the value of (x) >= (y).
10690 7.12.14.3 The isless macro
10692 1 #include <math.h>
10693 int isless(real-floating x, real-floating y);
10695 2 The isless macro determines whether its first argument is less than its second
10696 argument. The value of isless(x, y) is always equal to (x) < (y); however,
10697 unlike (x) < (y), isless(x, y) does not raise the ''invalid'' floating-point
10698 exception when x and y are unordered.
10700 3 The isless macro returns the value of (x) < (y).
10701 7.12.14.4 The islessequal macro
10703 1 #include <math.h>
10704 int islessequal(real-floating x, real-floating y);
10706 2 The islessequal macro determines whether its first argument is less than or equal to
10707 its second argument. The value of islessequal(x, y) is always equal to
10708 (x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raise
10709 the ''invalid'' floating-point exception when x and y are unordered.
10711 3 The islessequal macro returns the value of (x) <= (y).
10718 7.12.14.5 The islessgreater macro
10720 1 #include <math.h>
10721 int islessgreater(real-floating x, real-floating y);
10723 2 The islessgreater macro determines whether its first argument is less than or
10724 greater than its second argument. The islessgreater(x, y) macro is similar to
10725 (x) < (y) || (x) > (y); however, islessgreater(x, y) does not raise
10726 the ''invalid'' floating-point exception when x and y are unordered (nor does it evaluate x
10729 3 The islessgreater macro returns the value of (x) < (y) || (x) > (y).
10730 7.12.14.6 The isunordered macro
10732 1 #include <math.h>
10733 int isunordered(real-floating x, real-floating y);
10735 2 The isunordered macro determines whether its arguments are unordered.
10737 3 The isunordered macro returns 1 if its arguments are unordered and 0 otherwise.
10744 7.13 Nonlocal jumps <setjmp.h>
10745 1 The header <setjmp.h> defines the macro setjmp, and declares one function and
10746 one type, for bypassing the normal function call and return discipline.244)
10747 2 The type declared is
10749 which is an array type suitable for holding the information needed to restore a calling
10750 environment. The environment of a call to the setjmp macro consists of information
10751 sufficient for a call to the longjmp function to return execution to the correct block and
10752 invocation of that block, were it called recursively. It does not include the state of the
10753 floating-point status flags, of open files, or of any other component of the abstract
10755 3 It is unspecified whether setjmp is a macro or an identifier declared with external
10756 linkage. If a macro definition is suppressed in order to access an actual function, or a
10757 program defines an external identifier with the name setjmp, the behavior is undefined.
10758 7.13.1 Save calling environment
10759 7.13.1.1 The setjmp macro
10761 1 #include <setjmp.h>
10762 int setjmp(jmp_buf env);
10764 2 The setjmp macro saves its calling environment in its jmp_buf argument for later use
10765 by the longjmp function.
10767 3 If the return is from a direct invocation, the setjmp macro returns the value zero. If the
10768 return is from a call to the longjmp function, the setjmp macro returns a nonzero
10770 Environmental limits
10771 4 An invocation of the setjmp macro shall appear only in one of the following contexts:
10772 -- the entire controlling expression of a selection or iteration statement;
10773 -- one operand of a relational or equality operator with the other operand an integer
10774 constant expression, with the resulting expression being the entire controlling
10777 244) These functions are useful for dealing with unusual conditions encountered in a low-level function of
10782 expression of a selection or iteration statement;
10783 -- the operand of a unary ! operator with the resulting expression being the entire
10784 controlling expression of a selection or iteration statement; or
10785 -- the entire expression of an expression statement (possibly cast to void).
10786 5 If the invocation appears in any other context, the behavior is undefined.
10787 7.13.2 Restore calling environment
10788 7.13.2.1 The longjmp function
10790 1 #include <setjmp.h>
10791 _Noreturn void longjmp(jmp_buf env, int val);
10793 2 The longjmp function restores the environment saved by the most recent invocation of
10794 the setjmp macro in the same invocation of the program with the corresponding
10795 jmp_buf argument. If there has been no such invocation, or if the function containing
10796 the invocation of the setjmp macro has terminated execution245) in the interim, or if the
10797 invocation of the setjmp macro was within the scope of an identifier with variably
10798 modified type and execution has left that scope in the interim, the behavior is undefined.
10799 3 All accessible objects have values, and all other components of the abstract machine246)
10800 have state, as of the time the longjmp function was called, except that the values of
10801 objects of automatic storage duration that are local to the function containing the
10802 invocation of the corresponding setjmp macro that do not have volatile-qualified type
10803 and have been changed between the setjmp invocation and longjmp call are
10806 4 After longjmp is completed, program execution continues as if the corresponding
10807 invocation of the setjmp macro had just returned the value specified by val. The
10808 longjmp function cannot cause the setjmp macro to return the value 0; if val is 0,
10809 the setjmp macro returns the value 1.
10810 5 EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation
10811 might cause memory associated with a variable length array object to be squandered.
10816 245) For example, by executing a return statement or because another longjmp call has caused a
10817 transfer to a setjmp invocation in a function earlier in the set of nested calls.
10818 246) This includes, but is not limited to, the floating-point status flags and the state of open files.
10822 #include <setjmp.h>
10829 int x[n]; // valid: f is not terminated
10835 int a[n]; // a may remain allocated
10840 int b[n]; // b may remain allocated
10841 longjmp(buf, 2); // might cause memory loss
10849 7.14 Signal handling <signal.h>
10850 1 The header <signal.h> declares a type and two functions and defines several macros,
10851 for handling various signals (conditions that may be reported during program execution).
10852 2 The type defined is
10854 which is the (possibly volatile-qualified) integer type of an object that can be accessed as
10855 an atomic entity, even in the presence of asynchronous interrupts.
10856 3 The macros defined are
10860 which expand to constant expressions with distinct values that have type compatible with
10861 the second argument to, and the return value of, the signal function, and whose values
10862 compare unequal to the address of any declarable function; and the following, which
10863 expand to positive integer constant expressions with type int and distinct values that are
10864 the signal numbers, each corresponding to the specified condition:
10865 SIGABRT abnormal termination, such as is initiated by the abort function
10866 SIGFPE an erroneous arithmetic operation, such as zero divide or an operation
10867 resulting in overflow
10868 SIGILL detection of an invalid function image, such as an invalid instruction
10869 SIGINT receipt of an interactive attention signal
10870 SIGSEGV an invalid access to storage
10871 SIGTERM a termination request sent to the program
10872 4 An implementation need not generate any of these signals, except as a result of explicit
10873 calls to the raise function. Additional signals and pointers to undeclarable functions,
10874 with macro definitions beginning, respectively, with the letters SIG and an uppercase
10875 letter or with SIG_ and an uppercase letter,247) may also be specified by the
10876 implementation. The complete set of signals, their semantics, and their default handling
10877 is implementation-defined; all signal numbers shall be positive.
10882 247) See ''future library directions'' (7.30.6). The names of the signal numbers reflect the following terms
10883 (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation,
10888 7.14.1 Specify signal handling
10889 7.14.1.1 The signal function
10891 1 #include <signal.h>
10892 void (*signal(int sig, void (*func)(int)))(int);
10894 2 The signal function chooses one of three ways in which receipt of the signal number
10895 sig is to be subsequently handled. If the value of func is SIG_DFL, default handling
10896 for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored.
10897 Otherwise, func shall point to a function to be called when that signal occurs. An
10898 invocation of such a function because of a signal, or (recursively) of any further functions
10899 called by that invocation (other than functions in the standard library),248) is called a
10901 3 When a signal occurs and func points to a function, it is implementation-defined
10902 whether the equivalent of signal(sig, SIG_DFL); is executed or the
10903 implementation prevents some implementation-defined set of signals (at least including
10904 sig) from occurring until the current signal handling has completed; in the case of
10905 SIGILL, the implementation may alternatively define that no action is taken. Then the
10906 equivalent of (*func)(sig); is executed. If and when the function returns, if the
10907 value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined
10908 value corresponding to a computational exception, the behavior is undefined; otherwise
10909 the program will resume execution at the point it was interrupted.
10910 4 If the signal occurs as the result of calling the abort or raise function, the signal
10911 handler shall not call the raise function.
10912 5 If the signal occurs other than as the result of calling the abort or raise function, the
10913 behavior is undefined if the signal handler refers to any object with static or thread
10914 storage duration that is not a lock-free atomic object other than by assigning a value to an
10915 object declared as volatile sig_atomic_t, or the signal handler calls any function
10916 in the standard library other than the abort function, the _Exit function, the
10917 quick_exit function, or the signal function with the first argument equal to the
10918 signal number corresponding to the signal that caused the invocation of the handler.
10919 Furthermore, if such a call to the signal function results in a SIG_ERR return, the
10920 value of errno is indeterminate.249)
10923 248) This includes functions called indirectly via standard library functions (e.g., a SIGABRT handler
10924 called via the abort function).
10925 249) If any signal is generated by an asynchronous signal handler, the behavior is undefined.
10929 6 At program startup, the equivalent of
10930 signal(sig, SIG_IGN);
10931 may be executed for some signals selected in an implementation-defined manner; the
10933 signal(sig, SIG_DFL);
10934 is executed for all other signals defined by the implementation.
10935 7 The implementation shall behave as if no library function calls the signal function.
10937 8 If the request can be honored, the signal function returns the value of func for the
10938 most recent successful call to signal for the specified signal sig. Otherwise, a value of
10939 SIG_ERR is returned and a positive value is stored in errno.
10940 Forward references: the abort function (7.22.4.1), the exit function (7.22.4.4), the
10941 _Exit function (7.22.4.5), the quick_exit function (7.22.4.7).
10943 7.14.2.1 The raise function
10945 1 #include <signal.h>
10946 int raise(int sig);
10948 2 The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a
10949 signal handler is called, the raise function shall not return until after the signal handler
10952 3 The raise function returns zero if successful, nonzero if unsuccessful.
10959 7.15 Alignment <stdalign.h>
10960 1 The header <stdalign.h> defines two macros.
10963 expands to _Alignas.
10964 3 The remaining macro is suitable for use in #if preprocessing directives. It is
10965 __alignas_is_defined
10966 which expands to the integer constant 1.
10973 7.16 Variable arguments <stdarg.h>
10974 1 The header <stdarg.h> declares a type and defines four macros, for advancing
10975 through a list of arguments whose number and types are not known to the called function
10976 when it is translated.
10977 2 A function may be called with a variable number of arguments of varying types. As
10978 described in 6.9.1, its parameter list contains one or more parameters. The rightmost
10979 parameter plays a special role in the access mechanism, and will be designated parmN in
10981 3 The type declared is
10983 which is a complete object type suitable for holding information needed by the macros
10984 va_start, va_arg, va_end, and va_copy. If access to the varying arguments is
10985 desired, the called function shall declare an object (generally referred to as ap in this
10986 subclause) having type va_list. The object ap may be passed as an argument to
10987 another function; if that function invokes the va_arg macro with parameter ap, the
10988 value of ap in the calling function is indeterminate and shall be passed to the va_end
10989 macro prior to any further reference to ap.250)
10990 7.16.1 Variable argument list access macros
10991 1 The va_start and va_arg macros described in this subclause shall be implemented
10992 as macros, not functions. It is unspecified whether va_copy and va_end are macros or
10993 identifiers declared with external linkage. If a macro definition is suppressed in order to
10994 access an actual function, or a program defines an external identifier with the same name,
10995 the behavior is undefined. Each invocation of the va_start and va_copy macros
10996 shall be matched by a corresponding invocation of the va_end macro in the same
10998 7.16.1.1 The va_arg macro
11000 1 #include <stdarg.h>
11001 type va_arg(va_list ap, type);
11003 2 The va_arg macro expands to an expression that has the specified type and the value of
11004 the next argument in the call. The parameter ap shall have been initialized by the
11005 va_start or va_copy macro (without an intervening invocation of the va_end
11007 250) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which
11008 case the original function may make further use of the original list after the other function returns.
11012 macro for the same ap). Each invocation of the va_arg macro modifies ap so that the
11013 values of successive arguments are returned in turn. The parameter type shall be a type
11014 name specified such that the type of a pointer to an object that has the specified type can
11015 be obtained simply by postfixing a * to type. If there is no actual next argument, or if
11016 type is not compatible with the type of the actual next argument (as promoted according
11017 to the default argument promotions), the behavior is undefined, except for the following
11019 -- one type is a signed integer type, the other type is the corresponding unsigned integer
11020 type, and the value is representable in both types;
11021 -- one type is pointer to void and the other is a pointer to a character type.
11023 3 The first invocation of the va_arg macro after that of the va_start macro returns the
11024 value of the argument after that specified by parmN . Successive invocations return the
11025 values of the remaining arguments in succession.
11026 7.16.1.2 The va_copy macro
11028 1 #include <stdarg.h>
11029 void va_copy(va_list dest, va_list src);
11031 2 The va_copy macro initializes dest as a copy of src, as if the va_start macro had
11032 been applied to dest followed by the same sequence of uses of the va_arg macro as
11033 had previously been used to reach the present state of src. Neither the va_copy nor
11034 va_start macro shall be invoked to reinitialize dest without an intervening
11035 invocation of the va_end macro for the same dest.
11037 3 The va_copy macro returns no value.
11038 7.16.1.3 The va_end macro
11040 1 #include <stdarg.h>
11041 void va_end(va_list ap);
11043 2 The va_end macro facilitates a normal return from the function whose variable
11044 argument list was referred to by the expansion of the va_start macro, or the function
11045 containing the expansion of the va_copy macro, that initialized the va_list ap. The
11046 va_end macro may modify ap so that it is no longer usable (without being reinitialized
11050 by the va_start or va_copy macro). If there is no corresponding invocation of the
11051 va_start or va_copy macro, or if the va_end macro is not invoked before the
11052 return, the behavior is undefined.
11054 3 The va_end macro returns no value.
11055 7.16.1.4 The va_start macro
11057 1 #include <stdarg.h>
11058 void va_start(va_list ap, parmN);
11060 2 The va_start macro shall be invoked before any access to the unnamed arguments.
11061 3 The va_start macro initializes ap for subsequent use by the va_arg and va_end
11062 macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap
11063 without an intervening invocation of the va_end macro for the same ap.
11064 4 The parameter parmN is the identifier of the rightmost parameter in the variable
11065 parameter list in the function definition (the one just before the , ...). If the parameter
11066 parmN is declared with the register storage class, with a function or array type, or
11067 with a type that is not compatible with the type that results after application of the default
11068 argument promotions, the behavior is undefined.
11070 5 The va_start macro returns no value.
11071 6 EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not
11072 more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of
11073 pointers is specified by the first argument to f1.
11074 #include <stdarg.h>
11076 void f1(int n_ptrs, ...)
11079 char *array[MAXARGS];
11087 if (n_ptrs > MAXARGS)
11089 va_start(ap, n_ptrs);
11090 while (ptr_no < n_ptrs)
11091 array[ptr_no++] = va_arg(ap, char *);
11095 Each call to f1 is required to have visible the definition of the function or a declaration such as
11098 7 EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the
11099 indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list
11100 is gathered again and passed to function f4.
11101 #include <stdarg.h>
11103 void f3(int n_ptrs, int f4_after, ...)
11105 va_list ap, ap_save;
11106 char *array[MAXARGS];
11108 if (n_ptrs > MAXARGS)
11110 va_start(ap, f4_after);
11111 while (ptr_no < n_ptrs) {
11112 array[ptr_no++] = va_arg(ap, char *);
11113 if (ptr_no == f4_after)
11114 va_copy(ap_save, ap);
11118 // Now process the saved copy.
11119 n_ptrs -= f4_after;
11121 while (ptr_no < n_ptrs)
11122 array[ptr_no++] = va_arg(ap_save, char *);
11132 7.17 Atomics <stdatomic.h>
11133 7.17.1 Introduction
11134 1 The header <stdatomic.h> defines several macros and declares several types and
11135 functions for performing atomic operations on data shared between threads.
11136 2 Implementations that define the macro __STDC_NO_THREADS__ need not provide
11137 this header nor support any of its facilities.
11138 3 The macros defined are the atomic lock-free macros
11139 ATOMIC_CHAR_LOCK_FREE
11140 ATOMIC_CHAR16_T_LOCK_FREE
11141 ATOMIC_CHAR32_T_LOCK_FREE
11142 ATOMIC_WCHAR_T_LOCK_FREE
11143 ATOMIC_SHORT_LOCK_FREE
11144 ATOMIC_INT_LOCK_FREE
11145 ATOMIC_LONG_LOCK_FREE
11146 ATOMIC_LLONG_LOCK_FREE
11147 ATOMIC_ADDRESS_LOCK_FREE
11148 which indicate the lock-free property of the corresponding atomic types (both signed and
11151 which expands to an initializer for an object of type atomic_flag.
11152 4 The types include
11154 which is an enumerated type whose enumerators identify memory ordering constraints;
11156 which is a structure type representing a lock-free, primitive atomic flag;
11158 which is a structure type representing the atomic analog of the type _Bool;
11160 which is a structure type representing the atomic analog of a pointer type; and several
11161 atomic analogs of integer types.
11162 5 In the following operation definitions:
11163 -- An A refers to one of the atomic types.
11168 -- A C refers to its corresponding non-atomic type. The atomic_address atomic
11169 type corresponds to the void * non-atomic type.
11170 -- An M refers to the type of the other argument for arithmetic operations. For atomic
11171 integer types, M is C. For atomic address types, M is ptrdiff_t.
11172 -- The functions not ending in _explicit have the same semantics as the
11173 corresponding _explicit function with memory_order_seq_cst for the
11174 memory_order argument.
11175 6 NOTE Many operations are volatile-qualified. The ''volatile as device register'' semantics have not
11176 changed in the standard. This qualification means that volatility is preserved when applying these
11177 operations to volatile objects.
11179 7.17.2 Initialization
11180 7.17.2.1 The ATOMIC_VAR_INIT macro
11182 1 #include <stdatomic.h>
11183 #define ATOMIC_VAR_INIT(C value)
11185 2 The ATOMIC_VAR_INIT macro expands to a token sequence suitable for initializing an
11186 atomic object of a type that is initialization-compatible with value. An atomic object
11187 with automatic storage duration that is not explicitly initialized using
11188 ATOMIC_VAR_INIT is initially in an indeterminate state; however, the default (zero)
11189 initialization for objects with static or thread-local storage duration is guaranteed to
11190 produce a valid state.
11191 3 Concurrent access to the variable being initialized, even via an atomic operation,
11192 constitutes a data race.
11194 atomic_int guide = ATOMIC_VAR_INIT(42);
11196 7.17.2.2 The atomic_init generic function
11198 1 #include <stdatomic.h>
11199 void atomic_init(volatile A *obj, C value);
11201 2 The atomic_init generic function initializes the atomic object pointed to by obj to
11202 the value value, while also initializing any additional state that the implementation
11203 might need to carry for the atomic object.
11209 3 Although this function initializes an atomic object, it does not avoid data races;
11210 concurrent access to the variable being initialized, even via an atomic operation,
11211 constitutes a data race.
11213 4 The atomic_init generic function returns no value.
11216 atomic_init(&guide, 42);
11218 7.17.3 Order and consistency
11219 1 The enumerated type memory_order specifies the detailed regular (non-atomic)
11220 memory synchronization operations as defined in 5.1.2.4 and may provide for operation
11221 ordering. Its enumeration constants are as follows:
11222 memory_order_relaxed
11223 memory_order_consume
11224 memory_order_acquire
11225 memory_order_release
11226 memory_order_acq_rel
11227 memory_order_seq_cst
11228 2 For memory_order_relaxed, no operation orders memory.
11229 3 For memory_order_release, memory_order_acq_rel, and
11230 memory_order_seq_cst, a store operation performs a release operation on the
11231 affected memory location.
11232 4 For memory_order_acquire, memory_order_acq_rel, and
11233 memory_order_seq_cst, a load operation performs an acquire operation on the
11234 affected memory location.
11235 5 For memory_order_consume, a load operation performs a consume operation on the
11236 affected memory location.
11237 6 For memory_order_seq_cst, there shall be a single total order S on all operations,
11238 consistent with the ''happens before'' order and modification orders for all affected
11239 locations, such that each memory_order_seq_cst operation that loads a value
11240 observes either the last preceding modification according to this order S, or the result of
11241 an operation that is not memory_order_seq_cst.
11242 7 NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to
11243 an order that does include lock and unlock operations, since the ordering between those is already included
11244 in the ''happens before'' ordering.
11246 8 NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to
11247 memory ordering. Implementations must still guarantee that any given atomic access to a particular atomic
11251 object be indivisible with respect to all other atomic accesses to that object.
11253 9 For an atomic operation B that reads the value of an atomic object M, if there is a
11254 memory_order_seq_cst fence X sequenced before B, then B observes either the
11255 last memory_order_seq_cst modification of M preceding X in the total order S or
11256 a later modification of M in its modification order.
11257 10 For atomic operations A and B on an atomic object M, where A modifies M and B takes
11258 its value, if there is a memory_order_seq_cst fence X such that A is sequenced
11259 before X and B follows X in S, then B observes either the effects of A or a later
11260 modification of M in its modification order.
11261 11 For atomic operations A and B on an atomic object M, where A modifies M and B takes
11262 its value, if there are memory_order_seq_cst fences X and Y such that A is
11263 sequenced before X, Y is sequenced before B, and X precedes Y in S, then B observes
11264 either the effects of A or a later modification of M in its modification order.
11265 12 Atomic read-modify-write operations shall always read the last value (in the modification
11266 order) stored before the write associated with the read-modify-write operation.
11267 13 An atomic store shall only store a value that has been computed from constants and
11268 program input values by a finite sequence of program evaluations, such that each
11269 evaluation observes the values of variables as computed by the last prior assignment in
11270 the sequence.251) The ordering of evaluations in this sequence shall be such that
11271 -- If an evaluation B observes a value computed by A in a different thread, then B does
11272 not happen before A.
11273 -- If an evaluation A is included in the sequence, then all evaluations that assign to the
11274 same variable and happen before A are also included.
11275 14 NOTE 3 The second requirement disallows ''out-of-thin-air'', or ''speculative'' stores of atomics when
11276 relaxed atomics are used. Since unordered operations are involved, evaluations may appear in this
11277 sequence out of thread order. For example, with x and y initially zero,
11279 r1 = atomic_load_explicit(&y, memory_order_relaxed);
11280 atomic_store_explicit(&x, r1, memory_order_relaxed);
11283 r2 = atomic_load_explicit(&x, memory_order_relaxed);
11284 atomic_store_explicit(&y, 42, memory_order_relaxed);
11285 is allowed to produce r1 == 42 && r2 == 42. The sequence of evaluations justifying this consists of:
11290 251) Among other implications, atomic variables shall not decay.
11294 atomic_store_explicit(&y, 42, memory_order_relaxed);
11295 r1 = atomic_load_explicit(&y, memory_order_relaxed);
11296 atomic_store_explicit(&x, r1, memory_order_relaxed);
11297 r2 = atomic_load_explicit(&x, memory_order_relaxed);
11300 r1 = atomic_load_explicit(&y, memory_order_relaxed);
11301 atomic_store_explicit(&x, r1, memory_order_relaxed);
11304 r2 = atomic_load_explicit(&x, memory_order_relaxed);
11305 atomic_store_explicit(&y, r2, memory_order_relaxed);
11306 is not allowed to produce r1 == 42 && r2 = 42, since there is no sequence of evaluations that results
11307 in the computation of 42. In the absence of ''relaxed'' operations and read-modify-write operations with
11308 weaker than memory_order_acq_rel ordering, the second requirement has no impact.
11310 Recommended practice
11311 15 The requirements do not forbid r1 == 42 && r2 == 42 in the following example,
11312 with x and y initially zero:
11314 r1 = atomic_load_explicit(&x, memory_order_relaxed);
11316 atomic_store_explicit(&y, r1, memory_order_relaxed);
11319 r2 = atomic_load_explicit(&y, memory_order_relaxed);
11321 atomic_store_explicit(&x, 42, memory_order_relaxed);
11322 However, this is not useful behavior, and implementations should not allow it.
11323 16 Implementations should make atomic stores visible to atomic loads within a reasonable
11325 7.17.3.1 The kill_dependency macro
11327 1 #include <stdatomic.h>
11328 type kill_dependency(type y);
11330 2 The kill_dependency macro terminates a dependency chain; the argument does not
11331 carry a dependency to the return value.
11338 3 The kill_dependency macro returns the value of y.
11340 1 This subclause introduces synchronization primitives called fences. Fences can have
11341 acquire semantics, release semantics, or both. A fence with acquire semantics is called
11342 an acquire fence; a fence with release semantics is called a release fence.
11343 2 A release fence A synchronizes with an acquire fence B if there exist atomic operations
11344 X and Y , both operating on some atomic object M, such that A is sequenced before X, X
11345 modifies M, Y is sequenced before B, and Y reads the value written by X or a value
11346 written by any side effect in the hypothetical release sequence X would head if it were a
11348 3 A release fence A synchronizes with an atomic operation B that performs an acquire
11349 operation on an atomic object M if there exists an atomic operation X such that A is
11350 sequenced before X, X modifies M, and B reads the value written by X or a value written
11351 by any side effect in the hypothetical release sequence X would head if it were a release
11353 4 An atomic operation A that is a release operation on an atomic object M synchronizes
11354 with an acquire fence B if there exists some atomic operation X on M such that X is
11355 sequenced before B and reads the value written by A or a value written by any side effect
11356 in the release sequence headed by A.
11357 7.17.4.1 The atomic_thread_fence function
11359 1 #include <stdatomic.h>
11360 void atomic_thread_fence(memory_order order);
11362 2 Depending on the value of order, this operation:
11363 -- has no effects, if order == memory_order_relaxed;
11364 -- is an acquire fence, if order == memory_order_acquire or order ==
11365 memory_order_consume;
11366 -- is a release fence, if order == memory_order_release;
11367 -- is both an acquire fence and a release fence, if order ==
11368 memory_order_acq_rel;
11369 -- is a sequentially consistent acquire and release fence, if order ==
11370 memory_order_seq_cst.
11376 3 The atomic_thread_fence function returns no value.
11377 7.17.4.2 The atomic_signal_fence function
11379 1 #include <stdatomic.h>
11380 void atomic_signal_fence(memory_order order);
11382 2 Equivalent to atomic_thread_fence(order), except that ''synchronizes with''
11383 relationships are established only between a thread and a signal handler executed in the
11385 3 NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions
11386 performed by the thread become visible to the signal handler.
11388 4 NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with
11389 atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would
11390 have inserted are not emitted.
11393 5 The atomic_signal_fence function returns no value.
11394 7.17.5 Lock-free property
11395 1 The atomic lock-free macros indicate the lock-free property of integer and address atomic
11396 types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that
11397 the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free.
11398 2 NOTE Operations that are lock-free should also be address-free. That is, atomic operations on the same
11399 memory location via two different addresses will communicate atomically. The implementation should not
11400 depend on any per-process state. This restriction enables communication via memory mapped into a
11401 process more than once and memory shared between two processes.
11403 7.17.5.1 The atomic_is_lock_free generic function
11405 1 #include <stdatomic.h>
11406 _Bool atomic_is_lock_free(atomic_type const volatile *obj);
11408 2 The atomic_is_lock_free generic function indicates whether or not the object
11409 pointed to by obj is lock-free. atomic_type can be any atomic type.
11411 3 The atomic_is_lock_free generic function returns nonzero (true) if and only if the
11412 object's operations are lock-free. The result of a lock-free query on one object cannot be
11416 inferred from the result of a lock-free query on another object.
11417 7.17.6 Atomic integer and address types
11418 1 For each line in the following table, the atomic type name is declared as the
11419 corresponding direct type.
11426 Atomic type name Direct type
11427 atomic_char _Atomic char
11428 atomic_schar _Atomic signed char
11429 atomic_uchar _Atomic unsigned char
11430 atomic_short _Atomic short
11431 atomic_ushort _Atomic unsigned short
11432 atomic_int _Atomic int
11433 atomic_uint _Atomic unsigned int
11434 atomic_long _Atomic long
11435 atomic_ulong _Atomic unsigned long
11436 atomic_llong _Atomic long long
11437 atomic_ullong _Atomic unsigned long long
11438 atomic_char16_t _Atomic char16_t
11439 atomic_char32_t _Atomic char32_t
11440 atomic_wchar_t _Atomic wchar_t
11441 atomic_int_least8_t _Atomic int_least8_t
11442 atomic_uint_least8_t _Atomic uint_least8_t
11443 atomic_int_least16_t _Atomic int_least16_t
11444 atomic_uint_least16_t _Atomic uint_least16_t
11445 atomic_int_least32_t _Atomic int_least32_t
11446 atomic_uint_least32_t _Atomic uint_least32_t
11447 atomic_int_least64_t _Atomic int_least64_t
11448 atomic_uint_least64_t _Atomic uint_least64_t
11449 atomic_int_fast8_t _Atomic int_fast8_t
11450 atomic_uint_fast8_t _Atomic uint_fast8_t
11451 atomic_int_fast16_t _Atomic int_fast16_t
11452 atomic_uint_fast16_t _Atomic uint_fast16_t
11453 atomic_int_fast32_t _Atomic int_fast32_t
11454 atomic_uint_fast32_t _Atomic uint_fast32_t
11455 atomic_int_fast64_t _Atomic int_fast64_t
11456 atomic_uint_fast64_t _Atomic uint_fast64_t
11457 atomic_intptr_t _Atomic intptr_t
11458 atomic_uintptr_t _Atomic uintptr_t
11459 atomic_size_t _Atomic size_t
11460 atomic_ptrdiff_t _Atomic ptrdiff_t
11461 atomic_intmax_t _Atomic intmax_t
11462 atomic_uintmax_t _Atomic uintmax_t
11463 2 The semantics of the operations on these types are defined in 7.17.7.
11464 3 The atomic_bool type provides an atomic boolean.
11469 4 The atomic_address type provides atomic void * operations. The unit of
11470 addition/subtraction shall be one byte.
11471 5 NOTE The representation of atomic integer and address types need not have the same size as their
11472 corresponding regular types. They should have the same size whenever possible, as it eases effort required
11473 to port existing code.
11475 7.17.7 Operations on atomic types
11476 1 There are only a few kinds of operations on atomic types, though there are many
11477 instances of those kinds. This subclause specifies each general kind.
11478 7.17.7.1 The atomic_store generic functions
11480 1 #include <stdatomic.h>
11481 void atomic_store(volatile A *object, C desired);
11482 void atomic_store_explicit(volatile A *object,
11483 C desired, memory_order order);
11485 2 The order argument shall not be memory_order_acquire,
11486 memory_order_consume, nor memory_order_acq_rel. Atomically replace the
11487 value pointed to by object with the value of desired. Memory is affected according
11488 to the value of order.
11490 3 The atomic_store generic functions return no value.
11491 7.17.7.2 The atomic_load generic functions
11493 1 #include <stdatomic.h>
11494 C atomic_load(volatile A *object);
11495 C atomic_load_explicit(volatile A *object,
11496 memory_order order);
11498 2 The order argument shall not be memory_order_release nor
11499 memory_order_acq_rel. Memory is affected according to the value of order.
11501 Atomically returns the value pointed to by object.
11508 7.17.7.3 The atomic_exchange generic functions
11510 1 #include <stdatomic.h>
11511 C atomic_exchange(volatile A *object, C desired);
11512 C atomic_exchange_explicit(volatile A *object,
11513 C desired, memory_order order);
11515 2 Atomically replace the value pointed to by object with desired. Memory is affected
11516 according to the value of order. These operations are read-modify-write operations
11519 3 Atomically returns the value pointed to by object immediately before the effects.
11520 7.17.7.4 The atomic_compare_exchange generic functions
11522 1 #include <stdatomic.h>
11523 _Bool atomic_compare_exchange_strong(volatile A *object,
11524 C *expected, C desired);
11525 _Bool atomic_compare_exchange_strong_explicit(
11526 volatile A *object, C *expected, C desired,
11527 memory_order success, memory_order failure);
11528 _Bool atomic_compare_exchange_weak(volatile A *object,
11529 C *expected, C desired);
11530 _Bool atomic_compare_exchange_weak_explicit(
11531 volatile A *object, C *expected, C desired,
11532 memory_order success, memory_order failure);
11534 2 The failure argument shall not be memory_order_release nor
11535 memory_order_acq_rel. The failure argument shall be no stronger than the
11536 success argument. Atomically, compares the value pointed to by object for equality
11537 with that in expected, and if true, replaces the value pointed to by object with
11538 desired, and if false, updates the value in expected with the value pointed to by
11539 object. Further, if the comparison is true, memory is affected according to the value of
11540 success, and if the comparison is false, memory is affected according to the value of
11541 failure. These operations are atomic read-modify-write operations (5.1.2.4).
11542 3 NOTE 1 The effect of the compare-and-exchange operations is
11549 if (*object == *expected)
11552 *expected = *object;
11554 4 The weak compare-and-exchange operations may fail spuriously, that is, return zero
11555 while leaving the value pointed to by expected unchanged.
11556 5 NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of
11557 machines, e.g. load-locked store-conditional machines.
11559 6 EXAMPLE A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will
11561 exp = atomic_load(&cur);
11563 des = function(exp);
11564 } while (!atomic_compare_exchange_weak(&cur, &exp, des));
11565 When a compare-and-exchange is in a loop, the weak version will yield better performance on some
11566 platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the
11567 strong one is preferable.
11570 7 The result of the comparison.
11571 7.17.7.5 The atomic_fetch and modify generic functions
11572 1 The following operations perform arithmetic and bitwise computations. All of these
11573 operations are applicable to an object of any atomic integer type. Only addition and
11574 subtraction are applicable to atomic_address. None of these operations is applicable
11575 to atomic_bool. The key, operator, and computation correspondence is:
11579 or | bitwise inclusive or
11580 xor ^ bitwise exclusive or
11583 2 #include <stdatomic.h>
11584 C atomic_fetch_key(volatile A *object, M operand);
11585 C atomic_fetch_key_explicit(volatile A *object,
11586 M operand, memory_order order);
11588 3 Atomically replaces the value pointed to by object with the result of the computation
11589 applied to the value pointed to by object and the given operand. Memory is affected
11590 according to the value of order. These operations are atomic read-modify-write
11593 operations (5.1.2.4). For signed integer types, arithmetic is defined to use two's
11594 complement representation with silent wrap-around on overflow; there are no undefined
11595 results. For address types, the result may be an undefined address, but the operations
11596 otherwise have no undefined behavior.
11598 4 Atomically, the value pointed to by object immediately before the effects.
11599 5 NOTE The operation of the atomic_fetch and modify generic functions are nearly equivalent to the
11600 operation of the corresponding op= compound assignment operators. The only differences are that the
11601 compound assignment operators are not guaranteed to operate atomically, and the value yielded by a
11602 compound assignment operator is the updated value of the object, whereas the value returned by the
11603 atomic_fetch and modify generic functions is the previous value of the atomic object.
11605 7.17.8 Atomic flag type and operations
11606 1 The atomic_flag type provides the classic test-and-set functionality. It has two
11607 states, set and clear.
11608 2 Operations on an object of type atomic_flag shall be lock free.
11609 3 NOTE Hence the operations should also be address-free. No other type requires lock-free operations, so
11610 the atomic_flag type is the minimum hardware-implemented type needed to conform to this
11611 International standard. The remaining types can be emulated with atomic_flag, though with less than
11614 4 The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the
11615 clear state. An atomic_flag that is not explicitly initialized with
11616 ATOMIC_FLAG_INIT is initially in an indeterminate state.
11618 atomic_flag guard = ATOMIC_FLAG_INIT;
11620 7.17.8.1 The atomic_flag_test_and_set functions
11622 1 #include <stdatomic.h>
11623 bool atomic_flag_test_and_set(
11624 volatile atomic_flag *object);
11625 bool atomic_flag_test_and_set_explicit(
11626 volatile atomic_flag *object, memory_order order);
11628 2 Atomically sets the value pointed to by object to true. Memory is affected according
11629 to the value of order. These operations are atomic read-modify-write operations
11638 3 Atomically, the value of the object immediately before the effects.
11639 7.17.8.2 The atomic_flag_clear functions
11641 1 #include <stdatomic.h>
11642 void atomic_flag_clear(volatile atomic_flag *object);
11643 void atomic_flag_clear_explicit(
11644 volatile atomic_flag *object, memory_order order);
11646 2 The order argument shall not be memory_order_acquire nor
11647 memory_order_acq_rel. Atomically sets the value pointed to by object to false.
11648 Memory is affected according to the value of order.
11650 3 The atomic_flag_clear functions return no value.
11657 7.18 Boolean type and values <stdbool.h>
11658 1 The header <stdbool.h> defines four macros.
11662 3 The remaining three macros are suitable for use in #if preprocessing directives. They
11665 which expands to the integer constant 1,
11667 which expands to the integer constant 0, and
11668 __bool_true_false_are_defined
11669 which expands to the integer constant 1.
11670 4 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
11671 redefine the macros bool, true, and false.252)
11676 252) See ''future library directions'' (7.30.7).
11680 7.19 Common definitions <stddef.h>
11681 1 The header <stddef.h> defines the following macros and declares the following types.
11682 Some are also defined in other headers, as noted in their respective subclauses.
11685 which is the signed integer type of the result of subtracting two pointers;
11687 which is the unsigned integer type of the result of the sizeof operator;
11689 which is an object type whose alignment is as great as is supported by the implementation
11690 in all contexts; and
11692 which is an integer type whose range of values can represent distinct codes for all
11693 members of the largest extended character set specified among the supported locales; the
11694 null character shall have the code value zero. Each member of the basic character set
11695 shall have a code value equal to its value when used as the lone character in an integer
11696 character constant if an implementation does not define
11697 __STDC_MB_MIGHT_NEQ_WC__.
11700 which expands to an implementation-defined null pointer constant; and
11701 offsetof(type, member-designator)
11702 which expands to an integer constant expression that has type size_t, the value of
11703 which is the offset in bytes, to the structure member (designated by member-designator),
11704 from the beginning of its structure (designated by type). The type and member designator
11705 shall be such that given
11707 then the expression &(t.member-designator) evaluates to an address constant. (If the
11708 specified member is a bit-field, the behavior is undefined.)
11709 Recommended practice
11710 4 The types used for size_t and ptrdiff_t should not have an integer conversion rank
11711 greater than that of signed long int unless the implementation supports objects
11712 large enough to make this necessary.
11716 Forward references: localization (7.11).
11723 7.20 Integer types <stdint.h>
11724 1 The header <stdint.h> declares sets of integer types having specified widths, and
11725 defines corresponding sets of macros.253) It also defines macros that specify limits of
11726 integer types corresponding to types defined in other standard headers.
11727 2 Types are defined in the following categories:
11728 -- integer types having certain exact widths;
11729 -- integer types having at least certain specified widths;
11730 -- fastest integer types having at least certain specified widths;
11731 -- integer types wide enough to hold pointers to objects;
11732 -- integer types having greatest width.
11733 (Some of these types may denote the same type.)
11734 3 Corresponding macros specify limits of the declared types and construct suitable
11736 4 For each type described herein that the implementation provides,254) <stdint.h> shall
11737 declare that typedef name and define the associated macros. Conversely, for each type
11738 described herein that the implementation does not provide, <stdint.h> shall not
11739 declare that typedef name nor shall it define the associated macros. An implementation
11740 shall provide those types described as ''required'', but need not provide any of the others
11741 (described as ''optional'').
11742 7.20.1 Integer types
11743 1 When typedef names differing only in the absence or presence of the initial u are defined,
11744 they shall denote corresponding signed and unsigned types as described in 6.2.5; an
11745 implementation providing one of these corresponding types shall also provide the other.
11746 2 In the following descriptions, the symbol N represents an unsigned decimal integer with
11747 no leading zeros (e.g., 8 or 24, but not 04 or 048).
11752 253) See ''future library directions'' (7.30.8).
11753 254) Some of these types may denote implementation-defined extended integer types.
11757 7.20.1.1 Exact-width integer types
11758 1 The typedef name intN_t designates a signed integer type with width N , no padding
11759 bits, and a two's complement representation. Thus, int8_t denotes such a signed
11760 integer type with a width of exactly 8 bits.
11761 2 The typedef name uintN_t designates an unsigned integer type with width N and no
11762 padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of
11764 3 These types are optional. However, if an implementation provides integer types with
11765 widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a
11766 two's complement representation, it shall define the corresponding typedef names.
11767 7.20.1.2 Minimum-width integer types
11768 1 The typedef name int_leastN_t designates a signed integer type with a width of at
11769 least N , such that no signed integer type with lesser size has at least the specified width.
11770 Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits.
11771 2 The typedef name uint_leastN_t designates an unsigned integer type with a width
11772 of at least N , such that no unsigned integer type with lesser size has at least the specified
11773 width. Thus, uint_least16_t denotes an unsigned integer type with a width of at
11775 3 The following types are required:
11776 int_least8_t uint_least8_t
11777 int_least16_t uint_least16_t
11778 int_least32_t uint_least32_t
11779 int_least64_t uint_least64_t
11780 All other types of this form are optional.
11781 7.20.1.3 Fastest minimum-width integer types
11782 1 Each of the following types designates an integer type that is usually fastest255) to operate
11783 with among all integer types that have at least the specified width.
11784 2 The typedef name int_fastN_t designates the fastest signed integer type with a width
11785 of at least N . The typedef name uint_fastN_t designates the fastest unsigned integer
11786 type with a width of at least N .
11791 255) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear
11792 grounds for choosing one type over another, it will simply pick some integer type satisfying the
11793 signedness and width requirements.
11797 3 The following types are required:
11798 int_fast8_t uint_fast8_t
11799 int_fast16_t uint_fast16_t
11800 int_fast32_t uint_fast32_t
11801 int_fast64_t uint_fast64_t
11802 All other types of this form are optional.
11803 7.20.1.4 Integer types capable of holding object pointers
11804 1 The following type designates a signed integer type with the property that any valid
11805 pointer to void can be converted to this type, then converted back to pointer to void,
11806 and the result will compare equal to the original pointer:
11808 The following type designates an unsigned integer type with the property that any valid
11809 pointer to void can be converted to this type, then converted back to pointer to void,
11810 and the result will compare equal to the original pointer:
11812 These types are optional.
11813 7.20.1.5 Greatest-width integer types
11814 1 The following type designates a signed integer type capable of representing any value of
11815 any signed integer type:
11817 The following type designates an unsigned integer type capable of representing any value
11818 of any unsigned integer type:
11820 These types are required.
11821 7.20.2 Limits of specified-width integer types
11822 1 The following object-like macros specify the minimum and maximum limits of the types *
11823 declared in <stdint.h>. Each macro name corresponds to a similar type name in
11825 2 Each instance of any defined macro shall be replaced by a constant expression suitable
11826 for use in #if preprocessing directives, and this expression shall have the same type as
11827 would an expression that is an object of the corresponding type converted according to
11828 the integer promotions. Its implementation-defined value shall be equal to or greater in
11829 magnitude (absolute value) than the corresponding value given below, with the same sign,
11830 except where stated to be exactly the given value.
11834 7.20.2.1 Limits of exact-width integer types
11835 1 -- minimum values of exact-width signed integer types
11836 INTN_MIN exactly -(2 N -1 )
11837 -- maximum values of exact-width signed integer types
11838 INTN_MAX exactly 2 N -1 - 1
11839 -- maximum values of exact-width unsigned integer types
11840 UINTN_MAX exactly 2 N - 1
11841 7.20.2.2 Limits of minimum-width integer types
11842 1 -- minimum values of minimum-width signed integer types
11843 INT_LEASTN_MIN -(2 N -1 - 1)
11844 -- maximum values of minimum-width signed integer types
11845 INT_LEASTN_MAX 2 N -1 - 1
11846 -- maximum values of minimum-width unsigned integer types
11847 UINT_LEASTN_MAX 2N - 1
11848 7.20.2.3 Limits of fastest minimum-width integer types
11849 1 -- minimum values of fastest minimum-width signed integer types
11850 INT_FASTN_MIN -(2 N -1 - 1)
11851 -- maximum values of fastest minimum-width signed integer types
11852 INT_FASTN_MAX 2 N -1 - 1
11853 -- maximum values of fastest minimum-width unsigned integer types
11854 UINT_FASTN_MAX 2N - 1
11855 7.20.2.4 Limits of integer types capable of holding object pointers
11856 1 -- minimum value of pointer-holding signed integer type
11857 INTPTR_MIN -(215 - 1)
11858 -- maximum value of pointer-holding signed integer type
11860 -- maximum value of pointer-holding unsigned integer type
11861 UINTPTR_MAX 216 - 1
11867 7.20.2.5 Limits of greatest-width integer types
11868 1 -- minimum value of greatest-width signed integer type
11869 INTMAX_MIN -(263 - 1)
11870 -- maximum value of greatest-width signed integer type
11872 -- maximum value of greatest-width unsigned integer type
11873 UINTMAX_MAX 264 - 1
11874 7.20.3 Limits of other integer types
11875 1 The following object-like macros specify the minimum and maximum limits of integer *
11876 types corresponding to types defined in other standard headers.
11877 2 Each instance of these macros shall be replaced by a constant expression suitable for use
11878 in #if preprocessing directives, and this expression shall have the same type as would an
11879 expression that is an object of the corresponding type converted according to the integer
11880 promotions. Its implementation-defined value shall be equal to or greater in magnitude
11881 (absolute value) than the corresponding value given below, with the same sign. An
11882 implementation shall define only the macros corresponding to those typedef names it
11883 actually provides.256)
11884 -- limits of ptrdiff_t
11887 -- limits of sig_atomic_t
11888 SIG_ATOMIC_MIN see below
11889 SIG_ATOMIC_MAX see below
11892 -- limits of wchar_t
11893 WCHAR_MIN see below
11894 WCHAR_MAX see below
11895 -- limits of wint_t
11900 256) A freestanding implementation need not provide all of these types.
11906 3 If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of
11907 SIG_ATOMIC_MIN shall be no greater than -127 and the value of SIG_ATOMIC_MAX
11908 shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer
11909 type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of
11910 SIG_ATOMIC_MAX shall be no less than 255.
11911 4 If wchar_t (see 7.19) is defined as a signed integer type, the value of WCHAR_MIN
11912 shall be no greater than -127 and the value of WCHAR_MAX shall be no less than 127;
11913 otherwise, wchar_t is defined as an unsigned integer type, and the value of
11914 WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.257)
11915 5 If wint_t (see 7.28) is defined as a signed integer type, the value of WINT_MIN shall
11916 be no greater than -32767 and the value of WINT_MAX shall be no less than 32767;
11917 otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN
11918 shall be 0 and the value of WINT_MAX shall be no less than 65535.
11919 7.20.4 Macros for integer constants
11920 1 The following function-like macros expand to integer constants suitable for initializing *
11921 objects that have integer types corresponding to types defined in <stdint.h>. Each
11922 macro name corresponds to a similar type name in 7.20.1.2 or 7.20.1.5.
11923 2 The argument in any instance of these macros shall be an unsuffixed integer constant (as
11924 defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type.
11925 3 Each invocation of one of these macros shall expand to an integer constant expression
11926 suitable for use in #if preprocessing directives. The type of the expression shall have
11927 the same type as would an expression of the corresponding type converted according to
11928 the integer promotions. The value of the expression shall be that of the argument.
11929 7.20.4.1 Macros for minimum-width integer constants
11930 1 The macro INTN_C(value) shall expand to an integer constant expression
11931 corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand
11932 to an integer constant expression corresponding to the type uint_leastN_t. For
11933 example, if uint_least64_t is a name for the type unsigned long long int,
11934 then UINT64_C(0x123) might expand to the integer constant 0x123ULL.
11939 257) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended
11944 7.20.4.2 Macros for greatest-width integer constants
11945 1 The following macro expands to an integer constant expression having the value specified
11946 by its argument and the type intmax_t:
11948 The following macro expands to an integer constant expression having the value specified
11949 by its argument and the type uintmax_t:
11957 7.21 Input/output <stdio.h>
11958 7.21.1 Introduction
11959 1 The header <stdio.h> defines several macros, and declares three types and many
11960 functions for performing input and output.
11961 2 The types declared are size_t (described in 7.19);
11963 which is an object type capable of recording all the information needed to control a
11964 stream, including its file position indicator, a pointer to its associated buffer (if any), an
11965 error indicator that records whether a read/write error has occurred, and an end-of-file
11966 indicator that records whether the end of the file has been reached; and
11968 which is a complete object type other than an array type capable of recording all the
11969 information needed to specify uniquely every position within a file.
11970 3 The macros are NULL (described in 7.19);
11974 which expand to integer constant expressions with distinct values, suitable for use as the
11975 third argument to the setvbuf function;
11977 which expands to an integer constant expression that is the size of the buffer used by the
11980 which expands to an integer constant expression, with type int and a negative value, that
11981 is returned by several functions to indicate end-of-file, that is, no more input from a
11984 which expands to an integer constant expression that is the minimum number of files that
11985 the implementation guarantees can be open simultaneously;
11987 which expands to an integer constant expression that is the size needed for an array of
11988 char large enough to hold the longest file name string that the implementation
11994 guarantees can be opened;258)
11996 which expands to an integer constant expression that is the size needed for an array of
11997 char large enough to hold a temporary file name string generated by the tmpnam
12002 which expand to integer constant expressions with distinct values, suitable for use as the
12003 third argument to the fseek function;
12005 which expands to an integer constant expression that is the minimum number of unique
12006 file names that can be generated by the tmpnam function;
12010 which are expressions of type ''pointer to FILE'' that point to the FILE objects
12011 associated, respectively, with the standard error, input, and output streams.
12012 4 The header <wchar.h> declares a number of functions useful for wide character input
12013 and output. The wide character input/output functions described in that subclause
12014 provide operations analogous to most of those described here, except that the
12015 fundamental units internal to the program are wide characters. The external
12016 representation (in the file) is a sequence of ''generalized'' multibyte characters, as
12017 described further in 7.21.3.
12018 5 The input/output functions are given the following collective terms:
12019 -- The wide character input functions -- those functions described in 7.28 that perform
12020 input into wide characters and wide strings: fgetwc, fgetws, getwc, getwchar,
12021 fwscanf, wscanf, vfwscanf, and vwscanf.
12022 -- The wide character output functions -- those functions described in 7.28 that perform
12023 output from wide characters and wide strings: fputwc, fputws, putwc,
12024 putwchar, fwprintf, wprintf, vfwprintf, and vwprintf.
12027 258) If the implementation imposes no practical limit on the length of file name strings, the value of
12028 FILENAME_MAX should instead be the recommended size of an array intended to hold a file name
12029 string. Of course, file name string contents are subject to other system-specific constraints; therefore
12030 all possible strings of length FILENAME_MAX cannot be expected to be opened successfully.
12034 -- The wide character input/output functions -- the union of the ungetwc function, the
12035 wide character input functions, and the wide character output functions.
12036 -- The byte input/output functions -- those functions described in this subclause that
12037 perform input/output: fgetc, fgets, fprintf, fputc, fputs, fread,
12038 fscanf, fwrite, getc, getchar, printf, putc, putchar, puts, scanf, *
12039 ungetc, vfprintf, vfscanf, vprintf, and vscanf.
12040 Forward references: files (7.21.3), the fseek function (7.21.9.2), streams (7.21.2), the
12041 tmpnam function (7.21.4.4), <wchar.h> (7.28).
12043 1 Input and output, whether to or from physical devices such as terminals and tape drives,
12044 or whether to or from files supported on structured storage devices, are mapped into
12045 logical data streams, whose properties are more uniform than their various inputs and
12046 outputs. Two forms of mapping are supported, for text streams and for binary
12048 2 A text stream is an ordered sequence of characters composed into lines, each line
12049 consisting of zero or more characters plus a terminating new-line character. Whether the
12050 last line requires a terminating new-line character is implementation-defined. Characters
12051 may have to be added, altered, or deleted on input and output to conform to differing
12052 conventions for representing text in the host environment. Thus, there need not be a one-
12053 to-one correspondence between the characters in a stream and those in the external
12054 representation. Data read in from a text stream will necessarily compare equal to the data
12055 that were earlier written out to that stream only if: the data consist only of printing
12056 characters and the control characters horizontal tab and new-line; no new-line character is
12057 immediately preceded by space characters; and the last character is a new-line character.
12058 Whether space characters that are written out immediately before a new-line character
12059 appear when read in is implementation-defined.
12060 3 A binary stream is an ordered sequence of characters that can transparently record
12061 internal data. Data read in from a binary stream shall compare equal to the data that were
12062 earlier written out to that stream, under the same implementation. Such a stream may,
12063 however, have an implementation-defined number of null characters appended to the end
12065 4 Each stream has an orientation. After a stream is associated with an external file, but
12066 before any operations are performed on it, the stream is without orientation. Once a wide
12067 character input/output function has been applied to a stream without orientation, the
12070 259) An implementation need not distinguish between text streams and binary streams. In such an
12071 implementation, there need be no new-line characters in a text stream nor any limit to the length of a
12076 stream becomes a wide-oriented stream. Similarly, once a byte input/output function has
12077 been applied to a stream without orientation, the stream becomes a byte-oriented stream.
12078 Only a call to the freopen function or the fwide function can otherwise alter the
12079 orientation of a stream. (A successful call to freopen removes any orientation.)260)
12080 5 Byte input/output functions shall not be applied to a wide-oriented stream and wide
12081 character input/output functions shall not be applied to a byte-oriented stream. The
12082 remaining stream operations do not affect, and are not affected by, a stream's orientation,
12083 except for the following additional restrictions:
12084 -- Binary wide-oriented streams have the file-positioning restrictions ascribed to both
12085 text and binary streams.
12086 -- For wide-oriented streams, after a successful call to a file-positioning function that
12087 leaves the file position indicator prior to the end-of-file, a wide character output
12088 function can overwrite a partial multibyte character; any file contents beyond the
12089 byte(s) written are henceforth indeterminate.
12090 6 Each wide-oriented stream has an associated mbstate_t object that stores the current
12091 parse state of the stream. A successful call to fgetpos stores a representation of the
12092 value of this mbstate_t object as part of the value of the fpos_t object. A later
12093 successful call to fsetpos using the same stored fpos_t value restores the value of
12094 the associated mbstate_t object as well as the position within the controlled stream.
12095 Environmental limits
12096 7 An implementation shall support text files with lines containing at least 254 characters,
12097 including the terminating new-line character. The value of the macro BUFSIZ shall be at
12099 Forward references: the freopen function (7.21.5.4), the fwide function (7.28.3.5),
12100 mbstate_t (7.29.1), the fgetpos function (7.21.9.1), the fsetpos function
12106 260) The three predefined streams stdin, stdout, and stderr are unoriented at program startup.
12111 1 A stream is associated with an external file (which may be a physical device) by opening
12112 a file, which may involve creating a new file. Creating an existing file causes its former
12113 contents to be discarded, if necessary. If a file can support positioning requests (such as a
12114 disk file, as opposed to a terminal), then a file position indicator associated with the
12115 stream is positioned at the start (character number zero) of the file, unless the file is
12116 opened with append mode in which case it is implementation-defined whether the file
12117 position indicator is initially positioned at the beginning or the end of the file. The file
12118 position indicator is maintained by subsequent reads, writes, and positioning requests, to
12119 facilitate an orderly progression through the file.
12120 2 Binary files are not truncated, except as defined in 7.21.5.3. Whether a write on a text
12121 stream causes the associated file to be truncated beyond that point is implementation-
12123 3 When a stream is unbuffered, characters are intended to appear from the source or at the
12124 destination as soon as possible. Otherwise characters may be accumulated and
12125 transmitted to or from the host environment as a block. When a stream is fully buffered,
12126 characters are intended to be transmitted to or from the host environment as a block when
12127 a buffer is filled. When a stream is line buffered, characters are intended to be
12128 transmitted to or from the host environment as a block when a new-line character is
12129 encountered. Furthermore, characters are intended to be transmitted as a block to the host
12130 environment when a buffer is filled, when input is requested on an unbuffered stream, or
12131 when input is requested on a line buffered stream that requires the transmission of
12132 characters from the host environment. Support for these characteristics is
12133 implementation-defined, and may be affected via the setbuf and setvbuf functions.
12134 4 A file may be disassociated from a controlling stream by closing the file. Output streams
12135 are flushed (any unwritten buffer contents are transmitted to the host environment) before
12136 the stream is disassociated from the file. The value of a pointer to a FILE object is
12137 indeterminate after the associated file is closed (including the standard text streams).
12138 Whether a file of zero length (on which no characters have been written by an output
12139 stream) actually exists is implementation-defined.
12140 5 The file may be subsequently reopened, by the same or another program execution, and
12141 its contents reclaimed or modified (if it can be repositioned at its start). If the main
12142 function returns to its original caller, or if the exit function is called, all open files are
12143 closed (hence all output streams are flushed) before program termination. Other paths to
12144 program termination, such as calling the abort function, need not close all files
12146 6 The address of the FILE object used to control a stream may be significant; a copy of a
12147 FILE object need not serve in place of the original.
12151 7 At program startup, three text streams are predefined and need not be opened explicitly
12152 -- standard input (for reading conventional input), standard output (for writing
12153 conventional output), and standard error (for writing diagnostic output). As initially
12154 opened, the standard error stream is not fully buffered; the standard input and standard
12155 output streams are fully buffered if and only if the stream can be determined not to refer
12156 to an interactive device.
12157 8 Functions that open additional (nontemporary) files require a file name, which is a string.
12158 The rules for composing valid file names are implementation-defined. Whether the same
12159 file can be simultaneously open multiple times is also implementation-defined.
12160 9 Although both text and binary wide-oriented streams are conceptually sequences of wide
12161 characters, the external file associated with a wide-oriented stream is a sequence of
12162 multibyte characters, generalized as follows:
12163 -- Multibyte encodings within files may contain embedded null bytes (unlike multibyte
12164 encodings valid for use internal to the program).
12165 -- A file need not begin nor end in the initial shift state.261)
12166 10 Moreover, the encodings used for multibyte characters may differ among files. Both the
12167 nature and choice of such encodings are implementation-defined.
12168 11 The wide character input functions read multibyte characters from the stream and convert
12169 them to wide characters as if they were read by successive calls to the fgetwc function.
12170 Each conversion occurs as if by a call to the mbrtowc function, with the conversion state
12171 described by the stream's own mbstate_t object. The byte input functions read
12172 characters from the stream as if by successive calls to the fgetc function.
12173 12 The wide character output functions convert wide characters to multibyte characters and
12174 write them to the stream as if they were written by successive calls to the fputwc
12175 function. Each conversion occurs as if by a call to the wcrtomb function, with the
12176 conversion state described by the stream's own mbstate_t object. The byte output
12177 functions write characters to the stream as if by successive calls to the fputc function.
12178 13 In some cases, some of the byte input/output functions also perform conversions between
12179 multibyte characters and wide characters. These conversions also occur as if by calls to
12180 the mbrtowc and wcrtomb functions.
12181 14 An encoding error occurs if the character sequence presented to the underlying
12182 mbrtowc function does not form a valid (generalized) multibyte character, or if the code
12183 value passed to the underlying wcrtomb does not correspond to a valid (generalized)
12186 261) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has
12187 undefined behavior for a binary stream (because of possible trailing null characters) or for any stream
12188 with state-dependent encoding that does not assuredly end in the initial shift state.
12192 multibyte character. The wide character input/output functions and the byte input/output
12193 functions store the value of the macro EILSEQ in errno if and only if an encoding error
12195 Environmental limits
12196 15 The value of FOPEN_MAX shall be at least eight, including the three standard text
12198 Forward references: the exit function (7.22.4.4), the fgetc function (7.21.7.1), the
12199 fopen function (7.21.5.3), the fputc function (7.21.7.3), the setbuf function
12200 (7.21.5.5), the setvbuf function (7.21.5.6), the fgetwc function (7.28.3.1), the
12201 fputwc function (7.28.3.3), conversion state (7.28.6), the mbrtowc function
12202 (7.28.6.3.2), the wcrtomb function (7.28.6.3.3).
12203 7.21.4 Operations on files
12204 7.21.4.1 The remove function
12206 1 #include <stdio.h>
12207 int remove(const char *filename);
12209 2 The remove function causes the file whose name is the string pointed to by filename
12210 to be no longer accessible by that name. A subsequent attempt to open that file using that
12211 name will fail, unless it is created anew. If the file is open, the behavior of the remove
12212 function is implementation-defined.
12214 3 The remove function returns zero if the operation succeeds, nonzero if it fails.
12215 7.21.4.2 The rename function
12217 1 #include <stdio.h>
12218 int rename(const char *old, const char *new);
12220 2 The rename function causes the file whose name is the string pointed to by old to be
12221 henceforth known by the name given by the string pointed to by new. The file named
12222 old is no longer accessible by that name. If a file named by the string pointed to by new
12223 exists prior to the call to the rename function, the behavior is implementation-defined.
12231 3 The rename function returns zero if the operation succeeds, nonzero if it fails,262) in
12232 which case if the file existed previously it is still known by its original name.
12233 7.21.4.3 The tmpfile function
12235 1 #include <stdio.h>
12236 FILE *tmpfile(void);
12238 2 The tmpfile function creates a temporary binary file that is different from any other
12239 existing file and that will automatically be removed when it is closed or at program
12240 termination. If the program terminates abnormally, whether an open temporary file is
12241 removed is implementation-defined. The file is opened for update with "wb+" mode.
12242 Recommended practice
12243 3 It should be possible to open at least TMP_MAX temporary files during the lifetime of the
12244 program (this limit may be shared with tmpnam) and there should be no limit on the
12245 number simultaneously open other than this limit and any limit on the number of open
12248 4 The tmpfile function returns a pointer to the stream of the file that it created. If the file
12249 cannot be created, the tmpfile function returns a null pointer.
12250 Forward references: the fopen function (7.21.5.3).
12251 7.21.4.4 The tmpnam function
12253 1 #include <stdio.h>
12254 char *tmpnam(char *s);
12256 2 The tmpnam function generates a string that is a valid file name and that is not the same
12257 as the name of an existing file.263) The function is potentially capable of generating at
12260 262) Among the reasons the implementation may cause the rename function to fail are that the file is open
12261 or that it is necessary to copy its contents to effectuate its renaming.
12262 263) Files created using strings generated by the tmpnam function are temporary only in the sense that
12263 their names should not collide with those generated by conventional naming rules for the
12264 implementation. It is still necessary to use the remove function to remove such files when their use
12265 is ended, and before program termination.
12269 least TMP_MAX different strings, but any or all of them may already be in use by existing
12270 files and thus not be suitable return values.
12271 3 The tmpnam function generates a different string each time it is called.
12272 4 Calls to the tmpnam function with a null pointer argument may introduce data races with
12273 each other. The implementation shall behave as if no library function calls the tmpnam
12276 5 If no suitable string can be generated, the tmpnam function returns a null pointer.
12277 Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an
12278 internal static object and returns a pointer to that object (subsequent calls to the tmpnam
12279 function may modify the same object). If the argument is not a null pointer, it is assumed
12280 to point to an array of at least L_tmpnam chars; the tmpnam function writes its result
12281 in that array and returns the argument as its value.
12282 Environmental limits
12283 6 The value of the macro TMP_MAX shall be at least 25.
12284 7.21.5 File access functions
12285 7.21.5.1 The fclose function
12287 1 #include <stdio.h>
12288 int fclose(FILE *stream);
12290 2 A successful call to the fclose function causes the stream pointed to by stream to be
12291 flushed and the associated file to be closed. Any unwritten buffered data for the stream
12292 are delivered to the host environment to be written to the file; any unread buffered data
12293 are discarded. Whether or not the call succeeds, the stream is disassociated from the file
12294 and any buffer set by the setbuf or setvbuf function is disassociated from the stream
12295 (and deallocated if it was automatically allocated).
12297 3 The fclose function returns zero if the stream was successfully closed, or EOF if any
12298 errors were detected.
12305 7.21.5.2 The fflush function
12307 1 #include <stdio.h>
12308 int fflush(FILE *stream);
12310 2 If stream points to an output stream or an update stream in which the most recent
12311 operation was not input, the fflush function causes any unwritten data for that stream
12312 to be delivered to the host environment to be written to the file; otherwise, the behavior is
12314 3 If stream is a null pointer, the fflush function performs this flushing action on all
12315 streams for which the behavior is defined above.
12317 4 The fflush function sets the error indicator for the stream and returns EOF if a write
12318 error occurs, otherwise it returns zero.
12319 Forward references: the fopen function (7.21.5.3).
12320 7.21.5.3 The fopen function
12322 1 #include <stdio.h>
12323 FILE *fopen(const char * restrict filename,
12324 const char * restrict mode);
12326 2 The fopen function opens the file whose name is the string pointed to by filename,
12327 and associates a stream with it.
12328 3 The argument mode points to a string. If the string is one of the following, the file is
12329 open in the indicated mode. Otherwise, the behavior is undefined.264)
12330 r open text file for reading
12331 w truncate to zero length or create text file for writing
12332 wx create text file for writing
12333 a append; open or create text file for writing at end-of-file
12334 rb open binary file for reading
12335 wb truncate to zero length or create binary file for writing
12338 264) If the string begins with one of the above sequences, the implementation might choose to ignore the
12339 remaining characters, or it might use them to select different kinds of a file (some of which might not
12340 conform to the properties in 7.21.2).
12344 wbx create binary file for writing
12345 ab append; open or create binary file for writing at end-of-file
12346 r+ open text file for update (reading and writing)
12347 w+ truncate to zero length or create text file for update
12348 w+x create text file for update
12349 a+ append; open or create text file for update, writing at end-of-file
12350 r+b or rb+ open binary file for update (reading and writing)
12351 w+b or wb+ truncate to zero length or create binary file for update
12352 w+bx or wb+x create binary file for update
12353 a+b or ab+ append; open or create binary file for update, writing at end-of-file
12354 4 Opening a file with read mode ('r' as the first character in the mode argument) fails if
12355 the file does not exist or cannot be read.
12356 5 Opening a file with exclusive mode ('x' as the last character in the mode argument)
12357 fails if the file already exists or cannot be created. Otherwise, the file is created with
12358 exclusive (also known as non-shared) access to the extent that the underlying system
12359 supports exclusive access.
12360 6 Opening a file with append mode ('a' as the first character in the mode argument)
12361 causes all subsequent writes to the file to be forced to the then current end-of-file,
12362 regardless of intervening calls to the fseek function. In some implementations, opening
12363 a binary file with append mode ('b' as the second or third character in the above list of
12364 mode argument values) may initially position the file position indicator for the stream
12365 beyond the last data written, because of null character padding.
12366 7 When a file is opened with update mode ('+' as the second or third character in the
12367 above list of mode argument values), both input and output may be performed on the
12368 associated stream. However, output shall not be directly followed by input without an
12369 intervening call to the fflush function or to a file positioning function (fseek,
12370 fsetpos, or rewind), and input shall not be directly followed by output without an
12371 intervening call to a file positioning function, unless the input operation encounters end-
12372 of-file. Opening (or creating) a text file with update mode may instead open (or create) a
12373 binary stream in some implementations.
12374 8 When opened, a stream is fully buffered if and only if it can be determined not to refer to
12375 an interactive device. The error and end-of-file indicators for the stream are cleared.
12377 9 The fopen function returns a pointer to the object controlling the stream. If the open
12378 operation fails, fopen returns a null pointer.
12379 Forward references: file positioning functions (7.21.9).
12385 7.21.5.4 The freopen function
12387 1 #include <stdio.h>
12388 FILE *freopen(const char * restrict filename,
12389 const char * restrict mode,
12390 FILE * restrict stream);
12392 2 The freopen function opens the file whose name is the string pointed to by filename
12393 and associates the stream pointed to by stream with it. The mode argument is used just
12394 as in the fopen function.265)
12395 3 If filename is a null pointer, the freopen function attempts to change the mode of
12396 the stream to that specified by mode, as if the name of the file currently associated with
12397 the stream had been used. It is implementation-defined which changes of mode are
12398 permitted (if any), and under what circumstances.
12399 4 The freopen function first attempts to close any file that is associated with the specified
12400 stream. Failure to close the file is ignored. The error and end-of-file indicators for the
12401 stream are cleared.
12403 5 The freopen function returns a null pointer if the open operation fails. Otherwise,
12404 freopen returns the value of stream.
12405 7.21.5.5 The setbuf function
12407 1 #include <stdio.h>
12408 void setbuf(FILE * restrict stream,
12409 char * restrict buf);
12411 2 Except that it returns no value, the setbuf function is equivalent to the setvbuf
12412 function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf
12413 is a null pointer), with the value _IONBF for mode.
12418 265) The primary use of the freopen function is to change the file associated with a standard text stream
12419 (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value
12420 returned by the fopen function may be assigned.
12425 3 The setbuf function returns no value.
12426 Forward references: the setvbuf function (7.21.5.6).
12427 7.21.5.6 The setvbuf function
12429 1 #include <stdio.h>
12430 int setvbuf(FILE * restrict stream,
12431 char * restrict buf,
12432 int mode, size_t size);
12434 2 The setvbuf function may be used only after the stream pointed to by stream has
12435 been associated with an open file and before any other operation (other than an
12436 unsuccessful call to setvbuf) is performed on the stream. The argument mode
12437 determines how stream will be buffered, as follows: _IOFBF causes input/output to be
12438 fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes
12439 input/output to be unbuffered. If buf is not a null pointer, the array it points to may be
12440 used instead of a buffer allocated by the setvbuf function266) and the argument size
12441 specifies the size of the array; otherwise, size may determine the size of a buffer
12442 allocated by the setvbuf function. The contents of the array at any time are
12445 3 The setvbuf function returns zero on success, or nonzero if an invalid value is given
12446 for mode or if the request cannot be honored.
12451 266) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed
12452 before a buffer that has automatic storage duration is deallocated upon block exit.
12456 7.21.6 Formatted input/output functions
12457 1 The formatted input/output functions shall behave as if there is a sequence point after the
12458 actions associated with each specifier.267)
12459 7.21.6.1 The fprintf function
12461 1 #include <stdio.h>
12462 int fprintf(FILE * restrict stream,
12463 const char * restrict format, ...);
12465 2 The fprintf function writes output to the stream pointed to by stream, under control
12466 of the string pointed to by format that specifies how subsequent arguments are
12467 converted for output. If there are insufficient arguments for the format, the behavior is
12468 undefined. If the format is exhausted while arguments remain, the excess arguments are
12469 evaluated (as always) but are otherwise ignored. The fprintf function returns when
12470 the end of the format string is encountered.
12471 3 The format shall be a multibyte character sequence, beginning and ending in its initial
12472 shift state. The format is composed of zero or more directives: ordinary multibyte
12473 characters (not %), which are copied unchanged to the output stream; and conversion
12474 specifications, each of which results in fetching zero or more subsequent arguments,
12475 converting them, if applicable, according to the corresponding conversion specifier, and
12476 then writing the result to the output stream.
12477 4 Each conversion specification is introduced by the character %. After the %, the following
12478 appear in sequence:
12479 -- Zero or more flags (in any order) that modify the meaning of the conversion
12481 -- An optional minimum field width. If the converted value has fewer characters than the
12482 field width, it is padded with spaces (by default) on the left (or right, if the left
12483 adjustment flag, described later, has been given) to the field width. The field width
12484 takes the form of an asterisk * (described later) or a nonnegative decimal integer.268)
12485 -- An optional precision that gives the minimum number of digits to appear for the d, i,
12486 o, u, x, and X conversions, the number of digits to appear after the decimal-point
12487 character for a, A, e, E, f, and F conversions, the maximum number of significant
12488 digits for the g and G conversions, or the maximum number of bytes to be written for
12491 267) The fprintf functions perform writes to memory for the %n specifier.
12492 268) Note that 0 is taken as a flag, not as the beginning of a field width.
12496 s conversions. The precision takes the form of a period (.) followed either by an
12497 asterisk * (described later) or by an optional decimal integer; if only the period is
12498 specified, the precision is taken as zero. If a precision appears with any other
12499 conversion specifier, the behavior is undefined.
12500 -- An optional length modifier that specifies the size of the argument.
12501 -- A conversion specifier character that specifies the type of conversion to be applied.
12502 5 As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
12503 this case, an int argument supplies the field width or precision. The arguments
12504 specifying field width, or precision, or both, shall appear (in that order) before the
12505 argument (if any) to be converted. A negative field width argument is taken as a - flag
12506 followed by a positive field width. A negative precision argument is taken as if the
12507 precision were omitted.
12508 6 The flag characters and their meanings are:
12509 - The result of the conversion is left-justified within the field. (It is right-justified if
12510 this flag is not specified.)
12511 + The result of a signed conversion always begins with a plus or minus sign. (It
12512 begins with a sign only when a negative value is converted if this flag is not
12514 space If the first character of a signed conversion is not a sign, or if a signed conversion
12515 results in no characters, a space is prefixed to the result. If the space and + flags
12516 both appear, the space flag is ignored.
12517 # The result is converted to an ''alternative form''. For o conversion, it increases
12518 the precision, if and only if necessary, to force the first digit of the result to be a
12519 zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
12520 conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
12521 and G conversions, the result of converting a floating-point number always
12522 contains a decimal-point character, even if no digits follow it. (Normally, a
12523 decimal-point character appears in the result of these conversions only if a digit
12524 follows it.) For g and G conversions, trailing zeros are not removed from the
12525 result. For other conversions, the behavior is undefined.
12526 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
12527 (following any indication of sign or base) are used to pad to the field width rather
12528 than performing space padding, except when converting an infinity or NaN. If the
12529 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
12532 269) The results of all floating conversions of a negative zero, and of negative values that round to zero,
12533 include a minus sign.
12537 conversions, if a precision is specified, the 0 flag is ignored. For other
12538 conversions, the behavior is undefined.
12539 7 The length modifiers and their meanings are:
12540 hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12541 signed char or unsigned char argument (the argument will have
12542 been promoted according to the integer promotions, but its value shall be
12543 converted to signed char or unsigned char before printing); or that
12544 a following n conversion specifier applies to a pointer to a signed char
12546 h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12547 short int or unsigned short int argument (the argument will
12548 have been promoted according to the integer promotions, but its value shall
12549 be converted to short int or unsigned short int before printing);
12550 or that a following n conversion specifier applies to a pointer to a short
12552 l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12553 long int or unsigned long int argument; that a following n
12554 conversion specifier applies to a pointer to a long int argument; that a
12555 following c conversion specifier applies to a wint_t argument; that a
12556 following s conversion specifier applies to a pointer to a wchar_t
12557 argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
12559 ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12560 long long int or unsigned long long int argument; or that a
12561 following n conversion specifier applies to a pointer to a long long int
12563 j Specifies that a following d, i, o, u, x, or X conversion specifier applies to
12564 an intmax_t or uintmax_t argument; or that a following n conversion
12565 specifier applies to a pointer to an intmax_t argument.
12566 z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12567 size_t or the corresponding signed integer type argument; or that a
12568 following n conversion specifier applies to a pointer to a signed integer type
12569 corresponding to size_t argument.
12570 t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
12571 ptrdiff_t or the corresponding unsigned integer type argument; or that a
12572 following n conversion specifier applies to a pointer to a ptrdiff_t
12578 L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
12579 applies to a long double argument.
12580 If a length modifier appears with any conversion specifier other than as specified above,
12581 the behavior is undefined.
12582 8 The conversion specifiers and their meanings are:
12583 d,i The int argument is converted to signed decimal in the style [-]dddd. The
12584 precision specifies the minimum number of digits to appear; if the value
12585 being converted can be represented in fewer digits, it is expanded with
12586 leading zeros. The default precision is 1. The result of converting a zero
12587 value with a precision of zero is no characters.
12588 o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
12589 decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
12590 letters abcdef are used for x conversion and the letters ABCDEF for X
12591 conversion. The precision specifies the minimum number of digits to appear;
12592 if the value being converted can be represented in fewer digits, it is expanded
12593 with leading zeros. The default precision is 1. The result of converting a
12594 zero value with a precision of zero is no characters.
12595 f,F A double argument representing a floating-point number is converted to
12596 decimal notation in the style [-]ddd.ddd, where the number of digits after
12597 the decimal-point character is equal to the precision specification. If the
12598 precision is missing, it is taken as 6; if the precision is zero and the # flag is
12599 not specified, no decimal-point character appears. If a decimal-point
12600 character appears, at least one digit appears before it. The value is rounded to
12601 the appropriate number of digits.
12602 A double argument representing an infinity is converted in one of the styles
12603 [-]inf or [-]infinity -- which style is implementation-defined. A
12604 double argument representing a NaN is converted in one of the styles
12605 [-]nan or [-]nan(n-char-sequence) -- which style, and the meaning of
12606 any n-char-sequence, is implementation-defined. The F conversion specifier
12607 produces INF, INFINITY, or NAN instead of inf, infinity, or nan,
12609 e,E A double argument representing a floating-point number is converted in the
12610 style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the
12611 argument is nonzero) before the decimal-point character and the number of
12612 digits after it is equal to the precision; if the precision is missing, it is taken as
12615 270) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning;
12616 the # and 0 flag characters have no effect.
12620 6; if the precision is zero and the # flag is not specified, no decimal-point
12621 character appears. The value is rounded to the appropriate number of digits.
12622 The E conversion specifier produces a number with E instead of e
12623 introducing the exponent. The exponent always contains at least two digits,
12624 and only as many more digits as necessary to represent the exponent. If the
12625 value is zero, the exponent is zero.
12626 A double argument representing an infinity or NaN is converted in the style
12627 of an f or F conversion specifier.
12628 g,G A double argument representing a floating-point number is converted in
12629 style f or e (or in style F or E in the case of a G conversion specifier),
12630 depending on the value converted and the precision. Let P equal the
12631 precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
12632 Then, if a conversion with style E would have an exponent of X:
12633 -- if P > X >= -4, the conversion is with style f (or F) and precision
12635 -- otherwise, the conversion is with style e (or E) and precision P - 1.
12636 Finally, unless the # flag is used, any trailing zeros are removed from the
12637 fractional portion of the result and the decimal-point character is removed if
12638 there is no fractional portion remaining.
12639 A double argument representing an infinity or NaN is converted in the style
12640 of an f or F conversion specifier.
12641 a,A A double argument representing a floating-point number is converted in the
12642 style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
12643 nonzero if the argument is a normalized floating-point number and is
12644 otherwise unspecified) before the decimal-point character271) and the number
12645 of hexadecimal digits after it is equal to the precision; if the precision is
12646 missing and FLT_RADIX is a power of 2, then the precision is sufficient for
12647 an exact representation of the value; if the precision is missing and
12648 FLT_RADIX is not a power of 2, then the precision is sufficient to
12653 271) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so
12654 that subsequent digits align to nibble (4-bit) boundaries.
12658 distinguish272) values of type double, except that trailing zeros may be
12659 omitted; if the precision is zero and the # flag is not specified, no decimal-
12660 point character appears. The letters abcdef are used for a conversion and
12661 the letters ABCDEF for A conversion. The A conversion specifier produces a
12662 number with X and P instead of x and p. The exponent always contains at
12663 least one digit, and only as many more digits as necessary to represent the
12664 decimal exponent of 2. If the value is zero, the exponent is zero.
12665 A double argument representing an infinity or NaN is converted in the style
12666 of an f or F conversion specifier.
12667 c If no l length modifier is present, the int argument is converted to an
12668 unsigned char, and the resulting character is written.
12669 If an l length modifier is present, the wint_t argument is converted as if by
12670 an ls conversion specification with no precision and an argument that points
12671 to the initial element of a two-element array of wchar_t, the first element
12672 containing the wint_t argument to the lc conversion specification and the
12673 second a null wide character.
12674 s If no l length modifier is present, the argument shall be a pointer to the initial
12675 element of an array of character type.273) Characters from the array are
12676 written up to (but not including) the terminating null character. If the
12677 precision is specified, no more than that many bytes are written. If the
12678 precision is not specified or is greater than the size of the array, the array shall
12679 contain a null character.
12680 If an l length modifier is present, the argument shall be a pointer to the initial
12681 element of an array of wchar_t type. Wide characters from the array are
12682 converted to multibyte characters (each as if by a call to the wcrtomb
12683 function, with the conversion state described by an mbstate_t object
12684 initialized to zero before the first wide character is converted) up to and
12685 including a terminating null wide character. The resulting multibyte
12686 characters are written up to (but not including) the terminating null character
12687 (byte). If no precision is specified, the array shall contain a null wide
12688 character. If a precision is specified, no more than that many bytes are
12689 written (including shift sequences, if any), and the array shall contain a null
12690 wide character if, to equal the multibyte character sequence length given by
12692 272) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
12693 FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
12694 might suffice depending on the implementation's scheme for determining the digit to the left of the
12695 decimal-point character.
12696 273) No special provisions are made for multibyte characters.
12700 the precision, the function would need to access a wide character one past the
12701 end of the array. In no case is a partial multibyte character written.274)
12702 p The argument shall be a pointer to void. The value of the pointer is
12703 converted to a sequence of printing characters, in an implementation-defined
12705 n The argument shall be a pointer to signed integer into which is written the
12706 number of characters written to the output stream so far by this call to
12707 fprintf. No argument is converted, but one is consumed. If the conversion
12708 specification includes any flags, a field width, or a precision, the behavior is
12710 % A % character is written. No argument is converted. The complete
12711 conversion specification shall be %%.
12712 9 If a conversion specification is invalid, the behavior is undefined.275) If any argument is
12713 not the correct type for the corresponding conversion specification, the behavior is
12715 10 In no case does a nonexistent or small field width cause truncation of a field; if the result
12716 of a conversion is wider than the field width, the field is expanded to contain the
12718 11 For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
12719 to a hexadecimal floating number with the given precision.
12720 Recommended practice
12721 12 For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
12722 representable in the given precision, the result should be one of the two adjacent numbers
12723 in hexadecimal floating style with the given precision, with the extra stipulation that the
12724 error should have a correct sign for the current rounding direction.
12725 13 For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
12726 DECIMAL_DIG, then the result should be correctly rounded.276) If the number of
12727 significant decimal digits is more than DECIMAL_DIG but the source value is exactly
12728 representable with DECIMAL_DIG digits, then the result should be an exact
12729 representation with trailing zeros. Otherwise, the source value is bounded by two
12730 adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value
12733 274) Redundant shift sequences may result if multibyte characters have a state-dependent encoding.
12734 275) See ''future library directions'' (7.30.9).
12735 276) For binary-to-decimal conversion, the result format's values are the numbers representable with the
12736 given format specifier. The number of significant digits is determined by the format specifier, and in
12737 the case of fixed-point conversion by the source value as well.
12741 of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that
12742 the error should have a correct sign for the current rounding direction.
12744 14 The fprintf function returns the number of characters transmitted, or a negative value
12745 if an output or encoding error occurred.
12746 Environmental limits
12747 15 The number of characters that can be produced by any single conversion shall be at least
12749 16 EXAMPLE 1 To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal
12754 char *weekday, *month; // pointers to strings
12755 int day, hour, min;
12756 fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
12757 weekday, month, day, hour, min);
12758 fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
12760 17 EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the
12761 members of the extended character set that consist of more than one byte each consist of exactly two bytes,
12762 the first of which is denoted here by a and the second by an uppercase letter.
12763 18 Given the following wide string with length seven,
12764 static wchar_t wstr[] = L" X Yabc Z W";
12766 fprintf(stdout, "|1234567890123|\n");
12767 fprintf(stdout, "|%13ls|\n", wstr);
12768 fprintf(stdout, "|%-13.9ls|\n", wstr);
12769 fprintf(stdout, "|%13.10ls|\n", wstr);
12770 fprintf(stdout, "|%13.11ls|\n", wstr);
12771 fprintf(stdout, "|%13.15ls|\n", &wstr[2]);
12772 fprintf(stdout, "|%13lc|\n", (wint_t) wstr[5]);
12773 will print the following seven lines:
12782 Forward references: conversion state (7.28.6), the wcrtomb function (7.28.6.3.3).
12788 7.21.6.2 The fscanf function
12790 1 #include <stdio.h>
12791 int fscanf(FILE * restrict stream,
12792 const char * restrict format, ...);
12794 2 The fscanf function reads input from the stream pointed to by stream, under control
12795 of the string pointed to by format that specifies the admissible input sequences and how
12796 they are to be converted for assignment, using subsequent arguments as pointers to the
12797 objects to receive the converted input. If there are insufficient arguments for the format,
12798 the behavior is undefined. If the format is exhausted while arguments remain, the excess
12799 arguments are evaluated (as always) but are otherwise ignored.
12800 3 The format shall be a multibyte character sequence, beginning and ending in its initial
12801 shift state. The format is composed of zero or more directives: one or more white-space
12802 characters, an ordinary multibyte character (neither % nor a white-space character), or a
12803 conversion specification. Each conversion specification is introduced by the character %.
12804 After the %, the following appear in sequence:
12805 -- An optional assignment-suppressing character *.
12806 -- An optional decimal integer greater than zero that specifies the maximum field width
12808 -- An optional length modifier that specifies the size of the receiving object.
12809 -- A conversion specifier character that specifies the type of conversion to be applied.
12810 4 The fscanf function executes each directive of the format in turn. When all directives
12811 have been executed, or if a directive fails (as detailed below), the function returns.
12812 Failures are described as input failures (due to the occurrence of an encoding error or the
12813 unavailability of input characters), or matching failures (due to inappropriate input).
12814 5 A directive composed of white-space character(s) is executed by reading input up to the
12815 first non-white-space character (which remains unread), or until no more characters can
12817 6 A directive that is an ordinary multibyte character is executed by reading the next
12818 characters of the stream. If any of those characters differ from the ones composing the
12819 directive, the directive fails and the differing and subsequent characters remain unread.
12820 Similarly, if end-of-file, an encoding error, or a read error prevents a character from being
12821 read, the directive fails.
12822 7 A directive that is a conversion specification defines a set of matching input sequences, as
12823 described below for each specifier. A conversion specification is executed in the
12828 8 Input white-space characters (as specified by the isspace function) are skipped, unless
12829 the specification includes a [, c, or n specifier.277)
12830 9 An input item is read from the stream, unless the specification includes an n specifier. An
12831 input item is defined as the longest sequence of input characters which does not exceed
12832 any specified field width and which is, or is a prefix of, a matching input sequence.278)
12833 The first character, if any, after the input item remains unread. If the length of the input
12834 item is zero, the execution of the directive fails; this condition is a matching failure unless
12835 end-of-file, an encoding error, or a read error prevented input from the stream, in which
12836 case it is an input failure.
12837 10 Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
12838 count of input characters) is converted to a type appropriate to the conversion specifier. If
12839 the input item is not a matching sequence, the execution of the directive fails: this
12840 condition is a matching failure. Unless assignment suppression was indicated by a *, the
12841 result of the conversion is placed in the object pointed to by the first argument following
12842 the format argument that has not already received a conversion result. If this object
12843 does not have an appropriate type, or if the result of the conversion cannot be represented
12844 in the object, the behavior is undefined.
12845 11 The length modifiers and their meanings are:
12846 hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12847 to an argument with type pointer to signed char or unsigned char.
12848 h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12849 to an argument with type pointer to short int or unsigned short
12851 l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12852 to an argument with type pointer to long int or unsigned long
12853 int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
12854 an argument with type pointer to double; or that a following c, s, or [
12855 conversion specifier applies to an argument with type pointer to wchar_t.
12856 ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12857 to an argument with type pointer to long long int or unsigned
12862 277) These white-space characters are not counted against a specified field width.
12863 278) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences
12864 that are acceptable to strtod, strtol, etc., are unacceptable to fscanf.
12868 j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12869 to an argument with type pointer to intmax_t or uintmax_t.
12870 z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12871 to an argument with type pointer to size_t or the corresponding signed
12873 t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
12874 to an argument with type pointer to ptrdiff_t or the corresponding
12875 unsigned integer type.
12876 L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
12877 applies to an argument with type pointer to long double.
12878 If a length modifier appears with any conversion specifier other than as specified above,
12879 the behavior is undefined.
12880 12 The conversion specifiers and their meanings are:
12881 d Matches an optionally signed decimal integer, whose format is the same as
12882 expected for the subject sequence of the strtol function with the value 10
12883 for the base argument. The corresponding argument shall be a pointer to
12885 i Matches an optionally signed integer, whose format is the same as expected
12886 for the subject sequence of the strtol function with the value 0 for the
12887 base argument. The corresponding argument shall be a pointer to signed
12889 o Matches an optionally signed octal integer, whose format is the same as
12890 expected for the subject sequence of the strtoul function with the value 8
12891 for the base argument. The corresponding argument shall be a pointer to
12893 u Matches an optionally signed decimal integer, whose format is the same as
12894 expected for the subject sequence of the strtoul function with the value 10
12895 for the base argument. The corresponding argument shall be a pointer to
12897 x Matches an optionally signed hexadecimal integer, whose format is the same
12898 as expected for the subject sequence of the strtoul function with the value
12899 16 for the base argument. The corresponding argument shall be a pointer to
12901 a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
12902 format is the same as expected for the subject sequence of the strtod
12903 function. The corresponding argument shall be a pointer to floating.
12908 c Matches a sequence of characters of exactly the number specified by the field
12909 width (1 if no field width is present in the directive).279)
12910 If no l length modifier is present, the corresponding argument shall be a
12911 pointer to the initial element of a character array large enough to accept the
12912 sequence. No null character is added.
12913 If an l length modifier is present, the input shall be a sequence of multibyte
12914 characters that begins in the initial shift state. Each multibyte character in the
12915 sequence is converted to a wide character as if by a call to the mbrtowc
12916 function, with the conversion state described by an mbstate_t object
12917 initialized to zero before the first multibyte character is converted. The
12918 corresponding argument shall be a pointer to the initial element of an array of
12919 wchar_t large enough to accept the resulting sequence of wide characters.
12920 No null wide character is added.
12921 s Matches a sequence of non-white-space characters.279)
12922 If no l length modifier is present, the corresponding argument shall be a
12923 pointer to the initial element of a character array large enough to accept the
12924 sequence and a terminating null character, which will be added automatically.
12925 If an l length modifier is present, the input shall be a sequence of multibyte
12926 characters that begins in the initial shift state. Each multibyte character is
12927 converted to a wide character as if by a call to the mbrtowc function, with
12928 the conversion state described by an mbstate_t object initialized to zero
12929 before the first multibyte character is converted. The corresponding argument
12930 shall be a pointer to the initial element of an array of wchar_t large enough
12931 to accept the sequence and the terminating null wide character, which will be
12932 added automatically.
12933 [ Matches a nonempty sequence of characters from a set of expected characters
12935 If no l length modifier is present, the corresponding argument shall be a
12936 pointer to the initial element of a character array large enough to accept the
12937 sequence and a terminating null character, which will be added automatically.
12938 If an l length modifier is present, the input shall be a sequence of multibyte
12939 characters that begins in the initial shift state. Each multibyte character is
12940 converted to a wide character as if by a call to the mbrtowc function, with
12941 the conversion state described by an mbstate_t object initialized to zero
12943 279) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
12944 conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The
12945 resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.
12949 before the first multibyte character is converted. The corresponding argument
12950 shall be a pointer to the initial element of an array of wchar_t large enough
12951 to accept the sequence and the terminating null wide character, which will be
12952 added automatically.
12953 The conversion specifier includes all subsequent characters in the format
12954 string, up to and including the matching right bracket (]). The characters
12955 between the brackets (the scanlist) compose the scanset, unless the character
12956 after the left bracket is a circumflex (^), in which case the scanset contains all
12957 characters that do not appear in the scanlist between the circumflex and the
12958 right bracket. If the conversion specifier begins with [] or [^], the right
12959 bracket character is in the scanlist and the next following right bracket
12960 character is the matching right bracket that ends the specification; otherwise
12961 the first following right bracket character is the one that ends the
12962 specification. If a - character is in the scanlist and is not the first, nor the
12963 second where the first character is a ^, nor the last character, the behavior is
12964 implementation-defined.
12965 p Matches an implementation-defined set of sequences, which should be the
12966 same as the set of sequences that may be produced by the %p conversion of
12967 the fprintf function. The corresponding argument shall be a pointer to a
12968 pointer to void. The input item is converted to a pointer value in an
12969 implementation-defined manner. If the input item is a value converted earlier
12970 during the same program execution, the pointer that results shall compare
12971 equal to that value; otherwise the behavior of the %p conversion is undefined.
12972 n No input is consumed. The corresponding argument shall be a pointer to
12973 signed integer into which is to be written the number of characters read from
12974 the input stream so far by this call to the fscanf function. Execution of a
12975 %n directive does not increment the assignment count returned at the
12976 completion of execution of the fscanf function. No argument is converted,
12977 but one is consumed. If the conversion specification includes an assignment-
12978 suppressing character or a field width, the behavior is undefined.
12979 % Matches a single % character; no conversion or assignment occurs. The
12980 complete conversion specification shall be %%.
12981 13 If a conversion specification is invalid, the behavior is undefined.280)
12982 14 The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
12983 respectively, a, e, f, g, and x.
12987 280) See ''future library directions'' (7.30.9).
12991 15 Trailing white space (including new-line characters) is left unread unless matched by a
12992 directive. The success of literal matches and suppressed assignments is not directly
12993 determinable other than via the %n directive.
12995 16 The fscanf function returns the value of the macro EOF if an input failure occurs
12996 before the first conversion (if any) has completed. Otherwise, the function returns the
12997 number of input items assigned, which can be fewer than provided for, or even zero, in
12998 the event of an early matching failure.
12999 17 EXAMPLE 1 The call:
13002 int n, i; float x; char name[50];
13003 n = fscanf(stdin, "%d%f%s", &i, &x, name);
13004 with the input line:
13005 25 54.32E-1 thompson
13006 will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
13009 18 EXAMPLE 2 The call:
13012 int i; float x; char name[50];
13013 fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
13016 will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name the
13017 sequence 56\0. The next character read from the input stream will be a.
13019 19 EXAMPLE 3 To accept repeatedly from stdin a quantity, a unit of measure, and an item name:
13022 int count; float quant; char units[21], item[21];
13024 count = fscanf(stdin, "%f%20s of %20s", &quant, units, item);
13025 fscanf(stdin,"%*[^\n]");
13026 } while (!feof(stdin) && !ferror(stdin));
13027 20 If the stdin stream contains the following lines:
13029 -12.8degrees Celsius
13037 the execution of the above example will be analogous to the following assignments:
13038 quant = 2; strcpy(units, "quarts"); strcpy(item, "oil");
13040 quant = -12.8; strcpy(units, "degrees");
13041 count = 2; // "C" fails to match "o"
13042 count = 0; // "l" fails to match "%f"
13043 quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt");
13045 count = 0; // "100e" fails to match "%f"
13051 int d1, d2, n1, n2, i;
13052 i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
13053 the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure the value
13054 of 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i.
13056 22 EXAMPLE 5 In these examples, multibyte characters do have a state-dependent encoding, and the
13057 members of the extended character set that consist of more than one byte each consist of exactly two bytes,
13058 the first of which is denoted here by a and the second by an uppercase letter, but are only recognized as
13059 such when in the alternate shift state. The shift sequences are denoted by (uparrow) and (downarrow), in which the first causes
13060 entry into the alternate shift state.
13065 fscanf(stdin, "a%s", str);
13066 with the input line:
13067 a(uparrow) X Y(downarrow) bc
13068 str will contain (uparrow) X Y(downarrow)\0 assuming that none of the bytes of the shift sequences (or of the multibyte
13069 characters, in the more general case) appears to be a single-byte white-space character.
13070 24 In contrast, after the call:
13072 #include <stddef.h>
13075 fscanf(stdin, "a%ls", wstr);
13076 with the same input line, wstr will contain the two wide characters that correspond to X and Y and a
13077 terminating null wide character.
13078 25 However, the call:
13086 #include <stddef.h>
13089 fscanf(stdin, "a(uparrow) X(downarrow)%ls", wstr);
13090 with the same input line will return zero due to a matching failure against the (downarrow) sequence in the format
13092 26 Assuming that the first byte of the multibyte character X is the same as the first byte of the multibyte
13093 character Y, after the call:
13095 #include <stddef.h>
13098 fscanf(stdin, "a(uparrow) Y(downarrow)%ls", wstr);
13099 with the same input line, zero will again be returned, but stdin will be left with a partially consumed
13100 multibyte character.
13102 Forward references: the strtod, strtof, and strtold functions (7.22.1.3), the
13103 strtol, strtoll, strtoul, and strtoull functions (7.22.1.4), conversion state
13104 (7.28.6), the wcrtomb function (7.28.6.3.3).
13105 7.21.6.3 The printf function
13107 1 #include <stdio.h>
13108 int printf(const char * restrict format, ...);
13110 2 The printf function is equivalent to fprintf with the argument stdout interposed
13111 before the arguments to printf.
13113 3 The printf function returns the number of characters transmitted, or a negative value if
13114 an output or encoding error occurred.
13115 7.21.6.4 The scanf function
13117 1 #include <stdio.h>
13118 int scanf(const char * restrict format, ...);
13120 2 The scanf function is equivalent to fscanf with the argument stdin interposed
13121 before the arguments to scanf.
13128 3 The scanf function returns the value of the macro EOF if an input failure occurs before
13129 the first conversion (if any) has completed. Otherwise, the scanf function returns the
13130 number of input items assigned, which can be fewer than provided for, or even zero, in
13131 the event of an early matching failure.
13132 7.21.6.5 The snprintf function
13134 1 #include <stdio.h>
13135 int snprintf(char * restrict s, size_t n,
13136 const char * restrict format, ...);
13138 2 The snprintf function is equivalent to fprintf, except that the output is written into
13139 an array (specified by argument s) rather than to a stream. If n is zero, nothing is written,
13140 and s may be a null pointer. Otherwise, output characters beyond the n-1st are
13141 discarded rather than being written to the array, and a null character is written at the end
13142 of the characters actually written into the array. If copying takes place between objects
13143 that overlap, the behavior is undefined.
13145 3 The snprintf function returns the number of characters that would have been written
13146 had n been sufficiently large, not counting the terminating null character, or a negative
13147 value if an encoding error occurred. Thus, the null-terminated output has been
13148 completely written if and only if the returned value is nonnegative and less than n.
13149 7.21.6.6 The sprintf function
13151 1 #include <stdio.h>
13152 int sprintf(char * restrict s,
13153 const char * restrict format, ...);
13155 2 The sprintf function is equivalent to fprintf, except that the output is written into
13156 an array (specified by the argument s) rather than to a stream. A null character is written
13157 at the end of the characters written; it is not counted as part of the returned value. If
13158 copying takes place between objects that overlap, the behavior is undefined.
13160 3 The sprintf function returns the number of characters written in the array, not
13161 counting the terminating null character, or a negative value if an encoding error occurred.
13165 7.21.6.7 The sscanf function
13167 1 #include <stdio.h>
13168 int sscanf(const char * restrict s,
13169 const char * restrict format, ...);
13171 2 The sscanf function is equivalent to fscanf, except that input is obtained from a
13172 string (specified by the argument s) rather than from a stream. Reaching the end of the
13173 string is equivalent to encountering end-of-file for the fscanf function. If copying
13174 takes place between objects that overlap, the behavior is undefined.
13176 3 The sscanf function returns the value of the macro EOF if an input failure occurs
13177 before the first conversion (if any) has completed. Otherwise, the sscanf function
13178 returns the number of input items assigned, which can be fewer than provided for, or even
13179 zero, in the event of an early matching failure.
13180 7.21.6.8 The vfprintf function
13182 1 #include <stdarg.h>
13184 int vfprintf(FILE * restrict stream,
13185 const char * restrict format,
13188 2 The vfprintf function is equivalent to fprintf, with the variable argument list
13189 replaced by arg, which shall have been initialized by the va_start macro (and
13190 possibly subsequent va_arg calls). The vfprintf function does not invoke the
13193 3 The vfprintf function returns the number of characters transmitted, or a negative
13194 value if an output or encoding error occurred.
13195 4 EXAMPLE The following shows the use of the vfprintf function in a general error-reporting routine.
13200 281) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
13201 vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
13205 #include <stdarg.h>
13207 void error(char *function_name, char *format, ...)
13210 va_start(args, format);
13211 // print out name of function causing error
13212 fprintf(stderr, "ERROR in %s: ", function_name);
13213 // print out remainder of message
13214 vfprintf(stderr, format, args);
13218 7.21.6.9 The vfscanf function
13220 1 #include <stdarg.h>
13222 int vfscanf(FILE * restrict stream,
13223 const char * restrict format,
13226 2 The vfscanf function is equivalent to fscanf, with the variable argument list
13227 replaced by arg, which shall have been initialized by the va_start macro (and
13228 possibly subsequent va_arg calls). The vfscanf function does not invoke the
13231 3 The vfscanf function returns the value of the macro EOF if an input failure occurs
13232 before the first conversion (if any) has completed. Otherwise, the vfscanf function
13233 returns the number of input items assigned, which can be fewer than provided for, or even
13234 zero, in the event of an early matching failure.
13235 7.21.6.10 The vprintf function
13237 1 #include <stdarg.h>
13239 int vprintf(const char * restrict format,
13242 2 The vprintf function is equivalent to printf, with the variable argument list
13243 replaced by arg, which shall have been initialized by the va_start macro (and
13247 possibly subsequent va_arg calls). The vprintf function does not invoke the
13250 3 The vprintf function returns the number of characters transmitted, or a negative value
13251 if an output or encoding error occurred.
13252 7.21.6.11 The vscanf function
13254 1 #include <stdarg.h>
13256 int vscanf(const char * restrict format,
13259 2 The vscanf function is equivalent to scanf, with the variable argument list replaced
13260 by arg, which shall have been initialized by the va_start macro (and possibly
13261 subsequent va_arg calls). The vscanf function does not invoke the va_end
13264 3 The vscanf function returns the value of the macro EOF if an input failure occurs
13265 before the first conversion (if any) has completed. Otherwise, the vscanf function
13266 returns the number of input items assigned, which can be fewer than provided for, or even
13267 zero, in the event of an early matching failure.
13268 7.21.6.12 The vsnprintf function
13270 1 #include <stdarg.h>
13272 int vsnprintf(char * restrict s, size_t n,
13273 const char * restrict format,
13276 2 The vsnprintf function is equivalent to snprintf, with the variable argument list
13277 replaced by arg, which shall have been initialized by the va_start macro (and
13278 possibly subsequent va_arg calls). The vsnprintf function does not invoke the
13279 va_end macro.281) If copying takes place between objects that overlap, the behavior is
13287 3 The vsnprintf function returns the number of characters that would have been written
13288 had n been sufficiently large, not counting the terminating null character, or a negative
13289 value if an encoding error occurred. Thus, the null-terminated output has been
13290 completely written if and only if the returned value is nonnegative and less than n.
13291 7.21.6.13 The vsprintf function
13293 1 #include <stdarg.h>
13295 int vsprintf(char * restrict s,
13296 const char * restrict format,
13299 2 The vsprintf function is equivalent to sprintf, with the variable argument list
13300 replaced by arg, which shall have been initialized by the va_start macro (and
13301 possibly subsequent va_arg calls). The vsprintf function does not invoke the
13302 va_end macro.281) If copying takes place between objects that overlap, the behavior is
13305 3 The vsprintf function returns the number of characters written in the array, not
13306 counting the terminating null character, or a negative value if an encoding error occurred.
13307 7.21.6.14 The vsscanf function
13309 1 #include <stdarg.h>
13311 int vsscanf(const char * restrict s,
13312 const char * restrict format,
13315 2 The vsscanf function is equivalent to sscanf, with the variable argument list
13316 replaced by arg, which shall have been initialized by the va_start macro (and
13317 possibly subsequent va_arg calls). The vsscanf function does not invoke the
13320 3 The vsscanf function returns the value of the macro EOF if an input failure occurs
13321 before the first conversion (if any) has completed. Otherwise, the vsscanf function
13324 returns the number of input items assigned, which can be fewer than provided for, or even
13325 zero, in the event of an early matching failure.
13326 7.21.7 Character input/output functions
13327 7.21.7.1 The fgetc function
13329 1 #include <stdio.h>
13330 int fgetc(FILE *stream);
13332 2 If the end-of-file indicator for the input stream pointed to by stream is not set and a
13333 next character is present, the fgetc function obtains that character as an unsigned
13334 char converted to an int and advances the associated file position indicator for the
13335 stream (if defined).
13337 3 If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
13338 of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the
13339 fgetc function returns the next character from the input stream pointed to by stream.
13340 If a read error occurs, the error indicator for the stream is set and the fgetc function
13342 7.21.7.2 The fgets function
13344 1 #include <stdio.h>
13345 char *fgets(char * restrict s, int n,
13346 FILE * restrict stream);
13348 2 The fgets function reads at most one less than the number of characters specified by n
13349 from the stream pointed to by stream into the array pointed to by s. No additional
13350 characters are read after a new-line character (which is retained) or after end-of-file. A
13351 null character is written immediately after the last character read into the array.
13353 3 The fgets function returns s if successful. If end-of-file is encountered and no
13354 characters have been read into the array, the contents of the array remain unchanged and a
13355 null pointer is returned. If a read error occurs during the operation, the array contents are
13356 indeterminate and a null pointer is returned.
13358 282) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
13362 7.21.7.3 The fputc function
13364 1 #include <stdio.h>
13365 int fputc(int c, FILE *stream);
13367 2 The fputc function writes the character specified by c (converted to an unsigned
13368 char) to the output stream pointed to by stream, at the position indicated by the
13369 associated file position indicator for the stream (if defined), and advances the indicator
13370 appropriately. If the file cannot support positioning requests, or if the stream was opened
13371 with append mode, the character is appended to the output stream.
13373 3 The fputc function returns the character written. If a write error occurs, the error
13374 indicator for the stream is set and fputc returns EOF.
13375 7.21.7.4 The fputs function
13377 1 #include <stdio.h>
13378 int fputs(const char * restrict s,
13379 FILE * restrict stream);
13381 2 The fputs function writes the string pointed to by s to the stream pointed to by
13382 stream. The terminating null character is not written.
13384 3 The fputs function returns EOF if a write error occurs; otherwise it returns a
13386 7.21.7.5 The getc function
13388 1 #include <stdio.h>
13389 int getc(FILE *stream);
13391 2 The getc function is equivalent to fgetc, except that if it is implemented as a macro, it
13392 may evaluate stream more than once, so the argument should never be an expression
13401 3 The getc function returns the next character from the input stream pointed to by
13402 stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
13403 getc returns EOF. If a read error occurs, the error indicator for the stream is set and
13405 7.21.7.6 The getchar function
13407 1 #include <stdio.h>
13410 2 The getchar function is equivalent to getc with the argument stdin.
13412 3 The getchar function returns the next character from the input stream pointed to by
13413 stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
13414 getchar returns EOF. If a read error occurs, the error indicator for the stream is set and
13415 getchar returns EOF. *
13416 7.21.7.7 The putc function
13418 1 #include <stdio.h>
13419 int putc(int c, FILE *stream);
13421 2 The putc function is equivalent to fputc, except that if it is implemented as a macro, it
13422 may evaluate stream more than once, so that argument should never be an expression
13425 3 The putc function returns the character written. If a write error occurs, the error
13426 indicator for the stream is set and putc returns EOF.
13427 7.21.7.8 The putchar function
13429 1 #include <stdio.h>
13430 int putchar(int c);
13432 2 The putchar function is equivalent to putc with the second argument stdout.
13438 3 The putchar function returns the character written. If a write error occurs, the error
13439 indicator for the stream is set and putchar returns EOF.
13440 7.21.7.9 The puts function
13442 1 #include <stdio.h>
13443 int puts(const char *s);
13445 2 The puts function writes the string pointed to by s to the stream pointed to by stdout,
13446 and appends a new-line character to the output. The terminating null character is not
13449 3 The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative
13451 7.21.7.10 The ungetc function
13453 1 #include <stdio.h>
13454 int ungetc(int c, FILE *stream);
13456 2 The ungetc function pushes the character specified by c (converted to an unsigned
13457 char) back onto the input stream pointed to by stream. Pushed-back characters will be
13458 returned by subsequent reads on that stream in the reverse order of their pushing. A
13459 successful intervening call (with the stream pointed to by stream) to a file positioning
13460 function (fseek, fsetpos, or rewind) discards any pushed-back characters for the
13461 stream. The external storage corresponding to the stream is unchanged.
13462 3 One character of pushback is guaranteed. If the ungetc function is called too many
13463 times on the same stream without an intervening read or file positioning operation on that
13464 stream, the operation may fail.
13465 4 If the value of c equals that of the macro EOF, the operation fails and the input stream is
13467 5 A successful call to the ungetc function clears the end-of-file indicator for the stream.
13468 The value of the file position indicator for the stream after reading or discarding all
13469 pushed-back characters shall be the same as it was before the characters were pushed
13470 back. For a text stream, the value of its file position indicator after a successful call to the
13471 ungetc function is unspecified until all pushed-back characters are read or discarded.
13475 For a binary stream, its file position indicator is decremented by each successful call to
13476 the ungetc function; if its value was zero before a call, it is indeterminate after the
13479 6 The ungetc function returns the character pushed back after conversion, or EOF if the
13481 Forward references: file positioning functions (7.21.9).
13482 7.21.8 Direct input/output functions
13483 7.21.8.1 The fread function
13485 1 #include <stdio.h>
13486 size_t fread(void * restrict ptr,
13487 size_t size, size_t nmemb,
13488 FILE * restrict stream);
13490 2 The fread function reads, into the array pointed to by ptr, up to nmemb elements
13491 whose size is specified by size, from the stream pointed to by stream. For each
13492 object, size calls are made to the fgetc function and the results stored, in the order
13493 read, in an array of unsigned char exactly overlaying the object. The file position
13494 indicator for the stream (if defined) is advanced by the number of characters successfully
13495 read. If an error occurs, the resulting value of the file position indicator for the stream is
13496 indeterminate. If a partial element is read, its value is indeterminate.
13498 3 The fread function returns the number of elements successfully read, which may be
13499 less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero,
13500 fread returns zero and the contents of the array and the state of the stream remain
13506 283) See ''future library directions'' (7.30.9).
13510 7.21.8.2 The fwrite function
13512 1 #include <stdio.h>
13513 size_t fwrite(const void * restrict ptr,
13514 size_t size, size_t nmemb,
13515 FILE * restrict stream);
13517 2 The fwrite function writes, from the array pointed to by ptr, up to nmemb elements
13518 whose size is specified by size, to the stream pointed to by stream. For each object,
13519 size calls are made to the fputc function, taking the values (in order) from an array of
13520 unsigned char exactly overlaying the object. The file position indicator for the
13521 stream (if defined) is advanced by the number of characters successfully written. If an
13522 error occurs, the resulting value of the file position indicator for the stream is
13525 3 The fwrite function returns the number of elements successfully written, which will be
13526 less than nmemb only if a write error is encountered. If size or nmemb is zero,
13527 fwrite returns zero and the state of the stream remains unchanged.
13528 7.21.9 File positioning functions
13529 7.21.9.1 The fgetpos function
13531 1 #include <stdio.h>
13532 int fgetpos(FILE * restrict stream,
13533 fpos_t * restrict pos);
13535 2 The fgetpos function stores the current values of the parse state (if any) and file
13536 position indicator for the stream pointed to by stream in the object pointed to by pos.
13537 The values stored contain unspecified information usable by the fsetpos function for
13538 repositioning the stream to its position at the time of the call to the fgetpos function.
13540 3 If successful, the fgetpos function returns zero; on failure, the fgetpos function
13541 returns nonzero and stores an implementation-defined positive value in errno.
13542 Forward references: the fsetpos function (7.21.9.3).
13549 7.21.9.2 The fseek function
13551 1 #include <stdio.h>
13552 int fseek(FILE *stream, long int offset, int whence);
13554 2 The fseek function sets the file position indicator for the stream pointed to by stream.
13555 If a read or write error occurs, the error indicator for the stream is set and fseek fails.
13556 3 For a binary stream, the new position, measured in characters from the beginning of the
13557 file, is obtained by adding offset to the position specified by whence. The specified
13558 position is the beginning of the file if whence is SEEK_SET, the current value of the file
13559 position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not
13560 meaningfully support fseek calls with a whence value of SEEK_END.
13561 4 For a text stream, either offset shall be zero, or offset shall be a value returned by
13562 an earlier successful call to the ftell function on a stream associated with the same file
13563 and whence shall be SEEK_SET.
13564 5 After determining the new position, a successful call to the fseek function undoes any
13565 effects of the ungetc function on the stream, clears the end-of-file indicator for the
13566 stream, and then establishes the new position. After a successful fseek call, the next
13567 operation on an update stream may be either input or output.
13569 6 The fseek function returns nonzero only for a request that cannot be satisfied.
13570 Forward references: the ftell function (7.21.9.4).
13571 7.21.9.3 The fsetpos function
13573 1 #include <stdio.h>
13574 int fsetpos(FILE *stream, const fpos_t *pos);
13576 2 The fsetpos function sets the mbstate_t object (if any) and file position indicator
13577 for the stream pointed to by stream according to the value of the object pointed to by
13578 pos, which shall be a value obtained from an earlier successful call to the fgetpos
13579 function on a stream associated with the same file. If a read or write error occurs, the
13580 error indicator for the stream is set and fsetpos fails.
13581 3 A successful call to the fsetpos function undoes any effects of the ungetc function
13582 on the stream, clears the end-of-file indicator for the stream, and then establishes the new
13583 parse state and position. After a successful fsetpos call, the next operation on an
13587 update stream may be either input or output.
13589 4 If successful, the fsetpos function returns zero; on failure, the fsetpos function
13590 returns nonzero and stores an implementation-defined positive value in errno.
13591 7.21.9.4 The ftell function
13593 1 #include <stdio.h>
13594 long int ftell(FILE *stream);
13596 2 The ftell function obtains the current value of the file position indicator for the stream
13597 pointed to by stream. For a binary stream, the value is the number of characters from
13598 the beginning of the file. For a text stream, its file position indicator contains unspecified
13599 information, usable by the fseek function for returning the file position indicator for the
13600 stream to its position at the time of the ftell call; the difference between two such
13601 return values is not necessarily a meaningful measure of the number of characters written
13604 3 If successful, the ftell function returns the current value of the file position indicator
13605 for the stream. On failure, the ftell function returns -1L and stores an
13606 implementation-defined positive value in errno.
13607 7.21.9.5 The rewind function
13609 1 #include <stdio.h>
13610 void rewind(FILE *stream);
13612 2 The rewind function sets the file position indicator for the stream pointed to by
13613 stream to the beginning of the file. It is equivalent to
13614 (void)fseek(stream, 0L, SEEK_SET)
13615 except that the error indicator for the stream is also cleared.
13617 3 The rewind function returns no value.
13624 7.21.10 Error-handling functions
13625 7.21.10.1 The clearerr function
13627 1 #include <stdio.h>
13628 void clearerr(FILE *stream);
13630 2 The clearerr function clears the end-of-file and error indicators for the stream pointed
13633 3 The clearerr function returns no value.
13634 7.21.10.2 The feof function
13636 1 #include <stdio.h>
13637 int feof(FILE *stream);
13639 2 The feof function tests the end-of-file indicator for the stream pointed to by stream.
13641 3 The feof function returns nonzero if and only if the end-of-file indicator is set for
13643 7.21.10.3 The ferror function
13645 1 #include <stdio.h>
13646 int ferror(FILE *stream);
13648 2 The ferror function tests the error indicator for the stream pointed to by stream.
13650 3 The ferror function returns nonzero if and only if the error indicator is set for
13658 7.21.10.4 The perror function
13660 1 #include <stdio.h>
13661 void perror(const char *s);
13663 2 The perror function maps the error number in the integer expression errno to an
13664 error message. It writes a sequence of characters to the standard error stream thus: first
13665 (if s is not a null pointer and the character pointed to by s is not the null character), the
13666 string pointed to by s followed by a colon (:) and a space; then an appropriate error
13667 message string followed by a new-line character. The contents of the error message
13668 strings are the same as those returned by the strerror function with argument errno.
13670 3 The perror function returns no value.
13671 Forward references: the strerror function (7.23.6.2).
13678 7.22 General utilities <stdlib.h>
13679 1 The header <stdlib.h> declares five types and several functions of general utility, and
13680 defines several macros.284)
13681 2 The types declared are size_t and wchar_t (both described in 7.19),
13683 which is a structure type that is the type of the value returned by the div function,
13685 which is a structure type that is the type of the value returned by the ldiv function, and
13687 which is a structure type that is the type of the value returned by the lldiv function.
13688 3 The macros defined are NULL (described in 7.19);
13692 which expand to integer constant expressions that can be used as the argument to the
13693 exit function to return unsuccessful or successful termination status, respectively, to the
13696 which expands to an integer constant expression that is the maximum value returned by
13697 the rand function; and
13699 which expands to a positive integer expression with type size_t that is the maximum
13700 number of bytes in a multibyte character for the extended character set specified by the
13701 current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX.
13706 284) See ''future library directions'' (7.30.10).
13710 7.22.1 Numeric conversion functions
13711 1 The functions atof, atoi, atol, and atoll need not affect the value of the integer
13712 expression errno on an error. If the value of the result cannot be represented, the
13713 behavior is undefined.
13714 7.22.1.1 The atof function
13716 1 #include <stdlib.h>
13717 double atof(const char *nptr);
13719 2 The atof function converts the initial portion of the string pointed to by nptr to
13720 double representation. Except for the behavior on error, it is equivalent to
13721 strtod(nptr, (char **)NULL)
13723 3 The atof function returns the converted value.
13724 Forward references: the strtod, strtof, and strtold functions (7.22.1.3).
13725 7.22.1.2 The atoi, atol, and atoll functions
13727 1 #include <stdlib.h>
13728 int atoi(const char *nptr);
13729 long int atol(const char *nptr);
13730 long long int atoll(const char *nptr);
13732 2 The atoi, atol, and atoll functions convert the initial portion of the string pointed
13733 to by nptr to int, long int, and long long int representation, respectively.
13734 Except for the behavior on error, they are equivalent to
13735 atoi: (int)strtol(nptr, (char **)NULL, 10)
13736 atol: strtol(nptr, (char **)NULL, 10)
13737 atoll: strtoll(nptr, (char **)NULL, 10)
13739 3 The atoi, atol, and atoll functions return the converted value.
13740 Forward references: the strtol, strtoll, strtoul, and strtoull functions
13747 7.22.1.3 The strtod, strtof, and strtold functions
13749 1 #include <stdlib.h>
13750 double strtod(const char * restrict nptr,
13751 char ** restrict endptr);
13752 float strtof(const char * restrict nptr,
13753 char ** restrict endptr);
13754 long double strtold(const char * restrict nptr,
13755 char ** restrict endptr);
13757 2 The strtod, strtof, and strtold functions convert the initial portion of the string
13758 pointed to by nptr to double, float, and long double representation,
13759 respectively. First, they decompose the input string into three parts: an initial, possibly
13760 empty, sequence of white-space characters (as specified by the isspace function), a
13761 subject sequence resembling a floating-point constant or representing an infinity or NaN;
13762 and a final string of one or more unrecognized characters, including the terminating null
13763 character of the input string. Then, they attempt to convert the subject sequence to a
13764 floating-point number, and return the result.
13765 3 The expected form of the subject sequence is an optional plus or minus sign, then one of
13767 -- a nonempty sequence of decimal digits optionally containing a decimal-point
13768 character, then an optional exponent part as defined in 6.4.4.2;
13769 -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
13770 decimal-point character, then an optional binary exponent part as defined in 6.4.4.2;
13771 -- INF or INFINITY, ignoring case
13772 -- NAN or NAN(n-char-sequenceopt), ignoring case in the NAN part, where:
13776 n-char-sequence digit
13777 n-char-sequence nondigit
13778 The subject sequence is defined as the longest initial subsequence of the input string,
13779 starting with the first non-white-space character, that is of the expected form. The subject
13780 sequence contains no characters if the input string is not of the expected form.
13781 4 If the subject sequence has the expected form for a floating-point number, the sequence of
13782 characters starting with the first digit or the decimal-point character (whichever occurs
13783 first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the
13786 decimal-point character is used in place of a period, and that if neither an exponent part
13787 nor a decimal-point character appears in a decimal floating point number, or if a binary
13788 exponent part does not appear in a hexadecimal floating point number, an exponent part
13789 of the appropriate type with value zero is assumed to follow the last digit in the string. If
13790 the subject sequence begins with a minus sign, the sequence is interpreted as negated.285)
13791 A character sequence INF or INFINITY is interpreted as an infinity, if representable in
13792 the return type, else like a floating constant that is too large for the range of the return
13793 type. A character sequence NAN or NAN(n-char-sequenceopt), is interpreted as a quiet
13794 NaN, if supported in the return type, else like a subject sequence part that does not have
13795 the expected form; the meaning of the n-char sequences is implementation-defined.286) A
13796 pointer to the final string is stored in the object pointed to by endptr, provided that
13797 endptr is not a null pointer.
13798 5 If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
13799 value resulting from the conversion is correctly rounded.
13800 6 In other than the "C" locale, additional locale-specific subject sequence forms may be
13802 7 If the subject sequence is empty or does not have the expected form, no conversion is
13803 performed; the value of nptr is stored in the object pointed to by endptr, provided
13804 that endptr is not a null pointer.
13805 Recommended practice
13806 8 If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
13807 the result is not exactly representable, the result should be one of the two numbers in the
13808 appropriate internal format that are adjacent to the hexadecimal floating source value,
13809 with the extra stipulation that the error should have a correct sign for the current rounding
13811 9 If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
13812 <float.h>) significant digits, the result should be correctly rounded. If the subject
13813 sequence D has the decimal form and more than DECIMAL_DIG significant digits,
13814 consider the two bounding, adjacent decimal strings L and U, both having
13815 DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U.
13816 The result should be one of the (equal or adjacent) values that would be obtained by
13817 correctly rounding L and U according to the current rounding direction, with the extra
13819 285) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
13820 negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
13821 methods may yield different results if rounding is toward positive or negative infinity. In either case,
13822 the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
13823 286) An implementation may use the n-char sequence to determine extra information to be represented in
13824 the NaN's significand.
13828 stipulation that the error with respect to D should have a correct sign for the current
13829 rounding direction.287)
13831 10 The functions return the converted value, if any. If no conversion could be performed,
13832 zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
13833 plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
13834 return type and sign of the value), and the value of the macro ERANGE is stored in
13835 errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
13836 no greater than the smallest normalized positive number in the return type; whether
13837 errno acquires the value ERANGE is implementation-defined.
13838 7.22.1.4 The strtol, strtoll, strtoul, and strtoull functions
13840 1 #include <stdlib.h>
13842 const char * restrict nptr,
13843 char ** restrict endptr,
13845 long long int strtoll(
13846 const char * restrict nptr,
13847 char ** restrict endptr,
13849 unsigned long int strtoul(
13850 const char * restrict nptr,
13851 char ** restrict endptr,
13853 unsigned long long int strtoull(
13854 const char * restrict nptr,
13855 char ** restrict endptr,
13858 2 The strtol, strtoll, strtoul, and strtoull functions convert the initial
13859 portion of the string pointed to by nptr to long int, long long int, unsigned
13860 long int, and unsigned long long int representation, respectively. First,
13861 they decompose the input string into three parts: an initial, possibly empty, sequence of
13862 white-space characters (as specified by the isspace function), a subject sequence
13865 287) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
13866 to the same internal floating value, but if not will round to adjacent values.
13870 resembling an integer represented in some radix determined by the value of base, and a
13871 final string of one or more unrecognized characters, including the terminating null
13872 character of the input string. Then, they attempt to convert the subject sequence to an
13873 integer, and return the result.
13874 3 If the value of base is zero, the expected form of the subject sequence is that of an
13875 integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but
13876 not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the
13877 expected form of the subject sequence is a sequence of letters and digits representing an
13878 integer with the radix specified by base, optionally preceded by a plus or minus sign,
13879 but not including an integer suffix. The letters from a (or A) through z (or Z) are
13880 ascribed the values 10 through 35; only letters and digits whose ascribed values are less
13881 than that of base are permitted. If the value of base is 16, the characters 0x or 0X may
13882 optionally precede the sequence of letters and digits, following the sign if present.
13883 4 The subject sequence is defined as the longest initial subsequence of the input string,
13884 starting with the first non-white-space character, that is of the expected form. The subject
13885 sequence contains no characters if the input string is empty or consists entirely of white
13886 space, or if the first non-white-space character is other than a sign or a permissible letter
13888 5 If the subject sequence has the expected form and the value of base is zero, the sequence
13889 of characters starting with the first digit is interpreted as an integer constant according to
13890 the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base
13891 is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value
13892 as given above. If the subject sequence begins with a minus sign, the value resulting from
13893 the conversion is negated (in the return type). A pointer to the final string is stored in the
13894 object pointed to by endptr, provided that endptr is not a null pointer.
13895 6 In other than the "C" locale, additional locale-specific subject sequence forms may be
13897 7 If the subject sequence is empty or does not have the expected form, no conversion is
13898 performed; the value of nptr is stored in the object pointed to by endptr, provided
13899 that endptr is not a null pointer.
13901 8 The strtol, strtoll, strtoul, and strtoull functions return the converted
13902 value, if any. If no conversion could be performed, zero is returned. If the correct value
13903 is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
13904 LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
13905 and sign of the value, if any), and the value of the macro ERANGE is stored in errno.
13912 7.22.2 Pseudo-random sequence generation functions
13913 7.22.2.1 The rand function
13915 1 #include <stdlib.h>
13918 2 The rand function computes a sequence of pseudo-random integers in the range 0 to
13920 3 The rand function is not required to avoid data races. The implementation shall behave
13921 as if no library function calls the rand function.
13923 4 The rand function returns a pseudo-random integer.
13924 Environmental limits
13925 5 The value of the RAND_MAX macro shall be at least 32767.
13926 7.22.2.2 The srand function
13928 1 #include <stdlib.h>
13929 void srand(unsigned int seed);
13931 2 The srand function uses the argument as a seed for a new sequence of pseudo-random
13932 numbers to be returned by subsequent calls to rand. If srand is then called with the
13933 same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is
13934 called before any calls to srand have been made, the same sequence shall be generated
13935 as when srand is first called with a seed value of 1.
13936 3 The implementation shall behave as if no library function calls the srand function.
13938 4 The srand function returns no value.
13943 288) There are no guarantees as to the quality of the random sequence produced and some implementations
13944 are known to produce sequences with distressingly non-random low-order bits. Applications with
13945 particular requirements should use a generator that is known to be sufficient for their needs.
13949 5 EXAMPLE The following functions define a portable implementation of rand and srand.
13950 static unsigned long int next = 1;
13951 int rand(void) // RAND_MAX assumed to be 32767
13953 next = next * 1103515245 + 12345;
13954 return (unsigned int)(next/65536) % 32768;
13956 void srand(unsigned int seed)
13961 7.22.3 Memory management functions
13962 1 The order and contiguity of storage allocated by successive calls to the
13963 aligned_alloc, calloc, malloc, and realloc functions is unspecified. The
13964 pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to
13965 a pointer to any type of object with a fundamental alignment requirement and then used
13966 to access such an object or an array of such objects in the space allocated (until the space
13967 is explicitly deallocated). The lifetime of an allocated object extends from the allocation
13968 until the deallocation. Each such allocation shall yield a pointer to an object disjoint from
13969 any other object. The pointer returned points to the start (lowest byte address) of the
13970 allocated space. If the space cannot be allocated, a null pointer is returned. If the size of
13971 the space requested is zero, the behavior is implementation-defined: either a null pointer
13972 is returned, or the behavior is as if the size were some nonzero value, except that the
13973 returned pointer shall not be used to access an object.
13974 7.22.3.1 The aligned_alloc function
13976 1 #include <stdlib.h>
13977 void *aligned_alloc(size_t alignment, size_t size);
13979 2 The aligned_alloc function allocates space for an object whose alignment is
13980 specified by alignment, whose size is specified by size, and whose value is
13981 indeterminate. The value of alignment shall be a valid alignment supported by the
13982 implementation and the value of size shall be an integral multiple of alignment.
13984 3 The aligned_alloc function returns either a null pointer or a pointer to the allocated
13992 7.22.3.2 The calloc function
13994 1 #include <stdlib.h>
13995 void *calloc(size_t nmemb, size_t size);
13997 2 The calloc function allocates space for an array of nmemb objects, each of whose size
13998 is size. The space is initialized to all bits zero.289)
14000 3 The calloc function returns either a null pointer or a pointer to the allocated space.
14001 7.22.3.3 The free function
14003 1 #include <stdlib.h>
14004 void free(void *ptr);
14006 2 The free function causes the space pointed to by ptr to be deallocated, that is, made
14007 available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if
14008 the argument does not match a pointer earlier returned by a memory management
14009 function, or if the space has been deallocated by a call to free or realloc, the
14010 behavior is undefined.
14012 3 The free function returns no value.
14013 7.22.3.4 The malloc function
14015 1 #include <stdlib.h>
14016 void *malloc(size_t size);
14018 2 The malloc function allocates space for an object whose size is specified by size and
14019 whose value is indeterminate.
14024 289) Note that this need not be the same as the representation of floating-point zero or a null pointer
14030 3 The malloc function returns either a null pointer or a pointer to the allocated space.
14031 7.22.3.5 The realloc function
14033 1 #include <stdlib.h>
14034 void *realloc(void *ptr, size_t size);
14036 2 The realloc function deallocates the old object pointed to by ptr and returns a
14037 pointer to a new object that has the size specified by size. The contents of the new
14038 object shall be the same as that of the old object prior to deallocation, up to the lesser of
14039 the new and old sizes. Any bytes in the new object beyond the size of the old object have
14040 indeterminate values.
14041 3 If ptr is a null pointer, the realloc function behaves like the malloc function for the
14042 specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory
14043 management function, or if the space has been deallocated by a call to the free or
14044 realloc function, the behavior is undefined. If memory for the new object cannot be
14045 allocated, the old object is not deallocated and its value is unchanged.
14047 4 The realloc function returns a pointer to the new object (which may have the same
14048 value as a pointer to the old object), or a null pointer if the new object could not be
14050 7.22.4 Communication with the environment
14051 7.22.4.1 The abort function
14053 1 #include <stdlib.h>
14054 _Noreturn void abort(void);
14056 2 The abort function causes abnormal program termination to occur, unless the signal
14057 SIGABRT is being caught and the signal handler does not return. Whether open streams
14058 with unwritten buffered data are flushed, open streams are closed, or temporary files are
14059 removed is implementation-defined. An implementation-defined form of the status
14060 unsuccessful termination is returned to the host environment by means of the function
14061 call raise(SIGABRT).
14069 3 The abort function does not return to its caller.
14070 7.22.4.2 The atexit function
14072 1 #include <stdlib.h>
14073 int atexit(void (*func)(void));
14075 2 The atexit function registers the function pointed to by func, to be called without
14076 arguments at normal program termination.290)
14077 Environmental limits
14078 3 The implementation shall support the registration of at least 32 functions.
14080 4 The atexit function returns zero if the registration succeeds, nonzero if it fails.
14081 Forward references: the at_quick_exit function (7.22.4.3), the exit function
14083 7.22.4.3 The at_quick_exit function
14085 1 #include <stdlib.h>
14086 int at_quick_exit(void (*func)(void));
14088 2 The at_quick_exit function registers the function pointed to by func, to be called
14089 without arguments should quick_exit be called.291)
14090 Environmental limits
14091 3 The implementation shall support the registration of at least 32 functions.
14093 4 The at_quick_exit function returns zero if the registration succeeds, nonzero if it
14095 Forward references: the quick_exit function (7.22.4.7).
14098 290) The atexit function registrations are distinct from the at_quick_exit registrations, so
14099 applications may need to call both registration functions with the same argument.
14100 291) The at_quick_exit function registrations are distinct from the atexit registrations, so
14101 applications may need to call both registration functions with the same argument.
14105 7.22.4.4 The exit function
14107 1 #include <stdlib.h>
14108 _Noreturn void exit(int status);
14110 2 The exit function causes normal program termination to occur. No functions registered
14111 by the at_quick_exit function are called. If a program calls the exit function
14112 more than once, or calls the quick_exit function in addition to the exit function, the
14113 behavior is undefined.
14114 3 First, all functions registered by the atexit function are called, in the reverse order of
14115 their registration,292) except that a function is called after any previously registered
14116 functions that had already been called at the time it was registered. If, during the call to
14117 any such function, a call to the longjmp function is made that would terminate the call
14118 to the registered function, the behavior is undefined.
14119 4 Next, all open streams with unwritten buffered data are flushed, all open streams are
14120 closed, and all files created by the tmpfile function are removed.
14121 5 Finally, control is returned to the host environment. If the value of status is zero or
14122 EXIT_SUCCESS, an implementation-defined form of the status successful termination is
14123 returned. If the value of status is EXIT_FAILURE, an implementation-defined form
14124 of the status unsuccessful termination is returned. Otherwise the status returned is
14125 implementation-defined.
14127 6 The exit function cannot return to its caller.
14128 7.22.4.5 The _Exit function
14130 1 #include <stdlib.h>
14131 _Noreturn void _Exit(int status);
14133 2 The _Exit function causes normal program termination to occur and control to be
14134 returned to the host environment. No functions registered by the atexit function, the
14135 at_quick_exit function, or signal handlers registered by the signal function are
14136 called. The status returned to the host environment is determined in the same way as for
14139 292) Each function is called as many times as it was registered, and in the correct order with respect to
14140 other registered functions.
14144 the exit function (7.22.4.4). Whether open streams with unwritten buffered data are
14145 flushed, open streams are closed, or temporary files are removed is implementation-
14148 3 The _Exit function cannot return to its caller.
14149 7.22.4.6 The getenv function
14151 1 #include <stdlib.h>
14152 char *getenv(const char *name);
14154 2 The getenv function searches an environment list, provided by the host environment,
14155 for a string that matches the string pointed to by name. The set of environment names
14156 and the method for altering the environment list are implementation-defined. The
14157 getenv function need not avoid data races with other threads of execution that modify
14158 the environment list.293)
14159 3 The implementation shall behave as if no library function calls the getenv function.
14161 4 The getenv function returns a pointer to a string associated with the matched list
14162 member. The string pointed to shall not be modified by the program, but may be
14163 overwritten by a subsequent call to the getenv function. If the specified name cannot
14164 be found, a null pointer is returned.
14165 7.22.4.7 The quick_exit function
14167 1 #include <stdlib.h>
14168 _Noreturn void quick_exit(int status);
14170 2 The quick_exit function causes normal program termination to occur. No functions
14171 registered by the atexit function or signal handlers registered by the signal function
14172 are called. If a program calls the quick_exit function more than once, or calls the
14173 exit function in addition to the quick_exit function, the behavior is undefined.
14174 3 The quick_exit function first calls all functions registered by the at_quick_exit
14175 function, in the reverse order of their registration,294) except that a function is called after
14178 293) Many implementations provide non-standard functions that modify the environment list.
14182 any previously registered functions that had already been called at the time it was
14183 registered. If, during the call to any such function, a call to the longjmp function is
14184 made that would terminate the call to the registered function, the behavior is undefined.
14185 4 Then control is returned to the host environment by means of the function call
14188 5 The quick_exit function cannot return to its caller.
14189 7.22.4.8 The system function
14191 1 #include <stdlib.h>
14192 int system(const char *string);
14194 2 If string is a null pointer, the system function determines whether the host
14195 environment has a command processor. If string is not a null pointer, the system
14196 function passes the string pointed to by string to that command processor to be
14197 executed in a manner which the implementation shall document; this might then cause the
14198 program calling system to behave in a non-conforming manner or to terminate.
14200 3 If the argument is a null pointer, the system function returns nonzero only if a
14201 command processor is available. If the argument is not a null pointer, and the system
14202 function does return, it returns an implementation-defined value.
14203 7.22.5 Searching and sorting utilities
14204 1 These utilities make use of a comparison function to search or sort arrays of unspecified
14205 type. Where an argument declared as size_t nmemb specifies the length of the array
14206 for a function, nmemb can have the value zero on a call to that function; the comparison
14207 function is not called, a search finds no matching element, and sorting performs no
14208 rearrangement. Pointer arguments on such a call shall still have valid values, as described
14210 2 The implementation shall ensure that the second argument of the comparison function
14211 (when called from bsearch), or both arguments (when called from qsort), are
14212 pointers to elements of the array.295) The first argument when called from bsearch
14217 294) Each function is called as many times as it was registered, and in the correct order with respect to
14218 other registered functions.
14222 3 The comparison function shall not alter the contents of the array. The implementation
14223 may reorder elements of the array between calls to the comparison function, but shall not
14224 alter the contents of any individual element.
14225 4 When the same objects (consisting of size bytes, irrespective of their current positions
14226 in the array) are passed more than once to the comparison function, the results shall be
14227 consistent with one another. That is, for qsort they shall define a total ordering on the
14228 array, and for bsearch the same object shall always compare the same way with the
14230 5 A sequence point occurs immediately before and immediately after each call to the
14231 comparison function, and also between any call to the comparison function and any
14232 movement of the objects passed as arguments to that call.
14233 7.22.5.1 The bsearch function
14235 1 #include <stdlib.h>
14236 void *bsearch(const void *key, const void *base,
14237 size_t nmemb, size_t size,
14238 int (*compar)(const void *, const void *));
14240 2 The bsearch function searches an array of nmemb objects, the initial element of which
14241 is pointed to by base, for an element that matches the object pointed to by key. The
14242 size of each element of the array is specified by size.
14243 3 The comparison function pointed to by compar is called with two arguments that point
14244 to the key object and to an array element, in that order. The function shall return an
14245 integer less than, equal to, or greater than zero if the key object is considered,
14246 respectively, to be less than, to match, or to be greater than the array element. The array
14247 shall consist of: all the elements that compare less than, all the elements that compare
14248 equal to, and all the elements that compare greater than the key object, in that order.296)
14250 4 The bsearch function returns a pointer to a matching element of the array, or a null
14251 pointer if no match is found. If two elements compare as equal, which element is
14254 295) That is, if the value passed is p, then the following expressions are always nonzero:
14255 ((char *)p - (char *)base) % size == 0
14256 (char *)p >= (char *)base
14257 (char *)p < (char *)base + nmemb * size
14259 296) In practice, the entire array is sorted according to the comparison function.
14263 matched is unspecified.
14264 7.22.5.2 The qsort function
14266 1 #include <stdlib.h>
14267 void qsort(void *base, size_t nmemb, size_t size,
14268 int (*compar)(const void *, const void *));
14270 2 The qsort function sorts an array of nmemb objects, the initial element of which is
14271 pointed to by base. The size of each object is specified by size.
14272 3 The contents of the array are sorted into ascending order according to a comparison
14273 function pointed to by compar, which is called with two arguments that point to the
14274 objects being compared. The function shall return an integer less than, equal to, or
14275 greater than zero if the first argument is considered to be respectively less than, equal to,
14276 or greater than the second.
14277 4 If two elements compare as equal, their order in the resulting sorted array is unspecified.
14279 5 The qsort function returns no value.
14280 7.22.6 Integer arithmetic functions
14281 7.22.6.1 The abs, labs and llabs functions
14283 1 #include <stdlib.h>
14285 long int labs(long int j);
14286 long long int llabs(long long int j);
14288 2 The abs, labs, and llabs functions compute the absolute value of an integer j. If the
14289 result cannot be represented, the behavior is undefined.297)
14291 3 The abs, labs, and llabs, functions return the absolute value.
14296 297) The absolute value of the most negative number cannot be represented in two's complement.
14300 7.22.6.2 The div, ldiv, and lldiv functions
14302 1 #include <stdlib.h>
14303 div_t div(int numer, int denom);
14304 ldiv_t ldiv(long int numer, long int denom);
14305 lldiv_t lldiv(long long int numer, long long int denom);
14307 2 The div, ldiv, and lldiv, functions compute numer / denom and numer %
14308 denom in a single operation.
14310 3 The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and
14311 lldiv_t, respectively, comprising both the quotient and the remainder. The structures
14312 shall contain (in either order) the members quot (the quotient) and rem (the remainder),
14313 each of which has the same type as the arguments numer and denom. If either part of
14314 the result cannot be represented, the behavior is undefined.
14315 7.22.7 Multibyte/wide character conversion functions
14316 1 The behavior of the multibyte character functions is affected by the LC_CTYPE category
14317 of the current locale. For a state-dependent encoding, each function is placed into its
14318 initial conversion state at program startup and can be returned to that state by a call for
14319 which its character pointer argument, s, is a null pointer. Subsequent calls with s as
14320 other than a null pointer cause the internal conversion state of the function to be altered as
14321 necessary. A call with s as a null pointer causes these functions to return a nonzero value
14322 if encodings have state dependency, and zero otherwise.298) Changing the LC_CTYPE
14323 category causes the conversion state of these functions to be indeterminate.
14324 7.22.7.1 The mblen function
14326 1 #include <stdlib.h>
14327 int mblen(const char *s, size_t n);
14329 2 If s is not a null pointer, the mblen function determines the number of bytes contained
14330 in the multibyte character pointed to by s. Except that the conversion state of the
14331 mbtowc function is not affected, it is equivalent to
14335 298) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
14336 character codes, but are grouped with an adjacent multibyte character.
14340 mbtowc((wchar_t *)0, (const char *)0, 0);
14341 mbtowc((wchar_t *)0, s, n);
14342 3 The implementation shall behave as if no library function calls the mblen function.
14344 4 If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte
14345 character encodings, respectively, do or do not have state-dependent encodings. If s is
14346 not a null pointer, the mblen function either returns 0 (if s points to the null character),
14347 or returns the number of bytes that are contained in the multibyte character (if the next n
14348 or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid
14349 multibyte character).
14350 Forward references: the mbtowc function (7.22.7.2).
14351 7.22.7.2 The mbtowc function
14353 1 #include <stdlib.h>
14354 int mbtowc(wchar_t * restrict pwc,
14355 const char * restrict s,
14358 2 If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with
14359 the byte pointed to by s to determine the number of bytes needed to complete the next
14360 multibyte character (including any shift sequences). If the function determines that the
14361 next multibyte character is complete and valid, it determines the value of the
14362 corresponding wide character and then, if pwc is not a null pointer, stores that value in
14363 the object pointed to by pwc. If the corresponding wide character is the null wide
14364 character, the function is left in the initial conversion state.
14365 3 The implementation shall behave as if no library function calls the mbtowc function.
14367 4 If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte
14368 character encodings, respectively, do or do not have state-dependent encodings. If s is
14369 not a null pointer, the mbtowc function either returns 0 (if s points to the null character),
14370 or returns the number of bytes that are contained in the converted multibyte character (if
14371 the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not
14372 form a valid multibyte character).
14373 5 In no case will the value returned be greater than n or the value of the MB_CUR_MAX
14379 7.22.7.3 The wctomb function
14381 1 #include <stdlib.h>
14382 int wctomb(char *s, wchar_t wc);
14384 2 The wctomb function determines the number of bytes needed to represent the multibyte
14385 character corresponding to the wide character given by wc (including any shift
14386 sequences), and stores the multibyte character representation in the array whose first
14387 element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters
14388 are stored. If wc is a null wide character, a null byte is stored, preceded by any shift
14389 sequence needed to restore the initial shift state, and the function is left in the initial
14391 3 The implementation shall behave as if no library function calls the wctomb function.
14393 4 If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte
14394 character encodings, respectively, do or do not have state-dependent encodings. If s is
14395 not a null pointer, the wctomb function returns -1 if the value of wc does not correspond
14396 to a valid multibyte character, or returns the number of bytes that are contained in the
14397 multibyte character corresponding to the value of wc.
14398 5 In no case will the value returned be greater than the value of the MB_CUR_MAX macro.
14399 7.22.8 Multibyte/wide string conversion functions
14400 1 The behavior of the multibyte string functions is affected by the LC_CTYPE category of
14401 the current locale.
14402 7.22.8.1 The mbstowcs function
14404 1 #include <stdlib.h>
14405 size_t mbstowcs(wchar_t * restrict pwcs,
14406 const char * restrict s,
14409 2 The mbstowcs function converts a sequence of multibyte characters that begins in the
14410 initial shift state from the array pointed to by s into a sequence of corresponding wide
14411 characters and stores not more than n wide characters into the array pointed to by pwcs.
14412 No multibyte characters that follow a null character (which is converted into a null wide
14413 character) will be examined or converted. Each multibyte character is converted as if by
14414 a call to the mbtowc function, except that the conversion state of the mbtowc function is
14418 3 No more than n elements will be modified in the array pointed to by pwcs. If copying
14419 takes place between objects that overlap, the behavior is undefined.
14421 4 If an invalid multibyte character is encountered, the mbstowcs function returns
14422 (size_t)(-1). Otherwise, the mbstowcs function returns the number of array
14423 elements modified, not including a terminating null wide character, if any.299)
14424 7.22.8.2 The wcstombs function
14426 1 #include <stdlib.h>
14427 size_t wcstombs(char * restrict s,
14428 const wchar_t * restrict pwcs,
14431 2 The wcstombs function converts a sequence of wide characters from the array pointed
14432 to by pwcs into a sequence of corresponding multibyte characters that begins in the
14433 initial shift state, and stores these multibyte characters into the array pointed to by s,
14434 stopping if a multibyte character would exceed the limit of n total bytes or if a null
14435 character is stored. Each wide character is converted as if by a call to the wctomb
14436 function, except that the conversion state of the wctomb function is not affected.
14437 3 No more than n bytes will be modified in the array pointed to by s. If copying takes place
14438 between objects that overlap, the behavior is undefined.
14440 4 If a wide character is encountered that does not correspond to a valid multibyte character,
14441 the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function
14442 returns the number of bytes modified, not including a terminating null character, if
14448 299) The array will not be null-terminated if the value returned is n.
14452 7.23 String handling <string.h>
14453 7.23.1 String function conventions
14454 1 The header <string.h> declares one type and several functions, and defines one
14455 macro useful for manipulating arrays of character type and other objects treated as arrays
14456 of character type.300) The type is size_t and the macro is NULL (both described in
14457 7.19). Various methods are used for determining the lengths of the arrays, but in all cases
14458 a char * or void * argument points to the initial (lowest addressed) character of the
14459 array. If an array is accessed beyond the end of an object, the behavior is undefined.
14460 2 Where an argument declared as size_t n specifies the length of the array for a
14461 function, n can have the value zero on a call to that function. Unless explicitly stated
14462 otherwise in the description of a particular function in this subclause, pointer arguments
14463 on such a call shall still have valid values, as described in 7.1.4. On such a call, a
14464 function that locates a character finds no occurrence, a function that compares two
14465 character sequences returns zero, and a function that copies characters copies zero
14467 3 For all functions in this subclause, each character shall be interpreted as if it had the type
14468 unsigned char (and therefore every possible object representation is valid and has a
14470 7.23.2 Copying functions
14471 7.23.2.1 The memcpy function
14473 1 #include <string.h>
14474 void *memcpy(void * restrict s1,
14475 const void * restrict s2,
14478 2 The memcpy function copies n characters from the object pointed to by s2 into the
14479 object pointed to by s1. If copying takes place between objects that overlap, the behavior
14482 3 The memcpy function returns the value of s1.
14487 300) See ''future library directions'' (7.30.11).
14491 7.23.2.2 The memmove function
14493 1 #include <string.h>
14494 void *memmove(void *s1, const void *s2, size_t n);
14496 2 The memmove function copies n characters from the object pointed to by s2 into the
14497 object pointed to by s1. Copying takes place as if the n characters from the object
14498 pointed to by s2 are first copied into a temporary array of n characters that does not
14499 overlap the objects pointed to by s1 and s2, and then the n characters from the
14500 temporary array are copied into the object pointed to by s1.
14502 3 The memmove function returns the value of s1.
14503 7.23.2.3 The strcpy function
14505 1 #include <string.h>
14506 char *strcpy(char * restrict s1,
14507 const char * restrict s2);
14509 2 The strcpy function copies the string pointed to by s2 (including the terminating null
14510 character) into the array pointed to by s1. If copying takes place between objects that
14511 overlap, the behavior is undefined.
14513 3 The strcpy function returns the value of s1.
14514 7.23.2.4 The strncpy function
14516 1 #include <string.h>
14517 char *strncpy(char * restrict s1,
14518 const char * restrict s2,
14521 2 The strncpy function copies not more than n characters (characters that follow a null
14522 character are not copied) from the array pointed to by s2 to the array pointed to by
14529 s1.301) If copying takes place between objects that overlap, the behavior is undefined.
14530 3 If the array pointed to by s2 is a string that is shorter than n characters, null characters
14531 are appended to the copy in the array pointed to by s1, until n characters in all have been
14534 4 The strncpy function returns the value of s1.
14535 7.23.3 Concatenation functions
14536 7.23.3.1 The strcat function
14538 1 #include <string.h>
14539 char *strcat(char * restrict s1,
14540 const char * restrict s2);
14542 2 The strcat function appends a copy of the string pointed to by s2 (including the
14543 terminating null character) to the end of the string pointed to by s1. The initial character
14544 of s2 overwrites the null character at the end of s1. If copying takes place between
14545 objects that overlap, the behavior is undefined.
14547 3 The strcat function returns the value of s1.
14548 7.23.3.2 The strncat function
14550 1 #include <string.h>
14551 char *strncat(char * restrict s1,
14552 const char * restrict s2,
14555 2 The strncat function appends not more than n characters (a null character and
14556 characters that follow it are not appended) from the array pointed to by s2 to the end of
14557 the string pointed to by s1. The initial character of s2 overwrites the null character at the
14558 end of s1. A terminating null character is always appended to the result.302) If copying
14560 301) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will
14561 not be null-terminated.
14562 302) Thus, the maximum number of characters that can end up in the array pointed to by s1 is
14567 takes place between objects that overlap, the behavior is undefined.
14569 3 The strncat function returns the value of s1.
14570 Forward references: the strlen function (7.23.6.3).
14571 7.23.4 Comparison functions
14572 1 The sign of a nonzero value returned by the comparison functions memcmp, strcmp,
14573 and strncmp is determined by the sign of the difference between the values of the first
14574 pair of characters (both interpreted as unsigned char) that differ in the objects being
14576 7.23.4.1 The memcmp function
14578 1 #include <string.h>
14579 int memcmp(const void *s1, const void *s2, size_t n);
14581 2 The memcmp function compares the first n characters of the object pointed to by s1 to
14582 the first n characters of the object pointed to by s2.303)
14584 3 The memcmp function returns an integer greater than, equal to, or less than zero,
14585 accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
14587 7.23.4.2 The strcmp function
14589 1 #include <string.h>
14590 int strcmp(const char *s1, const char *s2);
14592 2 The strcmp function compares the string pointed to by s1 to the string pointed to by
14595 3 The strcmp function returns an integer greater than, equal to, or less than zero,
14596 accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
14598 303) The contents of ''holes'' used as padding for purposes of alignment within structure objects are
14599 indeterminate. Strings shorter than their allocated space and unions may also cause problems in
14605 7.23.4.3 The strcoll function
14607 1 #include <string.h>
14608 int strcoll(const char *s1, const char *s2);
14610 2 The strcoll function compares the string pointed to by s1 to the string pointed to by
14611 s2, both interpreted as appropriate to the LC_COLLATE category of the current locale.
14613 3 The strcoll function returns an integer greater than, equal to, or less than zero,
14614 accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
14615 pointed to by s2 when both are interpreted as appropriate to the current locale.
14616 7.23.4.4 The strncmp function
14618 1 #include <string.h>
14619 int strncmp(const char *s1, const char *s2, size_t n);
14621 2 The strncmp function compares not more than n characters (characters that follow a
14622 null character are not compared) from the array pointed to by s1 to the array pointed to
14625 3 The strncmp function returns an integer greater than, equal to, or less than zero,
14626 accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
14627 to, or less than the possibly null-terminated array pointed to by s2.
14628 7.23.4.5 The strxfrm function
14630 1 #include <string.h>
14631 size_t strxfrm(char * restrict s1,
14632 const char * restrict s2,
14635 2 The strxfrm function transforms the string pointed to by s2 and places the resulting
14636 string into the array pointed to by s1. The transformation is such that if the strcmp
14637 function is applied to two transformed strings, it returns a value greater than, equal to, or
14641 less than zero, corresponding to the result of the strcoll function applied to the same
14642 two original strings. No more than n characters are placed into the resulting array
14643 pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to
14644 be a null pointer. If copying takes place between objects that overlap, the behavior is
14647 3 The strxfrm function returns the length of the transformed string (not including the
14648 terminating null character). If the value returned is n or more, the contents of the array
14649 pointed to by s1 are indeterminate.
14650 4 EXAMPLE The value of the following expression is the size of the array needed to hold the
14651 transformation of the string pointed to by s.
14652 1 + strxfrm(NULL, s, 0)
14654 7.23.5 Search functions
14655 7.23.5.1 The memchr function
14657 1 #include <string.h>
14658 void *memchr(const void *s, int c, size_t n);
14660 2 The memchr function locates the first occurrence of c (converted to an unsigned
14661 char) in the initial n characters (each interpreted as unsigned char) of the object
14662 pointed to by s. The implementation shall behave as if it reads the characters sequentially
14663 and stops as soon as a matching character is found.
14665 3 The memchr function returns a pointer to the located character, or a null pointer if the
14666 character does not occur in the object.
14667 7.23.5.2 The strchr function
14669 1 #include <string.h>
14670 char *strchr(const char *s, int c);
14672 2 The strchr function locates the first occurrence of c (converted to a char) in the
14673 string pointed to by s. The terminating null character is considered to be part of the
14681 3 The strchr function returns a pointer to the located character, or a null pointer if the
14682 character does not occur in the string.
14683 7.23.5.3 The strcspn function
14685 1 #include <string.h>
14686 size_t strcspn(const char *s1, const char *s2);
14688 2 The strcspn function computes the length of the maximum initial segment of the string
14689 pointed to by s1 which consists entirely of characters not from the string pointed to by
14692 3 The strcspn function returns the length of the segment.
14693 7.23.5.4 The strpbrk function
14695 1 #include <string.h>
14696 char *strpbrk(const char *s1, const char *s2);
14698 2 The strpbrk function locates the first occurrence in the string pointed to by s1 of any
14699 character from the string pointed to by s2.
14701 3 The strpbrk function returns a pointer to the character, or a null pointer if no character
14702 from s2 occurs in s1.
14703 7.23.5.5 The strrchr function
14705 1 #include <string.h>
14706 char *strrchr(const char *s, int c);
14708 2 The strrchr function locates the last occurrence of c (converted to a char) in the
14709 string pointed to by s. The terminating null character is considered to be part of the
14718 3 The strrchr function returns a pointer to the character, or a null pointer if c does not
14719 occur in the string.
14720 7.23.5.6 The strspn function
14722 1 #include <string.h>
14723 size_t strspn(const char *s1, const char *s2);
14725 2 The strspn function computes the length of the maximum initial segment of the string
14726 pointed to by s1 which consists entirely of characters from the string pointed to by s2.
14728 3 The strspn function returns the length of the segment.
14729 7.23.5.7 The strstr function
14731 1 #include <string.h>
14732 char *strstr(const char *s1, const char *s2);
14734 2 The strstr function locates the first occurrence in the string pointed to by s1 of the
14735 sequence of characters (excluding the terminating null character) in the string pointed to
14738 3 The strstr function returns a pointer to the located string, or a null pointer if the string
14739 is not found. If s2 points to a string with zero length, the function returns s1.
14740 7.23.5.8 The strtok function
14742 1 #include <string.h>
14743 char *strtok(char * restrict s1,
14744 const char * restrict s2);
14746 2 A sequence of calls to the strtok function breaks the string pointed to by s1 into a
14747 sequence of tokens, each of which is delimited by a character from the string pointed to
14748 by s2. The first call in the sequence has a non-null first argument; subsequent calls in the
14749 sequence have a null first argument. The separator string pointed to by s2 may be
14750 different from call to call.
14753 3 The first call in the sequence searches the string pointed to by s1 for the first character
14754 that is not contained in the current separator string pointed to by s2. If no such character
14755 is found, then there are no tokens in the string pointed to by s1 and the strtok function
14756 returns a null pointer. If such a character is found, it is the start of the first token.
14757 4 The strtok function then searches from there for a character that is contained in the
14758 current separator string. If no such character is found, the current token extends to the
14759 end of the string pointed to by s1, and subsequent searches for a token will return a null
14760 pointer. If such a character is found, it is overwritten by a null character, which
14761 terminates the current token. The strtok function saves a pointer to the following
14762 character, from which the next search for a token will start.
14763 5 Each subsequent call, with a null pointer as the value of the first argument, starts
14764 searching from the saved pointer and behaves as described above.
14765 6 The strtok function is not required to avoid data races. The implementation shall
14766 behave as if no library function calls the strtok function.
14768 7 The strtok function returns a pointer to the first character of a token, or a null pointer
14769 if there is no token.
14771 #include <string.h>
14772 static char str[] = "?a???b,,,#c";
14774 t = strtok(str, "?"); // t points to the token "a"
14775 t = strtok(NULL, ","); // t points to the token "??b"
14776 t = strtok(NULL, "#,"); // t points to the token "c"
14777 t = strtok(NULL, "?"); // t is a null pointer
14779 7.23.6 Miscellaneous functions
14780 7.23.6.1 The memset function
14782 1 #include <string.h>
14783 void *memset(void *s, int c, size_t n);
14785 2 The memset function copies the value of c (converted to an unsigned char) into
14786 each of the first n characters of the object pointed to by s.
14788 3 The memset function returns the value of s.
14794 7.23.6.2 The strerror function
14796 1 #include <string.h>
14797 char *strerror(int errnum);
14799 2 The strerror function maps the number in errnum to a message string. Typically,
14800 the values for errnum come from errno, but strerror shall map any value of type
14802 3 The strerror function is not required to avoid data races. The implementation shall
14803 behave as if no library function calls the strerror function.
14805 4 The strerror function returns a pointer to the string, the contents of which are locale-
14806 specific. The array pointed to shall not be modified by the program, but may be
14807 overwritten by a subsequent call to the strerror function.
14808 7.23.6.3 The strlen function
14810 1 #include <string.h>
14811 size_t strlen(const char *s);
14813 2 The strlen function computes the length of the string pointed to by s.
14815 3 The strlen function returns the number of characters that precede the terminating null
14823 7.24 Type-generic math <tgmath.h>
14824 1 The header <tgmath.h> includes the headers <math.h> and <complex.h> and
14825 defines several type-generic macros.
14826 2 Of the <math.h> and <complex.h> functions without an f (float) or l (long
14827 double) suffix, several have one or more parameters whose corresponding real type is
14828 double. For each such function, except modf, there is a corresponding type-generic
14829 macro.304) The parameters whose corresponding real type is double in the function
14830 synopsis are generic parameters. Use of the macro invokes a function whose
14831 corresponding real type and type domain are determined by the arguments for the generic
14833 3 Use of the macro invokes a function whose generic parameters have the corresponding
14834 real type determined as follows:
14835 -- First, if any argument for generic parameters has type long double, the type
14836 determined is long double.
14837 -- Otherwise, if any argument for generic parameters has type double or is of integer
14838 type, the type determined is double.
14839 -- Otherwise, the type determined is float.
14840 4 For each unsuffixed function in <math.h> for which there is a function in
14841 <complex.h> with the same name except for a c prefix, the corresponding type-
14842 generic macro (for both functions) has the same name as the function in <math.h>. The
14843 corresponding type-generic macro for fabs and cabs is fabs.
14848 304) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed to
14849 make available the corresponding ordinary function.
14850 305) If the type of the argument is not compatible with the type of the parameter for the selected function,
14851 the behavior is undefined.
14855 <math.h> <complex.h> type-generic
14856 function function macro
14874 If at least one argument for a generic parameter is complex, then use of the macro invokes
14875 a complex function; otherwise, use of the macro invokes a real function.
14876 5 For each unsuffixed function in <math.h> without a c-prefixed counterpart in
14877 <complex.h> (except modf), the corresponding type-generic macro has the same
14878 name as the function. These type-generic macros are:
14879 atan2 fma llround remainder
14880 cbrt fmax log10 remquo
14881 ceil fmin log1p rint
14882 copysign fmod log2 round
14883 erf frexp logb scalbn
14884 erfc hypot lrint scalbln
14885 exp2 ilogb lround tgamma
14886 expm1 ldexp nearbyint trunc
14887 fdim lgamma nextafter
14888 floor llrint nexttoward
14889 If all arguments for generic parameters are real, then use of the macro invokes a real
14890 function; otherwise, use of the macro results in undefined behavior.
14897 6 For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to a
14898 function in <math.h>, the corresponding type-generic macro has the same name as the
14899 function. These type-generic macros are:
14902 Use of the macro with any real or complex argument invokes a complex function.
14903 7 EXAMPLE With the declarations
14904 #include <tgmath.h>
14911 long double complex ldc;
14912 functions invoked by use of type-generic macros are shown in the following table:
14914 exp(n) exp(n), the function
14916 sin(d) sin(d), the function
14920 pow(ldc, f) cpowl(ldc, f)
14921 remainder(n, n) remainder(n, n), the function
14922 nextafter(d, f) nextafter(d, f), the function
14923 nexttoward(f, ld) nexttowardf(f, ld)
14924 copysign(n, ld) copysignl(n, ld)
14925 ceil(fc) undefined behavior
14926 rint(dc) undefined behavior
14927 fmax(ldc, ld) undefined behavior
14928 carg(n) carg(n), the function
14930 creal(d) creal(d), the function
14931 cimag(ld) cimagl(ld)
14933 carg(dc) carg(dc), the function
14934 cproj(ldc) cprojl(ldc)
14941 7.25 Threads <threads.h>
14942 7.25.1 Introduction
14943 1 The header <threads.h> defines macros, and declares types, enumeration constants,
14944 and functions that support multiple threads of execution.
14945 2 Implementations that define the macro __STDC_NO_THREADS__ need not provide
14946 this header nor support any of its facilities.
14949 which expands to a value that can be used to initialize an object of type once_flag;
14951 TSS_DTOR_ITERATIONS
14952 which expands to an integer constant expression representing the maximum number of
14953 times that destructors will be called when a thread terminates.
14956 which is a complete object type that holds an identifier for a condition variable;
14958 which is a complete object type that holds an identifier for a thread;
14960 which is a complete object type that holds an identifier for a thread-specific storage
14963 which is a complete object type that holds an identifier for a mutex;
14965 which is the function pointer type void (*)(void*), used for a destructor for a
14966 thread-specific storage pointer;
14968 which is the function pointer type int (*)(void*) that is passed to thrd_create
14969 to create a new thread;
14971 which is a complete object type that holds a flag for use by call_once; and
14977 which is a structure type that holds a time specified in seconds and nanoseconds. The
14978 structure shall contain at least the following members, in any order.
14981 5 The enumeration constants are
14983 which is passed to mtx_init to create a mutex object that supports neither timeout nor
14986 which is passed to mtx_init to create a mutex object that supports recursive locking;
14988 which is passed to mtx_init to create a mutex object that supports timeout;
14990 which is passed to mtx_init to create a mutex object that supports test and return;
14992 which is returned by a timed wait function to indicate that the time specified in the call
14993 was reached without acquiring the requested resource;
14995 which is returned by a function to indicate that the requested operation succeeded;
14997 which is returned by a function to indicate that the requested operation failed because a
14998 resource requested by a test and return function is already in use;
15000 which is returned by a function to indicate that the requested operation failed; and
15002 which is returned by a function to indicate that the requested operation failed because it
15003 was unable to allocate memory.
15010 7.25.2 Initialization functions
15011 7.25.2.1 The call_once function
15013 1 #include <threads.h>
15014 void call_once(once_flag *flag, void (*func)(void));
15016 2 The call_once function uses the once_flag pointed to by flag to ensure that
15017 func is called exactly once, the first time the call_once function is called with that
15018 value of flag. Completion of an effective call to the call_once function synchronizes
15019 with all subsequent calls to the call_once function with the same value of flag.
15021 3 The call_once function returns no value.
15022 7.25.3 Condition variable functions
15023 7.25.3.1 The cnd_broadcast function
15025 1 #include <threads.h>
15026 int cnd_broadcast(cnd_t *cond);
15028 2 The cnd_broadcast function unblocks all of the threads that are blocked on the
15029 condition variable pointed to by cond at the time of the call. If no threads are blocked
15030 on the condition variable pointed to by cond at the time of the call, the function does
15033 3 The cnd_broadcast function returns thrd_success on success, or thrd_error
15034 if the request could not be honored.
15035 7.25.3.2 The cnd_destroy function
15037 1 #include <threads.h>
15038 void cnd_destroy(cnd_t *cond);
15040 2 The cnd_destroy function releases all resources used by the condition variable
15041 pointed to by cond. The cnd_destroy function requires that no threads be blocked
15042 waiting for the condition variable pointed to by cond.
15047 3 The cnd_destroy function returns no value.
15048 7.25.3.3 The cnd_init function
15050 1 #include <threads.h>
15051 int cnd_init(cnd_t *cond);
15053 2 The cnd_init function creates a condition variable. If it succeeds it sets the variable
15054 pointed to by cond to a value that uniquely identifies the newly created condition
15055 variable. A thread that calls cnd_wait on a newly created condition variable will
15058 3 The cnd_init function returns thrd_success on success, or thrd_nomem if no
15059 memory could be allocated for the newly created condition, or thrd_error if the
15060 request could not be honored.
15061 7.25.3.4 The cnd_signal function
15063 1 #include <threads.h>
15064 int cnd_signal(cnd_t *cond);
15066 2 The cnd_signal function unblocks one of the threads that are blocked on the
15067 condition variable pointed to by cond at the time of the call. If no threads are blocked
15068 on the condition variable at the time of the call, the function does nothing and return
15071 3 The cnd_signal function returns thrd_success on success or thrd_error if
15072 the request could not be honored.
15073 7.25.3.5 The cnd_timedwait function
15075 1 #include <threads.h>
15076 int cnd_timedwait(cnd_t *cond, mtx_t *mtx,
15085 2 The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and
15086 endeavors to block until the condition variable pointed to by cond is signaled by a call to
15087 cnd_signal or to cnd_broadcast, or until after the time specified by the xtime
15088 object pointed to by xt. When the calling thread becomes unblocked it locks the variable
15089 pointed to by mtx before it returns. The cnd_timedwait function requires that the
15090 mutex pointed to by mtx be locked by the calling thread.
15092 3 The cnd_timedwait function returns thrd_success upon success, or
15093 thrd_timeout if the time specified in the call was reached without acquiring the
15094 requested resource, or thrd_error if the request could not be honored.
15095 7.25.3.6 The cnd_wait function
15097 1 #include <threads.h>
15098 int cnd_wait(cnd_t *cond, mtx_t *mtx);
15100 2 The cnd_wait function atomically unlocks the mutex pointed to by mtx and endeavors
15101 to block until the condition variable pointed to by cond is signaled by a call to
15102 cnd_signal or to cnd_broadcast. When the calling thread becomes unblocked it
15103 locks the mutex pointed to by mtx before it returns. If the mutex pointed to by mtx is
15104 not locked by the calling thread, the cnd_wait function will act as if the abort
15105 function is called.
15107 3 The cnd_wait function returns thrd_success on success or thrd_error if the
15108 request could not be honored.
15109 7.25.4 Mutex functions
15110 7.25.4.1 The mtx_destroy function
15112 1 #include <threads.h>
15113 void mtx_destroy(mtx_t *mtx);
15115 2 The mtx_destroy function releases any resources used by the mutex pointed to by
15116 mtx. No threads can be blocked waiting for the mutex pointed to by mtx.
15123 3 The mtx_destroy function returns no value.
15124 7.25.4.2 The mtx_init function
15126 1 #include <threads.h>
15127 int mtx_init(mtx_t *mtx, int type);
15129 2 The mtx_init function creates a mutex object with properties indicated by type,
15130 which must have one of the six values:
15131 mtx_plain for a simple non-recursive mutex,
15132 mtx_timed for a non-recursive mutex that supports timeout,
15133 mtx_try for a non-recursive mutex that supports test and return,
15134 mtx_plain | mtx_recursive for a simple recursive mutex,
15135 mtx_timed | mtx_recursive for a recursive mutex that supports timeout, or
15136 mtx_try | mtx_recursive for a recursive mutex that supports test and return.
15137 3 If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that
15138 uniquely identifies the newly created mutex.
15140 4 The mtx_init function returns thrd_success on success, or thrd_error if the
15141 request could not be honored.
15142 7.25.4.3 The mtx_lock function
15144 1 #include <threads.h>
15145 int mtx_lock(mtx_t *mtx);
15147 2 The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex
15148 is non-recursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock
15149 on the same mutex shall synchronize with this operation.
15151 3 The mtx_lock function returns thrd_success on success, or thrd_busy if the
15152 resource requested is already in use, or thrd_error if the request could not be
15160 7.25.4.4 The mtx_timedlock function
15162 1 #include <threads.h>
15163 int mtx_timedlock(mtx_t *mtx, const xtime *xt);
15165 2 The mtx_timedlock function endeavors to block until it locks the mutex pointed to by
15166 mtx or until the time specified by the xtime object xt has passed. The specified mutex
15167 shall support timeout. If the operation succeeds, prior calls to mtx_unlock on the same
15168 mutex shall synchronize with this operation.
15170 3 The mtx_timedlock function returns thrd_success on success, or thrd_busy
15171 if the resource requested is already in use, or thrd_timeout if the time specified was
15172 reached without acquiring the requested resource, or thrd_error if the request could
15174 7.25.4.5 The mtx_trylock function
15176 1 #include <threads.h>
15177 int mtx_trylock(mtx_t *mtx);
15179 2 The mtx_trylock function endeavors to lock the mutex pointed to by mtx. The
15180 specified mutex shall support either test and return or timeout. If the mutex is already
15181 locked, the function returns without blocking. If the operation succeeds, prior calls to
15182 mtx_unlock on the same mutex shall synchronize with this operation.
15184 3 The mtx_trylock function returns thrd_success on success, or thrd_busy if
15185 the resource requested is already in use, or thrd_error if the request could not be
15187 7.25.4.6 The mtx_unlock function
15189 1 #include <threads.h>
15190 int mtx_unlock(mtx_t *mtx);
15192 2 The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to
15193 by mtx shall be locked by the calling thread.
15198 3 The mtx_unlock function returns thrd_success on success or thrd_error if
15199 the request could not be honored.
15200 7.25.5 Thread functions
15201 7.25.5.1 The thrd_create function
15203 1 #include <threads.h>
15204 int thrd_create(thrd_t *thr, thrd_start_t func,
15207 2 The thrd_create function creates a new thread executing func(arg). If the
15208 thrd_create function succeeds, it sets the object pointed to by thr to the identifier of
15209 the newly created thread. (A thread's identifier may be reused for a different thread once
15210 the original thread has exited and either been detached or joined to another thread.) The
15211 completion of the thrd_create function synchronizes with the beginning of the
15212 execution of the new thread.
15214 3 The thrd_create function returns thrd_success on success, or thrd_nomem if
15215 no memory could be allocated for the thread requested, or thrd_error if the request
15216 could not be honored.
15217 7.25.5.2 The thrd_current function
15219 1 #include <threads.h>
15220 thrd_t thrd_current(void);
15222 2 The thrd_current function identifies the thread that called it.
15224 3 The thrd_current function returns the identifier of the thread that called it.
15225 7.25.5.3 The thrd_detach function
15227 1 #include <threads.h>
15228 int thrd_detach(thrd_t thr);
15235 2 The thrd_detach function tells the operating system to dispose of any resources
15236 allocated to the thread identified by thr when that thread terminates. The thread
15237 identified by thr shall not have been previously detached or joined with another thread.
15239 3 The thrd_detach function returns thrd_success on success or thrd_error if
15240 the request could not be honored.
15241 7.25.5.4 The thrd_equal function
15243 1 #include <threads.h>
15244 int thrd_equal(thrd_t thr0, thrd_t thr1);
15246 2 The thrd_equal function will determine whether the thread identified by thr0 refers
15247 to the thread identified by thr1.
15249 3 The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to
15250 different threads. Otherwise the thrd_equal function returns a nonzero value.
15251 7.25.5.5 The thrd_exit function
15253 1 #include <threads.h>
15254 void thrd_exit(int res);
15256 2 The thrd_exit function terminates execution of the calling thread and sets its result
15259 3 The thrd_exit function returns no value.
15260 7.25.5.6 The thrd_join function
15262 1 #include <threads.h>
15263 int thrd_join(thrd_t thr, int *res);
15265 2 The thrd_join function joins the thread identified by thr with the current thread by
15266 blocking until the other thread has terminated. If the parameter res is not a null pointer,
15270 it stores the thread's result code in the integer pointed to by res. The termination of the
15271 other thread synchronizes with the completion of the thrd_join function. The thread
15272 identified by thr shall not have been previously detached or joined with another thread.
15274 3 The thrd_join function returns thrd_success on success or thrd_error if the
15275 request could not be honored.
15276 7.25.5.7 The thrd_sleep function
15278 1 #include <threads.h>
15279 void thrd_sleep(const xtime *xt);
15281 2 The thrd_sleep function suspends execution of the calling thread until after the time
15282 specified by the xtime object pointed to by xt.
15284 3 The thrd_sleep function returns no value.
15285 7.25.5.8 The thrd_yield function
15287 1 #include <threads.h>
15288 void thrd_yield(void);
15290 2 The thrd_yield function endeavors to permit other threads to run, even if the current
15291 thread would ordinarily continue to run.
15293 3 The thrd_yield function returns no value.
15294 7.25.6 Thread-specific storage functions
15295 7.25.6.1 The tss_create function
15297 1 #include <threads.h>
15298 int tss_create(tss_t *key, tss_dtor_t dtor);
15300 2 The tss_create function creates a thread-specific storage pointer with destructor
15301 dtor, which may be null.
15307 3 If the tss_create function is successful, it sets the thread-specific storage pointed to
15308 by key to a value that uniquely identifies the newly created pointer and returns
15309 thrd_success; otherwise, thrd_error is returned and the thread-specific storage
15310 pointed to by key is set to an undefined value.
15311 7.25.6.2 The tss_delete function
15313 1 #include <threads.h>
15314 void tss_delete(tss_t key);
15316 2 The tss_delete function releases any resources used by the thread-specific storage
15319 3 The tss_delete function returns no value.
15320 7.25.6.3 The tss_get function
15322 1 #include <threads.h>
15323 void *tss_get(tss_t key);
15325 2 The tss_get function returns the value for the current thread held in the thread-specific
15326 storage identified by key.
15328 3 The tss_get function returns the value for the current thread if successful, or zero if
15330 7.25.6.4 The tss_set function
15332 1 #include <threads.h>
15333 int tss_set(tss_t key, void *val);
15335 2 The tss_set function sets the value for the current thread held in the thread-specific
15336 storage identified by key to val.
15344 3 The tss_set function returns thrd_success on success or thrd_error if the
15345 request could not be honored.
15346 7.25.7 Time functions
15347 7.25.7.1 The xtime_get function
15349 1 #include <threads.h>
15350 int xtime_get(xtime *xt, int base);
15352 2 The xtime_get function sets the xtime object pointed to by xt to hold the current
15353 time based on the time base base.
15355 3 If the xtime_get function is successful it returns the nonzero value base, which must
15356 be TIME_UTC; otherwise, it returns zero.306)
15361 306) Although an xtime object describes times with nanosecond resolution, the actual resolution in an
15362 xtime object is system dependent.
15366 7.26 Date and time <time.h>
15367 7.26.1 Components of time
15368 1 The header <time.h> defines two macros, and declares several types and functions for
15369 manipulating time. Many functions deal with a calendar time that represents the current
15370 date (according to the Gregorian calendar) and time. Some functions deal with local
15371 time, which is the calendar time expressed for some specific time zone, and with Daylight
15372 Saving Time, which is a temporary change in the algorithm for determining local time.
15373 The local time zone and Daylight Saving Time are implementation-defined.
15374 2 The macros defined are NULL (described in 7.19); and
15376 which expands to an expression with type clock_t (described below) that is the
15377 number per second of the value returned by the clock function.
15378 3 The types declared are size_t (described in 7.19);
15382 which are arithmetic types capable of representing times; and
15384 which holds the components of a calendar time, called the broken-down time.
15385 4 The range and precision of times representable in clock_t and time_t are
15386 implementation-defined. The tm structure shall contain at least the following members,
15387 in any order. The semantics of the members and their normal ranges are expressed in the
15389 int tm_sec; // seconds after the minute -- [0, 60]
15390 int tm_min; // minutes after the hour -- [0, 59]
15391 int tm_hour; // hours since midnight -- [0, 23]
15392 int tm_mday; // day of the month -- [1, 31]
15393 int tm_mon; // months since January -- [0, 11]
15394 int tm_year; // years since 1900
15395 int tm_wday; // days since Sunday -- [0, 6]
15396 int tm_yday; // days since January 1 -- [0, 365]
15397 int tm_isdst; // Daylight Saving Time flag
15401 307) The range [0, 60] for tm_sec allows for a positive leap second.
15405 The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight
15406 Saving Time is not in effect, and negative if the information is not available.
15407 7.26.2 Time manipulation functions
15408 7.26.2.1 The clock function
15410 1 #include <time.h>
15411 clock_t clock(void);
15413 2 The clock function determines the processor time used.
15415 3 The clock function returns the implementation's best approximation to the processor
15416 time used by the program since the beginning of an implementation-defined era related
15417 only to the program invocation. To determine the time in seconds, the value returned by
15418 the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If
15419 the processor time used is not available or its value cannot be represented, the function
15420 returns the value (clock_t)(-1).308)
15421 7.26.2.2 The difftime function
15423 1 #include <time.h>
15424 double difftime(time_t time1, time_t time0);
15426 2 The difftime function computes the difference between two calendar times: time1 -
15429 3 The difftime function returns the difference expressed in seconds as a double.
15434 308) In order to measure the time spent in a program, the clock function should be called at the start of
15435 the program and its return value subtracted from the value returned by subsequent calls.
15439 7.26.2.3 The mktime function
15441 1 #include <time.h>
15442 time_t mktime(struct tm *timeptr);
15444 2 The mktime function converts the broken-down time, expressed as local time, in the
15445 structure pointed to by timeptr into a calendar time value with the same encoding as
15446 that of the values returned by the time function. The original values of the tm_wday
15447 and tm_yday components of the structure are ignored, and the original values of the
15448 other components are not restricted to the ranges indicated above.309) On successful
15449 completion, the values of the tm_wday and tm_yday components of the structure are
15450 set appropriately, and the other components are set to represent the specified calendar
15451 time, but with their values forced to the ranges indicated above; the final value of
15452 tm_mday is not set until tm_mon and tm_year are determined.
15454 3 The mktime function returns the specified calendar time encoded as a value of type
15455 time_t. If the calendar time cannot be represented, the function returns the value
15457 4 EXAMPLE What day of the week is July 4, 2001?
15460 static const char *const wday[] = {
15461 "Sunday", "Monday", "Tuesday", "Wednesday",
15462 "Thursday", "Friday", "Saturday", "-unknown-"
15464 struct tm time_str;
15470 309) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that
15471 Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value
15472 causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time.
15476 time_str.tm_year = 2001 - 1900;
15477 time_str.tm_mon = 7 - 1;
15478 time_str.tm_mday = 4;
15479 time_str.tm_hour = 0;
15480 time_str.tm_min = 0;
15481 time_str.tm_sec = 1;
15482 time_str.tm_isdst = -1;
15483 if (mktime(&time_str) == (time_t)(-1))
15484 time_str.tm_wday = 7;
15485 printf("%s\n", wday[time_str.tm_wday]);
15487 7.26.2.4 The time function
15489 1 #include <time.h>
15490 time_t time(time_t *timer);
15492 2 The time function determines the current calendar time. The encoding of the value is
15495 3 The time function returns the implementation's best approximation to the current
15496 calendar time. The value (time_t)(-1) is returned if the calendar time is not
15497 available. If timer is not a null pointer, the return value is also assigned to the object it
15499 7.26.3 Time conversion functions
15500 1 Except for the strftime function, these functions each return a pointer to one of two
15501 types of static objects: a broken-down time structure or an array of char. Execution of
15502 any of the functions that return a pointer to one of these object types may overwrite the
15503 information in any object of the same type pointed to by the value returned from any
15504 previous call to any of them and the functions are not required to avoid data races. The
15505 implementation shall behave as if no other library functions call these functions.
15506 7.26.3.1 The asctime function
15508 1 #include <time.h>
15509 char *asctime(const struct tm *timeptr);
15511 2 The asctime function converts the broken-down time in the structure pointed to by
15512 timeptr into a string in the form
15513 Sun Sep 16 01:03:52 1973\n\0
15517 using the equivalent of the following algorithm.
15518 char *asctime(const struct tm *timeptr)
15520 static const char wday_name[7][3] = {
15521 "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
15523 static const char mon_name[12][3] = {
15524 "Jan", "Feb", "Mar", "Apr", "May", "Jun",
15525 "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
15527 static char result[26];
15528 sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
15529 wday_name[timeptr->tm_wday],
15530 mon_name[timeptr->tm_mon],
15531 timeptr->tm_mday, timeptr->tm_hour,
15532 timeptr->tm_min, timeptr->tm_sec,
15533 1900 + timeptr->tm_year);
15536 3 If any of the fields of the broken-down time contain values that are outside their normal
15537 ranges,310) the behavior of the asctime function is undefined. Likewise, if the
15538 calculated year exceeds four digits or is less than the year 1000, the behavior is
15541 4 The asctime function returns a pointer to the string.
15542 7.26.3.2 The ctime function
15544 1 #include <time.h>
15545 char *ctime(const time_t *timer);
15547 2 The ctime function converts the calendar time pointed to by timer to local time in the
15548 form of a string. It is equivalent to
15549 asctime(localtime(timer))
15558 3 The ctime function returns the pointer returned by the asctime function with that
15559 broken-down time as argument.
15560 Forward references: the localtime function (7.26.3.4).
15561 7.26.3.3 The gmtime function
15563 1 #include <time.h>
15564 struct tm *gmtime(const time_t *timer);
15566 2 The gmtime function converts the calendar time pointed to by timer into a broken-
15567 down time, expressed as UTC.
15569 3 The gmtime function returns a pointer to the broken-down time, or a null pointer if the
15570 specified time cannot be converted to UTC.
15571 7.26.3.4 The localtime function
15573 1 #include <time.h>
15574 struct tm *localtime(const time_t *timer);
15576 2 The localtime function converts the calendar time pointed to by timer into a
15577 broken-down time, expressed as local time.
15579 3 The localtime function returns a pointer to the broken-down time, or a null pointer if
15580 the specified time cannot be converted to local time.
15581 7.26.3.5 The strftime function
15583 1 #include <time.h>
15584 size_t strftime(char * restrict s,
15586 const char * restrict format,
15587 const struct tm * restrict timeptr);
15595 2 The strftime function places characters into the array pointed to by s as controlled by
15596 the string pointed to by format. The format shall be a multibyte character sequence,
15597 beginning and ending in its initial shift state. The format string consists of zero or
15598 more conversion specifiers and ordinary multibyte characters. A conversion specifier
15599 consists of a % character, possibly followed by an E or O modifier character (described
15600 below), followed by a character that determines the behavior of the conversion specifier.
15601 All ordinary multibyte characters (including the terminating null character) are copied
15602 unchanged into the array. If copying takes place between objects that overlap, the
15603 behavior is undefined. No more than maxsize characters are placed into the array.
15604 3 Each conversion specifier is replaced by appropriate characters as described in the
15605 following list. The appropriate characters are determined using the LC_TIME category
15606 of the current locale and by the values of zero or more members of the broken-down time
15607 structure pointed to by timeptr, as specified in brackets in the description. If any of
15608 the specified values is outside the normal range, the characters stored are unspecified.
15609 %a is replaced by the locale's abbreviated weekday name. [tm_wday]
15610 %A is replaced by the locale's full weekday name. [tm_wday]
15611 %b is replaced by the locale's abbreviated month name. [tm_mon]
15612 %B is replaced by the locale's full month name. [tm_mon]
15613 %c is replaced by the locale's appropriate date and time representation. [all specified
15615 %C is replaced by the year divided by 100 and truncated to an integer, as a decimal
15616 number (00-99). [tm_year]
15617 %d is replaced by the day of the month as a decimal number (01-31). [tm_mday]
15618 %D is equivalent to ''%m/%d/%y''. [tm_mon, tm_mday, tm_year]
15619 %e is replaced by the day of the month as a decimal number (1-31); a single digit is
15620 preceded by a space. [tm_mday]
15621 %F is equivalent to ''%Y-%m-%d'' (the ISO 8601 date format). [tm_year, tm_mon,
15623 %g is replaced by the last 2 digits of the week-based year (see below) as a decimal
15624 number (00-99). [tm_year, tm_wday, tm_yday]
15625 %G is replaced by the week-based year (see below) as a decimal number (e.g., 1997).
15626 [tm_year, tm_wday, tm_yday]
15627 %h is equivalent to ''%b''. [tm_mon]
15628 %H is replaced by the hour (24-hour clock) as a decimal number (00-23). [tm_hour]
15629 %I is replaced by the hour (12-hour clock) as a decimal number (01-12). [tm_hour]
15630 %j is replaced by the day of the year as a decimal number (001-366). [tm_yday]
15631 %m is replaced by the month as a decimal number (01-12). [tm_mon]
15632 %M is replaced by the minute as a decimal number (00-59). [tm_min]
15633 %n is replaced by a new-line character.
15637 %p is replaced by the locale's equivalent of the AM/PM designations associated with a
15638 12-hour clock. [tm_hour]
15639 %r is replaced by the locale's 12-hour clock time. [tm_hour, tm_min, tm_sec]
15640 %R is equivalent to ''%H:%M''. [tm_hour, tm_min]
15641 %S is replaced by the second as a decimal number (00-60). [tm_sec]
15642 %t is replaced by a horizontal-tab character.
15643 %T is equivalent to ''%H:%M:%S'' (the ISO 8601 time format). [tm_hour, tm_min,
15645 %u is replaced by the ISO 8601 weekday as a decimal number (1-7), where Monday
15647 %U is replaced by the week number of the year (the first Sunday as the first day of week
15648 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
15649 %V is replaced by the ISO 8601 week number (see below) as a decimal number
15650 (01-53). [tm_year, tm_wday, tm_yday]
15651 %w is replaced by the weekday as a decimal number (0-6), where Sunday is 0.
15653 %W is replaced by the week number of the year (the first Monday as the first day of
15654 week 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
15655 %x is replaced by the locale's appropriate date representation. [all specified in 7.26.1]
15656 %X is replaced by the locale's appropriate time representation. [all specified in 7.26.1]
15657 %y is replaced by the last 2 digits of the year as a decimal number (00-99).
15659 %Y is replaced by the year as a decimal number (e.g., 1997). [tm_year]
15660 %z is replaced by the offset from UTC in the ISO 8601 format ''-0430'' (meaning 4
15661 hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time
15662 zone is determinable. [tm_isdst]
15663 %Z is replaced by the locale's time zone name or abbreviation, or by no characters if no
15664 time zone is determinable. [tm_isdst]
15665 %% is replaced by %.
15666 4 Some conversion specifiers can be modified by the inclusion of an E or O modifier
15667 character to indicate an alternative format or specification. If the alternative format or
15668 specification does not exist for the current locale, the modifier is ignored.
15669 %Ec is replaced by the locale's alternative date and time representation.
15670 %EC is replaced by the name of the base year (period) in the locale's alternative
15672 %Ex is replaced by the locale's alternative date representation.
15673 %EX is replaced by the locale's alternative time representation.
15674 %Ey is replaced by the offset from %EC (year only) in the locale's alternative
15676 %EY is replaced by the locale's full alternative year representation.
15680 %Od is replaced by the day of the month, using the locale's alternative numeric symbols
15681 (filled as needed with leading zeros, or with leading spaces if there is no alternative
15683 %Oe is replaced by the day of the month, using the locale's alternative numeric symbols
15684 (filled as needed with leading spaces).
15685 %OH is replaced by the hour (24-hour clock), using the locale's alternative numeric
15687 %OI is replaced by the hour (12-hour clock), using the locale's alternative numeric
15689 %Om is replaced by the month, using the locale's alternative numeric symbols.
15690 %OM is replaced by the minutes, using the locale's alternative numeric symbols.
15691 %OS is replaced by the seconds, using the locale's alternative numeric symbols.
15692 %Ou is replaced by the ISO 8601 weekday as a number in the locale's alternative
15693 representation, where Monday is 1.
15694 %OU is replaced by the week number, using the locale's alternative numeric symbols.
15695 %OV is replaced by the ISO 8601 week number, using the locale's alternative numeric
15697 %Ow is replaced by the weekday as a number, using the locale's alternative numeric
15699 %OW is replaced by the week number of the year, using the locale's alternative numeric
15701 %Oy is replaced by the last 2 digits of the year, using the locale's alternative numeric
15703 5 %g, %G, and %V give values according to the ISO 8601 week-based year. In this system,
15704 weeks begin on a Monday and week 1 of the year is the week that includes January 4th,
15705 which is also the week that includes the first Thursday of the year, and is also the first
15706 week that contains at least four days in the year. If the first Monday of January is the
15707 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus,
15708 for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If
15709 December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of
15710 the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and
15711 %V is replaced by 01.
15712 6 If a conversion specifier is not one of the above, the behavior is undefined.
15713 7 In the "C" locale, the E and O modifiers are ignored and the replacement strings for the
15714 following specifiers are:
15715 %a the first three characters of %A.
15716 %A one of ''Sunday'', ''Monday'', ... , ''Saturday''.
15717 %b the first three characters of %B.
15718 %B one of ''January'', ''February'', ... , ''December''.
15719 %c equivalent to ''%a %b %e %T %Y''.
15722 %p one of ''AM'' or ''PM''.
15723 %r equivalent to ''%I:%M:%S %p''.
15724 %x equivalent to ''%m/%d/%y''.
15725 %X equivalent to %T.
15726 %Z implementation-defined.
15728 8 If the total number of resulting characters including the terminating null character is not
15729 more than maxsize, the strftime function returns the number of characters placed
15730 into the array pointed to by s not including the terminating null character. Otherwise,
15731 zero is returned and the contents of the array are indeterminate.
15738 7.27 Unicode utilities <uchar.h>
15739 1 The header <uchar.h> declares types and functions for manipulating Unicode
15741 2 The types declared are mbstate_t (described in 7.29.1) and size_t (described in
15744 which is an unsigned integer type used for 16-bit characters and is the same type as
15745 uint_least16_t (described in 7.20.1.2); and
15747 which is an unsigned integer type used for 32-bit characters and is the same type as
15748 uint_least32_t (also described in 7.20.1.2).
15749 7.27.1 Restartable multibyte/wide character conversion functions
15750 1 These functions have a parameter, ps, of type pointer to mbstate_t that points to an
15751 object that can completely describe the current conversion state of the associated
15752 multibyte character sequence, which the functions alter as necessary. If ps is a null
15753 pointer, each function uses its own internal mbstate_t object instead, which is
15754 initialized at program startup to the initial conversion state; the functions are not required
15755 to avoid data races in this case. The implementation behaves as if no library function
15756 calls these functions with a null pointer for ps.
15757 7.27.1.1 The mbrtoc16 function
15759 1 #include <uchar.h>
15760 size_t mbrtoc16(char16_t * restrict pc16,
15761 const char * restrict s, size_t n,
15762 mbstate_t * restrict ps);
15764 2 If s is a null pointer, the mbrtoc16 function is equivalent to the call:
15765 mbrtoc16(NULL, "", 1, ps)
15766 In this case, the values of the parameters pc16 and n are ignored.
15767 3 If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with
15768 the byte pointed to by s to determine the number of bytes needed to complete the next
15769 multibyte character (including any shift sequences). If the function determines that the
15770 next multibyte character is complete and valid, it determines the values of the
15771 corresponding wide characters and then, if pc16 is not a null pointer, stores the value of
15772 the first (or only) such character in the object pointed to by pc16. Subsequent calls will
15775 store successive wide characters without consuming any additional input until all the
15776 characters have been stored. If the corresponding wide character is the null wide
15777 character, the resulting state described is the initial conversion state.
15779 4 The mbrtoc16 function returns the first of the following that applies (given the current
15781 0 if the next n or fewer bytes complete the multibyte character that
15782 corresponds to the null wide character (which is the value stored).
15783 between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
15784 character (which is the value stored); the value returned is the number
15785 of bytes that complete the multibyte character.
15786 (size_t)(-3) if the next character resulting from a previous call has been stored (no
15787 bytes from the input have been consumed by this call).
15788 (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
15789 multibyte character, and all n bytes have been processed (no value is
15791 (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
15792 do not contribute to a complete and valid multibyte character (no
15793 value is stored); the value of the macro EILSEQ is stored in errno,
15794 and the conversion state is unspecified.
15795 7.27.1.2 The c16rtomb function
15797 1 #include <uchar.h>
15798 size_t c16rtomb(char * restrict s, char16_t c16,
15799 mbstate_t * restrict ps);
15801 2 If s is a null pointer, the c16rtomb function is equivalent to the call
15802 c16rtomb(buf, L'\0', ps)
15803 where buf is an internal buffer.
15804 3 If s is not a null pointer, the c16rtomb function determines the number of bytes needed
15805 to represent the multibyte character that corresponds to the wide character given by c16
15806 (including any shift sequences), and stores the multibyte character representation in the
15809 311) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
15810 sequence of redundant shift sequences (for implementations with state-dependent encodings).
15814 array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
15815 c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed
15816 to restore the initial shift state; the resulting state described is the initial conversion state.
15818 4 The c16rtomb function returns the number of bytes stored in the array object (including
15819 any shift sequences). When c16 is not a valid wide character, an encoding error occurs:
15820 the function stores the value of the macro EILSEQ in errno and returns
15821 (size_t)(-1); the conversion state is unspecified.
15822 7.27.1.3 The mbrtoc32 function
15824 1 #include <uchar.h>
15825 size_t mbrtoc32(char32_t * restrict pc32,
15826 const char * restrict s, size_t n,
15827 mbstate_t * restrict ps);
15829 2 If s is a null pointer, the mbrtoc32 function is equivalent to the call:
15830 mbrtoc32(NULL, "", 1, ps)
15831 In this case, the values of the parameters pc32 and n are ignored.
15832 3 If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with
15833 the byte pointed to by s to determine the number of bytes needed to complete the next
15834 multibyte character (including any shift sequences). If the function determines that the
15835 next multibyte character is complete and valid, it determines the values of the
15836 corresponding wide characters and then, if pc32 is not a null pointer, stores the value of
15837 the first (or only) such character in the object pointed to by pc32. Subsequent calls will
15838 store successive wide characters without consuming any additional input until all the
15839 characters have been stored. If the corresponding wide character is the null wide
15840 character, the resulting state described is the initial conversion state.
15842 4 The mbrtoc32 function returns the first of the following that applies (given the current
15844 0 if the next n or fewer bytes complete the multibyte character that
15845 corresponds to the null wide character (which is the value stored).
15846 between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
15847 character (which is the value stored); the value returned is the number
15848 of bytes that complete the multibyte character.
15853 (size_t)(-3) if the next character resulting from a previous call has been stored (no
15854 bytes from the input have been consumed by this call).
15855 (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
15856 multibyte character, and all n bytes have been processed (no value is
15858 (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
15859 do not contribute to a complete and valid multibyte character (no
15860 value is stored); the value of the macro EILSEQ is stored in errno,
15861 and the conversion state is unspecified.
15862 7.27.1.4 The c32rtomb function
15864 1 #include <uchar.h>
15865 size_t c32rtomb(char * restrict s, char32_t c32,
15866 mbstate_t * restrict ps);
15868 2 If s is a null pointer, the c32rtomb function is equivalent to the call
15869 c32rtomb(buf, L'\0', ps)
15870 where buf is an internal buffer.
15871 3 If s is not a null pointer, the c32rtomb function determines the number of bytes needed
15872 to represent the multibyte character that corresponds to the wide character given by c32
15873 (including any shift sequences), and stores the multibyte character representation in the
15874 array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
15875 c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed
15876 to restore the initial shift state; the resulting state described is the initial conversion state.
15878 4 The c32rtomb function returns the number of bytes stored in the array object (including
15879 any shift sequences). When c32 is not a valid wide character, an encoding error occurs:
15880 the function stores the value of the macro EILSEQ in errno and returns
15881 (size_t)(-1); the conversion state is unspecified.
15886 312) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
15887 sequence of redundant shift sequences (for implementations with state-dependent encodings).
15891 7.28 Extended multibyte and wide character utilities <wchar.h>
15892 7.28.1 Introduction
15893 1 The header <wchar.h> defines four macros, and declares four data types, one tag, and
15894 many functions.313)
15895 2 The types declared are wchar_t and size_t (both described in 7.19);
15897 which is a complete object type other than an array type that can hold the conversion state
15898 information necessary to convert between sequences of multibyte characters and wide
15901 which is an integer type unchanged by default argument promotions that can hold any
15902 value corresponding to members of the extended character set, as well as at least one
15903 value that does not correspond to any member of the extended character set (see WEOF
15906 which is declared as an incomplete structure type (the contents are described in 7.26.1).
15907 3 The macros defined are NULL (described in 7.19); WCHAR_MIN and WCHAR_MAX
15908 (described in 7.20.3); and
15910 which expands to a constant expression of type wint_t whose value does not
15911 correspond to any member of the extended character set.315) It is accepted (and returned)
15912 by several functions in this subclause to indicate end-of-file, that is, no more input from a
15913 stream. It is also used as a wide character value that does not correspond to any member
15914 of the extended character set.
15915 4 The functions declared are grouped as follows:
15916 -- Functions that perform input and output of wide characters, or multibyte characters,
15918 -- Functions that provide wide string numeric conversion;
15919 -- Functions that perform general wide string manipulation;
15922 313) See ''future library directions'' (7.30.12).
15923 314) wchar_t and wint_t can be the same integer type.
15924 315) The value of the macro WEOF may differ from that of EOF and need not be negative.
15928 -- Functions for wide string date and time conversion; and
15929 -- Functions that provide extended capabilities for conversion between multibyte and
15930 wide character sequences.
15931 5 Unless explicitly stated otherwise, if the execution of a function described in this
15932 subclause causes copying to take place between objects that overlap, the behavior is
15934 7.28.2 Formatted wide character input/output functions
15935 1 The formatted wide character input/output functions shall behave as if there is a sequence
15936 point after the actions associated with each specifier.316)
15937 7.28.2.1 The fwprintf function
15939 1 #include <stdio.h>
15941 int fwprintf(FILE * restrict stream,
15942 const wchar_t * restrict format, ...);
15944 2 The fwprintf function writes output to the stream pointed to by stream, under
15945 control of the wide string pointed to by format that specifies how subsequent arguments
15946 are converted for output. If there are insufficient arguments for the format, the behavior
15947 is undefined. If the format is exhausted while arguments remain, the excess arguments
15948 are evaluated (as always) but are otherwise ignored. The fwprintf function returns
15949 when the end of the format string is encountered.
15950 3 The format is composed of zero or more directives: ordinary wide characters (not %),
15951 which are copied unchanged to the output stream; and conversion specifications, each of
15952 which results in fetching zero or more subsequent arguments, converting them, if
15953 applicable, according to the corresponding conversion specifier, and then writing the
15954 result to the output stream.
15955 4 Each conversion specification is introduced by the wide character %. After the %, the
15956 following appear in sequence:
15957 -- Zero or more flags (in any order) that modify the meaning of the conversion
15959 -- An optional minimum field width. If the converted value has fewer wide characters
15960 than the field width, it is padded with spaces (by default) on the left (or right, if the
15963 316) The fwprintf functions perform writes to memory for the %n specifier.
15967 left adjustment flag, described later, has been given) to the field width. The field
15968 width takes the form of an asterisk * (described later) or a nonnegative decimal
15970 -- An optional precision that gives the minimum number of digits to appear for the d, i,
15971 o, u, x, and X conversions, the number of digits to appear after the decimal-point
15972 wide character for a, A, e, E, f, and F conversions, the maximum number of
15973 significant digits for the g and G conversions, or the maximum number of wide
15974 characters to be written for s conversions. The precision takes the form of a period
15975 (.) followed either by an asterisk * (described later) or by an optional decimal
15976 integer; if only the period is specified, the precision is taken as zero. If a precision
15977 appears with any other conversion specifier, the behavior is undefined.
15978 -- An optional length modifier that specifies the size of the argument.
15979 -- A conversion specifier wide character that specifies the type of conversion to be
15981 5 As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
15982 this case, an int argument supplies the field width or precision. The arguments
15983 specifying field width, or precision, or both, shall appear (in that order) before the
15984 argument (if any) to be converted. A negative field width argument is taken as a - flag
15985 followed by a positive field width. A negative precision argument is taken as if the
15986 precision were omitted.
15987 6 The flag wide characters and their meanings are:
15988 - The result of the conversion is left-justified within the field. (It is right-justified if
15989 this flag is not specified.)
15990 + The result of a signed conversion always begins with a plus or minus sign. (It
15991 begins with a sign only when a negative value is converted if this flag is not
15993 space If the first wide character of a signed conversion is not a sign, or if a signed
15994 conversion results in no wide characters, a space is prefixed to the result. If the
15995 space and + flags both appear, the space flag is ignored.
15996 # The result is converted to an ''alternative form''. For o conversion, it increases
15997 the precision, if and only if necessary, to force the first digit of the result to be a
15998 zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
15999 conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
16002 317) Note that 0 is taken as a flag, not as the beginning of a field width.
16003 318) The results of all floating conversions of a negative zero, and of negative values that round to zero,
16004 include a minus sign.
16008 and G conversions, the result of converting a floating-point number always
16009 contains a decimal-point wide character, even if no digits follow it. (Normally, a
16010 decimal-point wide character appears in the result of these conversions only if a
16011 digit follows it.) For g and G conversions, trailing zeros are not removed from the
16012 result. For other conversions, the behavior is undefined.
16013 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
16014 (following any indication of sign or base) are used to pad to the field width rather
16015 than performing space padding, except when converting an infinity or NaN. If the
16016 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
16017 conversions, if a precision is specified, the 0 flag is ignored. For other
16018 conversions, the behavior is undefined.
16019 7 The length modifiers and their meanings are:
16020 hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
16021 signed char or unsigned char argument (the argument will have
16022 been promoted according to the integer promotions, but its value shall be
16023 converted to signed char or unsigned char before printing); or that
16024 a following n conversion specifier applies to a pointer to a signed char
16026 h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
16027 short int or unsigned short int argument (the argument will
16028 have been promoted according to the integer promotions, but its value shall
16029 be converted to short int or unsigned short int before printing);
16030 or that a following n conversion specifier applies to a pointer to a short
16032 l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
16033 long int or unsigned long int argument; that a following n
16034 conversion specifier applies to a pointer to a long int argument; that a
16035 following c conversion specifier applies to a wint_t argument; that a
16036 following s conversion specifier applies to a pointer to a wchar_t
16037 argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
16039 ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
16040 long long int or unsigned long long int argument; or that a
16041 following n conversion specifier applies to a pointer to a long long int
16043 j Specifies that a following d, i, o, u, x, or X conversion specifier applies to
16044 an intmax_t or uintmax_t argument; or that a following n conversion
16045 specifier applies to a pointer to an intmax_t argument.
16049 z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
16050 size_t or the corresponding signed integer type argument; or that a
16051 following n conversion specifier applies to a pointer to a signed integer type
16052 corresponding to size_t argument.
16053 t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
16054 ptrdiff_t or the corresponding unsigned integer type argument; or that a
16055 following n conversion specifier applies to a pointer to a ptrdiff_t
16057 L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
16058 applies to a long double argument.
16059 If a length modifier appears with any conversion specifier other than as specified above,
16060 the behavior is undefined.
16061 8 The conversion specifiers and their meanings are:
16062 d,i The int argument is converted to signed decimal in the style [-]dddd. The
16063 precision specifies the minimum number of digits to appear; if the value
16064 being converted can be represented in fewer digits, it is expanded with
16065 leading zeros. The default precision is 1. The result of converting a zero
16066 value with a precision of zero is no wide characters.
16067 o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
16068 decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
16069 letters abcdef are used for x conversion and the letters ABCDEF for X
16070 conversion. The precision specifies the minimum number of digits to appear;
16071 if the value being converted can be represented in fewer digits, it is expanded
16072 with leading zeros. The default precision is 1. The result of converting a
16073 zero value with a precision of zero is no wide characters.
16074 f,F A double argument representing a floating-point number is converted to
16075 decimal notation in the style [-]ddd.ddd, where the number of digits after
16076 the decimal-point wide character is equal to the precision specification. If the
16077 precision is missing, it is taken as 6; if the precision is zero and the # flag is
16078 not specified, no decimal-point wide character appears. If a decimal-point
16079 wide character appears, at least one digit appears before it. The value is
16080 rounded to the appropriate number of digits.
16081 A double argument representing an infinity is converted in one of the styles
16082 [-]inf or [-]infinity -- which style is implementation-defined. A
16083 double argument representing a NaN is converted in one of the styles
16084 [-]nan or [-]nan(n-wchar-sequence) -- which style, and the meaning of
16085 any n-wchar-sequence, is implementation-defined. The F conversion
16086 specifier produces INF, INFINITY, or NAN instead of inf, infinity, or
16090 nan, respectively.319)
16091 e,E A double argument representing a floating-point number is converted in the
16092 style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the
16093 argument is nonzero) before the decimal-point wide character and the number
16094 of digits after it is equal to the precision; if the precision is missing, it is taken
16095 as 6; if the precision is zero and the # flag is not specified, no decimal-point
16096 wide character appears. The value is rounded to the appropriate number of
16097 digits. The E conversion specifier produces a number with E instead of e
16098 introducing the exponent. The exponent always contains at least two digits,
16099 and only as many more digits as necessary to represent the exponent. If the
16100 value is zero, the exponent is zero.
16101 A double argument representing an infinity or NaN is converted in the style
16102 of an f or F conversion specifier.
16103 g,G A double argument representing a floating-point number is converted in
16104 style f or e (or in style F or E in the case of a G conversion specifier),
16105 depending on the value converted and the precision. Let P equal the
16106 precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
16107 Then, if a conversion with style E would have an exponent of X:
16108 -- if P > X >= -4, the conversion is with style f (or F) and precision
16110 -- otherwise, the conversion is with style e (or E) and precision P - 1.
16111 Finally, unless the # flag is used, any trailing zeros are removed from the
16112 fractional portion of the result and the decimal-point wide character is
16113 removed if there is no fractional portion remaining.
16114 A double argument representing an infinity or NaN is converted in the style
16115 of an f or F conversion specifier.
16116 a,A A double argument representing a floating-point number is converted in the
16117 style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
16118 nonzero if the argument is a normalized floating-point number and is
16119 otherwise unspecified) before the decimal-point wide character320) and the
16120 number of hexadecimal digits after it is equal to the precision; if the precision
16121 is missing and FLT_RADIX is a power of 2, then the precision is sufficient
16124 319) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual
16125 meaning; the # and 0 flag wide characters have no effect.
16126 320) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide
16127 character so that subsequent digits align to nibble (4-bit) boundaries.
16131 for an exact representation of the value; if the precision is missing and
16132 FLT_RADIX is not a power of 2, then the precision is sufficient to
16133 distinguish321) values of type double, except that trailing zeros may be
16134 omitted; if the precision is zero and the # flag is not specified, no decimal-
16135 point wide character appears. The letters abcdef are used for a conversion
16136 and the letters ABCDEF for A conversion. The A conversion specifier
16137 produces a number with X and P instead of x and p. The exponent always
16138 contains at least one digit, and only as many more digits as necessary to
16139 represent the decimal exponent of 2. If the value is zero, the exponent is
16141 A double argument representing an infinity or NaN is converted in the style
16142 of an f or F conversion specifier.
16143 c If no l length modifier is present, the int argument is converted to a wide
16144 character as if by calling btowc and the resulting wide character is written.
16145 If an l length modifier is present, the wint_t argument is converted to
16146 wchar_t and written.
16147 s If no l length modifier is present, the argument shall be a pointer to the initial
16148 element of a character array containing a multibyte character sequence
16149 beginning in the initial shift state. Characters from the array are converted as
16150 if by repeated calls to the mbrtowc function, with the conversion state
16151 described by an mbstate_t object initialized to zero before the first
16152 multibyte character is converted, and written up to (but not including) the
16153 terminating null wide character. If the precision is specified, no more than
16154 that many wide characters are written. If the precision is not specified or is
16155 greater than the size of the converted array, the converted array shall contain a
16156 null wide character.
16157 If an l length modifier is present, the argument shall be a pointer to the initial
16158 element of an array of wchar_t type. Wide characters from the array are
16159 written up to (but not including) a terminating null wide character. If the
16160 precision is specified, no more than that many wide characters are written. If
16161 the precision is not specified or is greater than the size of the array, the array
16162 shall contain a null wide character.
16163 p The argument shall be a pointer to void. The value of the pointer is
16164 converted to a sequence of printing wide characters, in an implementation-
16166 321) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
16167 FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
16168 might suffice depending on the implementation's scheme for determining the digit to the left of the
16169 decimal-point wide character.
16174 n The argument shall be a pointer to signed integer into which is written the
16175 number of wide characters written to the output stream so far by this call to
16176 fwprintf. No argument is converted, but one is consumed. If the
16177 conversion specification includes any flags, a field width, or a precision, the
16178 behavior is undefined.
16179 % A % wide character is written. No argument is converted. The complete
16180 conversion specification shall be %%.
16181 9 If a conversion specification is invalid, the behavior is undefined.322) If any argument is
16182 not the correct type for the corresponding conversion specification, the behavior is
16184 10 In no case does a nonexistent or small field width cause truncation of a field; if the result
16185 of a conversion is wider than the field width, the field is expanded to contain the
16187 11 For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
16188 to a hexadecimal floating number with the given precision.
16189 Recommended practice
16190 12 For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
16191 representable in the given precision, the result should be one of the two adjacent numbers
16192 in hexadecimal floating style with the given precision, with the extra stipulation that the
16193 error should have a correct sign for the current rounding direction.
16194 13 For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
16195 DECIMAL_DIG, then the result should be correctly rounded.323) If the number of
16196 significant decimal digits is more than DECIMAL_DIG but the source value is exactly
16197 representable with DECIMAL_DIG digits, then the result should be an exact
16198 representation with trailing zeros. Otherwise, the source value is bounded by two
16199 adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value
16200 of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that
16201 the error should have a correct sign for the current rounding direction.
16203 14 The fwprintf function returns the number of wide characters transmitted, or a negative
16204 value if an output or encoding error occurred.
16206 322) See ''future library directions'' (7.30.12).
16207 323) For binary-to-decimal conversion, the result format's values are the numbers representable with the
16208 given format specifier. The number of significant digits is determined by the format specifier, and in
16209 the case of fixed-point conversion by the source value as well.
16213 Environmental limits
16214 15 The number of wide characters that can be produced by any single conversion shall be at
16216 16 EXAMPLE To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal
16222 wchar_t *weekday, *month; // pointers to wide strings
16223 int day, hour, min;
16224 fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",
16225 weekday, month, day, hour, min);
16226 fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));
16228 Forward references: the btowc function (7.28.6.1.1), the mbrtowc function
16230 7.28.2.2 The fwscanf function
16232 1 #include <stdio.h>
16234 int fwscanf(FILE * restrict stream,
16235 const wchar_t * restrict format, ...);
16237 2 The fwscanf function reads input from the stream pointed to by stream, under
16238 control of the wide string pointed to by format that specifies the admissible input
16239 sequences and how they are to be converted for assignment, using subsequent arguments
16240 as pointers to the objects to receive the converted input. If there are insufficient
16241 arguments for the format, the behavior is undefined. If the format is exhausted while
16242 arguments remain, the excess arguments are evaluated (as always) but are otherwise
16244 3 The format is composed of zero or more directives: one or more white-space wide
16245 characters, an ordinary wide character (neither % nor a white-space wide character), or a
16246 conversion specification. Each conversion specification is introduced by the wide
16247 character %. After the %, the following appear in sequence:
16248 -- An optional assignment-suppressing wide character *.
16249 -- An optional decimal integer greater than zero that specifies the maximum field width
16250 (in wide characters).
16256 -- An optional length modifier that specifies the size of the receiving object.
16257 -- A conversion specifier wide character that specifies the type of conversion to be
16259 4 The fwscanf function executes each directive of the format in turn. When all directives
16260 have been executed, or if a directive fails (as detailed below), the function returns.
16261 Failures are described as input failures (due to the occurrence of an encoding error or the
16262 unavailability of input characters), or matching failures (due to inappropriate input).
16263 5 A directive composed of white-space wide character(s) is executed by reading input up to
16264 the first non-white-space wide character (which remains unread), or until no more wide
16265 characters can be read.
16266 6 A directive that is an ordinary wide character is executed by reading the next wide
16267 character of the stream. If that wide character differs from the directive, the directive
16268 fails and the differing and subsequent wide characters remain unread. Similarly, if end-
16269 of-file, an encoding error, or a read error prevents a wide character from being read, the
16271 7 A directive that is a conversion specification defines a set of matching input sequences, as
16272 described below for each specifier. A conversion specification is executed in the
16274 8 Input white-space wide characters (as specified by the iswspace function) are skipped,
16275 unless the specification includes a [, c, or n specifier.324)
16276 9 An input item is read from the stream, unless the specification includes an n specifier. An
16277 input item is defined as the longest sequence of input wide characters which does not
16278 exceed any specified field width and which is, or is a prefix of, a matching input
16279 sequence.325) The first wide character, if any, after the input item remains unread. If the
16280 length of the input item is zero, the execution of the directive fails; this condition is a
16281 matching failure unless end-of-file, an encoding error, or a read error prevented input
16282 from the stream, in which case it is an input failure.
16283 10 Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
16284 count of input wide characters) is converted to a type appropriate to the conversion
16285 specifier. If the input item is not a matching sequence, the execution of the directive fails:
16286 this condition is a matching failure. Unless assignment suppression was indicated by a *,
16287 the result of the conversion is placed in the object pointed to by the first argument
16288 following the format argument that has not already received a conversion result. If this
16291 324) These white-space wide characters are not counted against a specified field width.
16292 325) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some
16293 sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf.
16297 object does not have an appropriate type, or if the result of the conversion cannot be
16298 represented in the object, the behavior is undefined.
16299 11 The length modifiers and their meanings are:
16300 hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16301 to an argument with type pointer to signed char or unsigned char.
16302 h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16303 to an argument with type pointer to short int or unsigned short
16305 l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16306 to an argument with type pointer to long int or unsigned long
16307 int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
16308 an argument with type pointer to double; or that a following c, s, or [
16309 conversion specifier applies to an argument with type pointer to wchar_t.
16310 ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16311 to an argument with type pointer to long long int or unsigned
16313 j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16314 to an argument with type pointer to intmax_t or uintmax_t.
16315 z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16316 to an argument with type pointer to size_t or the corresponding signed
16318 t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
16319 to an argument with type pointer to ptrdiff_t or the corresponding
16320 unsigned integer type.
16321 L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
16322 applies to an argument with type pointer to long double.
16323 If a length modifier appears with any conversion specifier other than as specified above,
16324 the behavior is undefined.
16325 12 The conversion specifiers and their meanings are:
16326 d Matches an optionally signed decimal integer, whose format is the same as
16327 expected for the subject sequence of the wcstol function with the value 10
16328 for the base argument. The corresponding argument shall be a pointer to
16330 i Matches an optionally signed integer, whose format is the same as expected
16331 for the subject sequence of the wcstol function with the value 0 for the
16332 base argument. The corresponding argument shall be a pointer to signed
16337 o Matches an optionally signed octal integer, whose format is the same as
16338 expected for the subject sequence of the wcstoul function with the value 8
16339 for the base argument. The corresponding argument shall be a pointer to
16341 u Matches an optionally signed decimal integer, whose format is the same as
16342 expected for the subject sequence of the wcstoul function with the value 10
16343 for the base argument. The corresponding argument shall be a pointer to
16345 x Matches an optionally signed hexadecimal integer, whose format is the same
16346 as expected for the subject sequence of the wcstoul function with the value
16347 16 for the base argument. The corresponding argument shall be a pointer to
16349 a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
16350 format is the same as expected for the subject sequence of the wcstod
16351 function. The corresponding argument shall be a pointer to floating.
16352 c Matches a sequence of wide characters of exactly the number specified by the
16353 field width (1 if no field width is present in the directive).
16354 If no l length modifier is present, characters from the input field are
16355 converted as if by repeated calls to the wcrtomb function, with the
16356 conversion state described by an mbstate_t object initialized to zero
16357 before the first wide character is converted. The corresponding argument
16358 shall be a pointer to the initial element of a character array large enough to
16359 accept the sequence. No null character is added.
16360 If an l length modifier is present, the corresponding argument shall be a
16361 pointer to the initial element of an array of wchar_t large enough to accept
16362 the sequence. No null wide character is added.
16363 s Matches a sequence of non-white-space wide characters.
16364 If no l length modifier is present, characters from the input field are
16365 converted as if by repeated calls to the wcrtomb function, with the
16366 conversion state described by an mbstate_t object initialized to zero
16367 before the first wide character is converted. The corresponding argument
16368 shall be a pointer to the initial element of a character array large enough to
16369 accept the sequence and a terminating null character, which will be added
16371 If an l length modifier is present, the corresponding argument shall be a
16372 pointer to the initial element of an array of wchar_t large enough to accept
16376 the sequence and the terminating null wide character, which will be added
16378 [ Matches a nonempty sequence of wide characters from a set of expected
16379 characters (the scanset).
16380 If no l length modifier is present, characters from the input field are
16381 converted as if by repeated calls to the wcrtomb function, with the
16382 conversion state described by an mbstate_t object initialized to zero
16383 before the first wide character is converted. The corresponding argument
16384 shall be a pointer to the initial element of a character array large enough to
16385 accept the sequence and a terminating null character, which will be added
16387 If an l length modifier is present, the corresponding argument shall be a
16388 pointer to the initial element of an array of wchar_t large enough to accept
16389 the sequence and the terminating null wide character, which will be added
16391 The conversion specifier includes all subsequent wide characters in the
16392 format string, up to and including the matching right bracket (]). The wide
16393 characters between the brackets (the scanlist) compose the scanset, unless the
16394 wide character after the left bracket is a circumflex (^), in which case the
16395 scanset contains all wide characters that do not appear in the scanlist between
16396 the circumflex and the right bracket. If the conversion specifier begins with
16397 [] or [^], the right bracket wide character is in the scanlist and the next
16398 following right bracket wide character is the matching right bracket that ends
16399 the specification; otherwise the first following right bracket wide character is
16400 the one that ends the specification. If a - wide character is in the scanlist and
16401 is not the first, nor the second where the first wide character is a ^, nor the
16402 last character, the behavior is implementation-defined.
16403 p Matches an implementation-defined set of sequences, which should be the
16404 same as the set of sequences that may be produced by the %p conversion of
16405 the fwprintf function. The corresponding argument shall be a pointer to a
16406 pointer to void. The input item is converted to a pointer value in an
16407 implementation-defined manner. If the input item is a value converted earlier
16408 during the same program execution, the pointer that results shall compare
16409 equal to that value; otherwise the behavior of the %p conversion is undefined.
16410 n No input is consumed. The corresponding argument shall be a pointer to
16411 signed integer into which is to be written the number of wide characters read
16412 from the input stream so far by this call to the fwscanf function. Execution
16413 of a %n directive does not increment the assignment count returned at the
16414 completion of execution of the fwscanf function. No argument is
16417 converted, but one is consumed. If the conversion specification includes an
16418 assignment-suppressing wide character or a field width, the behavior is
16420 % Matches a single % wide character; no conversion or assignment occurs. The
16421 complete conversion specification shall be %%.
16422 13 If a conversion specification is invalid, the behavior is undefined.326)
16423 14 The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
16424 respectively, a, e, f, g, and x.
16425 15 Trailing white space (including new-line wide characters) is left unread unless matched
16426 by a directive. The success of literal matches and suppressed assignments is not directly
16427 determinable other than via the %n directive.
16429 16 The fwscanf function returns the value of the macro EOF if an input failure occurs
16430 before the first conversion (if any) has completed. Otherwise, the function returns the
16431 number of input items assigned, which can be fewer than provided for, or even zero, in
16432 the event of an early matching failure.
16433 17 EXAMPLE 1 The call:
16437 int n, i; float x; wchar_t name[50];
16438 n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);
16439 with the input line:
16440 25 54.32E-1 thompson
16441 will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
16444 18 EXAMPLE 2 The call:
16448 int i; float x; double y;
16449 fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);
16452 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
16453 56.0. The next wide character read from the input stream will be a.
16456 326) See ''future library directions'' (7.30.12).
16460 Forward references: the wcstod, wcstof, and wcstold functions (7.28.4.1.1), the
16461 wcstol, wcstoll, wcstoul, and wcstoull functions (7.28.4.1.2), the wcrtomb
16462 function (7.28.6.3.3).
16463 7.28.2.3 The swprintf function
16465 1 #include <wchar.h>
16466 int swprintf(wchar_t * restrict s,
16468 const wchar_t * restrict format, ...);
16470 2 The swprintf function is equivalent to fwprintf, except that the argument s
16471 specifies an array of wide characters into which the generated output is to be written,
16472 rather than written to a stream. No more than n wide characters are written, including a
16473 terminating null wide character, which is always added (unless n is zero).
16475 3 The swprintf function returns the number of wide characters written in the array, not
16476 counting the terminating null wide character, or a negative value if an encoding error
16477 occurred or if n or more wide characters were requested to be written.
16478 7.28.2.4 The swscanf function
16480 1 #include <wchar.h>
16481 int swscanf(const wchar_t * restrict s,
16482 const wchar_t * restrict format, ...);
16484 2 The swscanf function is equivalent to fwscanf, except that the argument s specifies a
16485 wide string from which the input is to be obtained, rather than from a stream. Reaching
16486 the end of the wide string is equivalent to encountering end-of-file for the fwscanf
16489 3 The swscanf function returns the value of the macro EOF if an input failure occurs
16490 before the first conversion (if any) has completed. Otherwise, the swscanf function
16491 returns the number of input items assigned, which can be fewer than provided for, or even
16492 zero, in the event of an early matching failure.
16499 7.28.2.5 The vfwprintf function
16501 1 #include <stdarg.h>
16504 int vfwprintf(FILE * restrict stream,
16505 const wchar_t * restrict format,
16508 2 The vfwprintf function is equivalent to fwprintf, with the variable argument list
16509 replaced by arg, which shall have been initialized by the va_start macro (and
16510 possibly subsequent va_arg calls). The vfwprintf function does not invoke the
16513 3 The vfwprintf function returns the number of wide characters transmitted, or a
16514 negative value if an output or encoding error occurred.
16515 4 EXAMPLE The following shows the use of the vfwprintf function in a general error-reporting
16517 #include <stdarg.h>
16520 void error(char *function_name, wchar_t *format, ...)
16523 va_start(args, format);
16524 // print out name of function causing error
16525 fwprintf(stderr, L"ERROR in %s: ", function_name);
16526 // print out remainder of message
16527 vfwprintf(stderr, format, args);
16534 327) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
16535 invoke the va_arg macro, the value of arg after the return is indeterminate.
16539 7.28.2.6 The vfwscanf function
16541 1 #include <stdarg.h>
16544 int vfwscanf(FILE * restrict stream,
16545 const wchar_t * restrict format,
16548 2 The vfwscanf function is equivalent to fwscanf, with the variable argument list
16549 replaced by arg, which shall have been initialized by the va_start macro (and
16550 possibly subsequent va_arg calls). The vfwscanf function does not invoke the
16553 3 The vfwscanf function returns the value of the macro EOF if an input failure occurs
16554 before the first conversion (if any) has completed. Otherwise, the vfwscanf function
16555 returns the number of input items assigned, which can be fewer than provided for, or even
16556 zero, in the event of an early matching failure.
16557 7.28.2.7 The vswprintf function
16559 1 #include <stdarg.h>
16561 int vswprintf(wchar_t * restrict s,
16563 const wchar_t * restrict format,
16566 2 The vswprintf function is equivalent to swprintf, with the variable argument list
16567 replaced by arg, which shall have been initialized by the va_start macro (and
16568 possibly subsequent va_arg calls). The vswprintf function does not invoke the
16571 3 The vswprintf function returns the number of wide characters written in the array, not
16572 counting the terminating null wide character, or a negative value if an encoding error
16573 occurred or if n or more wide characters were requested to be generated.
16578 7.28.2.8 The vswscanf function
16580 1 #include <stdarg.h>
16582 int vswscanf(const wchar_t * restrict s,
16583 const wchar_t * restrict format,
16586 2 The vswscanf function is equivalent to swscanf, with the variable argument list
16587 replaced by arg, which shall have been initialized by the va_start macro (and
16588 possibly subsequent va_arg calls). The vswscanf function does not invoke the
16591 3 The vswscanf function returns the value of the macro EOF if an input failure occurs
16592 before the first conversion (if any) has completed. Otherwise, the vswscanf function
16593 returns the number of input items assigned, which can be fewer than provided for, or even
16594 zero, in the event of an early matching failure.
16595 7.28.2.9 The vwprintf function
16597 1 #include <stdarg.h>
16599 int vwprintf(const wchar_t * restrict format,
16602 2 The vwprintf function is equivalent to wprintf, with the variable argument list
16603 replaced by arg, which shall have been initialized by the va_start macro (and
16604 possibly subsequent va_arg calls). The vwprintf function does not invoke the
16607 3 The vwprintf function returns the number of wide characters transmitted, or a negative
16608 value if an output or encoding error occurred.
16615 7.28.2.10 The vwscanf function
16617 1 #include <stdarg.h>
16619 int vwscanf(const wchar_t * restrict format,
16622 2 The vwscanf function is equivalent to wscanf, with the variable argument list
16623 replaced by arg, which shall have been initialized by the va_start macro (and
16624 possibly subsequent va_arg calls). The vwscanf function does not invoke the
16627 3 The vwscanf function returns the value of the macro EOF if an input failure occurs
16628 before the first conversion (if any) has completed. Otherwise, the vwscanf function
16629 returns the number of input items assigned, which can be fewer than provided for, or even
16630 zero, in the event of an early matching failure.
16631 7.28.2.11 The wprintf function
16633 1 #include <wchar.h>
16634 int wprintf(const wchar_t * restrict format, ...);
16636 2 The wprintf function is equivalent to fwprintf with the argument stdout
16637 interposed before the arguments to wprintf.
16639 3 The wprintf function returns the number of wide characters transmitted, or a negative
16640 value if an output or encoding error occurred.
16641 7.28.2.12 The wscanf function
16643 1 #include <wchar.h>
16644 int wscanf(const wchar_t * restrict format, ...);
16646 2 The wscanf function is equivalent to fwscanf with the argument stdin interposed
16647 before the arguments to wscanf.
16653 3 The wscanf function returns the value of the macro EOF if an input failure occurs
16654 before the first conversion (if any) has completed. Otherwise, the wscanf function
16655 returns the number of input items assigned, which can be fewer than provided for, or even
16656 zero, in the event of an early matching failure.
16657 7.28.3 Wide character input/output functions
16658 7.28.3.1 The fgetwc function
16660 1 #include <stdio.h>
16662 wint_t fgetwc(FILE *stream);
16664 2 If the end-of-file indicator for the input stream pointed to by stream is not set and a
16665 next wide character is present, the fgetwc function obtains that wide character as a
16666 wchar_t converted to a wint_t and advances the associated file position indicator for
16667 the stream (if defined).
16669 3 If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
16670 of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise,
16671 the fgetwc function returns the next wide character from the input stream pointed to by
16672 stream. If a read error occurs, the error indicator for the stream is set and the fgetwc
16673 function returns WEOF. If an encoding error occurs (including too few bytes), the value of
16674 the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.328)
16675 7.28.3.2 The fgetws function
16677 1 #include <stdio.h>
16679 wchar_t *fgetws(wchar_t * restrict s,
16680 int n, FILE * restrict stream);
16682 2 The fgetws function reads at most one less than the number of wide characters
16683 specified by n from the stream pointed to by stream into the array pointed to by s. No
16686 328) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
16687 Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs.
16691 additional wide characters are read after a new-line wide character (which is retained) or
16692 after end-of-file. A null wide character is written immediately after the last wide
16693 character read into the array.
16695 3 The fgetws function returns s if successful. If end-of-file is encountered and no
16696 characters have been read into the array, the contents of the array remain unchanged and a
16697 null pointer is returned. If a read or encoding error occurs during the operation, the array
16698 contents are indeterminate and a null pointer is returned.
16699 7.28.3.3 The fputwc function
16701 1 #include <stdio.h>
16703 wint_t fputwc(wchar_t c, FILE *stream);
16705 2 The fputwc function writes the wide character specified by c to the output stream
16706 pointed to by stream, at the position indicated by the associated file position indicator
16707 for the stream (if defined), and advances the indicator appropriately. If the file cannot
16708 support positioning requests, or if the stream was opened with append mode, the
16709 character is appended to the output stream.
16711 3 The fputwc function returns the wide character written. If a write error occurs, the
16712 error indicator for the stream is set and fputwc returns WEOF. If an encoding error
16713 occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF.
16714 7.28.3.4 The fputws function
16716 1 #include <stdio.h>
16718 int fputws(const wchar_t * restrict s,
16719 FILE * restrict stream);
16721 2 The fputws function writes the wide string pointed to by s to the stream pointed to by
16722 stream. The terminating null wide character is not written.
16724 3 The fputws function returns EOF if a write or encoding error occurs; otherwise, it
16725 returns a nonnegative value.
16729 7.28.3.5 The fwide function
16731 1 #include <stdio.h>
16733 int fwide(FILE *stream, int mode);
16735 2 The fwide function determines the orientation of the stream pointed to by stream. If
16736 mode is greater than zero, the function first attempts to make the stream wide oriented. If
16737 mode is less than zero, the function first attempts to make the stream byte oriented.329)
16738 Otherwise, mode is zero and the function does not alter the orientation of the stream.
16740 3 The fwide function returns a value greater than zero if, after the call, the stream has
16741 wide orientation, a value less than zero if the stream has byte orientation, or zero if the
16742 stream has no orientation.
16743 7.28.3.6 The getwc function
16745 1 #include <stdio.h>
16747 wint_t getwc(FILE *stream);
16749 2 The getwc function is equivalent to fgetwc, except that if it is implemented as a
16750 macro, it may evaluate stream more than once, so the argument should never be an
16751 expression with side effects.
16753 3 The getwc function returns the next wide character from the input stream pointed to by
16755 7.28.3.7 The getwchar function
16757 1 #include <wchar.h>
16758 wint_t getwchar(void);
16763 329) If the orientation of the stream has already been determined, fwide does not change it.
16768 2 The getwchar function is equivalent to getwc with the argument stdin.
16770 3 The getwchar function returns the next wide character from the input stream pointed to
16772 7.28.3.8 The putwc function
16774 1 #include <stdio.h>
16776 wint_t putwc(wchar_t c, FILE *stream);
16778 2 The putwc function is equivalent to fputwc, except that if it is implemented as a
16779 macro, it may evaluate stream more than once, so that argument should never be an
16780 expression with side effects.
16782 3 The putwc function returns the wide character written, or WEOF.
16783 7.28.3.9 The putwchar function
16785 1 #include <wchar.h>
16786 wint_t putwchar(wchar_t c);
16788 2 The putwchar function is equivalent to putwc with the second argument stdout.
16790 3 The putwchar function returns the character written, or WEOF.
16791 7.28.3.10 The ungetwc function
16793 1 #include <stdio.h>
16795 wint_t ungetwc(wint_t c, FILE *stream);
16797 2 The ungetwc function pushes the wide character specified by c back onto the input
16798 stream pointed to by stream. Pushed-back wide characters will be returned by
16799 subsequent reads on that stream in the reverse order of their pushing. A successful
16803 intervening call (with the stream pointed to by stream) to a file positioning function
16804 (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the
16805 stream. The external storage corresponding to the stream is unchanged.
16806 3 One wide character of pushback is guaranteed, even if the call to the ungetwc function
16807 follows just after a call to a formatted wide character input function fwscanf,
16808 vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times
16809 on the same stream without an intervening read or file positioning operation on that
16810 stream, the operation may fail.
16811 4 If the value of c equals that of the macro WEOF, the operation fails and the input stream is
16813 5 A successful call to the ungetwc function clears the end-of-file indicator for the stream.
16814 The value of the file position indicator for the stream after reading or discarding all
16815 pushed-back wide characters is the same as it was before the wide characters were pushed
16816 back. For a text or binary stream, the value of its file position indicator after a successful
16817 call to the ungetwc function is unspecified until all pushed-back wide characters are
16820 6 The ungetwc function returns the wide character pushed back, or WEOF if the operation
16822 7.28.4 General wide string utilities
16823 1 The header <wchar.h> declares a number of functions useful for wide string
16824 manipulation. Various methods are used for determining the lengths of the arrays, but in
16825 all cases a wchar_t * argument points to the initial (lowest addressed) element of the
16826 array. If an array is accessed beyond the end of an object, the behavior is undefined.
16827 2 Where an argument declared as size_t n determines the length of the array for a
16828 function, n can have the value zero on a call to that function. Unless explicitly stated
16829 otherwise in the description of a particular function in this subclause, pointer arguments
16830 on such a call shall still have valid values, as described in 7.1.4. On such a call, a
16831 function that locates a wide character finds no occurrence, a function that compares two
16832 wide character sequences returns zero, and a function that copies wide characters copies
16833 zero wide characters.
16840 7.28.4.1 Wide string numeric conversion functions
16841 7.28.4.1.1 The wcstod, wcstof, and wcstold functions
16843 1 #include <wchar.h>
16844 double wcstod(const wchar_t * restrict nptr,
16845 wchar_t ** restrict endptr);
16846 float wcstof(const wchar_t * restrict nptr,
16847 wchar_t ** restrict endptr);
16848 long double wcstold(const wchar_t * restrict nptr,
16849 wchar_t ** restrict endptr);
16851 2 The wcstod, wcstof, and wcstold functions convert the initial portion of the wide
16852 string pointed to by nptr to double, float, and long double representation,
16853 respectively. First, they decompose the input string into three parts: an initial, possibly
16854 empty, sequence of white-space wide characters (as specified by the iswspace
16855 function), a subject sequence resembling a floating-point constant or representing an
16856 infinity or NaN; and a final wide string of one or more unrecognized wide characters,
16857 including the terminating null wide character of the input wide string. Then, they attempt
16858 to convert the subject sequence to a floating-point number, and return the result.
16859 3 The expected form of the subject sequence is an optional plus or minus sign, then one of
16861 -- a nonempty sequence of decimal digits optionally containing a decimal-point wide
16862 character, then an optional exponent part as defined for the corresponding single-byte
16863 characters in 6.4.4.2;
16864 -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
16865 decimal-point wide character, then an optional binary exponent part as defined in
16867 -- INF or INFINITY, or any other wide string equivalent except for case
16868 -- NAN or NAN(n-wchar-sequenceopt), or any other wide string equivalent except for
16869 case in the NAN part, where:
16873 n-wchar-sequence digit
16874 n-wchar-sequence nondigit
16875 The subject sequence is defined as the longest initial subsequence of the input wide
16876 string, starting with the first non-white-space wide character, that is of the expected form.
16879 The subject sequence contains no wide characters if the input wide string is not of the
16881 4 If the subject sequence has the expected form for a floating-point number, the sequence of
16882 wide characters starting with the first digit or the decimal-point wide character
16883 (whichever occurs first) is interpreted as a floating constant according to the rules of
16884 6.4.4.2, except that the decimal-point wide character is used in place of a period, and that
16885 if neither an exponent part nor a decimal-point wide character appears in a decimal
16886 floating point number, or if a binary exponent part does not appear in a hexadecimal
16887 floating point number, an exponent part of the appropriate type with value zero is
16888 assumed to follow the last digit in the string. If the subject sequence begins with a minus
16889 sign, the sequence is interpreted as negated.330) A wide character sequence INF or
16890 INFINITY is interpreted as an infinity, if representable in the return type, else like a
16891 floating constant that is too large for the range of the return type. A wide character
16892 sequence NAN or NAN(n-wchar-sequenceopt) is interpreted as a quiet NaN, if supported
16893 in the return type, else like a subject sequence part that does not have the expected form;
16894 the meaning of the n-wchar sequences is implementation-defined.331) A pointer to the
16895 final wide string is stored in the object pointed to by endptr, provided that endptr is
16896 not a null pointer.
16897 5 If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
16898 value resulting from the conversion is correctly rounded.
16899 6 In other than the "C" locale, additional locale-specific subject sequence forms may be
16901 7 If the subject sequence is empty or does not have the expected form, no conversion is
16902 performed; the value of nptr is stored in the object pointed to by endptr, provided
16903 that endptr is not a null pointer.
16904 Recommended practice
16905 8 If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
16906 the result is not exactly representable, the result should be one of the two numbers in the
16907 appropriate internal format that are adjacent to the hexadecimal floating source value,
16908 with the extra stipulation that the error should have a correct sign for the current rounding
16913 330) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
16914 negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
16915 methods may yield different results if rounding is toward positive or negative infinity. In either case,
16916 the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
16917 331) An implementation may use the n-wchar sequence to determine extra information to be represented in
16918 the NaN's significand.
16922 9 If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
16923 <float.h>) significant digits, the result should be correctly rounded. If the subject
16924 sequence D has the decimal form and more than DECIMAL_DIG significant digits,
16925 consider the two bounding, adjacent decimal strings L and U, both having
16926 DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U.
16927 The result should be one of the (equal or adjacent) values that would be obtained by
16928 correctly rounding L and U according to the current rounding direction, with the extra
16929 stipulation that the error with respect to D should have a correct sign for the current
16930 rounding direction.332)
16932 10 The functions return the converted value, if any. If no conversion could be performed,
16933 zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
16934 plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
16935 return type and sign of the value), and the value of the macro ERANGE is stored in
16936 errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
16937 no greater than the smallest normalized positive number in the return type; whether
16938 errno acquires the value ERANGE is implementation-defined.
16943 332) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
16944 to the same internal floating value, but if not will round to adjacent values.
16948 7.28.4.1.2 The wcstol, wcstoll, wcstoul, and wcstoull functions
16950 1 #include <wchar.h>
16952 const wchar_t * restrict nptr,
16953 wchar_t ** restrict endptr,
16955 long long int wcstoll(
16956 const wchar_t * restrict nptr,
16957 wchar_t ** restrict endptr,
16959 unsigned long int wcstoul(
16960 const wchar_t * restrict nptr,
16961 wchar_t ** restrict endptr,
16963 unsigned long long int wcstoull(
16964 const wchar_t * restrict nptr,
16965 wchar_t ** restrict endptr,
16968 2 The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial
16969 portion of the wide string pointed to by nptr to long int, long long int,
16970 unsigned long int, and unsigned long long int representation,
16971 respectively. First, they decompose the input string into three parts: an initial, possibly
16972 empty, sequence of white-space wide characters (as specified by the iswspace
16973 function), a subject sequence resembling an integer represented in some radix determined
16974 by the value of base, and a final wide string of one or more unrecognized wide
16975 characters, including the terminating null wide character of the input wide string. Then,
16976 they attempt to convert the subject sequence to an integer, and return the result.
16977 3 If the value of base is zero, the expected form of the subject sequence is that of an
16978 integer constant as described for the corresponding single-byte characters in 6.4.4.1,
16979 optionally preceded by a plus or minus sign, but not including an integer suffix. If the
16980 value of base is between 2 and 36 (inclusive), the expected form of the subject sequence
16981 is a sequence of letters and digits representing an integer with the radix specified by
16982 base, optionally preceded by a plus or minus sign, but not including an integer suffix.
16983 The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only
16984 letters and digits whose ascribed values are less than that of base are permitted. If the
16985 value of base is 16, the wide characters 0x or 0X may optionally precede the sequence
16986 of letters and digits, following the sign if present.
16990 4 The subject sequence is defined as the longest initial subsequence of the input wide
16991 string, starting with the first non-white-space wide character, that is of the expected form.
16992 The subject sequence contains no wide characters if the input wide string is empty or
16993 consists entirely of white space, or if the first non-white-space wide character is other
16994 than a sign or a permissible letter or digit.
16995 5 If the subject sequence has the expected form and the value of base is zero, the sequence
16996 of wide characters starting with the first digit is interpreted as an integer constant
16997 according to the rules of 6.4.4.1. If the subject sequence has the expected form and the
16998 value of base is between 2 and 36, it is used as the base for conversion, ascribing to each
16999 letter its value as given above. If the subject sequence begins with a minus sign, the value
17000 resulting from the conversion is negated (in the return type). A pointer to the final wide
17001 string is stored in the object pointed to by endptr, provided that endptr is not a null
17003 6 In other than the "C" locale, additional locale-specific subject sequence forms may be
17005 7 If the subject sequence is empty or does not have the expected form, no conversion is
17006 performed; the value of nptr is stored in the object pointed to by endptr, provided
17007 that endptr is not a null pointer.
17009 8 The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted
17010 value, if any. If no conversion could be performed, zero is returned. If the correct value
17011 is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
17012 LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
17013 sign of the value, if any), and the value of the macro ERANGE is stored in errno.
17014 7.28.4.2 Wide string copying functions
17015 7.28.4.2.1 The wcscpy function
17017 1 #include <wchar.h>
17018 wchar_t *wcscpy(wchar_t * restrict s1,
17019 const wchar_t * restrict s2);
17021 2 The wcscpy function copies the wide string pointed to by s2 (including the terminating
17022 null wide character) into the array pointed to by s1.
17024 3 The wcscpy function returns the value of s1.
17029 7.28.4.2.2 The wcsncpy function
17031 1 #include <wchar.h>
17032 wchar_t *wcsncpy(wchar_t * restrict s1,
17033 const wchar_t * restrict s2,
17036 2 The wcsncpy function copies not more than n wide characters (those that follow a null
17037 wide character are not copied) from the array pointed to by s2 to the array pointed to by
17039 3 If the array pointed to by s2 is a wide string that is shorter than n wide characters, null
17040 wide characters are appended to the copy in the array pointed to by s1, until n wide
17041 characters in all have been written.
17043 4 The wcsncpy function returns the value of s1.
17044 7.28.4.2.3 The wmemcpy function
17046 1 #include <wchar.h>
17047 wchar_t *wmemcpy(wchar_t * restrict s1,
17048 const wchar_t * restrict s2,
17051 2 The wmemcpy function copies n wide characters from the object pointed to by s2 to the
17052 object pointed to by s1.
17054 3 The wmemcpy function returns the value of s1.
17059 333) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the
17060 result will not be null-terminated.
17064 7.28.4.2.4 The wmemmove function
17066 1 #include <wchar.h>
17067 wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
17070 2 The wmemmove function copies n wide characters from the object pointed to by s2 to
17071 the object pointed to by s1. Copying takes place as if the n wide characters from the
17072 object pointed to by s2 are first copied into a temporary array of n wide characters that
17073 does not overlap the objects pointed to by s1 or s2, and then the n wide characters from
17074 the temporary array are copied into the object pointed to by s1.
17076 3 The wmemmove function returns the value of s1.
17077 7.28.4.3 Wide string concatenation functions
17078 7.28.4.3.1 The wcscat function
17080 1 #include <wchar.h>
17081 wchar_t *wcscat(wchar_t * restrict s1,
17082 const wchar_t * restrict s2);
17084 2 The wcscat function appends a copy of the wide string pointed to by s2 (including the
17085 terminating null wide character) to the end of the wide string pointed to by s1. The initial
17086 wide character of s2 overwrites the null wide character at the end of s1.
17088 3 The wcscat function returns the value of s1.
17089 7.28.4.3.2 The wcsncat function
17091 1 #include <wchar.h>
17092 wchar_t *wcsncat(wchar_t * restrict s1,
17093 const wchar_t * restrict s2,
17096 2 The wcsncat function appends not more than n wide characters (a null wide character
17097 and those that follow it are not appended) from the array pointed to by s2 to the end of
17101 the wide string pointed to by s1. The initial wide character of s2 overwrites the null
17102 wide character at the end of s1. A terminating null wide character is always appended to
17105 3 The wcsncat function returns the value of s1.
17106 7.28.4.4 Wide string comparison functions
17107 1 Unless explicitly stated otherwise, the functions described in this subclause order two
17108 wide characters the same way as two integers of the underlying integer type designated
17110 7.28.4.4.1 The wcscmp function
17112 1 #include <wchar.h>
17113 int wcscmp(const wchar_t *s1, const wchar_t *s2);
17115 2 The wcscmp function compares the wide string pointed to by s1 to the wide string
17118 3 The wcscmp function returns an integer greater than, equal to, or less than zero,
17119 accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
17120 wide string pointed to by s2.
17121 7.28.4.4.2 The wcscoll function
17123 1 #include <wchar.h>
17124 int wcscoll(const wchar_t *s1, const wchar_t *s2);
17126 2 The wcscoll function compares the wide string pointed to by s1 to the wide string
17127 pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the
17130 3 The wcscoll function returns an integer greater than, equal to, or less than zero,
17131 accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
17134 334) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is
17139 wide string pointed to by s2 when both are interpreted as appropriate to the current
17141 7.28.4.4.3 The wcsncmp function
17143 1 #include <wchar.h>
17144 int wcsncmp(const wchar_t *s1, const wchar_t *s2,
17147 2 The wcsncmp function compares not more than n wide characters (those that follow a
17148 null wide character are not compared) from the array pointed to by s1 to the array
17151 3 The wcsncmp function returns an integer greater than, equal to, or less than zero,
17152 accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
17153 to, or less than the possibly null-terminated array pointed to by s2.
17154 7.28.4.4.4 The wcsxfrm function
17156 1 #include <wchar.h>
17157 size_t wcsxfrm(wchar_t * restrict s1,
17158 const wchar_t * restrict s2,
17161 2 The wcsxfrm function transforms the wide string pointed to by s2 and places the
17162 resulting wide string into the array pointed to by s1. The transformation is such that if
17163 the wcscmp function is applied to two transformed wide strings, it returns a value greater
17164 than, equal to, or less than zero, corresponding to the result of the wcscoll function
17165 applied to the same two original wide strings. No more than n wide characters are placed
17166 into the resulting array pointed to by s1, including the terminating null wide character. If
17167 n is zero, s1 is permitted to be a null pointer.
17169 3 The wcsxfrm function returns the length of the transformed wide string (not including
17170 the terminating null wide character). If the value returned is n or greater, the contents of
17171 the array pointed to by s1 are indeterminate.
17172 4 EXAMPLE The value of the following expression is the length of the array needed to hold the
17173 transformation of the wide string pointed to by s:
17178 1 + wcsxfrm(NULL, s, 0)
17180 7.28.4.4.5 The wmemcmp function
17182 1 #include <wchar.h>
17183 int wmemcmp(const wchar_t *s1, const wchar_t *s2,
17186 2 The wmemcmp function compares the first n wide characters of the object pointed to by
17187 s1 to the first n wide characters of the object pointed to by s2.
17189 3 The wmemcmp function returns an integer greater than, equal to, or less than zero,
17190 accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
17192 7.28.4.5 Wide string search functions
17193 7.28.4.5.1 The wcschr function
17195 1 #include <wchar.h>
17196 wchar_t *wcschr(const wchar_t *s, wchar_t c);
17198 2 The wcschr function locates the first occurrence of c in the wide string pointed to by s.
17199 The terminating null wide character is considered to be part of the wide string.
17201 3 The wcschr function returns a pointer to the located wide character, or a null pointer if
17202 the wide character does not occur in the wide string.
17203 7.28.4.5.2 The wcscspn function
17205 1 #include <wchar.h>
17206 size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
17208 2 The wcscspn function computes the length of the maximum initial segment of the wide
17209 string pointed to by s1 which consists entirely of wide characters not from the wide
17210 string pointed to by s2.
17217 3 The wcscspn function returns the length of the segment.
17218 7.28.4.5.3 The wcspbrk function
17220 1 #include <wchar.h>
17221 wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
17223 2 The wcspbrk function locates the first occurrence in the wide string pointed to by s1 of
17224 any wide character from the wide string pointed to by s2.
17226 3 The wcspbrk function returns a pointer to the wide character in s1, or a null pointer if
17227 no wide character from s2 occurs in s1.
17228 7.28.4.5.4 The wcsrchr function
17230 1 #include <wchar.h>
17231 wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
17233 2 The wcsrchr function locates the last occurrence of c in the wide string pointed to by
17234 s. The terminating null wide character is considered to be part of the wide string.
17236 3 The wcsrchr function returns a pointer to the wide character, or a null pointer if c does
17237 not occur in the wide string.
17238 7.28.4.5.5 The wcsspn function
17240 1 #include <wchar.h>
17241 size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
17243 2 The wcsspn function computes the length of the maximum initial segment of the wide
17244 string pointed to by s1 which consists entirely of wide characters from the wide string
17247 3 The wcsspn function returns the length of the segment.
17252 7.28.4.5.6 The wcsstr function
17254 1 #include <wchar.h>
17255 wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
17257 2 The wcsstr function locates the first occurrence in the wide string pointed to by s1 of
17258 the sequence of wide characters (excluding the terminating null wide character) in the
17259 wide string pointed to by s2.
17261 3 The wcsstr function returns a pointer to the located wide string, or a null pointer if the
17262 wide string is not found. If s2 points to a wide string with zero length, the function
17264 7.28.4.5.7 The wcstok function
17266 1 #include <wchar.h>
17267 wchar_t *wcstok(wchar_t * restrict s1,
17268 const wchar_t * restrict s2,
17269 wchar_t ** restrict ptr);
17271 2 A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into
17272 a sequence of tokens, each of which is delimited by a wide character from the wide string
17273 pointed to by s2. The third argument points to a caller-provided wchar_t pointer into
17274 which the wcstok function stores information necessary for it to continue scanning the
17276 3 The first call in a sequence has a non-null first argument and stores an initial value in the
17277 object pointed to by ptr. Subsequent calls in the sequence have a null first argument and
17278 the object pointed to by ptr is required to have the value stored by the previous call in
17279 the sequence, which is then updated. The separator wide string pointed to by s2 may be
17280 different from call to call.
17281 4 The first call in the sequence searches the wide string pointed to by s1 for the first wide
17282 character that is not contained in the current separator wide string pointed to by s2. If no
17283 such wide character is found, then there are no tokens in the wide string pointed to by s1
17284 and the wcstok function returns a null pointer. If such a wide character is found, it is
17285 the start of the first token.
17286 5 The wcstok function then searches from there for a wide character that is contained in
17287 the current separator wide string. If no such wide character is found, the current token
17290 extends to the end of the wide string pointed to by s1, and subsequent searches in the
17291 same wide string for a token return a null pointer. If such a wide character is found, it is
17292 overwritten by a null wide character, which terminates the current token.
17293 6 In all cases, the wcstok function stores sufficient information in the pointer pointed to
17294 by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
17295 value for ptr, shall start searching just past the element overwritten by a null wide
17296 character (if any).
17298 7 The wcstok function returns a pointer to the first wide character of a token, or a null
17299 pointer if there is no token.
17302 static wchar_t str1[] = L"?a???b,,,#c";
17303 static wchar_t str2[] = L"\t \t";
17304 wchar_t *t, *ptr1, *ptr2;
17305 t = wcstok(str1, L"?", &ptr1); // t points to the token L"a"
17306 t = wcstok(NULL, L",", &ptr1); // t points to the token L"??b"
17307 t = wcstok(str2, L" \t", &ptr2); // t is a null pointer
17308 t = wcstok(NULL, L"#,", &ptr1); // t points to the token L"c"
17309 t = wcstok(NULL, L"?", &ptr1); // t is a null pointer
17311 7.28.4.5.8 The wmemchr function
17313 1 #include <wchar.h>
17314 wchar_t *wmemchr(const wchar_t *s, wchar_t c,
17317 2 The wmemchr function locates the first occurrence of c in the initial n wide characters of
17318 the object pointed to by s.
17320 3 The wmemchr function returns a pointer to the located wide character, or a null pointer if
17321 the wide character does not occur in the object.
17328 7.28.4.6 Miscellaneous functions
17329 7.28.4.6.1 The wcslen function
17331 1 #include <wchar.h>
17332 size_t wcslen(const wchar_t *s);
17334 2 The wcslen function computes the length of the wide string pointed to by s.
17336 3 The wcslen function returns the number of wide characters that precede the terminating
17337 null wide character.
17338 7.28.4.6.2 The wmemset function
17340 1 #include <wchar.h>
17341 wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
17343 2 The wmemset function copies the value of c into each of the first n wide characters of
17344 the object pointed to by s.
17346 3 The wmemset function returns the value of s.
17347 7.28.5 Wide character time conversion functions
17348 7.28.5.1 The wcsftime function
17350 1 #include <time.h>
17352 size_t wcsftime(wchar_t * restrict s,
17354 const wchar_t * restrict format,
17355 const struct tm * restrict timeptr);
17357 2 The wcsftime function is equivalent to the strftime function, except that:
17358 -- The argument s points to the initial element of an array of wide characters into which
17359 the generated output is to be placed.
17364 -- The argument maxsize indicates the limiting number of wide characters.
17365 -- The argument format is a wide string and the conversion specifiers are replaced by
17366 corresponding sequences of wide characters.
17367 -- The return value indicates the number of wide characters.
17369 3 If the total number of resulting wide characters including the terminating null wide
17370 character is not more than maxsize, the wcsftime function returns the number of
17371 wide characters placed into the array pointed to by s not including the terminating null
17372 wide character. Otherwise, zero is returned and the contents of the array are
17374 7.28.6 Extended multibyte/wide character conversion utilities
17375 1 The header <wchar.h> declares an extended set of functions useful for conversion
17376 between multibyte characters and wide characters.
17377 2 Most of the following functions -- those that are listed as ''restartable'', 7.28.6.3 and
17378 7.28.6.4 -- take as a last argument a pointer to an object of type mbstate_t that is used
17379 to describe the current conversion state from a particular multibyte character sequence to
17380 a wide character sequence (or the reverse) under the rules of a particular setting for the
17381 LC_CTYPE category of the current locale.
17382 3 The initial conversion state corresponds, for a conversion in either direction, to the
17383 beginning of a new multibyte character in the initial shift state. A zero-valued
17384 mbstate_t object is (at least) one way to describe an initial conversion state. A zero-
17385 valued mbstate_t object can be used to initiate conversion involving any multibyte
17386 character sequence, in any LC_CTYPE category setting. If an mbstate_t object has
17387 been altered by any of the functions described in this subclause, and is then used with a
17388 different multibyte character sequence, or in the other conversion direction, or with a
17389 different LC_CTYPE category setting than on earlier function calls, the behavior is
17391 4 On entry, each function takes the described conversion state (either internal or pointed to
17392 by an argument) as current. The conversion state described by the referenced object is
17393 altered as needed to track the shift state, and the position within a multibyte character, for
17394 the associated multibyte character sequence.
17399 335) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc and
17400 mbsrtowcs functions as long as they are used to step sequentially through the same multibyte
17405 7.28.6.1 Single-byte/wide character conversion functions
17406 7.28.6.1.1 The btowc function
17408 1 #include <wchar.h> *
17409 wint_t btowc(int c);
17411 2 The btowc function determines whether c constitutes a valid single-byte character in the
17412 initial shift state.
17414 3 The btowc function returns WEOF if c has the value EOF or if (unsigned char)c
17415 does not constitute a valid single-byte character in the initial shift state. Otherwise, it
17416 returns the wide character representation of that character.
17417 7.28.6.1.2 The wctob function
17419 1 #include <wchar.h> *
17420 int wctob(wint_t c);
17422 2 The wctob function determines whether c corresponds to a member of the extended
17423 character set whose multibyte character representation is a single byte when in the initial
17426 3 The wctob function returns EOF if c does not correspond to a multibyte character with
17427 length one in the initial shift state. Otherwise, it returns the single-byte representation of
17428 that character as an unsigned char converted to an int.
17429 7.28.6.2 Conversion state functions
17430 7.28.6.2.1 The mbsinit function
17432 1 #include <wchar.h>
17433 int mbsinit(const mbstate_t *ps);
17435 2 If ps is not a null pointer, the mbsinit function determines whether the referenced
17436 mbstate_t object describes an initial conversion state.
17443 3 The mbsinit function returns nonzero if ps is a null pointer or if the referenced object
17444 describes an initial conversion state; otherwise, it returns zero.
17445 7.28.6.3 Restartable multibyte/wide character conversion functions
17446 1 These functions differ from the corresponding multibyte character functions of 7.22.7
17447 (mblen, mbtowc, and wctomb) in that they have an extra parameter, ps, of type
17448 pointer to mbstate_t that points to an object that can completely describe the current
17449 conversion state of the associated multibyte character sequence. If ps is a null pointer,
17450 each function uses its own internal mbstate_t object instead, which is initialized at
17451 program startup to the initial conversion state; the functions are not required to avoid data
17452 races in this case. The implementation behaves as if no library function calls these
17453 functions with a null pointer for ps.
17454 2 Also unlike their corresponding functions, the return value does not represent whether the
17455 encoding is state-dependent.
17456 7.28.6.3.1 The mbrlen function
17458 1 #include <wchar.h>
17459 size_t mbrlen(const char * restrict s,
17461 mbstate_t * restrict ps);
17463 2 The mbrlen function is equivalent to the call:
17464 mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)
17465 where internal is the mbstate_t object for the mbrlen function, except that the
17466 expression designated by ps is evaluated only once.
17468 3 The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2),
17470 Forward references: the mbrtowc function (7.28.6.3.2).
17477 7.28.6.3.2 The mbrtowc function
17479 1 #include <wchar.h>
17480 size_t mbrtowc(wchar_t * restrict pwc,
17481 const char * restrict s,
17483 mbstate_t * restrict ps);
17485 2 If s is a null pointer, the mbrtowc function is equivalent to the call:
17486 mbrtowc(NULL, "", 1, ps)
17487 In this case, the values of the parameters pwc and n are ignored.
17488 3 If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning with
17489 the byte pointed to by s to determine the number of bytes needed to complete the next
17490 multibyte character (including any shift sequences). If the function determines that the
17491 next multibyte character is complete and valid, it determines the value of the
17492 corresponding wide character and then, if pwc is not a null pointer, stores that value in
17493 the object pointed to by pwc. If the corresponding wide character is the null wide
17494 character, the resulting state described is the initial conversion state.
17496 4 The mbrtowc function returns the first of the following that applies (given the current
17498 0 if the next n or fewer bytes complete the multibyte character that
17499 corresponds to the null wide character (which is the value stored).
17500 between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
17501 character (which is the value stored); the value returned is the number
17502 of bytes that complete the multibyte character.
17503 (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
17504 multibyte character, and all n bytes have been processed (no value is
17506 (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
17507 do not contribute to a complete and valid multibyte character (no
17508 value is stored); the value of the macro EILSEQ is stored in errno,
17509 and the conversion state is unspecified.
17511 336) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
17512 sequence of redundant shift sequences (for implementations with state-dependent encodings).
17516 7.28.6.3.3 The wcrtomb function
17518 1 #include <wchar.h>
17519 size_t wcrtomb(char * restrict s,
17521 mbstate_t * restrict ps);
17523 2 If s is a null pointer, the wcrtomb function is equivalent to the call
17524 wcrtomb(buf, L'\0', ps)
17525 where buf is an internal buffer.
17526 3 If s is not a null pointer, the wcrtomb function determines the number of bytes needed
17527 to represent the multibyte character that corresponds to the wide character given by wc
17528 (including any shift sequences), and stores the multibyte character representation in the
17529 array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
17530 wc is a null wide character, a null byte is stored, preceded by any shift sequence needed
17531 to restore the initial shift state; the resulting state described is the initial conversion state.
17533 4 The wcrtomb function returns the number of bytes stored in the array object (including
17534 any shift sequences). When wc is not a valid wide character, an encoding error occurs:
17535 the function stores the value of the macro EILSEQ in errno and returns
17536 (size_t)(-1); the conversion state is unspecified.
17537 7.28.6.4 Restartable multibyte/wide string conversion functions
17538 1 These functions differ from the corresponding multibyte string functions of 7.22.8
17539 (mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer to
17540 mbstate_t that points to an object that can completely describe the current conversion
17541 state of the associated multibyte character sequence. If ps is a null pointer, each function
17542 uses its own internal mbstate_t object instead, which is initialized at program startup
17543 to the initial conversion state; the functions are not required to avoid data races in this
17544 case. The implementation behaves as if no library function calls these functions with a
17545 null pointer for ps.
17546 2 Also unlike their corresponding functions, the conversion source parameter, src, has a
17547 pointer-to-pointer type. When the function is storing the results of conversions (that is,
17548 when dst is not a null pointer), the pointer object pointed to by this parameter is updated
17549 to reflect the amount of the source processed by that invocation.
17556 7.28.6.4.1 The mbsrtowcs function
17558 1 #include <wchar.h>
17559 size_t mbsrtowcs(wchar_t * restrict dst,
17560 const char ** restrict src,
17562 mbstate_t * restrict ps);
17564 2 The mbsrtowcs function converts a sequence of multibyte characters that begins in the
17565 conversion state described by the object pointed to by ps, from the array indirectly
17566 pointed to by src into a sequence of corresponding wide characters. If dst is not a null
17567 pointer, the converted characters are stored into the array pointed to by dst. Conversion
17568 continues up to and including a terminating null character, which is also stored.
17569 Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
17570 not form a valid multibyte character, or (if dst is not a null pointer) when len wide
17571 characters have been stored into the array pointed to by dst.337) Each conversion takes
17572 place as if by a call to the mbrtowc function.
17573 3 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
17574 pointer (if conversion stopped due to reaching a terminating null character) or the address
17575 just past the last multibyte character converted (if any). If conversion stopped due to
17576 reaching a terminating null character and if dst is not a null pointer, the resulting state
17577 described is the initial conversion state.
17579 4 If the input conversion encounters a sequence of bytes that do not form a valid multibyte
17580 character, an encoding error occurs: the mbsrtowcs function stores the value of the
17581 macro EILSEQ in errno and returns (size_t)(-1); the conversion state is
17582 unspecified. Otherwise, it returns the number of multibyte characters successfully
17583 converted, not including the terminating null character (if any).
17588 337) Thus, the value of len is ignored if dst is a null pointer.
17592 7.28.6.4.2 The wcsrtombs function
17594 1 #include <wchar.h>
17595 size_t wcsrtombs(char * restrict dst,
17596 const wchar_t ** restrict src,
17598 mbstate_t * restrict ps);
17600 2 The wcsrtombs function converts a sequence of wide characters from the array
17601 indirectly pointed to by src into a sequence of corresponding multibyte characters that
17602 begins in the conversion state described by the object pointed to by ps. If dst is not a
17603 null pointer, the converted characters are then stored into the array pointed to by dst.
17604 Conversion continues up to and including a terminating null wide character, which is also
17605 stored. Conversion stops earlier in two cases: when a wide character is reached that does
17606 not correspond to a valid multibyte character, or (if dst is not a null pointer) when the
17607 next multibyte character would exceed the limit of len total bytes to be stored into the
17608 array pointed to by dst. Each conversion takes place as if by a call to the wcrtomb
17610 3 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
17611 pointer (if conversion stopped due to reaching a terminating null wide character) or the
17612 address just past the last wide character converted (if any). If conversion stopped due to
17613 reaching a terminating null wide character, the resulting state described is the initial
17616 4 If conversion stops because a wide character is reached that does not correspond to a
17617 valid multibyte character, an encoding error occurs: the wcsrtombs function stores the
17618 value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion
17619 state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte
17620 character sequence, not including the terminating null character (if any).
17625 338) If conversion stops because a terminating null wide character has been reached, the bytes stored
17626 include those necessary to reach the initial shift state immediately before the null byte.
17630 7.29 Wide character classification and mapping utilities <wctype.h>
17631 7.29.1 Introduction
17632 1 The header <wctype.h> defines one macro, and declares three data types and many
17634 2 The types declared are
17636 described in 7.28.1;
17638 which is a scalar type that can hold values which represent locale-specific character
17641 which is a scalar type that can hold values which represent locale-specific character
17643 3 The macro defined is WEOF (described in 7.28.1).
17644 4 The functions declared are grouped as follows:
17645 -- Functions that provide wide character classification;
17646 -- Extensible functions that provide wide character classification;
17647 -- Functions that provide wide character case mapping;
17648 -- Extensible functions that provide wide character mapping.
17649 5 For all functions described in this subclause that accept an argument of type wint_t, the
17650 value shall be representable as a wchar_t or shall equal the value of the macro WEOF. If
17651 this argument has any other value, the behavior is undefined.
17652 6 The behavior of these functions is affected by the LC_CTYPE category of the current
17658 339) See ''future library directions'' (7.30.13).
17662 7.29.2 Wide character classification utilities
17663 1 The header <wctype.h> declares several functions useful for classifying wide
17665 2 The term printing wide character refers to a member of a locale-specific set of wide
17666 characters, each of which occupies at least one printing position on a display device. The
17667 term control wide character refers to a member of a locale-specific set of wide characters
17668 that are not printing wide characters.
17669 7.29.2.1 Wide character classification functions
17670 1 The functions in this subclause return nonzero (true) if and only if the value of the
17671 argument wc conforms to that in the description of the function.
17672 2 Each of the following functions returns true for each wide character that corresponds (as
17673 if by a call to the wctob function) to a single-byte character for which the corresponding
17674 character classification function from 7.4.1 returns true, except that the iswgraph and
17675 iswpunct functions may differ with respect to wide characters other than L' ' that are
17676 both printing and white-space wide characters.340)
17677 Forward references: the wctob function (7.28.6.1.2).
17678 7.29.2.1.1 The iswalnum function
17680 1 #include <wctype.h>
17681 int iswalnum(wint_t wc);
17683 2 The iswalnum function tests for any wide character for which iswalpha or
17685 7.29.2.1.2 The iswalpha function
17687 1 #include <wctype.h>
17688 int iswalpha(wint_t wc);
17690 2 The iswalpha function tests for any wide character for which iswupper or
17691 iswlower is true, or any wide character that is one of a locale-specific set of alphabetic
17693 340) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call
17694 iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true
17695 (which cannot occur for wc == L' ' of course), then either iswgraph(wc) or iswprint(wc)
17696 && iswspace(wc) is true, but not both.
17700 wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace
17702 7.29.2.1.3 The iswblank function
17704 1 #include <wctype.h>
17705 int iswblank(wint_t wc);
17707 2 The iswblank function tests for any wide character that is a standard blank wide
17708 character or is one of a locale-specific set of wide characters for which iswspace is true
17709 and that is used to separate words within a line of text. The standard blank wide
17710 characters are the following: space (L' '), and horizontal tab (L'\t'). In the "C"
17711 locale, iswblank returns true only for the standard blank characters.
17712 7.29.2.1.4 The iswcntrl function
17714 1 #include <wctype.h>
17715 int iswcntrl(wint_t wc);
17717 2 The iswcntrl function tests for any control wide character.
17718 7.29.2.1.5 The iswdigit function
17720 1 #include <wctype.h>
17721 int iswdigit(wint_t wc);
17723 2 The iswdigit function tests for any wide character that corresponds to a decimal-digit
17724 character (as defined in 5.2.1).
17725 7.29.2.1.6 The iswgraph function
17727 1 #include <wctype.h>
17728 int iswgraph(wint_t wc);
17733 341) The functions iswlower and iswupper test true or false separately for each of these additional
17734 wide characters; all four combinations are possible.
17739 2 The iswgraph function tests for any wide character for which iswprint is true and
17740 iswspace is false.342)
17741 7.29.2.1.7 The iswlower function
17743 1 #include <wctype.h>
17744 int iswlower(wint_t wc);
17746 2 The iswlower function tests for any wide character that corresponds to a lowercase
17747 letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
17748 iswdigit, iswpunct, or iswspace is true.
17749 7.29.2.1.8 The iswprint function
17751 1 #include <wctype.h>
17752 int iswprint(wint_t wc);
17754 2 The iswprint function tests for any printing wide character.
17755 7.29.2.1.9 The iswpunct function
17757 1 #include <wctype.h>
17758 int iswpunct(wint_t wc);
17760 2 The iswpunct function tests for any printing wide character that is one of a locale-
17761 specific set of punctuation wide characters for which neither iswspace nor iswalnum
17763 7.29.2.1.10 The iswspace function
17765 1 #include <wctype.h>
17766 int iswspace(wint_t wc);
17770 342) Note that the behavior of the iswgraph and iswpunct functions may differ from their
17771 corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution
17772 characters other than ' '.
17777 2 The iswspace function tests for any wide character that corresponds to a locale-specific
17778 set of white-space wide characters for which none of iswalnum, iswgraph, or
17780 7.29.2.1.11 The iswupper function
17782 1 #include <wctype.h>
17783 int iswupper(wint_t wc);
17785 2 The iswupper function tests for any wide character that corresponds to an uppercase
17786 letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
17787 iswdigit, iswpunct, or iswspace is true.
17788 7.29.2.1.12 The iswxdigit function
17790 1 #include <wctype.h>
17791 int iswxdigit(wint_t wc);
17793 2 The iswxdigit function tests for any wide character that corresponds to a
17794 hexadecimal-digit character (as defined in 6.4.4.1).
17795 7.29.2.2 Extensible wide character classification functions
17796 1 The functions wctype and iswctype provide extensible wide character classification
17797 as well as testing equivalent to that performed by the functions described in the previous
17798 subclause (7.29.2.1).
17799 7.29.2.2.1 The iswctype function
17801 1 #include <wctype.h>
17802 int iswctype(wint_t wc, wctype_t desc);
17804 2 The iswctype function determines whether the wide character wc has the property
17805 described by desc. The current setting of the LC_CTYPE category shall be the same as
17806 during the call to wctype that returned the value desc.
17807 3 Each of the following expressions has a truth-value equivalent to the call to the wide
17808 character classification function (7.29.2.1) in the comment that follows the expression:
17813 iswctype(wc, wctype("alnum")) // iswalnum(wc)
17814 iswctype(wc, wctype("alpha")) // iswalpha(wc)
17815 iswctype(wc, wctype("blank")) // iswblank(wc)
17816 iswctype(wc, wctype("cntrl")) // iswcntrl(wc)
17817 iswctype(wc, wctype("digit")) // iswdigit(wc)
17818 iswctype(wc, wctype("graph")) // iswgraph(wc)
17819 iswctype(wc, wctype("lower")) // iswlower(wc)
17820 iswctype(wc, wctype("print")) // iswprint(wc)
17821 iswctype(wc, wctype("punct")) // iswpunct(wc)
17822 iswctype(wc, wctype("space")) // iswspace(wc)
17823 iswctype(wc, wctype("upper")) // iswupper(wc)
17824 iswctype(wc, wctype("xdigit")) // iswxdigit(wc)
17826 4 The iswctype function returns nonzero (true) if and only if the value of the wide
17827 character wc has the property described by desc. If desc is zero, the iswctype
17828 function returns zero (false).
17829 Forward references: the wctype function (7.29.2.2.2).
17830 7.29.2.2.2 The wctype function
17832 1 #include <wctype.h>
17833 wctype_t wctype(const char *property);
17835 2 The wctype function constructs a value with type wctype_t that describes a class of
17836 wide characters identified by the string argument property.
17837 3 The strings listed in the description of the iswctype function shall be valid in all
17838 locales as property arguments to the wctype function.
17840 4 If property identifies a valid class of wide characters according to the LC_CTYPE
17841 category of the current locale, the wctype function returns a nonzero value that is valid
17842 as the second argument to the iswctype function; otherwise, it returns zero.
17849 7.29.3 Wide character case mapping utilities
17850 1 The header <wctype.h> declares several functions useful for mapping wide characters.
17851 7.29.3.1 Wide character case mapping functions
17852 7.29.3.1.1 The towlower function
17854 1 #include <wctype.h>
17855 wint_t towlower(wint_t wc);
17857 2 The towlower function converts an uppercase letter to a corresponding lowercase letter.
17859 3 If the argument is a wide character for which iswupper is true and there are one or
17860 more corresponding wide characters, as specified by the current locale, for which
17861 iswlower is true, the towlower function returns one of the corresponding wide
17862 characters (always the same one for any given locale); otherwise, the argument is
17863 returned unchanged.
17864 7.29.3.1.2 The towupper function
17866 1 #include <wctype.h>
17867 wint_t towupper(wint_t wc);
17869 2 The towupper function converts a lowercase letter to a corresponding uppercase letter.
17871 3 If the argument is a wide character for which iswlower is true and there are one or
17872 more corresponding wide characters, as specified by the current locale, for which
17873 iswupper is true, the towupper function returns one of the corresponding wide
17874 characters (always the same one for any given locale); otherwise, the argument is
17875 returned unchanged.
17876 7.29.3.2 Extensible wide character case mapping functions
17877 1 The functions wctrans and towctrans provide extensible wide character mapping as
17878 well as case mapping equivalent to that performed by the functions described in the
17879 previous subclause (7.29.3.1).
17886 7.29.3.2.1 The towctrans function
17888 1 #include <wctype.h>
17889 wint_t towctrans(wint_t wc, wctrans_t desc);
17891 2 The towctrans function maps the wide character wc using the mapping described by
17892 desc. The current setting of the LC_CTYPE category shall be the same as during the call
17893 to wctrans that returned the value desc.
17894 3 Each of the following expressions behaves the same as the call to the wide character case
17895 mapping function (7.29.3.1) in the comment that follows the expression:
17896 towctrans(wc, wctrans("tolower")) // towlower(wc)
17897 towctrans(wc, wctrans("toupper")) // towupper(wc)
17899 4 The towctrans function returns the mapped value of wc using the mapping described
17900 by desc. If desc is zero, the towctrans function returns the value of wc.
17901 7.29.3.2.2 The wctrans function
17903 1 #include <wctype.h>
17904 wctrans_t wctrans(const char *property);
17906 2 The wctrans function constructs a value with type wctrans_t that describes a
17907 mapping between wide characters identified by the string argument property.
17908 3 The strings listed in the description of the towctrans function shall be valid in all
17909 locales as property arguments to the wctrans function.
17911 4 If property identifies a valid mapping of wide characters according to the LC_CTYPE
17912 category of the current locale, the wctrans function returns a nonzero value that is valid
17913 as the second argument to the towctrans function; otherwise, it returns zero.
17920 7.30 Future library directions
17921 1 The following names are grouped under individual headers for convenience. All external
17922 names described below are reserved no matter what headers are included by the program.
17923 7.30.1 Complex arithmetic <complex.h>
17924 1 The function names
17926 cerfc clog10 clgamma
17927 cexp2 clog1p ctgamma
17928 and the same names suffixed with f or l may be added to the declarations in the
17929 <complex.h> header.
17930 7.30.2 Character handling <ctype.h>
17931 1 Function names that begin with either is or to, and a lowercase letter may be added to
17932 the declarations in the <ctype.h> header.
17933 7.30.3 Errors <errno.h>
17934 1 Macros that begin with E and a digit or E and an uppercase letter may be added to the
17935 declarations in the <errno.h> header.
17936 7.30.4 Format conversion of integer types <inttypes.h>
17937 1 Macro names beginning with PRI or SCN followed by any lowercase letter or X may be
17938 added to the macros defined in the <inttypes.h> header.
17939 7.30.5 Localization <locale.h>
17940 1 Macros that begin with LC_ and an uppercase letter may be added to the definitions in
17941 the <locale.h> header.
17942 7.30.6 Signal handling <signal.h>
17943 1 Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase
17944 letter may be added to the definitions in the <signal.h> header.
17945 7.30.7 Boolean type and values <stdbool.h>
17946 1 The ability to undefine and perhaps then redefine the macros bool, true, and false is
17947 an obsolescent feature.
17948 7.30.8 Integer types <stdint.h>
17949 1 Typedef names beginning with int or uint and ending with _t may be added to the
17950 types defined in the <stdint.h> header. Macro names beginning with INT or UINT
17951 and ending with _MAX, _MIN, or _C may be added to the macros defined in the
17956 7.30.9 Input/output <stdio.h>
17957 1 Lowercase letters may be added to the conversion specifiers and length modifiers in
17958 fprintf and fscanf. Other characters may be used in extensions.
17959 2 The use of ungetc on a binary stream where the file position indicator is zero prior to *
17960 the call is an obsolescent feature.
17961 7.30.10 General utilities <stdlib.h>
17962 1 Function names that begin with str and a lowercase letter may be added to the
17963 declarations in the <stdlib.h> header.
17964 7.30.11 String handling <string.h>
17965 1 Function names that begin with str, mem, or wcs and a lowercase letter may be added
17966 to the declarations in the <string.h> header.
17967 7.30.12 Extended multibyte and wide character utilities <wchar.h>
17968 1 Function names that begin with wcs and a lowercase letter may be added to the
17969 declarations in the <wchar.h> header.
17970 2 Lowercase letters may be added to the conversion specifiers and length modifiers in
17971 fwprintf and fwscanf. Other characters may be used in extensions.
17972 7.30.13 Wide character classification and mapping utilities
17974 1 Function names that begin with is or to and a lowercase letter may be added to the
17975 declarations in the <wctype.h> header.
17984 Language syntax summary
17985 1 NOTE The notation is described in 6.1.
17987 A.1 Lexical grammar
17988 A.1.1 Lexical elements
17995 (6.4) preprocessing-token:
18002 each non-white-space character that cannot be one of the above
18010 (6.4.1) keyword: one of
18016 const register _Alignas
18017 continue restrict _Atomic
18018 default return _Bool
18020 double signed _Generic
18021 else sizeof _Imaginary
18022 enum static _Noreturn
18023 extern struct _Static_assert
18024 float switch _Thread_local
18027 (6.4.2.1) identifier:
18028 identifier-nondigit
18029 identifier identifier-nondigit
18031 (6.4.2.1) identifier-nondigit:
18033 universal-character-name
18034 other implementation-defined characters
18035 (6.4.2.1) nondigit: one of
18036 _ a b c d e f g h i j k l m
18037 n o p q r s t u v w x y z
18038 A B C D E F G H I J K L M
18039 N O P Q R S T U V W X Y Z
18040 (6.4.2.1) digit: one of
18041 0 1 2 3 4 5 6 7 8 9
18048 A.1.4 Universal character names
18049 (6.4.3) universal-character-name:
18051 \U hex-quad hex-quad
18053 hexadecimal-digit hexadecimal-digit
18054 hexadecimal-digit hexadecimal-digit
18059 enumeration-constant
18061 (6.4.4.1) integer-constant:
18062 decimal-constant integer-suffixopt
18063 octal-constant integer-suffixopt
18064 hexadecimal-constant integer-suffixopt
18065 (6.4.4.1) decimal-constant:
18067 decimal-constant digit
18068 (6.4.4.1) octal-constant:
18070 octal-constant octal-digit
18071 (6.4.4.1) hexadecimal-constant:
18072 hexadecimal-prefix hexadecimal-digit
18073 hexadecimal-constant hexadecimal-digit
18074 (6.4.4.1) hexadecimal-prefix: one of
18076 (6.4.4.1) nonzero-digit: one of
18078 (6.4.4.1) octal-digit: one of
18086 (6.4.4.1) hexadecimal-digit: one of
18087 0 1 2 3 4 5 6 7 8 9
18090 (6.4.4.1) integer-suffix:
18091 unsigned-suffix long-suffixopt
18092 unsigned-suffix long-long-suffix
18093 long-suffix unsigned-suffixopt
18094 long-long-suffix unsigned-suffixopt
18095 (6.4.4.1) unsigned-suffix: one of
18097 (6.4.4.1) long-suffix: one of
18099 (6.4.4.1) long-long-suffix: one of
18101 (6.4.4.2) floating-constant:
18102 decimal-floating-constant
18103 hexadecimal-floating-constant
18104 (6.4.4.2) decimal-floating-constant:
18105 fractional-constant exponent-partopt floating-suffixopt
18106 digit-sequence exponent-part floating-suffixopt
18107 (6.4.4.2) hexadecimal-floating-constant:
18108 hexadecimal-prefix hexadecimal-fractional-constant
18109 binary-exponent-part floating-suffixopt
18110 hexadecimal-prefix hexadecimal-digit-sequence
18111 binary-exponent-part floating-suffixopt
18112 (6.4.4.2) fractional-constant:
18113 digit-sequenceopt . digit-sequence
18115 (6.4.4.2) exponent-part:
18116 e signopt digit-sequence
18117 E signopt digit-sequence
18118 (6.4.4.2) sign: one of
18125 (6.4.4.2) digit-sequence:
18127 digit-sequence digit
18128 (6.4.4.2) hexadecimal-fractional-constant:
18129 hexadecimal-digit-sequenceopt .
18130 hexadecimal-digit-sequence
18131 hexadecimal-digit-sequence .
18132 (6.4.4.2) binary-exponent-part:
18133 p signopt digit-sequence
18134 P signopt digit-sequence
18135 (6.4.4.2) hexadecimal-digit-sequence:
18137 hexadecimal-digit-sequence hexadecimal-digit
18138 (6.4.4.2) floating-suffix: one of
18140 (6.4.4.3) enumeration-constant:
18142 (6.4.4.4) character-constant:
18143 ' c-char-sequence '
18144 L' c-char-sequence '
18145 u' c-char-sequence '
18146 U' c-char-sequence '
18147 (6.4.4.4) c-char-sequence:
18149 c-char-sequence c-char
18151 any member of the source character set except
18152 the single-quote ', backslash \, or new-line character
18154 (6.4.4.4) escape-sequence:
18155 simple-escape-sequence
18156 octal-escape-sequence
18157 hexadecimal-escape-sequence
18158 universal-character-name
18165 (6.4.4.4) simple-escape-sequence: one of
18167 \a \b \f \n \r \t \v
18168 (6.4.4.4) octal-escape-sequence:
18170 \ octal-digit octal-digit
18171 \ octal-digit octal-digit octal-digit
18172 (6.4.4.4) hexadecimal-escape-sequence:
18173 \x hexadecimal-digit
18174 hexadecimal-escape-sequence hexadecimal-digit
18175 A.1.6 String literals
18176 (6.4.5) string-literal:
18177 encoding-prefixopt " s-char-sequenceopt "
18178 (6.4.5) encoding-prefix:
18183 (6.4.5) s-char-sequence:
18185 s-char-sequence s-char
18187 any member of the source character set except
18188 the double-quote ", backslash \, or new-line character
18191 (6.4.6) punctuator: one of
18194 / % << >> < > <= >= == != ^ | && ||
18196 = *= /= %= += -= <<= >>= &= ^= |=
18198 <: :> <% %> %: %:%:
18206 (6.4.7) header-name:
18207 < h-char-sequence >
18208 " q-char-sequence "
18209 (6.4.7) h-char-sequence:
18211 h-char-sequence h-char
18213 any member of the source character set except
18214 the new-line character and >
18215 (6.4.7) q-char-sequence:
18217 q-char-sequence q-char
18219 any member of the source character set except
18220 the new-line character and "
18221 A.1.9 Preprocessing numbers
18226 pp-number identifier-nondigit
18238 A.2 Phrase structure grammar
18240 (6.5.1) primary-expression:
18246 (6.5.1.1) generic-selection:
18247 _Generic ( assignment-expression , generic-assoc-list )
18248 (6.5.1.1) generic-assoc-list:
18249 generic-association
18250 generic-assoc-list , generic-association
18251 (6.5.1.1) generic-association:
18252 type-name : assignment-expression
18253 default : assignment-expression
18254 (6.5.2) postfix-expression:
18256 postfix-expression [ expression ]
18257 postfix-expression ( argument-expression-listopt )
18258 postfix-expression . identifier
18259 postfix-expression -> identifier
18260 postfix-expression ++
18261 postfix-expression --
18262 ( type-name ) { initializer-list }
18263 ( type-name ) { initializer-list , }
18264 (6.5.2) argument-expression-list:
18265 assignment-expression
18266 argument-expression-list , assignment-expression
18267 (6.5.3) unary-expression:
18269 ++ unary-expression
18270 -- unary-expression
18271 unary-operator cast-expression
18272 sizeof unary-expression
18273 sizeof ( type-name )
18274 alignof ( type-name )
18278 (6.5.3) unary-operator: one of
18280 (6.5.4) cast-expression:
18282 ( type-name ) cast-expression
18283 (6.5.5) multiplicative-expression:
18285 multiplicative-expression * cast-expression
18286 multiplicative-expression / cast-expression
18287 multiplicative-expression % cast-expression
18288 (6.5.6) additive-expression:
18289 multiplicative-expression
18290 additive-expression + multiplicative-expression
18291 additive-expression - multiplicative-expression
18292 (6.5.7) shift-expression:
18293 additive-expression
18294 shift-expression << additive-expression
18295 shift-expression >> additive-expression
18296 (6.5.8) relational-expression:
18298 relational-expression < shift-expression
18299 relational-expression > shift-expression
18300 relational-expression <= shift-expression
18301 relational-expression >= shift-expression
18302 (6.5.9) equality-expression:
18303 relational-expression
18304 equality-expression == relational-expression
18305 equality-expression != relational-expression
18306 (6.5.10) AND-expression:
18307 equality-expression
18308 AND-expression & equality-expression
18309 (6.5.11) exclusive-OR-expression:
18311 exclusive-OR-expression ^ AND-expression
18318 (6.5.12) inclusive-OR-expression:
18319 exclusive-OR-expression
18320 inclusive-OR-expression | exclusive-OR-expression
18321 (6.5.13) logical-AND-expression:
18322 inclusive-OR-expression
18323 logical-AND-expression && inclusive-OR-expression
18324 (6.5.14) logical-OR-expression:
18325 logical-AND-expression
18326 logical-OR-expression || logical-AND-expression
18327 (6.5.15) conditional-expression:
18328 logical-OR-expression
18329 logical-OR-expression ? expression : conditional-expression
18330 (6.5.16) assignment-expression:
18331 conditional-expression
18332 unary-expression assignment-operator assignment-expression
18333 (6.5.16) assignment-operator: one of
18334 = *= /= %= += -= <<= >>= &= ^= |=
18335 (6.5.17) expression:
18336 assignment-expression
18337 expression , assignment-expression
18338 (6.6) constant-expression:
18339 conditional-expression
18342 declaration-specifiers init-declarator-listopt ;
18343 static_assert-declaration
18344 (6.7) declaration-specifiers:
18345 storage-class-specifier declaration-specifiersopt
18346 type-specifier declaration-specifiersopt
18347 type-qualifier declaration-specifiersopt
18348 function-specifier declaration-specifiersopt
18349 alignment-specifier declaration-specifiersopt
18350 (6.7) init-declarator-list:
18352 init-declarator-list , init-declarator
18357 (6.7) init-declarator:
18359 declarator = initializer
18360 (6.7.1) storage-class-specifier:
18367 (6.7.2) type-specifier:
18379 atomic-type-specifier
18380 struct-or-union-specifier
18383 (6.7.2.1) struct-or-union-specifier:
18384 struct-or-union identifieropt { struct-declaration-list }
18385 struct-or-union identifier
18386 (6.7.2.1) struct-or-union:
18389 (6.7.2.1) struct-declaration-list:
18391 struct-declaration-list struct-declaration
18392 (6.7.2.1) struct-declaration:
18393 specifier-qualifier-list struct-declarator-listopt ;
18394 static_assert-declaration
18398 (6.7.2.1) specifier-qualifier-list:
18399 type-specifier specifier-qualifier-listopt
18400 type-qualifier specifier-qualifier-listopt
18401 (6.7.2.1) struct-declarator-list:
18403 struct-declarator-list , struct-declarator
18404 (6.7.2.1) struct-declarator:
18406 declaratoropt : constant-expression
18407 (6.7.2.2) enum-specifier:
18408 enum identifieropt { enumerator-list }
18409 enum identifieropt { enumerator-list , }
18411 (6.7.2.2) enumerator-list:
18413 enumerator-list , enumerator
18414 (6.7.2.2) enumerator:
18415 enumeration-constant
18416 enumeration-constant = constant-expression
18417 (6.7.2.4) atomic-type-specifier:
18418 _Atomic ( type-name )
18419 (6.7.3) type-qualifier:
18424 (6.7.4) function-specifier:
18427 (6.7.5) alignment-specifier:
18428 _Alignas ( type-name )
18429 _Alignas ( constant-expression )
18430 (6.7.6) declarator:
18431 pointeropt direct-declarator
18437 (6.7.6) direct-declarator:
18440 direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
18441 direct-declarator [ static type-qualifier-listopt assignment-expression ]
18442 direct-declarator [ type-qualifier-list static assignment-expression ]
18443 direct-declarator [ type-qualifier-listopt * ]
18444 direct-declarator ( parameter-type-list )
18445 direct-declarator ( identifier-listopt )
18447 * type-qualifier-listopt
18448 * type-qualifier-listopt pointer
18449 (6.7.6) type-qualifier-list:
18451 type-qualifier-list type-qualifier
18452 (6.7.6) parameter-type-list:
18454 parameter-list , ...
18455 (6.7.6) parameter-list:
18456 parameter-declaration
18457 parameter-list , parameter-declaration
18458 (6.7.6) parameter-declaration:
18459 declaration-specifiers declarator
18460 declaration-specifiers abstract-declaratoropt
18461 (6.7.6) identifier-list:
18463 identifier-list , identifier
18465 specifier-qualifier-list abstract-declaratoropt
18466 (6.7.7) abstract-declarator:
18468 pointeropt direct-abstract-declarator
18475 (6.7.7) direct-abstract-declarator:
18476 ( abstract-declarator )
18477 direct-abstract-declaratoropt [ type-qualifier-listopt
18478 assignment-expressionopt ]
18479 direct-abstract-declaratoropt [ static type-qualifier-listopt
18480 assignment-expression ]
18481 direct-abstract-declaratoropt [ type-qualifier-list static
18482 assignment-expression ]
18483 direct-abstract-declaratoropt [ * ]
18484 direct-abstract-declaratoropt ( parameter-type-listopt )
18485 (6.7.8) typedef-name:
18487 (6.7.9) initializer:
18488 assignment-expression
18489 { initializer-list }
18490 { initializer-list , }
18491 (6.7.9) initializer-list:
18492 designationopt initializer
18493 initializer-list , designationopt initializer
18494 (6.7.9) designation:
18496 (6.7.9) designator-list:
18498 designator-list designator
18499 (6.7.9) designator:
18500 [ constant-expression ]
18502 (6.7.10) static_assert-declaration:
18503 _Static_assert ( constant-expression , string-literal ) ;
18514 expression-statement
18515 selection-statement
18516 iteration-statement
18518 (6.8.1) labeled-statement:
18519 identifier : statement
18520 case constant-expression : statement
18521 default : statement
18522 (6.8.2) compound-statement:
18523 { block-item-listopt }
18524 (6.8.2) block-item-list:
18526 block-item-list block-item
18527 (6.8.2) block-item:
18530 (6.8.3) expression-statement:
18532 (6.8.4) selection-statement:
18533 if ( expression ) statement
18534 if ( expression ) statement else statement
18535 switch ( expression ) statement
18536 (6.8.5) iteration-statement:
18537 while ( expression ) statement
18538 do statement while ( expression ) ;
18539 for ( expressionopt ; expressionopt ; expressionopt ) statement
18540 for ( declaration expressionopt ; expressionopt ) statement
18541 (6.8.6) jump-statement:
18545 return expressionopt ;
18549 A.2.4 External definitions
18550 (6.9) translation-unit:
18551 external-declaration
18552 translation-unit external-declaration
18553 (6.9) external-declaration:
18554 function-definition
18556 (6.9.1) function-definition:
18557 declaration-specifiers declarator declaration-listopt compound-statement
18558 (6.9.1) declaration-list:
18560 declaration-list declaration
18561 A.3 Preprocessing directives
18562 (6.10) preprocessing-file:
18573 if-group elif-groupsopt else-groupopt endif-line
18575 # if constant-expression new-line groupopt
18576 # ifdef identifier new-line groupopt
18577 # ifndef identifier new-line groupopt
18578 (6.10) elif-groups:
18580 elif-groups elif-group
18582 # elif constant-expression new-line groupopt
18588 # else new-line groupopt
18591 (6.10) control-line:
18592 # include pp-tokens new-line
18593 # define identifier replacement-list new-line
18594 # define identifier lparen identifier-listopt )
18595 replacement-list new-line
18596 # define identifier lparen ... ) replacement-list new-line
18597 # define identifier lparen identifier-list , ... )
18598 replacement-list new-line
18599 # undef identifier new-line
18600 # line pp-tokens new-line
18601 # error pp-tokensopt new-line
18602 # pragma pp-tokensopt new-line
18605 pp-tokensopt new-line
18606 (6.10) non-directive:
18609 a ( character not immediately preceded by white-space
18610 (6.10) replacement-list:
18613 preprocessing-token
18614 pp-tokens preprocessing-token
18616 the new-line character
18626 B.1 Diagnostics <assert.h>
18629 void assert(scalar expression);
18630 B.2 Complex <complex.h>
18631 __STDC_NO_COMPLEX__ imaginary
18632 complex _Imaginary_I
18634 #pragma STDC CX_LIMITED_RANGE on-off-switch
18635 double complex cacos(double complex z);
18636 float complex cacosf(float complex z);
18637 long double complex cacosl(long double complex z);
18638 double complex casin(double complex z);
18639 float complex casinf(float complex z);
18640 long double complex casinl(long double complex z);
18641 double complex catan(double complex z);
18642 float complex catanf(float complex z);
18643 long double complex catanl(long double complex z);
18644 double complex ccos(double complex z);
18645 float complex ccosf(float complex z);
18646 long double complex ccosl(long double complex z);
18647 double complex csin(double complex z);
18648 float complex csinf(float complex z);
18649 long double complex csinl(long double complex z);
18650 double complex ctan(double complex z);
18651 float complex ctanf(float complex z);
18652 long double complex ctanl(long double complex z);
18653 double complex cacosh(double complex z);
18654 float complex cacoshf(float complex z);
18655 long double complex cacoshl(long double complex z);
18656 double complex casinh(double complex z);
18657 float complex casinhf(float complex z);
18658 long double complex casinhl(long double complex z);
18662 double complex catanh(double complex z);
18663 float complex catanhf(float complex z);
18664 long double complex catanhl(long double complex z);
18665 double complex ccosh(double complex z);
18666 float complex ccoshf(float complex z);
18667 long double complex ccoshl(long double complex z);
18668 double complex csinh(double complex z);
18669 float complex csinhf(float complex z);
18670 long double complex csinhl(long double complex z);
18671 double complex ctanh(double complex z);
18672 float complex ctanhf(float complex z);
18673 long double complex ctanhl(long double complex z);
18674 double complex cexp(double complex z);
18675 float complex cexpf(float complex z);
18676 long double complex cexpl(long double complex z);
18677 double complex clog(double complex z);
18678 float complex clogf(float complex z);
18679 long double complex clogl(long double complex z);
18680 double cabs(double complex z);
18681 float cabsf(float complex z);
18682 long double cabsl(long double complex z);
18683 double complex cpow(double complex x, double complex y);
18684 float complex cpowf(float complex x, float complex y);
18685 long double complex cpowl(long double complex x,
18686 long double complex y);
18687 double complex csqrt(double complex z);
18688 float complex csqrtf(float complex z);
18689 long double complex csqrtl(long double complex z);
18690 double carg(double complex z);
18691 float cargf(float complex z);
18692 long double cargl(long double complex z);
18693 double cimag(double complex z);
18694 float cimagf(float complex z);
18695 long double cimagl(long double complex z);
18696 double complex CMPLX(double x, double y);
18697 float complex CMPLXF(float x, float y);
18698 long double complex CMPLXL(long double x, long double y);
18699 double complex conj(double complex z);
18700 float complex conjf(float complex z);
18701 long double complex conjl(long double complex z);
18702 double complex cproj(double complex z);
18706 float complex cprojf(float complex z);
18707 long double complex cprojl(long double complex z);
18708 double creal(double complex z);
18709 float crealf(float complex z);
18710 long double creall(long double complex z);
18711 B.3 Character handling <ctype.h>
18712 int isalnum(int c);
18713 int isalpha(int c);
18714 int isblank(int c);
18715 int iscntrl(int c);
18716 int isdigit(int c);
18717 int isgraph(int c);
18718 int islower(int c);
18719 int isprint(int c);
18720 int ispunct(int c);
18721 int isspace(int c);
18722 int isupper(int c);
18723 int isxdigit(int c);
18724 int tolower(int c);
18725 int toupper(int c);
18726 B.4 Errors <errno.h>
18727 EDOM EILSEQ ERANGE errno
18728 __STDC_WANT_LIB_EXT1__
18730 B.5 Floating-point environment <fenv.h>
18731 fenv_t FE_OVERFLOW FE_TOWARDZERO
18732 fexcept_t FE_UNDERFLOW FE_UPWARD
18733 FE_DIVBYZERO FE_ALL_EXCEPT FE_DFL_ENV
18734 FE_INEXACT FE_DOWNWARD
18735 FE_INVALID FE_TONEAREST
18736 #pragma STDC FENV_ACCESS on-off-switch
18737 int feclearexcept(int excepts);
18738 int fegetexceptflag(fexcept_t *flagp, int excepts);
18739 int feraiseexcept(int excepts);
18740 int fesetexceptflag(const fexcept_t *flagp,
18742 int fetestexcept(int excepts);
18746 int fegetround(void);
18747 int fesetround(int round);
18748 int fegetenv(fenv_t *envp);
18749 int feholdexcept(fenv_t *envp);
18750 int fesetenv(const fenv_t *envp);
18751 int feupdateenv(const fenv_t *envp);
18752 B.6 Characteristics of floating types <float.h>
18753 FLT_ROUNDS DBL_DIG FLT_MAX
18754 FLT_EVAL_METHOD LDBL_DIG DBL_MAX
18755 FLT_HAS_SUBNORM FLT_MIN_EXP LDBL_MAX
18756 DBL_HAS_SUBNORM DBL_MIN_EXP FLT_EPSILON
18757 LDBL_HAS_SUBNORM LDBL_MIN_EXP DBL_EPSILON
18758 FLT_RADIX FLT_MIN_10_EXP LDBL_EPSILON
18759 FLT_MANT_DIG DBL_MIN_10_EXP FLT_MIN
18760 DBL_MANT_DIG LDBL_MIN_10_EXP DBL_MIN
18761 LDBL_MANT_DIG FLT_MAX_EXP LDBL_MIN
18762 FLT_DECIMAL_DIG DBL_MAX_EXP FLT_TRUE_MIN
18763 DBL_DECIMAL_DIG LDBL_MAX_EXP DBL_TRUE_MIN
18764 LDBL_DECIMAL_DIG FLT_MAX_10_EXP LDBL_TRUE_MIN
18765 DECIMAL_DIG DBL_MAX_10_EXP
18766 FLT_DIG LDBL_MAX_10_EXP
18767 B.7 Format conversion of integer types <inttypes.h>
18769 PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR
18770 PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR
18771 PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR
18772 PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR
18773 PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR
18774 PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR
18775 SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR
18776 SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR
18777 SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR
18778 SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR
18779 SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR
18780 intmax_t imaxabs(intmax_t j);
18781 imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
18782 intmax_t strtoimax(const char * restrict nptr,
18783 char ** restrict endptr, int base);
18787 uintmax_t strtoumax(const char * restrict nptr,
18788 char ** restrict endptr, int base);
18789 intmax_t wcstoimax(const wchar_t * restrict nptr,
18790 wchar_t ** restrict endptr, int base);
18791 uintmax_t wcstoumax(const wchar_t * restrict nptr,
18792 wchar_t ** restrict endptr, int base);
18793 B.8 Alternative spellings <iso646.h>
18794 and bitor not_eq xor
18795 and_eq compl or xor_eq
18797 B.9 Sizes of integer types <limits.h>
18798 CHAR_BIT CHAR_MAX INT_MIN ULONG_MAX
18799 SCHAR_MIN MB_LEN_MAX INT_MAX LLONG_MIN
18800 SCHAR_MAX SHRT_MIN UINT_MAX LLONG_MAX
18801 UCHAR_MAX SHRT_MAX LONG_MIN ULLONG_MAX
18802 CHAR_MIN USHRT_MAX LONG_MAX
18803 B.10 Localization <locale.h>
18804 struct lconv LC_ALL LC_CTYPE LC_NUMERIC
18805 NULL LC_COLLATE LC_MONETARY LC_TIME
18806 char *setlocale(int category, const char *locale);
18807 struct lconv *localeconv(void);
18808 B.11 Mathematics <math.h>
18809 float_t FP_INFINITE FP_FAST_FMAL
18810 double_t FP_NAN FP_ILOGB0
18811 HUGE_VAL FP_NORMAL FP_ILOGBNAN
18812 HUGE_VALF FP_SUBNORMAL MATH_ERRNO
18813 HUGE_VALL FP_ZERO MATH_ERREXCEPT
18814 INFINITY FP_FAST_FMA math_errhandling
18816 #pragma STDC FP_CONTRACT on-off-switch
18817 int fpclassify(real-floating x);
18818 int isfinite(real-floating x);
18819 int isinf(real-floating x);
18820 int isnan(real-floating x);
18821 int isnormal(real-floating x);
18822 int signbit(real-floating x);
18825 double acos(double x);
18826 float acosf(float x);
18827 long double acosl(long double x);
18828 double asin(double x);
18829 float asinf(float x);
18830 long double asinl(long double x);
18831 double atan(double x);
18832 float atanf(float x);
18833 long double atanl(long double x);
18834 double atan2(double y, double x);
18835 float atan2f(float y, float x);
18836 long double atan2l(long double y, long double x);
18837 double cos(double x);
18838 float cosf(float x);
18839 long double cosl(long double x);
18840 double sin(double x);
18841 float sinf(float x);
18842 long double sinl(long double x);
18843 double tan(double x);
18844 float tanf(float x);
18845 long double tanl(long double x);
18846 double acosh(double x);
18847 float acoshf(float x);
18848 long double acoshl(long double x);
18849 double asinh(double x);
18850 float asinhf(float x);
18851 long double asinhl(long double x);
18852 double atanh(double x);
18853 float atanhf(float x);
18854 long double atanhl(long double x);
18855 double cosh(double x);
18856 float coshf(float x);
18857 long double coshl(long double x);
18858 double sinh(double x);
18859 float sinhf(float x);
18860 long double sinhl(long double x);
18861 double tanh(double x);
18862 float tanhf(float x);
18863 long double tanhl(long double x);
18864 double exp(double x);
18865 float expf(float x);
18869 long double expl(long double x);
18870 double exp2(double x);
18871 float exp2f(float x);
18872 long double exp2l(long double x);
18873 double expm1(double x);
18874 float expm1f(float x);
18875 long double expm1l(long double x);
18876 double frexp(double value, int *exp);
18877 float frexpf(float value, int *exp);
18878 long double frexpl(long double value, int *exp);
18879 int ilogb(double x);
18880 int ilogbf(float x);
18881 int ilogbl(long double x);
18882 double ldexp(double x, int exp);
18883 float ldexpf(float x, int exp);
18884 long double ldexpl(long double x, int exp);
18885 double log(double x);
18886 float logf(float x);
18887 long double logl(long double x);
18888 double log10(double x);
18889 float log10f(float x);
18890 long double log10l(long double x);
18891 double log1p(double x);
18892 float log1pf(float x);
18893 long double log1pl(long double x);
18894 double log2(double x);
18895 float log2f(float x);
18896 long double log2l(long double x);
18897 double logb(double x);
18898 float logbf(float x);
18899 long double logbl(long double x);
18900 double modf(double value, double *iptr);
18901 float modff(float value, float *iptr);
18902 long double modfl(long double value, long double *iptr);
18903 double scalbn(double x, int n);
18904 float scalbnf(float x, int n);
18905 long double scalbnl(long double x, int n);
18906 double scalbln(double x, long int n);
18907 float scalblnf(float x, long int n);
18908 long double scalblnl(long double x, long int n);
18909 double cbrt(double x);
18913 float cbrtf(float x);
18914 long double cbrtl(long double x);
18915 double fabs(double x);
18916 float fabsf(float x);
18917 long double fabsl(long double x);
18918 double hypot(double x, double y);
18919 float hypotf(float x, float y);
18920 long double hypotl(long double x, long double y);
18921 double pow(double x, double y);
18922 float powf(float x, float y);
18923 long double powl(long double x, long double y);
18924 double sqrt(double x);
18925 float sqrtf(float x);
18926 long double sqrtl(long double x);
18927 double erf(double x);
18928 float erff(float x);
18929 long double erfl(long double x);
18930 double erfc(double x);
18931 float erfcf(float x);
18932 long double erfcl(long double x);
18933 double lgamma(double x);
18934 float lgammaf(float x);
18935 long double lgammal(long double x);
18936 double tgamma(double x);
18937 float tgammaf(float x);
18938 long double tgammal(long double x);
18939 double ceil(double x);
18940 float ceilf(float x);
18941 long double ceill(long double x);
18942 double floor(double x);
18943 float floorf(float x);
18944 long double floorl(long double x);
18945 double nearbyint(double x);
18946 float nearbyintf(float x);
18947 long double nearbyintl(long double x);
18948 double rint(double x);
18949 float rintf(float x);
18950 long double rintl(long double x);
18951 long int lrint(double x);
18952 long int lrintf(float x);
18953 long int lrintl(long double x);
18957 long long int llrint(double x);
18958 long long int llrintf(float x);
18959 long long int llrintl(long double x);
18960 double round(double x);
18961 float roundf(float x);
18962 long double roundl(long double x);
18963 long int lround(double x);
18964 long int lroundf(float x);
18965 long int lroundl(long double x);
18966 long long int llround(double x);
18967 long long int llroundf(float x);
18968 long long int llroundl(long double x);
18969 double trunc(double x);
18970 float truncf(float x);
18971 long double truncl(long double x);
18972 double fmod(double x, double y);
18973 float fmodf(float x, float y);
18974 long double fmodl(long double x, long double y);
18975 double remainder(double x, double y);
18976 float remainderf(float x, float y);
18977 long double remainderl(long double x, long double y);
18978 double remquo(double x, double y, int *quo);
18979 float remquof(float x, float y, int *quo);
18980 long double remquol(long double x, long double y,
18982 double copysign(double x, double y);
18983 float copysignf(float x, float y);
18984 long double copysignl(long double x, long double y);
18985 double nan(const char *tagp);
18986 float nanf(const char *tagp);
18987 long double nanl(const char *tagp);
18988 double nextafter(double x, double y);
18989 float nextafterf(float x, float y);
18990 long double nextafterl(long double x, long double y);
18991 double nexttoward(double x, long double y);
18992 float nexttowardf(float x, long double y);
18993 long double nexttowardl(long double x, long double y);
18994 double fdim(double x, double y);
18995 float fdimf(float x, float y);
18996 long double fdiml(long double x, long double y);
18997 double fmax(double x, double y);
19001 float fmaxf(float x, float y);
19002 long double fmaxl(long double x, long double y);
19003 double fmin(double x, double y);
19004 float fminf(float x, float y);
19005 long double fminl(long double x, long double y);
19006 double fma(double x, double y, double z);
19007 float fmaf(float x, float y, float z);
19008 long double fmal(long double x, long double y,
19010 int isgreater(real-floating x, real-floating y);
19011 int isgreaterequal(real-floating x, real-floating y);
19012 int isless(real-floating x, real-floating y);
19013 int islessequal(real-floating x, real-floating y);
19014 int islessgreater(real-floating x, real-floating y);
19015 int isunordered(real-floating x, real-floating y);
19016 B.12 Nonlocal jumps <setjmp.h>
19018 int setjmp(jmp_buf env);
19019 _Noreturn void longjmp(jmp_buf env, int val);
19020 B.13 Signal handling <signal.h>
19021 sig_atomic_t SIG_IGN SIGILL SIGTERM
19022 SIG_DFL SIGABRT SIGINT
19023 SIG_ERR SIGFPE SIGSEGV
19024 void (*signal(int sig, void (*func)(int)))(int);
19025 int raise(int sig);
19032 B.14 Alignment <stdalign.h>
19034 __alignas_is_defined
19035 B.15 Variable arguments <stdarg.h>
19037 type va_arg(va_list ap, type);
19038 void va_copy(va_list dest, va_list src);
19039 void va_end(va_list ap);
19040 void va_start(va_list ap, parmN);
19041 B.16 Atomics <stdatomic.h>
19042 ATOMIC_CHAR_LOCK_FREE atomic_uint
19043 ATOMIC_CHAR16_T_LOCK_FREE atomic_long
19044 ATOMIC_CHAR32_T_LOCK_FREE atomic_ulong
19045 ATOMIC_WCHAR_T_LOCK_FREE atomic_llong
19046 ATOMIC_SHORT_LOCK_FREE atomic_ullong
19047 ATOMIC_INT_LOCK_FREE atomic_char16_t
19048 ATOMIC_LONG_LOCK_FREE atomic_char32_t
19049 ATOMIC_LLONG_LOCK_FREE atomic_wchar_t
19050 ATOMIC_ADDRESS_LOCK_FREE atomic_int_least8_t
19051 ATOMIC_FLAG_INIT atomic_uint_least8_t
19052 memory_order atomic_int_least16_t
19053 atomic_flag atomic_uint_least16_t
19054 atomic_bool atomic_int_least32_t
19055 atomic_address atomic_uint_least32_t
19056 memory_order_relaxed atomic_int_least64_t
19057 memory_order_consume atomic_uint_least64_t
19058 memory_order_acquire atomic_int_fast8_t
19059 memory_order_release atomic_uint_fast8_t
19060 memory_order_acq_rel atomic_int_fast16_t
19061 memory_order_seq_cst atomic_uint_fast16_t
19062 atomic_char atomic_int_fast32_t
19063 atomic_schar atomic_uint_fast32_t
19064 atomic_uchar atomic_int_fast64_t
19065 atomic_short atomic_uint_fast64_t
19066 atomic_ushort atomic_intptr_t
19067 atomic_int atomic_uintptr_t
19073 atomic_size_t atomic_intmax_t
19074 atomic_ptrdiff_t atomic_uintmax_t
19075 #define ATOMIC_VAR_INIT(C value)
19076 void atomic_init(volatile A *obj, C value);
19077 type kill_dependency(type y);
19078 void atomic_thread_fence(memory_order order);
19079 void atomic_signal_fence(memory_order order);
19080 _Bool atomic_is_lock_free(atomic_type const volatile *obj);
19081 void atomic_store(volatile A *object, C desired);
19082 void atomic_store_explicit(volatile A *object,
19083 C desired, memory_order order);
19084 C atomic_load(volatile A *object);
19085 C atomic_load_explicit(volatile A *object,
19086 memory_order order);
19087 C atomic_exchange(volatile A *object, C desired);
19088 C atomic_exchange_explicit(volatile A *object,
19089 C desired, memory_order order);
19090 _Bool atomic_compare_exchange_strong(volatile A *object,
19091 C *expected, C desired);
19092 _Bool atomic_compare_exchange_strong_explicit(
19093 volatile A *object, C *expected, C desired,
19094 memory_order success, memory_order failure);
19095 _Bool atomic_compare_exchange_weak(volatile A *object,
19096 C *expected, C desired);
19097 _Bool atomic_compare_exchange_weak_explicit(
19098 volatile A *object, C *expected, C desired,
19099 memory_order success, memory_order failure);
19100 C atomic_fetch_key(volatile A *object, M operand);
19101 C atomic_fetch_key_explicit(volatile A *object,
19102 M operand, memory_order order);
19103 bool atomic_flag_test_and_set(
19104 volatile atomic_flag *object);
19105 bool atomic_flag_test_and_set_explicit(
19106 volatile atomic_flag *object, memory_order order);
19107 void atomic_flag_clear(volatile atomic_flag *object);
19108 void atomic_flag_clear_explicit(
19109 volatile atomic_flag *object, memory_order order);
19116 B.17 Boolean type and values <stdbool.h>
19120 __bool_true_false_are_defined
19121 B.18 Common definitions <stddef.h>
19122 ptrdiff_t max_align_t NULL
19124 offsetof(type, member-designator)
19125 __STDC_WANT_LIB_EXT1__
19127 B.19 Integer types <stdint.h>
19128 intN_t INT_LEASTN_MIN PTRDIFF_MAX
19129 uintN_t INT_LEASTN_MAX SIG_ATOMIC_MIN
19130 int_leastN_t UINT_LEASTN_MAX SIG_ATOMIC_MAX
19131 uint_leastN_t INT_FASTN_MIN SIZE_MAX
19132 int_fastN_t INT_FASTN_MAX WCHAR_MIN
19133 uint_fastN_t UINT_FASTN_MAX WCHAR_MAX
19134 intptr_t INTPTR_MIN WINT_MIN
19135 uintptr_t INTPTR_MAX WINT_MAX
19136 intmax_t UINTPTR_MAX INTN_C(value)
19137 uintmax_t INTMAX_MIN UINTN_C(value)
19138 INTN_MIN INTMAX_MAX INTMAX_C(value)
19139 INTN_MAX UINTMAX_MAX UINTMAX_C(value)
19140 UINTN_MAX PTRDIFF_MIN
19141 __STDC_WANT_LIB_EXT1__
19149 B.20 Input/output <stdio.h>
19150 size_t _IOLBF FILENAME_MAX TMP_MAX
19151 FILE _IONBF L_tmpnam stderr
19152 fpos_t BUFSIZ SEEK_CUR stdin
19153 NULL EOF SEEK_END stdout
19154 _IOFBF FOPEN_MAX SEEK_SET
19155 int remove(const char *filename);
19156 int rename(const char *old, const char *new);
19157 FILE *tmpfile(void);
19158 char *tmpnam(char *s);
19159 int fclose(FILE *stream);
19160 int fflush(FILE *stream);
19161 FILE *fopen(const char * restrict filename,
19162 const char * restrict mode);
19163 FILE *freopen(const char * restrict filename,
19164 const char * restrict mode,
19165 FILE * restrict stream);
19166 void setbuf(FILE * restrict stream,
19167 char * restrict buf);
19168 int setvbuf(FILE * restrict stream,
19169 char * restrict buf,
19170 int mode, size_t size);
19171 int fprintf(FILE * restrict stream,
19172 const char * restrict format, ...);
19173 int fscanf(FILE * restrict stream,
19174 const char * restrict format, ...);
19175 int printf(const char * restrict format, ...);
19176 int scanf(const char * restrict format, ...);
19177 int snprintf(char * restrict s, size_t n,
19178 const char * restrict format, ...);
19179 int sprintf(char * restrict s,
19180 const char * restrict format, ...);
19181 int sscanf(const char * restrict s,
19182 const char * restrict format, ...);
19183 int vfprintf(FILE * restrict stream,
19184 const char * restrict format, va_list arg);
19185 int vfscanf(FILE * restrict stream,
19186 const char * restrict format, va_list arg);
19187 int vprintf(const char * restrict format, va_list arg);
19188 int vscanf(const char * restrict format, va_list arg);
19192 int vsnprintf(char * restrict s, size_t n,
19193 const char * restrict format, va_list arg);
19194 int vsprintf(char * restrict s,
19195 const char * restrict format, va_list arg);
19196 int vsscanf(const char * restrict s,
19197 const char * restrict format, va_list arg);
19198 int fgetc(FILE *stream);
19199 char *fgets(char * restrict s, int n,
19200 FILE * restrict stream);
19201 int fputc(int c, FILE *stream);
19202 int fputs(const char * restrict s,
19203 FILE * restrict stream);
19204 int getc(FILE *stream);
19206 int putc(int c, FILE *stream); *
19207 int putchar(int c);
19208 int puts(const char *s);
19209 int ungetc(int c, FILE *stream);
19210 size_t fread(void * restrict ptr,
19211 size_t size, size_t nmemb,
19212 FILE * restrict stream);
19213 size_t fwrite(const void * restrict ptr,
19214 size_t size, size_t nmemb,
19215 FILE * restrict stream);
19216 int fgetpos(FILE * restrict stream,
19217 fpos_t * restrict pos);
19218 int fseek(FILE *stream, long int offset, int whence);
19219 int fsetpos(FILE *stream, const fpos_t *pos);
19220 long int ftell(FILE *stream);
19221 void rewind(FILE *stream);
19222 void clearerr(FILE *stream);
19223 int feof(FILE *stream);
19224 int ferror(FILE *stream);
19225 void perror(const char *s);
19226 __STDC_WANT_LIB_EXT1__
19227 L_tmpnam_s TMP_MAX_S errno_t rsize_t
19228 errno_t tmpfile_s(FILE * restrict * restrict streamptr);
19229 errno_t tmpnam_s(char *s, rsize_t maxsize);
19235 errno_t fopen_s(FILE * restrict * restrict streamptr,
19236 const char * restrict filename,
19237 const char * restrict mode);
19238 errno_t freopen_s(FILE * restrict * restrict newstreamptr,
19239 const char * restrict filename,
19240 const char * restrict mode,
19241 FILE * restrict stream);
19242 int fprintf_s(FILE * restrict stream,
19243 const char * restrict format, ...);
19244 int fscanf_s(FILE * restrict stream,
19245 const char * restrict format, ...);
19246 int printf_s(const char * restrict format, ...);
19247 int scanf_s(const char * restrict format, ...);
19248 int snprintf_s(char * restrict s, rsize_t n,
19249 const char * restrict format, ...);
19250 int sprintf_s(char * restrict s, rsize_t n,
19251 const char * restrict format, ...);
19252 int sscanf_s(const char * restrict s,
19253 const char * restrict format, ...);
19254 int vfprintf_s(FILE * restrict stream,
19255 const char * restrict format,
19257 int vfscanf_s(FILE * restrict stream,
19258 const char * restrict format,
19260 int vprintf_s(const char * restrict format,
19262 int vscanf_s(const char * restrict format,
19264 int vsnprintf_s(char * restrict s, rsize_t n,
19265 const char * restrict format,
19267 int vsprintf_s(char * restrict s, rsize_t n,
19268 const char * restrict format,
19270 int vsscanf_s(const char * restrict s,
19271 const char * restrict format,
19273 char *gets_s(char *s, rsize_t n);
19279 B.21 General utilities <stdlib.h>
19280 size_t ldiv_t EXIT_FAILURE MB_CUR_MAX
19281 wchar_t lldiv_t EXIT_SUCCESS
19282 div_t NULL RAND_MAX
19283 double atof(const char *nptr);
19284 int atoi(const char *nptr);
19285 long int atol(const char *nptr);
19286 long long int atoll(const char *nptr);
19287 double strtod(const char * restrict nptr,
19288 char ** restrict endptr);
19289 float strtof(const char * restrict nptr,
19290 char ** restrict endptr);
19291 long double strtold(const char * restrict nptr,
19292 char ** restrict endptr);
19293 long int strtol(const char * restrict nptr,
19294 char ** restrict endptr, int base);
19295 long long int strtoll(const char * restrict nptr,
19296 char ** restrict endptr, int base);
19297 unsigned long int strtoul(
19298 const char * restrict nptr,
19299 char ** restrict endptr, int base);
19300 unsigned long long int strtoull(
19301 const char * restrict nptr,
19302 char ** restrict endptr, int base);
19304 void srand(unsigned int seed);
19305 void *aligned_alloc(size_t alignment, size_t size);
19306 void *calloc(size_t nmemb, size_t size);
19307 void free(void *ptr);
19308 void *malloc(size_t size);
19309 void *realloc(void *ptr, size_t size);
19310 _Noreturn void abort(void);
19311 int atexit(void (*func)(void));
19312 int at_quick_exit(void (*func)(void));
19313 _Noreturn void exit(int status);
19314 _Noreturn void _Exit(int status);
19315 char *getenv(const char *name);
19316 _Noreturn void quick_exit(int status);
19317 int system(const char *string);
19322 void *bsearch(const void *key, const void *base,
19323 size_t nmemb, size_t size,
19324 int (*compar)(const void *, const void *));
19325 void qsort(void *base, size_t nmemb, size_t size,
19326 int (*compar)(const void *, const void *));
19328 long int labs(long int j);
19329 long long int llabs(long long int j);
19330 div_t div(int numer, int denom);
19331 ldiv_t ldiv(long int numer, long int denom);
19332 lldiv_t lldiv(long long int numer,
19333 long long int denom);
19334 int mblen(const char *s, size_t n);
19335 int mbtowc(wchar_t * restrict pwc,
19336 const char * restrict s, size_t n);
19337 int wctomb(char *s, wchar_t wchar);
19338 size_t mbstowcs(wchar_t * restrict pwcs,
19339 const char * restrict s, size_t n);
19340 size_t wcstombs(char * restrict s,
19341 const wchar_t * restrict pwcs, size_t n);
19342 __STDC_WANT_LIB_EXT1__
19345 constraint_handler_t
19346 constraint_handler_t set_constraint_handler_s(
19347 constraint_handler_t handler);
19348 void abort_handler_s(
19349 const char * restrict msg,
19350 void * restrict ptr,
19352 void ignore_handler_s(
19353 const char * restrict msg,
19354 void * restrict ptr,
19356 errno_t getenv_s(size_t * restrict len,
19357 char * restrict value, rsize_t maxsize,
19358 const char * restrict name);
19365 void *bsearch_s(const void *key, const void *base,
19366 rsize_t nmemb, rsize_t size,
19367 int (*compar)(const void *k, const void *y,
19370 errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size,
19371 int (*compar)(const void *x, const void *y,
19374 errno_t wctomb_s(int * restrict status,
19378 errno_t mbstowcs_s(size_t * restrict retval,
19379 wchar_t * restrict dst, rsize_t dstmax,
19380 const char * restrict src, rsize_t len);
19381 errno_t wcstombs_s(size_t * restrict retval,
19382 char * restrict dst, rsize_t dstmax,
19383 const wchar_t * restrict src, rsize_t len);
19384 B.22 String handling <string.h>
19387 void *memcpy(void * restrict s1,
19388 const void * restrict s2, size_t n);
19389 void *memmove(void *s1, const void *s2, size_t n);
19390 char *strcpy(char * restrict s1,
19391 const char * restrict s2);
19392 char *strncpy(char * restrict s1,
19393 const char * restrict s2, size_t n);
19394 char *strcat(char * restrict s1,
19395 const char * restrict s2);
19396 char *strncat(char * restrict s1,
19397 const char * restrict s2, size_t n);
19398 int memcmp(const void *s1, const void *s2, size_t n);
19399 int strcmp(const char *s1, const char *s2);
19400 int strcoll(const char *s1, const char *s2);
19401 int strncmp(const char *s1, const char *s2, size_t n);
19402 size_t strxfrm(char * restrict s1,
19403 const char * restrict s2, size_t n);
19404 void *memchr(const void *s, int c, size_t n);
19407 char *strchr(const char *s, int c);
19408 size_t strcspn(const char *s1, const char *s2);
19409 char *strpbrk(const char *s1, const char *s2);
19410 char *strrchr(const char *s, int c);
19411 size_t strspn(const char *s1, const char *s2);
19412 char *strstr(const char *s1, const char *s2);
19413 char *strtok(char * restrict s1,
19414 const char * restrict s2);
19415 void *memset(void *s, int c, size_t n);
19416 char *strerror(int errnum);
19417 size_t strlen(const char *s);
19418 __STDC_WANT_LIB_EXT1__
19421 errno_t memcpy_s(void * restrict s1, rsize_t s1max,
19422 const void * restrict s2, rsize_t n);
19423 errno_t memmove_s(void *s1, rsize_t s1max,
19424 const void *s2, rsize_t n);
19425 errno_t strcpy_s(char * restrict s1,
19427 const char * restrict s2);
19428 errno_t strncpy_s(char * restrict s1,
19430 const char * restrict s2,
19432 errno_t strcat_s(char * restrict s1,
19434 const char * restrict s2);
19435 errno_t strncat_s(char * restrict s1,
19437 const char * restrict s2,
19439 char *strtok_s(char * restrict s1,
19440 rsize_t * restrict s1max,
19441 const char * restrict s2,
19442 char ** restrict ptr);
19443 errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
19444 errno_t strerror_s(char *s, rsize_t maxsize,
19446 size_t strerrorlen_s(errno_t errnum);
19450 size_t strnlen_s(const char *s, size_t maxsize);
19451 B.23 Type-generic math <tgmath.h>
19452 acos sqrt fmod nextafter
19453 asin fabs frexp nexttoward
19454 atan atan2 hypot remainder
19455 acosh cbrt ilogb remquo
19456 asinh ceil ldexp rint
19457 atanh copysign lgamma round
19458 cos erf llrint scalbn
19459 sin erfc llround scalbln
19460 tan exp2 log10 tgamma
19461 cosh expm1 log1p trunc
19462 sinh fdim log2 carg
19463 tanh floor logb cimag
19465 log fmax lround cproj
19466 pow fmin nearbyint creal
19467 B.24 Threads <threads.h>
19468 ONCE_FLAG_INIT mtx_plain
19469 TSS_DTOR_ITERATIONS mtx_recursive
19474 tss_dtor_t thrd_busy
19475 thrd_start_t thrd_error
19476 once_flag thrd_nomem
19478 void call_once(once_flag *flag, void (*func)(void));
19479 int cnd_broadcast(cnd_t *cond);
19480 void cnd_destroy(cnd_t *cond);
19481 int cnd_init(cnd_t *cond);
19482 int cnd_signal(cnd_t *cond);
19483 int cnd_timedwait(cnd_t *cond, mtx_t *mtx,
19485 int cnd_wait(cnd_t *cond, mtx_t *mtx);
19486 void mtx_destroy(mtx_t *mtx);
19487 int mtx_init(mtx_t *mtx, int type);
19488 int mtx_lock(mtx_t *mtx);
19491 int mtx_timedlock(mtx_t *mtx, const xtime *xt);
19492 int mtx_trylock(mtx_t *mtx);
19493 int mtx_unlock(mtx_t *mtx);
19494 int thrd_create(thrd_t *thr, thrd_start_t func,
19496 thrd_t thrd_current(void);
19497 int thrd_detach(thrd_t thr);
19498 int thrd_equal(thrd_t thr0, thrd_t thr1);
19499 void thrd_exit(int res);
19500 int thrd_join(thrd_t thr, int *res);
19501 void thrd_sleep(const xtime *xt);
19502 void thrd_yield(void);
19503 int tss_create(tss_t *key, tss_dtor_t dtor);
19504 void tss_delete(tss_t key);
19505 void *tss_get(tss_t key);
19506 int tss_set(tss_t key, void *val);
19507 int xtime_get(xtime *xt, int base);
19508 B.25 Date and time <time.h>
19510 CLOCKS_PER_SEC clock_t struct tm
19511 clock_t clock(void);
19512 double difftime(time_t time1, time_t time0);
19513 time_t mktime(struct tm *timeptr);
19514 time_t time(time_t *timer);
19515 char *asctime(const struct tm *timeptr);
19516 char *ctime(const time_t *timer);
19517 struct tm *gmtime(const time_t *timer);
19518 struct tm *localtime(const time_t *timer);
19519 size_t strftime(char * restrict s,
19521 const char * restrict format,
19522 const struct tm * restrict timeptr);
19523 __STDC_WANT_LIB_EXT1__
19526 errno_t asctime_s(char *s, rsize_t maxsize,
19527 const struct tm *timeptr);
19533 errno_t ctime_s(char *s, rsize_t maxsize,
19534 const time_t *timer);
19535 struct tm *gmtime_s(const time_t * restrict timer,
19536 struct tm * restrict result);
19537 struct tm *localtime_s(const time_t * restrict timer,
19538 struct tm * restrict result);
19539 B.26 Unicode utilities <uchar.h>
19540 mbstate_t size_t char16_t char32_t
19541 size_t mbrtoc16(char16_t * restrict pc16,
19542 const char * restrict s, size_t n,
19543 mbstate_t * restrict ps);
19544 size_t c16rtomb(char * restrict s, char16_t c16,
19545 mbstate_t * restrict ps);
19546 size_t mbrtoc32(char32_t * restrict pc32,
19547 const char * restrict s, size_t n,
19548 mbstate_t * restrict ps);
19549 size_t c32rtomb(char * restrict s, char32_t c32,
19550 mbstate_t * restrict ps);
19551 B.27 Extended multibyte/wide character utilities <wchar.h>
19552 wchar_t wint_t WCHAR_MAX
19553 size_t struct tm WCHAR_MIN
19554 mbstate_t NULL WEOF
19555 int fwprintf(FILE * restrict stream,
19556 const wchar_t * restrict format, ...);
19557 int fwscanf(FILE * restrict stream,
19558 const wchar_t * restrict format, ...);
19559 int swprintf(wchar_t * restrict s, size_t n,
19560 const wchar_t * restrict format, ...);
19561 int swscanf(const wchar_t * restrict s,
19562 const wchar_t * restrict format, ...);
19563 int vfwprintf(FILE * restrict stream,
19564 const wchar_t * restrict format, va_list arg);
19565 int vfwscanf(FILE * restrict stream,
19566 const wchar_t * restrict format, va_list arg);
19567 int vswprintf(wchar_t * restrict s, size_t n,
19568 const wchar_t * restrict format, va_list arg);
19574 int vswscanf(const wchar_t * restrict s,
19575 const wchar_t * restrict format, va_list arg);
19576 int vwprintf(const wchar_t * restrict format,
19578 int vwscanf(const wchar_t * restrict format,
19580 int wprintf(const wchar_t * restrict format, ...);
19581 int wscanf(const wchar_t * restrict format, ...);
19582 wint_t fgetwc(FILE *stream);
19583 wchar_t *fgetws(wchar_t * restrict s, int n,
19584 FILE * restrict stream);
19585 wint_t fputwc(wchar_t c, FILE *stream);
19586 int fputws(const wchar_t * restrict s,
19587 FILE * restrict stream);
19588 int fwide(FILE *stream, int mode);
19589 wint_t getwc(FILE *stream);
19590 wint_t getwchar(void);
19591 wint_t putwc(wchar_t c, FILE *stream);
19592 wint_t putwchar(wchar_t c);
19593 wint_t ungetwc(wint_t c, FILE *stream);
19594 double wcstod(const wchar_t * restrict nptr,
19595 wchar_t ** restrict endptr);
19596 float wcstof(const wchar_t * restrict nptr,
19597 wchar_t ** restrict endptr);
19598 long double wcstold(const wchar_t * restrict nptr,
19599 wchar_t ** restrict endptr);
19600 long int wcstol(const wchar_t * restrict nptr,
19601 wchar_t ** restrict endptr, int base);
19602 long long int wcstoll(const wchar_t * restrict nptr,
19603 wchar_t ** restrict endptr, int base);
19604 unsigned long int wcstoul(const wchar_t * restrict nptr,
19605 wchar_t ** restrict endptr, int base);
19606 unsigned long long int wcstoull(
19607 const wchar_t * restrict nptr,
19608 wchar_t ** restrict endptr, int base);
19609 wchar_t *wcscpy(wchar_t * restrict s1,
19610 const wchar_t * restrict s2);
19611 wchar_t *wcsncpy(wchar_t * restrict s1,
19612 const wchar_t * restrict s2, size_t n);
19618 wchar_t *wmemcpy(wchar_t * restrict s1,
19619 const wchar_t * restrict s2, size_t n);
19620 wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
19622 wchar_t *wcscat(wchar_t * restrict s1,
19623 const wchar_t * restrict s2);
19624 wchar_t *wcsncat(wchar_t * restrict s1,
19625 const wchar_t * restrict s2, size_t n);
19626 int wcscmp(const wchar_t *s1, const wchar_t *s2);
19627 int wcscoll(const wchar_t *s1, const wchar_t *s2);
19628 int wcsncmp(const wchar_t *s1, const wchar_t *s2,
19630 size_t wcsxfrm(wchar_t * restrict s1,
19631 const wchar_t * restrict s2, size_t n);
19632 int wmemcmp(const wchar_t *s1, const wchar_t *s2,
19634 wchar_t *wcschr(const wchar_t *s, wchar_t c);
19635 size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
19636 wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
19637 wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
19638 size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
19639 wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
19640 wchar_t *wcstok(wchar_t * restrict s1,
19641 const wchar_t * restrict s2,
19642 wchar_t ** restrict ptr);
19643 wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n);
19644 size_t wcslen(const wchar_t *s);
19645 wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
19646 size_t wcsftime(wchar_t * restrict s, size_t maxsize,
19647 const wchar_t * restrict format,
19648 const struct tm * restrict timeptr);
19649 wint_t btowc(int c);
19650 int wctob(wint_t c);
19651 int mbsinit(const mbstate_t *ps);
19652 size_t mbrlen(const char * restrict s, size_t n,
19653 mbstate_t * restrict ps);
19654 size_t mbrtowc(wchar_t * restrict pwc,
19655 const char * restrict s, size_t n,
19656 mbstate_t * restrict ps);
19662 size_t wcrtomb(char * restrict s, wchar_t wc,
19663 mbstate_t * restrict ps);
19664 size_t mbsrtowcs(wchar_t * restrict dst,
19665 const char ** restrict src, size_t len,
19666 mbstate_t * restrict ps);
19667 size_t wcsrtombs(char * restrict dst,
19668 const wchar_t ** restrict src, size_t len,
19669 mbstate_t * restrict ps);
19670 __STDC_WANT_LIB_EXT1__
19673 int fwprintf_s(FILE * restrict stream,
19674 const wchar_t * restrict format, ...);
19675 int fwscanf_s(FILE * restrict stream,
19676 const wchar_t * restrict format, ...);
19677 int snwprintf_s(wchar_t * restrict s,
19679 const wchar_t * restrict format, ...);
19680 int swprintf_s(wchar_t * restrict s, rsize_t n,
19681 const wchar_t * restrict format, ...);
19682 int swscanf_s(const wchar_t * restrict s,
19683 const wchar_t * restrict format, ...);
19684 int vfwprintf_s(FILE * restrict stream,
19685 const wchar_t * restrict format,
19687 int vfwscanf_s(FILE * restrict stream,
19688 const wchar_t * restrict format, va_list arg);
19689 int vsnwprintf_s(wchar_t * restrict s,
19691 const wchar_t * restrict format,
19693 int vswprintf_s(wchar_t * restrict s,
19695 const wchar_t * restrict format,
19697 int vswscanf_s(const wchar_t * restrict s,
19698 const wchar_t * restrict format,
19705 int vwprintf_s(const wchar_t * restrict format,
19707 int vwscanf_s(const wchar_t * restrict format,
19709 int wprintf_s(const wchar_t * restrict format, ...);
19710 int wscanf_s(const wchar_t * restrict format, ...);
19711 errno_t wcscpy_s(wchar_t * restrict s1,
19713 const wchar_t * restrict s2);
19714 errno_t wcsncpy_s(wchar_t * restrict s1,
19716 const wchar_t * restrict s2,
19718 errno_t wmemcpy_s(wchar_t * restrict s1,
19720 const wchar_t * restrict s2,
19722 errno_t wmemmove_s(wchar_t *s1, rsize_t s1max,
19723 const wchar_t *s2, rsize_t n);
19724 errno_t wcscat_s(wchar_t * restrict s1,
19726 const wchar_t * restrict s2);
19727 errno_t wcsncat_s(wchar_t * restrict s1,
19729 const wchar_t * restrict s2,
19731 wchar_t *wcstok_s(wchar_t * restrict s1,
19732 rsize_t * restrict s1max,
19733 const wchar_t * restrict s2,
19734 wchar_t ** restrict ptr);
19735 size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
19736 errno_t wcrtomb_s(size_t * restrict retval,
19737 char * restrict s, rsize_t smax,
19738 wchar_t wc, mbstate_t * restrict ps);
19739 errno_t mbsrtowcs_s(size_t * restrict retval,
19740 wchar_t * restrict dst, rsize_t dstmax,
19741 const char ** restrict src, rsize_t len,
19742 mbstate_t * restrict ps);
19749 errno_t wcsrtombs_s(size_t * restrict retval,
19750 char * restrict dst, rsize_t dstmax,
19751 const wchar_t ** restrict src, rsize_t len,
19752 mbstate_t * restrict ps);
19753 B.28 Wide character classification and mapping utilities <wctype.h>
19754 wint_t wctrans_t wctype_t WEOF
19755 int iswalnum(wint_t wc);
19756 int iswalpha(wint_t wc);
19757 int iswblank(wint_t wc);
19758 int iswcntrl(wint_t wc);
19759 int iswdigit(wint_t wc);
19760 int iswgraph(wint_t wc);
19761 int iswlower(wint_t wc);
19762 int iswprint(wint_t wc);
19763 int iswpunct(wint_t wc);
19764 int iswspace(wint_t wc);
19765 int iswupper(wint_t wc);
19766 int iswxdigit(wint_t wc);
19767 int iswctype(wint_t wc, wctype_t desc);
19768 wctype_t wctype(const char *property);
19769 wint_t towlower(wint_t wc);
19770 wint_t towupper(wint_t wc);
19771 wint_t towctrans(wint_t wc, wctrans_t desc);
19772 wctrans_t wctrans(const char *property);
19782 1 The following are the sequence points described in 5.1.2.3:
19783 -- Between the evaluations of the function designator and actual arguments in a function
19784 call and the actual call. (6.5.2.2).
19785 -- Between the evaluations of the first and second operands of the following operators:
19786 logical AND && (6.5.13); logical OR || (6.5.14); comma , (6.5.17). *
19787 -- Between the evaluations of the first operand of the conditional ? : operator and
19788 whichever of the second and third operands is evaluated (6.5.15).
19789 -- The end of a full declarator: declarators (6.7.6);
19790 -- Between the evaluation of a full expression and the next full expression to be
19791 evaluated. The following are full expressions: an initializer that is not part of a
19792 compound literal (6.7.9); the expression in an expression statement (6.8.3); the
19793 controlling expression of a selection statement (if or switch) (6.8.4); the
19794 controlling expression of a while or do statement (6.8.5); each of the (optional)
19795 expressions of a for statement (6.8.5.3); the (optional) expression in a return
19796 statement (6.8.6.4).
19797 -- Immediately before a library function returns (7.1.4).
19798 -- After the actions associated with each formatted input/output function conversion
19799 specifier (7.21.6, 7.28.2).
19800 -- Immediately before and immediately after each call to a comparison function, and
19801 also between any call to a comparison function and any movement of the objects
19802 passed as arguments to that call (7.22.5).
19811 Universal character names for identifiers
19812 1 This clause lists the hexadecimal code values that are valid in universal character names
19814 D.1 Ranges of characters allowed
19815 1 00A8, 00AA, 00AD, 00AF, 00B2-00B5, 00B7-00BA, 00BC-00BE, 00C0-00D6,
19816 00D8-00F6, 00F8-00FF
19817 2 0100-167F, 1681-180D, 180F-1FFF
19818 3 200B-200D, 202A-202E, 203F-2040, 2054, 2060-206F
19819 4 2070-218F, 2460-24FF, 2776-2793, 2C00-2DFF, 2E80-2FFF
19820 5 3004-3007, 3021-302F, 3031-303F
19822 7 F900-FD3D, FD40-FDCF, FDF0-FE44, FE47-FFFD
19823 8 10000-1FFFD, 20000-2FFFD, 30000-3FFFD, 40000-4FFFD, 50000-5FFFD,
19824 60000-6FFFD, 70000-7FFFD, 80000-8FFFD, 90000-9FFFD, A0000-AFFFD,
19825 B0000-BFFFD, C0000-CFFFD, D0000-DFFFD, E0000-EFFFD
19826 D.2 Ranges of characters disallowed initially
19827 1 0300-036F, 1DC0-1DFF, 20D0-20FF, FE20-FE2F
19836 Implementation limits
19837 1 The contents of the header <limits.h> are given below, in alphabetical order. The
19838 minimum magnitudes shown shall be replaced by implementation-defined magnitudes
19839 with the same sign. The values shall all be constant expressions suitable for use in #if
19840 preprocessing directives. The components are described further in 5.2.4.2.1.
19842 #define CHAR_MAX UCHAR_MAX or SCHAR_MAX
19843 #define CHAR_MIN 0 or SCHAR_MIN
19844 #define INT_MAX +32767
19845 #define INT_MIN -32767
19846 #define LONG_MAX +2147483647
19847 #define LONG_MIN -2147483647
19848 #define LLONG_MAX +9223372036854775807
19849 #define LLONG_MIN -9223372036854775807
19850 #define MB_LEN_MAX 1
19851 #define SCHAR_MAX +127
19852 #define SCHAR_MIN -127
19853 #define SHRT_MAX +32767
19854 #define SHRT_MIN -32767
19855 #define UCHAR_MAX 255
19856 #define USHRT_MAX 65535
19857 #define UINT_MAX 65535
19858 #define ULONG_MAX 4294967295
19859 #define ULLONG_MAX 18446744073709551615
19860 2 The contents of the header <float.h> are given below. All integer values, except
19861 FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing
19862 directives; all floating values shall be constant expressions. The components are
19863 described further in 5.2.4.2.2.
19864 3 The values given in the following list shall be replaced by implementation-defined
19866 #define FLT_EVAL_METHOD
19868 4 The values given in the following list shall be replaced by implementation-defined
19869 constant expressions that are greater or equal in magnitude (absolute value) to those
19870 shown, with the same sign:
19873 #define DLB_DECIMAL_DIG 10
19875 #define DBL_MANT_DIG
19876 #define DBL_MAX_10_EXP +37
19877 #define DBL_MAX_EXP
19878 #define DBL_MIN_10_EXP -37
19879 #define DBL_MIN_EXP
19880 #define DECIMAL_DIG 10
19881 #define FLT_DECIMAL_DIG 6
19883 #define FLT_MANT_DIG
19884 #define FLT_MAX_10_EXP +37
19885 #define FLT_MAX_EXP
19886 #define FLT_MIN_10_EXP -37
19887 #define FLT_MIN_EXP
19888 #define FLT_RADIX 2
19889 #define LDLB_DECIMAL_DIG 10
19890 #define LDBL_DIG 10
19891 #define LDBL_MANT_DIG
19892 #define LDBL_MAX_10_EXP +37
19893 #define LDBL_MAX_EXP
19894 #define LDBL_MIN_10_EXP -37
19895 #define LDBL_MIN_EXP
19896 5 The values given in the following list shall be replaced by implementation-defined
19897 constant expressions with values that are greater than or equal to those shown:
19898 #define DBL_MAX 1E+37
19899 #define FLT_MAX 1E+37
19900 #define LDBL_MAX 1E+37
19901 6 The values given in the following list shall be replaced by implementation-defined
19902 constant expressions with (positive) values that are less than or equal to those shown:
19903 #define DBL_EPSILON 1E-9
19904 #define DBL_MIN 1E-37
19905 #define FLT_EPSILON 1E-5
19906 #define FLT_MIN 1E-37
19907 #define LDBL_EPSILON 1E-9
19908 #define LDBL_MIN 1E-37
19917 IEC 60559 floating-point arithmetic
19919 1 This annex specifies C language support for the IEC 60559 floating-point standard. The
19920 IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for
19921 microprocessor systems, second edition (IEC 60559:1989), previously designated
19922 IEC 559:1989 and as IEEE Standard for Binary Floating-Point Arithmetic
19923 (ANSI/IEEE 754-1985). IEEE Standard for Radix-Independent Floating-Point
19924 Arithmetic (ANSI/IEEE 854-1987) generalizes the binary standard to remove
19925 dependencies on radix and word length. IEC 60559 generally refers to the floating-point
19926 standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation that
19927 defines __STDC_IEC_559__ shall conform to the specifications in this annex.343)
19928 Where a binding between the C language and IEC 60559 is indicated, the
19929 IEC 60559-specified behavior is adopted by reference, unless stated otherwise. Since
19930 negative and positive infinity are representable in IEC 60559 formats, all real numbers lie
19931 within the range of representable values.
19933 1 The C floating types match the IEC 60559 formats as follows:
19934 -- The float type matches the IEC 60559 single format.
19935 -- The double type matches the IEC 60559 double format.
19936 -- The long double type matches an IEC 60559 extended format,344) else a
19937 non-IEC 60559 extended format, else the IEC 60559 double format.
19938 Any non-IEC 60559 extended format used for the long double type shall have more
19939 precision than IEC 60559 double and at least the range of IEC 60559 double.345)
19944 343) Implementations that do not define __STDC_IEC_559__ are not required to conform to these
19946 344) ''Extended'' is IEC 60559's double-extended data format. Extended refers to both the common 80-bit
19947 and quadruple 128-bit IEC 60559 formats.
19948 345) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include
19953 Recommended practice
19954 2 The long double type should match an IEC 60559 extended format.
19955 F.2.1 Infinities, signed zeros, and NaNs
19956 1 This specification does not define the behavior of signaling NaNs.346) It generally uses
19957 the term NaN to denote quiet NaNs. The NAN and INFINITY macros and the nan
19958 functions in <math.h> provide designations for IEC 60559 NaNs and infinities.
19959 F.3 Operators and functions
19960 1 C operators and functions provide IEC 60559 required and recommended facilities as
19962 -- The +, -, *, and / operators provide the IEC 60559 add, subtract, multiply, and
19964 -- The sqrt functions in <math.h> provide the IEC 60559 square root operation.
19965 -- The remainder functions in <math.h> provide the IEC 60559 remainder
19966 operation. The remquo functions in <math.h> provide the same operation but
19967 with additional information.
19968 -- The rint functions in <math.h> provide the IEC 60559 operation that rounds a
19969 floating-point number to an integer value (in the same precision). The nearbyint
19970 functions in <math.h> provide the nearbyinteger function recommended in the
19971 Appendix to ANSI/IEEE 854.
19972 -- The conversions for floating types provide the IEC 60559 conversions between
19973 floating-point precisions.
19974 -- The conversions from integer to floating types provide the IEC 60559 conversions
19975 from integer to floating point.
19976 -- The conversions from floating to integer types provide IEC 60559-like conversions
19977 but always round toward zero.
19978 -- The lrint and llrint functions in <math.h> provide the IEC 60559
19979 conversions, which honor the directed rounding mode, from floating point to the
19980 long int and long long int integer formats. The lrint and llrint
19981 functions can be used to implement IEC 60559 conversions from floating to other
19983 -- The translation time conversion of floating constants and the strtod, strtof,
19984 strtold, fprintf, fscanf, and related library functions in <stdlib.h>,
19987 346) Since NaNs created by IEC 60559 operations are always quiet, quiet NaNs (along with infinities) are
19988 sufficient for closure of the arithmetic.
19992 <stdio.h>, and <wchar.h> provide IEC 60559 binary-decimal conversions. The
19993 strtold function in <stdlib.h> provides the conv function recommended in the
19994 Appendix to ANSI/IEEE 854.
19995 -- The relational and equality operators provide IEC 60559 comparisons. IEC 60559
19996 identifies a need for additional comparison predicates to facilitate writing code that
19997 accounts for NaNs. The comparison macros (isgreater, isgreaterequal,
19998 isless, islessequal, islessgreater, and isunordered) in <math.h>
19999 supplement the language operators to address this need. The islessgreater and
20000 isunordered macros provide respectively a quiet version of the <> predicate and
20001 the unordered predicate recommended in the Appendix to IEC 60559.
20002 -- The feclearexcept, feraiseexcept, and fetestexcept functions in
20003 <fenv.h> provide the facility to test and alter the IEC 60559 floating-point
20004 exception status flags. The fegetexceptflag and fesetexceptflag
20005 functions in <fenv.h> provide the facility to save and restore all five status flags at
20006 one time. These functions are used in conjunction with the type fexcept_t and the
20007 floating-point exception macros (FE_INEXACT, FE_DIVBYZERO,
20008 FE_UNDERFLOW, FE_OVERFLOW, FE_INVALID) also in <fenv.h>.
20009 -- The fegetround and fesetround functions in <fenv.h> provide the facility
20010 to select among the IEC 60559 directed rounding modes represented by the rounding
20011 direction macros in <fenv.h> (FE_TONEAREST, FE_UPWARD, FE_DOWNWARD,
20012 FE_TOWARDZERO) and the values 0, 1, 2, and 3 of FLT_ROUNDS are the
20013 IEC 60559 directed rounding modes.
20014 -- The fegetenv, feholdexcept, fesetenv, and feupdateenv functions in
20015 <fenv.h> provide a facility to manage the floating-point environment, comprising
20016 the IEC 60559 status flags and control modes.
20017 -- The copysign functions in <math.h> provide the copysign function
20018 recommended in the Appendix to IEC 60559.
20019 -- The fabs functions in <math.h> provide the abs function recommended in the
20020 Appendix to IEC 60559.
20021 -- The unary minus (-) operator provides the unary minus (-) operation recommended
20022 in the Appendix to IEC 60559.
20023 -- The scalbn and scalbln functions in <math.h> provide the scalb function
20024 recommended in the Appendix to IEC 60559.
20025 -- The logb functions in <math.h> provide the logb function recommended in the
20026 Appendix to IEC 60559, but following the newer specifications in ANSI/IEEE 854.
20027 -- The nextafter and nexttoward functions in <math.h> provide the nextafter
20028 function recommended in the Appendix to IEC 60559 (but with a minor change to
20032 better handle signed zeros).
20033 -- The isfinite macro in <math.h> provides the finite function recommended in
20034 the Appendix to IEC 60559.
20035 -- The isnan macro in <math.h> provides the isnan function recommended in the
20036 Appendix to IEC 60559.
20037 -- The signbit macro and the fpclassify macro in <math.h>, used in
20038 conjunction with the number classification macros (FP_NAN, FP_INFINITE,
20039 FP_NORMAL, FP_SUBNORMAL, FP_ZERO), provide the facility of the class
20040 function recommended in the Appendix to IEC 60559 (except that the classification
20041 macros defined in 7.12.3 do not distinguish signaling from quiet NaNs).
20042 F.4 Floating to integer conversion
20043 1 If the integer type is _Bool, 6.3.1.2 applies and no floating-point exceptions are raised
20044 (even for NaN). Otherwise, if the floating value is infinite or NaN or if the integral part
20045 of the floating value exceeds the range of the integer type, then the ''invalid'' floating-
20046 point exception is raised and the resulting value is unspecified. Otherwise, the resulting
20047 value is determined by 6.3.1.4. Conversion of an integral floating value that does not
20048 exceed the range of the integer type raises no floating-point exceptions; whether
20049 conversion of a non-integral floating value raises the ''inexact'' floating-point exception is
20051 F.5 Binary-decimal conversion
20052 1 Conversion from the widest supported IEC 60559 format to decimal with
20053 DECIMAL_DIG digits and back is the identity function.348)
20054 2 Conversions involving IEC 60559 formats follow all pertinent recommended practice. In
20055 particular, conversion between any supported IEC 60559 format and decimal with
20056 DECIMAL_DIG or fewer significant digits is correctly rounded (honoring the current
20057 rounding mode), which assures that conversion from the widest supported IEC 60559
20058 format to decimal with DECIMAL_DIG digits and back is the identity function.
20062 347) ANSI/IEEE 854, but not IEC 60559 (ANSI/IEEE 754), directly specifies that floating-to-integer
20063 conversions raise the ''inexact'' floating-point exception for non-integer in-range values. In those
20064 cases where it matters, library functions can be used to effect such conversions with or without raising
20065 the ''inexact'' floating-point exception. See rint, lrint, llrint, and nearbyint in
20067 348) If the minimum-width IEC 60559 extended format (64 bits of precision) is supported,
20068 DECIMAL_DIG shall be at least 21. If IEC 60559 double (53 bits of precision) is the widest
20069 IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and
20070 DBL_DIG are 18 and 15, respectively, for these formats.)
20074 3 Functions such as strtod that convert character sequences to floating types honor the
20075 rounding direction. Hence, if the rounding direction might be upward or downward, the
20076 implementation cannot convert a minus-signed sequence by negating the converted
20078 F.6 The return statement
20079 If the return expression is evaluated in a floating-point format different from the return
20080 type, the expression is converted as if by assignment349) to the return type of the function
20081 and the resulting value is returned to the caller.
20082 F.7 Contracted expressions
20083 1 A contracted expression is correctly rounded (once) and treats infinities, NaNs, signed
20084 zeros, subnormals, and the rounding directions in a manner consistent with the basic
20085 arithmetic operations covered by IEC 60559.
20086 Recommended practice
20087 2 A contracted expression should raise floating-point exceptions in a manner generally
20088 consistent with the basic arithmetic operations. *
20089 F.8 Floating-point environment
20090 1 The floating-point environment defined in <fenv.h> includes the IEC 60559 floating-
20091 point exception status flags and directed-rounding control modes. It includes also
20092 IEC 60559 dynamic rounding precision and trap enablement modes, if the
20093 implementation supports them.350)
20094 F.8.1 Environment management
20095 1 IEC 60559 requires that floating-point operations implicitly raise floating-point exception
20096 status flags, and that rounding control modes can be set explicitly to affect result values of
20097 floating-point operations. When the state for the FENV_ACCESS pragma (defined in
20098 <fenv.h>) is ''on'', these changes to the floating-point state are treated as side effects
20099 which respect sequence points.351)
20104 349) Assignment removes any extra range and precision.
20105 350) This specification does not require dynamic rounding precision nor trap enablement modes.
20106 351) If the state for the FENV_ACCESS pragma is ''off'', the implementation is free to assume the floating-
20107 point control modes will be the default ones and the floating-point status flags will not be tested,
20108 which allows certain optimizations (see F.9).
20113 1 During translation the IEC 60559 default modes are in effect:
20114 -- The rounding direction mode is rounding to nearest.
20115 -- The rounding precision mode (if supported) is set so that results are not shortened.
20116 -- Trapping or stopping (if supported) is disabled on all floating-point exceptions.
20117 Recommended practice
20118 2 The implementation should produce a diagnostic message for each translation-time
20119 floating-point exception, other than ''inexact'';352) the implementation should then
20120 proceed with the translation of the program.
20122 1 At program startup the floating-point environment is initialized as prescribed by
20124 -- All floating-point exception status flags are cleared.
20125 -- The rounding direction mode is rounding to nearest.
20126 -- The dynamic rounding precision mode (if supported) is set so that results are not
20128 -- Trapping or stopping (if supported) is disabled on all floating-point exceptions.
20129 F.8.4 Constant expressions
20130 1 An arithmetic constant expression of floating type, other than one in an initializer for an
20131 object that has static or thread storage duration, is evaluated (as if) during execution; thus,
20132 it is affected by any operative floating-point control modes and raises floating-point
20133 exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma
20139 352) As floating constants are converted to appropriate internal representations at translation time, their
20140 conversion is subject to default rounding modes and raises no execution-time floating-point exceptions
20141 (even where the state of the FENV_ACCESS pragma is ''on''). Library functions, for example
20142 strtod, provide execution-time conversion of numeric strings.
20143 353) Where the state for the FENV_ACCESS pragma is ''on'', results of inexact expressions like 1.0/3.0
20144 are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and
20145 1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve the
20146 efficiency of translation-time evaluation through static initialization, such as
20147 const static double one_third = 1.0/3.0;
20153 #pragma STDC FENV_ACCESS ON
20156 float w[] = { 0.0/0.0 }; // raises an exception
20157 static float x = 0.0/0.0; // does not raise an exception
20158 float y = 0.0/0.0; // raises an exception
20159 double z = 0.0/0.0; // raises an exception
20162 3 For the static initialization, the division is done at translation time, raising no (execution-time) floating-
20163 point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at
20166 F.8.5 Initialization
20167 1 All computation for automatic initialization is done (as if) at execution time; thus, it is
20168 affected by any operative modes and raises floating-point exceptions as required by
20169 IEC 60559 (provided the state for the FENV_ACCESS pragma is ''on''). All computation
20170 for initialization of objects that have static or thread storage duration is done (as if) at
20174 #pragma STDC FENV_ACCESS ON
20177 float u[] = { 1.1e75 }; // raises exceptions
20178 static float v = 1.1e75; // does not raise exceptions
20179 float w = 1.1e75; // raises exceptions
20180 double x = 1.1e75; // may raise exceptions
20181 float y = 1.1e75f; // may raise exceptions
20182 long double z = 1.1e75; // does not raise exceptions
20185 3 The static initialization of v raises no (execution-time) floating-point exceptions because its computation is
20186 done at translation time. The automatic initialization of u and w require an execution-time conversion to
20187 float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializations
20188 of x and y entail execution-time conversion; however, in some expression evaluation methods, the
20189 conversions is not to a narrower format, in which case no floating-point exception is raised.354) The
20190 automatic initialization of z entails execution-time conversion, but not to a narrower format, so no floating-
20191 point exception is raised. Note that the conversions of the floating constants 1.1e75 and 1.1e75f to
20195 354) Use of float_t and double_t variables increases the likelihood of translation-time computation.
20196 For example, the automatic initialization
20197 double_t x = 1.1e75;
20198 could be done at translation time, regardless of the expression evaluation method.
20202 their internal representations occur at translation time in all cases.
20204 F.8.6 Changing the environment
20205 1 Operations defined in 6.5 and functions and macros defined for the standard libraries
20206 change floating-point status flags and control modes just as indicated by their
20207 specifications (including conformance to IEC 60559). They do not change flags or modes
20208 (so as to be detectable by the user) in any other cases.
20209 2 If the argument to the feraiseexcept function in <fenv.h> represents IEC 60559
20210 valid coincident floating-point exceptions for atomic operations (namely ''overflow'' and
20211 ''inexact'', or ''underflow'' and ''inexact''), then ''overflow'' or ''underflow'' is raised
20212 before ''inexact''.
20214 1 This section identifies code transformations that might subvert IEC 60559-specified
20215 behavior, and others that do not.
20216 F.9.1 Global transformations
20217 1 Floating-point arithmetic operations and external function calls may entail side effects
20218 which optimization shall honor, at least where the state of the FENV_ACCESS pragma is
20219 ''on''. The flags and modes in the floating-point environment may be regarded as global
20220 variables; floating-point operations (+, *, etc.) implicitly read the modes and write the
20222 2 Concern about side effects may inhibit code motion and removal of seemingly useless
20223 code. For example, in
20225 #pragma STDC FENV_ACCESS ON
20229 for (i = 0; i < n; i++) x + 1;
20232 x + 1 might raise floating-point exceptions, so cannot be removed. And since the loop
20233 body might not execute (maybe 0 >= n), x + 1 cannot be moved out of the loop. (Of
20234 course these optimizations are valid if the implementation can rule out the nettlesome
20236 3 This specification does not require support for trap handlers that maintain information
20237 about the order or count of floating-point exceptions. Therefore, between function calls,
20238 floating-point exceptions need not be precise: the actual order and number of occurrences
20239 of floating-point exceptions (> 1) may vary from what the source code expresses. Thus,
20242 the preceding loop could be treated as
20244 F.9.2 Expression transformations
20245 1 x/2 (<->) x x 0.5 Although similar transformations involving inexact constants
20246 generally do not yield numerically equivalent expressions, if the
20247 constants are exact then such transformations can be made on
20248 IEC 60559 machines and others that round perfectly.
20249 1 x x and x/1 (->) x The expressions 1 x x, x/1, and x are equivalent (on IEC 60559
20250 machines, among others).355)
20251 x/x (->) 1.0 The expressions x/x and 1.0 are not equivalent if x can be zero,
20253 x - y (<->) x + (-y) The expressions x - y, x + (-y), and (-y) + x are equivalent (on
20254 IEC 60559 machines, among others).
20255 x - y (<->) -(y - x) The expressions x - y and -(y - x) are not equivalent because 1 - 1
20256 is +0 but -(1 - 1) is -0 (in the default rounding direction).356)
20257 x - x (->) 0.0 The expressions x - x and 0.0 are not equivalent if x is a NaN or
20259 0 x x (->) 0.0 The expressions 0 x x and 0.0 are not equivalent if x is a NaN,
20261 x+0(->) x The expressions x + 0 and x are not equivalent if x is -0, because
20262 (-0) + (+0) yields +0 (in the default rounding direction), not -0.
20263 x-0(->) x (+0) - (+0) yields -0 when rounding is downward (toward -(inf)), but
20264 +0 otherwise, and (-0) - (+0) always yields -0; so, if the state of the
20265 FENV_ACCESS pragma is ''off'', promising default rounding, then
20266 the implementation can replace x - 0 by x, even if x might be zero.
20267 -x (<->) 0 - x The expressions -x and 0 - x are not equivalent if x is +0, because
20268 -(+0) yields -0, but 0 - (+0) yields +0 (unless rounding is
20271 355) Strict support for signaling NaNs -- not required by this specification -- would invalidate these and
20272 other transformations that remove arithmetic operators.
20273 356) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities.
20275 1/(1/ (+-) (inf)) is (+-) (inf)
20277 conj(csqrt(z)) is csqrt(conj(z)),
20282 F.9.3 Relational operators
20283 1 x != x (->) false The expression x != x is true if x is a NaN.
20284 x = x (->) true The expression x = x is false if x is a NaN.
20285 x < y (->) isless(x,y) (and similarly for <=, >, >=) Though numerically equal, these
20286 expressions are not equivalent because of side effects when x or y is a
20287 NaN and the state of the FENV_ACCESS pragma is ''on''. This
20288 transformation, which would be desirable if extra code were required
20289 to cause the ''invalid'' floating-point exception for unordered cases,
20290 could be performed provided the state of the FENV_ACCESS pragma
20292 The sense of relational operators shall be maintained. This includes handling unordered
20293 cases as expressed by the source code.
20295 // calls g and raises ''invalid'' if a and b are unordered
20300 is not equivalent to
20301 // calls f and raises ''invalid'' if a and b are unordered
20307 // calls f without raising ''invalid'' if a and b are unordered
20308 if (isgreaterequal(a,b))
20312 nor, unless the state of the FENV_ACCESS pragma is ''off'', to
20313 // calls g without raising ''invalid'' if a and b are unordered
20318 but is equivalent to
20330 F.9.4 Constant arithmetic
20331 1 The implementation shall honor floating-point exceptions raised by execution-time
20332 constant arithmetic wherever the state of the FENV_ACCESS pragma is ''on''. (See F.8.4
20333 and F.8.5.) An operation on constants that raises no floating-point exception can be
20334 folded during translation, except, if the state of the FENV_ACCESS pragma is ''on'', a
20335 further check is required to assure that changing the rounding direction to downward does
20336 not alter the sign of the result,357) and implementations that support dynamic rounding
20337 precision modes shall assure further that the result of the operation raises no floating-
20338 point exception when converted to the semantic type of the operation.
20339 F.10 Mathematics <math.h>
20340 1 This subclause contains specifications of <math.h> facilities that are particularly suited
20341 for IEC 60559 implementations.
20342 2 The Standard C macro HUGE_VAL and its float and long double analogs,
20343 HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive
20345 3 Special cases for functions in <math.h> are covered directly or indirectly by
20346 IEC 60559. The functions that IEC 60559 specifies directly are identified in F.3. The
20347 other functions in <math.h> treat infinities, NaNs, signed zeros, subnormals, and
20348 (provided the state of the FENV_ACCESS pragma is ''on'') the floating-point status flags
20349 in a manner consistent with the basic arithmetic operations covered by IEC 60559.
20350 4 The expression math_errhandling & MATH_ERREXCEPT shall evaluate to a
20352 5 The ''invalid'' and ''divide-by-zero'' floating-point exceptions are raised as specified in
20353 subsequent subclauses of this annex.
20354 6 The ''overflow'' floating-point exception is raised whenever an infinity -- or, because of
20355 rounding direction, a maximal-magnitude finite number -- is returned in lieu of a value
20356 whose magnitude is too large.
20357 7 The ''underflow'' floating-point exception is raised whenever a result is tiny (essentially
20358 subnormal or zero) and suffers loss of accuracy.358)
20361 357) 0 - 0 yields -0 instead of +0 just when the rounding direction is downward.
20362 358) IEC 60559 allows different definitions of underflow. They all result in the same values, but differ on
20363 when the floating-point exception is raised.
20367 8 Whether or when library functions raise the ''inexact'' floating-point exception is
20368 unspecified, unless explicitly specified otherwise.
20369 9 Whether or when library functions raise an undeserved ''underflow'' floating-point
20370 exception is unspecified.359) Otherwise, as implied by F.8.6, the <math.h> functions do
20371 not raise spurious floating-point exceptions (detectable by the user), other than the
20372 ''inexact'' floating-point exception.
20373 10 Whether the functions honor the rounding direction mode is implementation-defined,
20374 unless explicitly specified otherwise.
20375 11 Functions with a NaN argument return a NaN result and raise no floating-point exception,
20376 except where stated otherwise.
20377 12 The specifications in the following subclauses append to the definitions in <math.h>.
20378 For families of functions, the specifications apply to all of the functions even though only
20379 the principal function is shown. Unless otherwise specified, where the symbol ''(+-)''
20380 occurs in both an argument and the result, the result has the same sign as the argument.
20381 Recommended practice
20382 13 If a function with one or more NaN arguments returns a NaN result, the result should be
20383 the same as one of the NaN arguments (after possible type conversion), except perhaps
20385 F.10.1 Trigonometric functions
20386 F.10.1.1 The acos functions
20387 1 -- acos(1) returns +0.
20388 -- acos(x) returns a NaN and raises the ''invalid'' floating-point exception for
20390 F.10.1.2 The asin functions
20391 1 -- asin((+-)0) returns (+-)0.
20392 -- asin(x) returns a NaN and raises the ''invalid'' floating-point exception for
20398 359) It is intended that undeserved ''underflow'' and ''inexact'' floating-point exceptions are raised only if
20399 avoiding them would be too costly.
20403 F.10.1.3 The atan functions
20404 1 -- atan((+-)0) returns (+-)0.
20405 -- atan((+-)(inf)) returns (+-)pi /2.
20406 F.10.1.4 The atan2 functions
20407 1 -- atan2((+-)0, -0) returns (+-)pi .360)
20408 -- atan2((+-)0, +0) returns (+-)0.
20409 -- atan2((+-)0, x) returns (+-)pi for x < 0.
20410 -- atan2((+-)0, x) returns (+-)0 for x > 0.
20411 -- atan2(y, (+-)0) returns -pi /2 for y < 0.
20412 -- atan2(y, (+-)0) returns pi /2 for y > 0.
20413 -- atan2((+-)y, -(inf)) returns (+-)pi for finite y > 0.
20414 -- atan2((+-)y, +(inf)) returns (+-)0 for finite y > 0.
20415 -- atan2((+-)(inf), x) returns (+-)pi /2 for finite x.
20416 -- atan2((+-)(inf), -(inf)) returns (+-)3pi /4.
20417 -- atan2((+-)(inf), +(inf)) returns (+-)pi /4.
20418 F.10.1.5 The cos functions
20419 1 -- cos((+-)0) returns 1.
20420 -- cos((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
20421 F.10.1.6 The sin functions
20422 1 -- sin((+-)0) returns (+-)0.
20423 -- sin((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
20424 F.10.1.7 The tan functions
20425 1 -- tan((+-)0) returns (+-)0.
20426 -- tan((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
20431 360) atan2(0, 0) does not raise the ''invalid'' floating-point exception, nor does atan2( y , 0) raise
20432 the ''divide-by-zero'' floating-point exception.
20436 F.10.2 Hyperbolic functions
20437 F.10.2.1 The acosh functions
20438 1 -- acosh(1) returns +0.
20439 -- acosh(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 1.
20440 -- acosh(+(inf)) returns +(inf).
20441 F.10.2.2 The asinh functions
20442 1 -- asinh((+-)0) returns (+-)0.
20443 -- asinh((+-)(inf)) returns (+-)(inf).
20444 F.10.2.3 The atanh functions
20445 1 -- atanh((+-)0) returns (+-)0.
20446 -- atanh((+-)1) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception.
20447 -- atanh(x) returns a NaN and raises the ''invalid'' floating-point exception for
20449 F.10.2.4 The cosh functions
20450 1 -- cosh((+-)0) returns 1.
20451 -- cosh((+-)(inf)) returns +(inf).
20452 F.10.2.5 The sinh functions
20453 1 -- sinh((+-)0) returns (+-)0.
20454 -- sinh((+-)(inf)) returns (+-)(inf).
20455 F.10.2.6 The tanh functions
20456 1 -- tanh((+-)0) returns (+-)0.
20457 -- tanh((+-)(inf)) returns (+-)1.
20458 F.10.3 Exponential and logarithmic functions
20459 F.10.3.1 The exp functions
20460 1 -- exp((+-)0) returns 1.
20461 -- exp(-(inf)) returns +0.
20462 -- exp(+(inf)) returns +(inf).
20469 F.10.3.2 The exp2 functions
20470 1 -- exp2((+-)0) returns 1.
20471 -- exp2(-(inf)) returns +0.
20472 -- exp2(+(inf)) returns +(inf).
20473 F.10.3.3 The expm1 functions
20474 1 -- expm1((+-)0) returns (+-)0.
20475 -- expm1(-(inf)) returns -1.
20476 -- expm1(+(inf)) returns +(inf).
20477 F.10.3.4 The frexp functions
20478 1 -- frexp((+-)0, exp) returns (+-)0, and stores 0 in the object pointed to by exp.
20479 -- frexp((+-)(inf), exp) returns (+-)(inf), and stores an unspecified value in the object
20481 -- frexp(NaN, exp) stores an unspecified value in the object pointed to by exp
20482 (and returns a NaN).
20483 2 frexp raises no floating-point exceptions.
20484 3 When the radix of the argument is a power of 2, the returned value is exact and is
20485 independent of the current rounding direction mode.
20486 4 On a binary system, the body of the frexp function might be
20488 *exp = (value == 0) ? 0 : (int)(1 + logb(value));
20489 return scalbn(value, -(*exp));
20491 F.10.3.5 The ilogb functions
20492 1 When the correct result is representable in the range of the return type, the returned value
20493 is exact and is independent of the current rounding direction mode.
20494 2 If the correct result is outside the range of the return type, the numeric result is
20495 unspecified and the ''invalid'' floating-point exception is raised.
20502 F.10.3.6 The ldexp functions
20503 1 On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp).
20504 F.10.3.7 The log functions
20505 1 -- log((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
20506 -- log(1) returns +0.
20507 -- log(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
20508 -- log(+(inf)) returns +(inf).
20509 F.10.3.8 The log10 functions
20510 1 -- log10((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
20511 -- log10(1) returns +0.
20512 -- log10(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
20513 -- log10(+(inf)) returns +(inf).
20514 F.10.3.9 The log1p functions
20515 1 -- log1p((+-)0) returns (+-)0.
20516 -- log1p(-1) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
20517 -- log1p(x) returns a NaN and raises the ''invalid'' floating-point exception for
20519 -- log1p(+(inf)) returns +(inf).
20520 F.10.3.10 The log2 functions
20521 1 -- log2((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
20522 -- log2(1) returns +0.
20523 -- log2(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
20524 -- log2(+(inf)) returns +(inf).
20525 F.10.3.11 The logb functions
20526 1 -- logb((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
20527 -- logb((+-)(inf)) returns +(inf).
20528 2 The returned value is exact and is independent of the current rounding direction mode.
20535 F.10.3.12 The modf functions
20536 1 -- modf((+-)x, iptr) returns a result with the same sign as x.
20537 -- modf((+-)(inf), iptr) returns (+-)0 and stores (+-)(inf) in the object pointed to by iptr.
20538 -- modf(NaN, iptr) stores a NaN in the object pointed to by iptr (and returns a
20540 2 The returned values are exact and are independent of the current rounding direction
20542 3 modf behaves as though implemented by
20545 #pragma STDC FENV_ACCESS ON
20546 double modf(double value, double *iptr)
20548 int save_round = fegetround();
20549 fesetround(FE_TOWARDZERO);
20550 *iptr = nearbyint(value);
20551 fesetround(save_round);
20553 isinf(value) ? 0.0 :
20554 value - (*iptr), value);
20556 F.10.3.13 The scalbn and scalbln functions
20557 1 -- scalbn((+-)0, n) returns (+-)0.
20558 -- scalbn(x, 0) returns x.
20559 -- scalbn((+-)(inf), n) returns (+-)(inf).
20560 2 If the calculation does not overflow or underflow, the returned value is exact and
20561 independent of the current rounding direction mode.
20568 F.10.4 Power and absolute value functions
20569 F.10.4.1 The cbrt functions
20570 1 -- cbrt((+-)0) returns (+-)0.
20571 -- cbrt((+-)(inf)) returns (+-)(inf).
20572 F.10.4.2 The fabs functions
20573 1 -- fabs((+-)0) returns +0.
20574 -- fabs((+-)(inf)) returns +(inf).
20575 2 The returned value is exact and is independent of the current rounding direction mode.
20576 F.10.4.3 The hypot functions
20577 1 -- hypot(x, y), hypot(y, x), and hypot(x, -y) are equivalent.
20578 -- hypot(x, (+-)0) is equivalent to fabs(x).
20579 -- hypot((+-)(inf), y) returns +(inf), even if y is a NaN.
20580 F.10.4.4 The pow functions
20581 1 -- pow((+-)0, y) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception
20582 for y an odd integer < 0.
20583 -- pow((+-)0, y) returns +(inf) and raises the ''divide-by-zero'' floating-point exception
20584 for y < 0, finite, and not an odd integer.
20585 -- pow((+-)0, -(inf)) returns +(inf) and may raise the ''divide-by-zero'' floating-point
20587 -- pow((+-)0, y) returns (+-)0 for y an odd integer > 0.
20588 -- pow((+-)0, y) returns +0 for y > 0 and not an odd integer.
20589 -- pow(-1, (+-)(inf)) returns 1.
20590 -- pow(+1, y) returns 1 for any y, even a NaN.
20591 -- pow(x, (+-)0) returns 1 for any x, even a NaN.
20592 -- pow(x, y) returns a NaN and raises the ''invalid'' floating-point exception for
20593 finite x < 0 and finite non-integer y.
20594 -- pow(x, -(inf)) returns +(inf) for | x | < 1.
20595 -- pow(x, -(inf)) returns +0 for | x | > 1.
20596 -- pow(x, +(inf)) returns +0 for | x | < 1.
20597 -- pow(x, +(inf)) returns +(inf) for | x | > 1.
20602 -- pow(-(inf), y) returns -0 for y an odd integer < 0.
20603 -- pow(-(inf), y) returns +0 for y < 0 and not an odd integer.
20604 -- pow(-(inf), y) returns -(inf) for y an odd integer > 0.
20605 -- pow(-(inf), y) returns +(inf) for y > 0 and not an odd integer.
20606 -- pow(+(inf), y) returns +0 for y < 0.
20607 -- pow(+(inf), y) returns +(inf) for y > 0.
20608 F.10.4.5 The sqrt functions
20609 1 sqrt is fully specified as a basic arithmetic operation in IEC 60559. The returned value
20610 is dependent on the current rounding direction mode.
20611 F.10.5 Error and gamma functions
20612 F.10.5.1 The erf functions
20613 1 -- erf((+-)0) returns (+-)0.
20614 -- erf((+-)(inf)) returns (+-)1.
20615 F.10.5.2 The erfc functions
20616 1 -- erfc(-(inf)) returns 2.
20617 -- erfc(+(inf)) returns +0.
20618 F.10.5.3 The lgamma functions
20619 1 -- lgamma(1) returns +0.
20620 -- lgamma(2) returns +0.
20621 -- lgamma(x) returns +(inf) and raises the ''divide-by-zero'' floating-point exception for
20622 x a negative integer or zero.
20623 -- lgamma(-(inf)) returns +(inf).
20624 -- lgamma(+(inf)) returns +(inf).
20625 F.10.5.4 The tgamma functions
20626 1 -- tgamma((+-)0) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception.
20627 -- tgamma(x) returns a NaN and raises the ''invalid'' floating-point exception for x a
20629 -- tgamma(-(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
20630 -- tgamma(+(inf)) returns +(inf).
20636 F.10.6 Nearest integer functions
20637 F.10.6.1 The ceil functions
20638 1 -- ceil((+-)0) returns (+-)0.
20639 -- ceil((+-)(inf)) returns (+-)(inf).
20640 2 The returned value is independent of the current rounding direction mode.
20641 3 The double version of ceil behaves as though implemented by
20644 #pragma STDC FENV_ACCESS ON
20645 double ceil(double x)
20648 int save_round = fegetround();
20649 fesetround(FE_UPWARD);
20650 result = rint(x); // or nearbyint instead of rint
20651 fesetround(save_round);
20654 4 The ceil functions may, but are not required to, raise the ''inexact'' floating-point
20655 exception for finite non-integer arguments, as this implementation does.
20656 F.10.6.2 The floor functions
20657 1 -- floor((+-)0) returns (+-)0.
20658 -- floor((+-)(inf)) returns (+-)(inf).
20659 2 The returned value and is independent of the current rounding direction mode.
20660 3 See the sample implementation for ceil in F.10.6.1. The floor functions may, but are
20661 not required to, raise the ''inexact'' floating-point exception for finite non-integer
20662 arguments, as that implementation does.
20663 F.10.6.3 The nearbyint functions
20664 1 The nearbyint functions use IEC 60559 rounding according to the current rounding
20665 direction. They do not raise the ''inexact'' floating-point exception if the result differs in
20666 value from the argument.
20667 -- nearbyint((+-)0) returns (+-)0 (for all rounding directions).
20668 -- nearbyint((+-)(inf)) returns (+-)(inf) (for all rounding directions).
20674 F.10.6.4 The rint functions
20675 1 The rint functions differ from the nearbyint functions only in that they do raise the
20676 ''inexact'' floating-point exception if the result differs in value from the argument.
20677 F.10.6.5 The lrint and llrint functions
20678 1 The lrint and llrint functions provide floating-to-integer conversion as prescribed
20679 by IEC 60559. They round according to the current rounding direction. If the rounded
20680 value is outside the range of the return type, the numeric result is unspecified and the
20681 ''invalid'' floating-point exception is raised. When they raise no other floating-point
20682 exception and the result differs from the argument, they raise the ''inexact'' floating-point
20684 F.10.6.6 The round functions
20685 1 -- round((+-)0) returns (+-)0.
20686 -- round((+-)(inf)) returns (+-)(inf).
20687 2 The returned value is independent of the current rounding direction mode.
20688 3 The double version of round behaves as though implemented by
20691 #pragma STDC FENV_ACCESS ON
20692 double round(double x)
20696 feholdexcept(&save_env);
20698 if (fetestexcept(FE_INEXACT)) {
20699 fesetround(FE_TOWARDZERO);
20700 result = rint(copysign(0.5 + fabs(x), x));
20702 feupdateenv(&save_env);
20705 The round functions may, but are not required to, raise the ''inexact'' floating-point
20706 exception for finite non-integer numeric arguments, as this implementation does.
20713 F.10.6.7 The lround and llround functions
20714 1 The lround and llround functions differ from the lrint and llrint functions
20715 with the default rounding direction just in that the lround and llround functions
20716 round halfway cases away from zero and need not raise the ''inexact'' floating-point
20717 exception for non-integer arguments that round to within the range of the return type.
20718 F.10.6.8 The trunc functions
20719 1 The trunc functions use IEC 60559 rounding toward zero (regardless of the current
20720 rounding direction). The returned value is exact.
20721 -- trunc((+-)0) returns (+-)0.
20722 -- trunc((+-)(inf)) returns (+-)(inf).
20723 2 The returned value is independent of the current rounding direction mode. The trunc
20724 functions may, but are not required to, raise the ''inexact'' floating-point exception for
20725 finite non-integer arguments.
20726 F.10.7 Remainder functions
20727 F.10.7.1 The fmod functions
20728 1 -- fmod((+-)0, y) returns (+-)0 for y not zero.
20729 -- fmod(x, y) returns a NaN and raises the ''invalid'' floating-point exception for x
20730 infinite or y zero (and neither is a NaN).
20731 -- fmod(x, (+-)(inf)) returns x for x not infinite.
20732 2 When subnormal results are supported, the returned value is exact and is independent of
20733 the current rounding direction mode.
20734 3 The double version of fmod behaves as though implemented by
20737 #pragma STDC FENV_ACCESS ON
20738 double fmod(double x, double y)
20741 result = remainder(fabs(x), (y = fabs(y)));
20742 if (signbit(result)) result += y;
20743 return copysign(result, x);
20751 F.10.7.2 The remainder functions
20752 1 The remainder functions are fully specified as a basic arithmetic operation in
20754 2 When subnormal results are supported, the returned value is exact and is independent of
20755 the current rounding direction mode.
20756 F.10.7.3 The remquo functions
20757 1 The remquo functions follow the specifications for the remainder functions. They
20758 have no further specifications special to IEC 60559 implementations.
20759 2 When subnormal results are supported, the returned value is exact and is independent of
20760 the current rounding direction mode.
20761 F.10.8 Manipulation functions
20762 F.10.8.1 The copysign functions
20763 1 copysign is specified in the Appendix to IEC 60559.
20764 2 The returned value is exact and is independent of the current rounding direction mode.
20765 F.10.8.2 The nan functions
20766 1 All IEC 60559 implementations support quiet NaNs, in all floating formats.
20767 2 The returned value is exact and is independent of the current rounding direction mode.
20768 F.10.8.3 The nextafter functions
20769 1 -- nextafter(x, y) raises the ''overflow'' and ''inexact'' floating-point exceptions
20770 for x finite and the function value infinite.
20771 -- nextafter(x, y) raises the ''underflow'' and ''inexact'' floating-point
20772 exceptions for the function value subnormal or zero and x != y.
20773 2 Even though underflow or overflow can occur, the returned value is independent of the
20774 current rounding direction mode.
20775 F.10.8.4 The nexttoward functions
20776 1 No additional requirements beyond those on nextafter.
20777 2 Even though underflow or overflow can occur, the returned value is independent of the
20778 current rounding direction mode.
20785 F.10.9 Maximum, minimum, and positive difference functions
20786 F.10.9.1 The fdim functions
20787 1 No additional requirements.
20788 F.10.9.2 The fmax functions
20789 1 If just one argument is a NaN, the fmax functions return the other argument (if both
20790 arguments are NaNs, the functions return a NaN).
20791 2 The returned value is exact and is independent of the current rounding direction mode.
20792 3 The body of the fmax function might be361)
20793 { return (isgreaterequal(x, y) ||
20794 isnan(y)) ? x : y; }
20795 F.10.9.3 The fmin functions
20796 1 The fmin functions are analogous to the fmax functions (see F.10.9.2).
20797 2 The returned value is exact and is independent of the current rounding direction mode.
20798 F.10.10 Floating multiply-add
20799 F.10.10.1 The fma functions
20800 1 -- fma(x, y, z) computes xy + z, correctly rounded once.
20801 -- fma(x, y, z) returns a NaN and optionally raises the ''invalid'' floating-point
20802 exception if one of x and y is infinite, the other is zero, and z is a NaN.
20803 -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if
20804 one of x and y is infinite, the other is zero, and z is not a NaN.
20805 -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if x
20806 times y is an exact infinity and z is also an infinity but with the opposite sign.
20811 361) Ideally, fmax would be sensitive to the sign of zero, for example fmax(-0.0, +0.0) would
20812 return +0; however, implementation in software might be impractical.
20816 F.10.11 Comparison macros
20817 1 Relational operators and their corresponding comparison macros (7.12.14) produce
20818 equivalent result values, even if argument values are represented in wider formats. Thus,
20819 comparison macro arguments represented in formats wider than their semantic types are
20820 not converted to the semantic types, unless the wide evaluation method converts operands
20821 of relational operators to their semantic types. The standard wide evaluation methods
20822 characterized by FLT_EVAL_METHOD equal to 1 or 2 (5.2.4.2.2), do not convert
20823 operands of relational operators to their semantic types.
20832 IEC 60559-compatible complex arithmetic
20834 1 This annex supplements annex F to specify complex arithmetic for compatibility with
20835 IEC 60559 real floating-point arithmetic. An implementation that defines *
20836 __STDC_IEC_559_COMPLEX__ shall conform to the specifications in this annex.362)
20838 1 There is a new keyword _Imaginary, which is used to specify imaginary types. It is
20839 used as a type specifier within declaration specifiers in the same way as _Complex is
20840 (thus, _Imaginary float is a valid type name).
20841 2 There are three imaginary types, designated as float _Imaginary, double
20842 _Imaginary, and long double _Imaginary. The imaginary types (along with
20843 the real floating and complex types) are floating types.
20844 3 For imaginary types, the corresponding real type is given by deleting the keyword
20845 _Imaginary from the type name.
20846 4 Each imaginary type has the same representation and alignment requirements as the
20847 corresponding real type. The value of an object of imaginary type is the value of the real
20848 representation times the imaginary unit.
20849 5 The imaginary type domain comprises the imaginary types.
20851 1 A complex or imaginary value with at least one infinite part is regarded as an infinity
20852 (even if its other part is a NaN). A complex or imaginary value is a finite number if each
20853 of its parts is a finite number (neither infinite nor NaN). A complex or imaginary value is
20854 a zero if each of its parts is a zero.
20859 362) Implementations that do not define __STDC_IEC_559_COMPLEX__ are not required to conform
20860 to these specifications.
20865 G.4.1 Imaginary types
20866 1 Conversions among imaginary types follow rules analogous to those for real floating
20868 G.4.2 Real and imaginary
20869 1 When a value of imaginary type is converted to a real type other than _Bool,363) the
20870 result is a positive zero.
20871 2 When a value of real type is converted to an imaginary type, the result is a positive
20873 G.4.3 Imaginary and complex
20874 1 When a value of imaginary type is converted to a complex type, the real part of the
20875 complex result value is a positive zero and the imaginary part of the complex result value
20876 is determined by the conversion rules for the corresponding real types.
20877 2 When a value of complex type is converted to an imaginary type, the real part of the
20878 complex value is discarded and the value of the imaginary part is converted according to
20879 the conversion rules for the corresponding real types.
20880 G.5 Binary operators
20881 1 The following subclauses supplement 6.5 in order to specify the type of the result for an
20882 operation with an imaginary operand.
20883 2 For most operand types, the value of the result of a binary operator with an imaginary or
20884 complex operand is completely determined, with reference to real arithmetic, by the usual
20885 mathematical formula. For some operand types, the usual mathematical formula is
20886 problematic because of its treatment of infinities and because of undue overflow or
20887 underflow; in these cases the result satisfies certain properties (specified in G.5.1), but is
20888 not completely determined.
20897 G.5.1 Multiplicative operators
20899 1 If one operand has real type and the other operand has imaginary type, then the result has
20900 imaginary type. If both operands have imaginary type, then the result has real type. (If
20901 either operand has complex type, then the result has complex type.)
20902 2 If the operands are not both complex, then the result and floating-point exception
20903 behavior of the * operator is defined by the usual mathematical formula:
20906 x xu i(xv) (xu) + i(xv)
20908 iy i(yu) -yv (-yv) + i(yu)
20910 x + iy (xu) + i(yu) (-yv) + i(xv)
20911 3 If the second operand is not complex, then the result and floating-point exception
20912 behavior of the / operator is defined by the usual mathematical formula:
20919 x + iy (x/u) + i(y/u) (y/v) + i(-x/v)
20920 4 The * and / operators satisfy the following infinity properties for all real, imaginary, and
20921 complex operands:364)
20922 -- if one operand is an infinity and the other operand is a nonzero finite number or an
20923 infinity, then the result of the * operator is an infinity;
20924 -- if the first operand is an infinity and the second operand is a finite number, then the
20925 result of the / operator is an infinity;
20926 -- if the first operand is a finite number and the second operand is an infinity, then the
20927 result of the / operator is a zero;
20932 364) These properties are already implied for those cases covered in the tables, but are required for all cases
20933 (at least where the state for CX_LIMITED_RANGE is ''off'').
20937 -- if the first operand is a nonzero finite number or an infinity and the second operand is
20938 a zero, then the result of the / operator is an infinity.
20939 5 If both operands of the * operator are complex or if the second operand of the / operator
20940 is complex, the operator raises floating-point exceptions if appropriate for the calculation
20941 of the parts of the result, and may raise spurious floating-point exceptions.
20942 6 EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Note
20943 that the imaginary unit I has imaginary type (see G.6).
20945 #include <complex.h>
20946 /* Multiply z * w ... */
20947 double complex _Cmultd(double complex z, double complex w)
20949 #pragma STDC FP_CONTRACT OFF
20950 double a, b, c, d, ac, bd, ad, bc, x, y;
20951 a = creal(z); b = cimag(z);
20952 c = creal(w); d = cimag(w);
20953 ac = a * c; bd = b * d;
20954 ad = a * d; bc = b * c;
20955 x = ac - bd; y = ad + bc;
20956 if (isnan(x) && isnan(y)) {
20957 /* Recover infinities that computed as NaN+iNaN ... */
20959 if ( isinf(a) || isinf(b) ) { // z is infinite
20960 /* "Box" the infinity and change NaNs in the other factor to 0 */
20961 a = copysign(isinf(a) ? 1.0 : 0.0, a);
20962 b = copysign(isinf(b) ? 1.0 : 0.0, b);
20963 if (isnan(c)) c = copysign(0.0, c);
20964 if (isnan(d)) d = copysign(0.0, d);
20967 if ( isinf(c) || isinf(d) ) { // w is infinite
20968 /* "Box" the infinity and change NaNs in the other factor to 0 */
20969 c = copysign(isinf(c) ? 1.0 : 0.0, c);
20970 d = copysign(isinf(d) ? 1.0 : 0.0, d);
20971 if (isnan(a)) a = copysign(0.0, a);
20972 if (isnan(b)) b = copysign(0.0, b);
20975 if (!recalc && (isinf(ac) || isinf(bd) ||
20976 isinf(ad) || isinf(bc))) {
20977 /* Recover infinities from overflow by changing NaNs to 0 ... */
20978 if (isnan(a)) a = copysign(0.0, a);
20979 if (isnan(b)) b = copysign(0.0, b);
20980 if (isnan(c)) c = copysign(0.0, c);
20981 if (isnan(d)) d = copysign(0.0, d);
20988 x = INFINITY * ( a * c - b * d );
20989 y = INFINITY * ( a * d + b * c );
20994 7 This implementation achieves the required treatment of infinities at the cost of only one isnan test in
20995 ordinary (finite) cases. It is less than ideal in that undue overflow and underflow may occur.
20997 8 EXAMPLE 2 Division of two double _Complex operands could be implemented as follows.
20999 #include <complex.h>
21000 /* Divide z / w ... */
21001 double complex _Cdivd(double complex z, double complex w)
21003 #pragma STDC FP_CONTRACT OFF
21004 double a, b, c, d, logbw, denom, x, y;
21006 a = creal(z); b = cimag(z);
21007 c = creal(w); d = cimag(w);
21008 logbw = logb(fmax(fabs(c), fabs(d)));
21009 if (logbw == INFINITY) {
21010 ilogbw = (int)logbw;
21011 c = scalbn(c, -ilogbw); d = scalbn(d, -ilogbw);
21013 denom = c * c + d * d;
21014 x = scalbn((a * c + b * d) / denom, -ilogbw);
21015 y = scalbn((b * c - a * d) / denom, -ilogbw);
21016 /* Recover infinities and zeros that computed as NaN+iNaN; */
21017 /* the only cases are nonzero/zero, infinite/finite, and finite/infinite, ... */
21018 if (isnan(x) && isnan(y)) {
21019 if ((denom == 0.0) &&
21020 (!isnan(a) || !isnan(b))) {
21021 x = copysign(INFINITY, c) * a;
21022 y = copysign(INFINITY, c) * b;
21024 else if ((isinf(a) || isinf(b)) &&
21025 isfinite(c) && isfinite(d)) {
21026 a = copysign(isinf(a) ? 1.0 : 0.0, a);
21027 b = copysign(isinf(b) ? 1.0 : 0.0, b);
21028 x = INFINITY * ( a * c + b * d );
21029 y = INFINITY * ( b * c - a * d );
21031 else if (isinf(logbw) &&
21032 isfinite(a) && isfinite(b)) {
21033 c = copysign(isinf(c) ? 1.0 : 0.0, c);
21034 d = copysign(isinf(d) ? 1.0 : 0.0, d);
21035 x = 0.0 * ( a * c + b * d );
21036 y = 0.0 * ( b * c - a * d );
21044 9 Scaling the denominator alleviates the main overflow and underflow problem, which is more serious than
21045 for multiplication. In the spirit of the multiplication example above, this code does not defend against
21046 overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead of
21047 with division, provides better roundoff characteristics.
21049 G.5.2 Additive operators
21051 1 If both operands have imaginary type, then the result has imaginary type. (If one operand
21052 has real type and the other operand has imaginary type, or if either operand has complex
21053 type, then the result has complex type.)
21054 2 In all cases the result and floating-point exception behavior of a + or - operator is defined
21055 by the usual mathematical formula:
21058 x x(+-)u x (+-) iv (x (+-) u) (+-) iv
21060 iy (+-)u + iy i(y (+-) v) (+-)u + i(y (+-) v)
21062 x + iy (x (+-) u) + iy x + i(y (+-) v) (x (+-) u) + i(y (+-) v)
21063 G.6 Complex arithmetic <complex.h>
21068 are defined, respectively, as _Imaginary and a constant expression of type const
21069 float _Imaginary with the value of the imaginary unit. The macro
21071 is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding
21072 the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro
21074 2 This subclause contains specifications for the <complex.h> functions that are
21075 particularly suited to IEC 60559 implementations. For families of functions, the
21076 specifications apply to all of the functions even though only the principal function is
21080 shown. Unless otherwise specified, where the symbol ''(+-)'' occurs in both an argument
21081 and the result, the result has the same sign as the argument.
21082 3 The functions are continuous onto both sides of their branch cuts, taking into account the
21083 sign of zero. For example, csqrt(-2 (+-) i0) = (+-)isqrt:2. -
21084 4 Since complex and imaginary values are composed of real values, each function may be
21085 regarded as computing real values from real values. Except as noted, the functions treat
21086 real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in a
21087 manner consistent with the specifications for real functions in F.10.365)
21088 5 The functions cimag, conj, cproj, and creal are fully specified for all
21089 implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floating-
21091 6 Each of the functions cabs and carg is specified by a formula in terms of a real
21092 function (whose special cases are covered in annex F):
21093 cabs(x + iy) = hypot(x, y)
21094 carg(x + iy) = atan2(y, x)
21095 7 Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by
21096 a formula in terms of other complex functions (whose special cases are specified below):
21097 casin(z) = -i casinh(iz)
21098 catan(z) = -i catanh(iz)
21099 ccos(z) = ccosh(iz)
21100 csin(z) = -i csinh(iz)
21101 ctan(z) = -i ctanh(iz)
21102 8 For the other functions, the following subclauses specify behavior for special cases,
21103 including treatment of the ''invalid'' and ''divide-by-zero'' floating-point exceptions. For
21104 families of functions, the specifications apply to all of the functions even though only the
21105 principal function is shown. For a function f satisfying f (conj(z)) = conj( f (z)), the
21106 specifications for the upper half-plane imply the specifications for the lower half-plane; if
21107 the function f is also either even, f (-z) = f (z), or odd, f (-z) = - f (z), then the
21108 specifications for the first quadrant imply the specifications for the other three quadrants.
21109 9 In the following subclauses, cis(y) is defined as cos(y) + i sin(y).
21114 365) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its
21115 other part is a NaN.
21119 G.6.1 Trigonometric functions
21120 G.6.1.1 The cacos functions
21121 1 -- cacos(conj(z)) = conj(cacos(z)).
21122 -- cacos((+-)0 + i0) returns pi /2 - i0.
21123 -- cacos((+-)0 + iNaN) returns pi /2 + iNaN.
21124 -- cacos(x + i (inf)) returns pi /2 - i (inf), for finite x.
21125 -- cacos(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21126 point exception, for nonzero finite x.
21127 -- cacos(-(inf) + iy) returns pi - i (inf), for positive-signed finite y.
21128 -- cacos(+(inf) + iy) returns +0 - i (inf), for positive-signed finite y.
21129 -- cacos(-(inf) + i (inf)) returns 3pi /4 - i (inf).
21130 -- cacos(+(inf) + i (inf)) returns pi /4 - i (inf).
21131 -- cacos((+-)(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the
21132 result is unspecified).
21133 -- cacos(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21134 point exception, for finite y.
21135 -- cacos(NaN + i (inf)) returns NaN - i (inf).
21136 -- cacos(NaN + iNaN) returns NaN + iNaN.
21137 G.6.2 Hyperbolic functions
21138 G.6.2.1 The cacosh functions
21139 1 -- cacosh(conj(z)) = conj(cacosh(z)).
21140 -- cacosh((+-)0 + i0) returns +0 + ipi /2.
21141 -- cacosh(x + i (inf)) returns +(inf) + ipi /2, for finite x.
21142 -- cacosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
21143 floating-point exception, for finite x.
21144 -- cacosh(-(inf) + iy) returns +(inf) + ipi , for positive-signed finite y.
21145 -- cacosh(+(inf) + iy) returns +(inf) + i0, for positive-signed finite y.
21146 -- cacosh(-(inf) + i (inf)) returns +(inf) + i3pi /4.
21147 -- cacosh(+(inf) + i (inf)) returns +(inf) + ipi /4.
21148 -- cacosh((+-)(inf) + iNaN) returns +(inf) + iNaN.
21153 -- cacosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
21154 floating-point exception, for finite y.
21155 -- cacosh(NaN + i (inf)) returns +(inf) + iNaN.
21156 -- cacosh(NaN + iNaN) returns NaN + iNaN.
21157 G.6.2.2 The casinh functions
21158 1 -- casinh(conj(z)) = conj(casinh(z)) and casinh is odd.
21159 -- casinh(+0 + i0) returns 0 + i0.
21160 -- casinh(x + i (inf)) returns +(inf) + ipi /2 for positive-signed finite x.
21161 -- casinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
21162 floating-point exception, for finite x.
21163 -- casinh(+(inf) + iy) returns +(inf) + i0 for positive-signed finite y.
21164 -- casinh(+(inf) + i (inf)) returns +(inf) + ipi /4.
21165 -- casinh(+(inf) + iNaN) returns +(inf) + iNaN.
21166 -- casinh(NaN + i0) returns NaN + i0.
21167 -- casinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
21168 floating-point exception, for finite nonzero y.
21169 -- casinh(NaN + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result
21171 -- casinh(NaN + iNaN) returns NaN + iNaN.
21172 G.6.2.3 The catanh functions
21173 1 -- catanh(conj(z)) = conj(catanh(z)) and catanh is odd.
21174 -- catanh(+0 + i0) returns +0 + i0.
21175 -- catanh(+0 + iNaN) returns +0 + iNaN.
21176 -- catanh(+1 + i0) returns +(inf) + i0 and raises the ''divide-by-zero'' floating-point
21178 -- catanh(x + i (inf)) returns +0 + ipi /2, for finite positive-signed x.
21179 -- catanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
21180 floating-point exception, for nonzero finite x.
21181 -- catanh(+(inf) + iy) returns +0 + ipi /2, for finite positive-signed y.
21182 -- catanh(+(inf) + i (inf)) returns +0 + ipi /2.
21183 -- catanh(+(inf) + iNaN) returns +0 + iNaN.
21187 -- catanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
21188 floating-point exception, for finite y.
21189 -- catanh(NaN + i (inf)) returns (+-)0 + ipi /2 (where the sign of the real part of the result is
21191 -- catanh(NaN + iNaN) returns NaN + iNaN.
21192 G.6.2.4 The ccosh functions
21193 1 -- ccosh(conj(z)) = conj(ccosh(z)) and ccosh is even.
21194 -- ccosh(+0 + i0) returns 1 + i0.
21195 -- ccosh(+0 + i (inf)) returns NaN (+-) i0 (where the sign of the imaginary part of the
21196 result is unspecified) and raises the ''invalid'' floating-point exception.
21197 -- ccosh(+0 + iNaN) returns NaN (+-) i0 (where the sign of the imaginary part of the
21198 result is unspecified).
21199 -- ccosh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
21200 exception, for finite nonzero x.
21201 -- ccosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21202 point exception, for finite nonzero x.
21203 -- ccosh(+(inf) + i0) returns +(inf) + i0.
21204 -- ccosh(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y.
21205 -- ccosh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is
21206 unspecified) and raises the ''invalid'' floating-point exception.
21207 -- ccosh(+(inf) + iNaN) returns +(inf) + iNaN.
21208 -- ccosh(NaN + i0) returns NaN (+-) i0 (where the sign of the imaginary part of the
21209 result is unspecified).
21210 -- ccosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21211 point exception, for all nonzero numbers y.
21212 -- ccosh(NaN + iNaN) returns NaN + iNaN.
21213 G.6.2.5 The csinh functions
21214 1 -- csinh(conj(z)) = conj(csinh(z)) and csinh is odd.
21215 -- csinh(+0 + i0) returns +0 + i0.
21216 -- csinh(+0 + i (inf)) returns (+-)0 + iNaN (where the sign of the real part of the result is
21217 unspecified) and raises the ''invalid'' floating-point exception.
21218 -- csinh(+0 + iNaN) returns (+-)0 + iNaN (where the sign of the real part of the result is
21222 -- csinh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
21223 exception, for positive finite x.
21224 -- csinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21225 point exception, for finite nonzero x.
21226 -- csinh(+(inf) + i0) returns +(inf) + i0.
21227 -- csinh(+(inf) + iy) returns +(inf) cis(y), for positive finite y.
21228 -- csinh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is
21229 unspecified) and raises the ''invalid'' floating-point exception.
21230 -- csinh(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result
21232 -- csinh(NaN + i0) returns NaN + i0.
21233 -- csinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21234 point exception, for all nonzero numbers y.
21235 -- csinh(NaN + iNaN) returns NaN + iNaN.
21236 G.6.2.6 The ctanh functions
21237 1 -- ctanh(conj(z)) = conj(ctanh(z))and ctanh is odd.
21238 -- ctanh(+0 + i0) returns +0 + i0.
21239 -- ctanh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
21240 exception, for finite x.
21241 -- ctanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21242 point exception, for finite x.
21243 -- ctanh(+(inf) + iy) returns 1 + i0 sin(2y), for positive-signed finite y.
21244 -- ctanh(+(inf) + i (inf)) returns 1 (+-) i0 (where the sign of the imaginary part of the result
21246 -- ctanh(+(inf) + iNaN) returns 1 (+-) i0 (where the sign of the imaginary part of the
21247 result is unspecified).
21248 -- ctanh(NaN + i0) returns NaN + i0.
21249 -- ctanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21250 point exception, for all nonzero numbers y.
21251 -- ctanh(NaN + iNaN) returns NaN + iNaN.
21258 G.6.3 Exponential and logarithmic functions
21259 G.6.3.1 The cexp functions
21260 1 -- cexp(conj(z)) = conj(cexp(z)).
21261 -- cexp((+-)0 + i0) returns 1 + i0.
21262 -- cexp(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
21263 exception, for finite x.
21264 -- cexp(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21265 point exception, for finite x.
21266 -- cexp(+(inf) + i0) returns +(inf) + i0.
21267 -- cexp(-(inf) + iy) returns +0 cis(y), for finite y.
21268 -- cexp(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y.
21269 -- cexp(-(inf) + i (inf)) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts of
21270 the result are unspecified).
21271 -- cexp(+(inf) + i (inf)) returns (+-)(inf) + iNaN and raises the ''invalid'' floating-point
21272 exception (where the sign of the real part of the result is unspecified).
21273 -- cexp(-(inf) + iNaN) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts
21274 of the result are unspecified).
21275 -- cexp(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result
21277 -- cexp(NaN + i0) returns NaN + i0.
21278 -- cexp(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21279 point exception, for all nonzero numbers y.
21280 -- cexp(NaN + iNaN) returns NaN + iNaN.
21281 G.6.3.2 The clog functions
21282 1 -- clog(conj(z)) = conj(clog(z)).
21283 -- clog(-0 + i0) returns -(inf) + ipi and raises the ''divide-by-zero'' floating-point
21285 -- clog(+0 + i0) returns -(inf) + i0 and raises the ''divide-by-zero'' floating-point
21287 -- clog(x + i (inf)) returns +(inf) + ipi /2, for finite x.
21288 -- clog(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21289 point exception, for finite x.
21293 -- clog(-(inf) + iy) returns +(inf) + ipi , for finite positive-signed y.
21294 -- clog(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y.
21295 -- clog(-(inf) + i (inf)) returns +(inf) + i3pi /4.
21296 -- clog(+(inf) + i (inf)) returns +(inf) + ipi /4.
21297 -- clog((+-)(inf) + iNaN) returns +(inf) + iNaN.
21298 -- clog(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21299 point exception, for finite y.
21300 -- clog(NaN + i (inf)) returns +(inf) + iNaN.
21301 -- clog(NaN + iNaN) returns NaN + iNaN.
21302 G.6.4 Power and absolute-value functions
21303 G.6.4.1 The cpow functions
21304 1 The cpow functions raise floating-point exceptions if appropriate for the calculation of
21305 the parts of the result, and may also raise spurious floating-point exceptions.366)
21306 G.6.4.2 The csqrt functions
21307 1 -- csqrt(conj(z)) = conj(csqrt(z)).
21308 -- csqrt((+-)0 + i0) returns +0 + i0.
21309 -- csqrt(x + i (inf)) returns +(inf) + i (inf), for all x (including NaN).
21310 -- csqrt(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21311 point exception, for finite x.
21312 -- csqrt(-(inf) + iy) returns +0 + i (inf), for finite positive-signed y.
21313 -- csqrt(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y.
21314 -- csqrt(-(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the
21315 result is unspecified).
21316 -- csqrt(+(inf) + iNaN) returns +(inf) + iNaN.
21317 -- csqrt(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
21318 point exception, for finite y.
21319 -- csqrt(NaN + iNaN) returns NaN + iNaN.
21324 366) This allows cpow( z , c ) to be implemented as cexp(c clog( z )) without precluding
21325 implementations that treat special cases more carefully.
21329 G.7 Type-generic math <tgmath.h>
21330 1 Type-generic macros that accept complex arguments also accept imaginary arguments. If
21331 an argument is imaginary, the macro expands to an expression whose type is real,
21332 imaginary, or complex, as appropriate for the particular function: if the argument is
21333 imaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; the
21334 types of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; and
21335 the types of the others are complex.
21336 2 Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh,
21337 sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of real
21340 sin(iy) = i sinh(y)
21341 tan(iy) = i tanh(y)
21343 sinh(iy) = i sin(y)
21344 tanh(iy) = i tan(y)
21345 asin(iy) = i asinh(y)
21346 atan(iy) = i atanh(y)
21347 asinh(iy) = i asin(y)
21348 atanh(iy) = i atan(y)
21357 Language independent arithmetic
21359 1 This annex documents the extent to which the C language supports the ISO/IEC 10967-1
21360 standard for language-independent arithmetic (LIA-1). LIA-1 is more general than
21361 IEC 60559 (annex F) in that it covers integer and diverse floating-point arithmetics.
21363 1 The relevant C arithmetic types meet the requirements of LIA-1 types if an
21364 implementation adds notification of exceptional arithmetic operations and meets the 1
21365 unit in the last place (ULP) accuracy requirement (LIA-1 subclause 5.2.8).
21367 1 The LIA-1 data type Boolean is implemented by the C data type bool with values of
21368 true and false, all from <stdbool.h>.
21369 H.2.2 Integer types
21370 1 The signed C integer types int, long int, long long int, and the corresponding
21371 unsigned types are compatible with LIA-1. If an implementation adds support for the
21372 LIA-1 exceptional values ''integer_overflow'' and ''undefined'', then those types are
21373 LIA-1 conformant types. C's unsigned integer types are ''modulo'' in the LIA-1 sense
21374 in that overflows or out-of-bounds results silently wrap. An implementation that defines
21375 signed integer types as also being modulo need not detect integer overflow, in which case,
21376 only integer divide-by-zero need be detected.
21377 2 The parameters for the integer data types can be accessed by the following:
21378 maxint INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX, ULONG_MAX,
21380 minint INT_MIN, LONG_MIN, LLONG_MIN
21381 3 The parameter ''bounded'' is always true, and is not provided. The parameter ''minint''
21382 is always 0 for the unsigned types, and is not provided for those types.
21389 H.2.2.1 Integer operations
21390 1 The integer operations on integer types are the following:
21397 absI abs(x), labs(x), llabs(x)
21404 where x and y are expressions of the same integer type.
21405 H.2.3 Floating-point types
21406 1 The C floating-point types float, double, and long double are compatible with
21407 LIA-1. If an implementation adds support for the LIA-1 exceptional values
21408 ''underflow'', ''floating_overflow'', and ''"undefined'', then those types are conformant
21409 with LIA-1. An implementation that uses IEC 60559 floating-point formats and
21410 operations (see annex F) along with IEC 60559 status flags and traps has LIA-1
21412 H.2.3.1 Floating-point parameters
21413 1 The parameters for a floating point data type can be accessed by the following:
21415 p FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG
21416 emax FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP
21417 emin FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP
21418 2 The derived constants for the floating point types are accessed by the following:
21423 fmax FLT_MAX, DBL_MAX, LDBL_MAX
21424 fminN FLT_MIN, DBL_MIN, LDBL_MIN
21425 epsilon FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON
21426 rnd_style FLT_ROUNDS
21427 H.2.3.2 Floating-point operations
21428 1 The floating-point operations on floating-point types are the following:
21434 absF fabsf(x), fabs(x), fabsl(x)
21435 exponentF 1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x)
21436 scaleF scalbnf(x, n), scalbn(x, n), scalbnl(x, n),
21437 scalblnf(x, li), scalbln(x, li), scalblnl(x, li)
21438 intpartF modff(x, &y), modf(x, &y), modfl(x, &y)
21439 fractpartF modff(x, &y), modf(x, &y), modfl(x, &y)
21446 where x and y are expressions of the same floating point type, n is of type int, and li
21447 is of type long int.
21448 H.2.3.3 Rounding styles
21449 1 The C Standard requires all floating types to use the same radix and rounding style, so
21450 that only one identifier for each is provided to map to LIA-1.
21451 2 The FLT_ROUNDS parameter can be used to indicate the LIA-1 rounding styles:
21452 truncate FLT_ROUNDS == 0
21457 nearest FLT_ROUNDS == 1
21458 other FLT_ROUNDS != 0 && FLT_ROUNDS != 1
21459 provided that an implementation extends FLT_ROUNDS to cover the rounding style used
21460 in all relevant LIA-1 operations, not just addition as in C.
21461 H.2.4 Type conversions
21462 1 The LIA-1 type conversions are the following type casts:
21463 cvtI' (->) I (int)i, (long int)i, (long long int)i,
21464 (unsigned int)i, (unsigned long int)i,
21465 (unsigned long long int)i
21466 cvtF (->) I (int)x, (long int)x, (long long int)x,
21467 (unsigned int)x, (unsigned long int)x,
21468 (unsigned long long int)x
21469 cvtI (->) F (float)i, (double)i, (long double)i
21470 cvtF' (->) F (float)x, (double)x, (long double)x
21471 2 In the above conversions from floating to integer, the use of (cast)x can be replaced with
21472 (cast)round(x), (cast)rint(x), (cast)nearbyint(x), (cast)trunc(x),
21473 (cast)ceil(x), or (cast)floor(x). In addition, C's floating-point to integer
21474 conversion functions, lrint(), llrint(), lround(), and llround(), can be
21475 used. They all meet LIA-1's requirements on floating to integer rounding for in-range
21476 values. For out-of-range values, the conversions shall silently wrap for the modulo types.
21477 3 The fmod() function is useful for doing silent wrapping to unsigned integer types, e.g.,
21478 fmod( fabs(rint(x)), 65536.0 ) or (0.0 <= (y = fmod( rint(x),
21479 65536.0 )) ? y : 65536.0 + y) will compute an integer value in the range 0.0
21480 to 65535.0 which can then be cast to unsigned short int. But, the
21481 remainder() function is not useful for doing silent wrapping to signed integer types,
21482 e.g., remainder( rint(x), 65536.0 ) will compute an integer value in the
21483 range -32767.0 to +32768.0 which is not, in general, in the range of signed short
21485 4 C's conversions (casts) from floating-point to floating-point can meet LIA-1
21486 requirements if an implementation uses round-to-nearest (IEC 60559 default).
21487 5 C's conversions (casts) from integer to floating-point can meet LIA-1 requirements if an
21488 implementation uses round-to-nearest.
21496 1 Notification is the process by which a user or program is informed that an exceptional
21497 arithmetic operation has occurred. C's operations are compatible with LIA-1 in that C
21498 allows an implementation to cause a notification to occur when any arithmetic operation
21499 returns an exceptional value as defined in LIA-1 clause 5.
21500 H.3.1 Notification alternatives
21501 1 LIA-1 requires at least the following two alternatives for handling of notifications:
21502 setting indicators or trap-and-terminate. LIA-1 allows a third alternative: trap-and-
21504 2 An implementation need only support a given notification alternative for the entire
21505 program. An implementation may support the ability to switch between notification
21506 alternatives during execution, but is not required to do so. An implementation can
21507 provide separate selection for each kind of notification, but this is not required.
21508 3 C allows an implementation to provide notification. C's SIGFPE (for traps) and
21509 FE_INVALID, FE_DIVBYZERO, FE_OVERFLOW, FE_UNDERFLOW (for indicators)
21510 can provide LIA-1 notification.
21511 4 C's signal handlers are compatible with LIA-1. Default handling of SIGFPE can
21512 provide trap-and-terminate behavior, except for those LIA-1 operations implemented by
21513 math library function calls. User-provided signal handlers for SIGFPE allow for trap-
21514 and-resume behavior with the same constraint.
21516 1 C's <fenv.h> status flags are compatible with the LIA-1 indicators.
21517 2 The following mapping is for floating-point types:
21518 undefined FE_INVALID, FE_DIVBYZERO
21519 floating_overflow FE_OVERFLOW
21520 underflow FE_UNDERFLOW
21521 3 The floating-point indicator interrogation and manipulation operations are:
21522 set_indicators feraiseexcept(i)
21523 clear_indicators feclearexcept(i)
21524 test_indicators fetestexcept(i)
21525 current_indicators fetestexcept(FE_ALL_EXCEPT)
21526 where i is an expression of type int representing a subset of the LIA-1 indicators.
21527 4 C allows an implementation to provide the following LIA-1 required behavior: at
21528 program termination if any indicator is set the implementation shall send an unambiguous
21531 and ''hard to ignore'' message (see LIA-1 subclause 6.1.2)
21532 5 LIA-1 does not make the distinction between floating-point and integer for ''undefined''.
21533 This documentation makes that distinction because <fenv.h> covers only the floating-
21536 1 C is compatible with LIA-1's trap requirements for arithmetic operations, but not for
21537 math library functions (which are not permitted to invoke a user's signal handler for
21538 SIGFPE). An implementation can provide an alternative of notification through
21539 termination with a ''hard-to-ignore'' message (see LIA-1 subclause 6.1.3).
21540 2 LIA-1 does not require that traps be precise.
21541 3 C does require that SIGFPE be the signal corresponding to LIA-1 arithmetic exceptions,
21542 if there is any signal raised for them.
21543 4 C supports signal handlers for SIGFPE and allows trapping of LIA-1 arithmetic
21544 exceptions. When LIA-1 arithmetic exceptions do trap, C's signal-handler mechanism
21545 allows trap-and-terminate (either default implementation behavior or user replacement for
21546 it) or trap-and-resume, at the programmer's option.
21556 1 An implementation may generate warnings in many situations, none of which are
21557 specified as part of this International Standard. The following are a few of the more
21559 2 -- A new struct or union type appears in a function prototype (6.2.1, 6.7.2.3).
21560 -- A block with initialization of an object that has automatic storage duration is jumped
21562 -- An implicit narrowing conversion is encountered, such as the assignment of a long
21563 int or a double to an int, or a pointer to void to a pointer to any type other than
21564 a character type (6.3).
21565 -- A hexadecimal floating constant cannot be represented exactly in its evaluation format
21567 -- An integer character constant includes more than one character or a wide character
21568 constant includes more than one multibyte character (6.4.4.4).
21569 -- The characters /* are found in a comment (6.4.7).
21570 -- An ''unordered'' binary operator (not comma, &&, or ||) contains a side effect to an
21571 lvalue in one operand, and a side effect to, or an access to the value of, the identical
21572 lvalue in the other operand (6.5).
21573 -- A function is called but no prototype has been supplied (6.5.2.2).
21574 -- The arguments in a function call do not agree in number and type with those of the
21575 parameters in a function definition that is not a prototype (6.5.2.2).
21576 -- An object is defined but not used (6.7).
21577 -- A value is given to an object of an enumerated type other than by assignment of an
21578 enumeration constant that is a member of that type, or an enumeration object that has
21579 the same type, or the value of a function that returns the same enumerated type
21581 -- An aggregate has a partly bracketed initialization (6.7.8).
21582 -- A statement cannot be reached (6.8).
21583 -- A statement with no apparent effect is encountered (6.8).
21584 -- A constant expression is used as the controlling expression of a selection statement
21588 -- An incorrectly formed preprocessing group is encountered while skipping a
21589 preprocessing group (6.10.1).
21590 -- An unrecognized #pragma directive is encountered (6.10.6).
21600 1 This annex collects some information about portability that appears in this International
21602 J.1 Unspecified behavior
21603 1 The following are unspecified:
21604 -- The manner and timing of static initialization (5.1.2).
21605 -- The termination status returned to the hosted environment if the return type of main
21606 is not compatible with int (5.1.2.2.3).
21607 -- The behavior of the display device if a printing character is written when the active
21608 position is at the final position of a line (5.2.2).
21609 -- The behavior of the display device if a backspace character is written when the active
21610 position is at the initial position of a line (5.2.2).
21611 -- The behavior of the display device if a horizontal tab character is written when the
21612 active position is at or past the last defined horizontal tabulation position (5.2.2).
21613 -- The behavior of the display device if a vertical tab character is written when the active
21614 position is at or past the last defined vertical tabulation position (5.2.2).
21615 -- How an extended source character that does not correspond to a universal character
21616 name counts toward the significant initial characters in an external identifier (5.2.4.1).
21617 -- Many aspects of the representations of types (6.2.6).
21618 -- The value of padding bytes when storing values in structures or unions (6.2.6.1).
21619 -- The values of bytes that correspond to union members other than the one last stored
21621 -- The representation used when storing a value in an object that has more than one
21622 object representation for that value (6.2.6.1).
21623 -- The values of any padding bits in integer representations (6.2.6.2).
21624 -- Whether certain operators can generate negative zeros and whether a negative zero
21625 becomes a normal zero when stored in an object (6.2.6.2).
21626 -- Whether two string literals result in distinct arrays (6.4.5).
21627 -- The order in which subexpressions are evaluated and the order in which side effects
21628 take place, except as specified for the function-call (), &&, ||, ? :, and comma
21632 -- The order in which the function designator, arguments, and subexpressions within the
21633 arguments are evaluated in a function call (6.5.2.2).
21634 -- The order of side effects among compound literal initialization list expressions
21636 -- The order in which the operands of an assignment operator are evaluated (6.5.16).
21637 -- The alignment of the addressable storage unit allocated to hold a bit-field (6.7.2.1).
21638 -- Whether a call to an inline function uses the inline definition or the external definition
21639 of the function (6.7.4).
21640 -- Whether or not a size expression is evaluated when it is part of the operand of a
21641 sizeof operator and changing the value of the size expression would not affect the
21642 result of the operator (6.7.6.2).
21643 -- The order in which any side effects occur among the initialization list expressions in
21644 an initializer (6.7.9).
21645 -- The layout of storage for function parameters (6.9.1).
21646 -- When a fully expanded macro replacement list contains a function-like macro name
21647 as its last preprocessing token and the next preprocessing token from the source file is
21648 a (, and the fully expanded replacement of that macro ends with the name of the first
21649 macro and the next preprocessing token from the source file is again a (, whether that
21650 is considered a nested replacement (6.10.3).
21651 -- The order in which # and ## operations are evaluated during macro substitution
21652 (6.10.3.2, 6.10.3.3).
21653 -- The state of the floating-point status flags when execution passes from a part of the *
21654 program translated with FENV_ACCESS ''off'' to a part translated with
21655 FENV_ACCESS ''on'' (7.6.1).
21656 -- The order in which feraiseexcept raises floating-point exceptions, except as
21657 stated in F.8.6 (7.6.2.3).
21658 -- Whether math_errhandling is a macro or an identifier with external linkage
21660 -- The results of the frexp functions when the specified value is not a floating-point
21662 -- The numeric result of the ilogb functions when the correct value is outside the
21663 range of the return type (7.12.6.5, F.10.3.5).
21664 -- The result of rounding when the value is out of range (7.12.9.5, 7.12.9.7, F.10.6.5).
21669 -- The value stored by the remquo functions in the object pointed to by quo when y is
21671 -- Whether a comparison macro argument that is represented in a format wider than its
21672 semantic type is converted to the semantic type (7.12.14).
21673 -- Whether setjmp is a macro or an identifier with external linkage (7.13).
21674 -- Whether va_copy and va_end are macros or identifiers with external linkage
21676 -- The hexadecimal digit before the decimal point when a non-normalized floating-point
21677 number is printed with an a or A conversion specifier (7.21.6.1, 7.28.2.1).
21678 -- The value of the file position indicator after a successful call to the ungetc function
21679 for a text stream, or the ungetwc function for any stream, until all pushed-back
21680 characters are read or discarded (7.21.7.10, 7.28.3.10).
21681 -- The details of the value stored by the fgetpos function (7.21.9.1).
21682 -- The details of the value returned by the ftell function for a text stream (7.21.9.4).
21683 -- Whether the strtod, strtof, strtold, wcstod, wcstof, and wcstold
21684 functions convert a minus-signed sequence to a negative number directly or by
21685 negating the value resulting from converting the corresponding unsigned sequence
21686 (7.22.1.3, 7.28.4.1.1).
21687 -- The order and contiguity of storage allocated by successive calls to the calloc,
21688 malloc, and realloc functions (7.22.3).
21689 -- The amount of storage allocated by a successful call to the calloc, malloc, or
21690 realloc function when 0 bytes was requested (7.22.3).
21691 -- Which of two elements that compare as equal is matched by the bsearch function
21693 -- The order of two elements that compare as equal in an array sorted by the qsort
21694 function (7.22.5.2).
21695 -- The encoding of the calendar time returned by the time function (7.26.2.4).
21696 -- The characters stored by the strftime or wcsftime function if any of the time
21697 values being converted is outside the normal range (7.26.3.5, 7.28.5.1).
21698 -- The conversion state after an encoding error occurs (7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1,
21700 -- The resulting value when the ''invalid'' floating-point exception is raised during
21701 IEC 60559 floating to integer conversion (F.4).
21707 -- Whether conversion of non-integer IEC 60559 floating values to integer raises the
21708 ''inexact'' floating-point exception (F.4).
21709 -- Whether or when library functions in <math.h> raise the ''inexact'' floating-point
21710 exception in an IEC 60559 conformant implementation (F.10).
21711 -- Whether or when library functions in <math.h> raise an undeserved ''underflow''
21712 floating-point exception in an IEC 60559 conformant implementation (F.10).
21713 -- The exponent value stored by frexp for a NaN or infinity (F.10.3.4).
21714 -- The numeric result returned by the lrint, llrint, lround, and llround
21715 functions if the rounded value is outside the range of the return type (F.10.6.5,
21717 -- The sign of one part of the complex result of several math functions for certain
21718 special cases in IEC 60559 compatible implementations (G.6.1.1, G.6.2.2, G.6.2.3,
21719 G.6.2.4, G.6.2.5, G.6.2.6, G.6.3.1, G.6.4.2).
21720 J.2 Undefined behavior
21721 1 The behavior is undefined in the following circumstances:
21722 -- A ''shall'' or ''shall not'' requirement that appears outside of a constraint is violated
21724 -- A nonempty source file does not end in a new-line character which is not immediately
21725 preceded by a backslash character or ends in a partial preprocessing token or
21727 -- Token concatenation produces a character sequence matching the syntax of a
21728 universal character name (5.1.1.2).
21729 -- A program in a hosted environment does not define a function named main using one
21730 of the specified forms (5.1.2.2.1).
21731 -- The execution of a program contains a data race (5.1.2.4).
21732 -- A character not in the basic source character set is encountered in a source file, except
21733 in an identifier, a character constant, a string literal, a header name, a comment, or a
21734 preprocessing token that is never converted to a token (5.2.1).
21735 -- An identifier, comment, string literal, character constant, or header name contains an
21736 invalid multibyte character or does not begin and end in the initial shift state (5.2.1.2).
21737 -- The same identifier has both internal and external linkage in the same translation unit
21739 -- An object is referred to outside of its lifetime (6.2.4).
21745 -- The value of a pointer to an object whose lifetime has ended is used (6.2.4).
21746 -- The value of an object with automatic storage duration is used while it is
21747 indeterminate (6.2.4, 6.7.9, 6.8).
21748 -- A trap representation is read by an lvalue expression that does not have character type
21750 -- A trap representation is produced by a side effect that modifies any part of the object
21751 using an lvalue expression that does not have character type (6.2.6.1).
21752 -- The operands to certain operators are such that they could produce a negative zero
21753 result, but the implementation does not support negative zeros (6.2.6.2).
21754 -- Two declarations of the same object or function specify types that are not compatible
21756 -- A program requires the formation of a composite type from a variable length array
21757 type whose size is specified by an expression that is not evaluated (6.2.7).
21758 -- Conversion to or from an integer type produces a value outside the range that can be
21759 represented (6.3.1.4).
21760 -- Demotion of one real floating type to another produces a value outside the range that
21761 can be represented (6.3.1.5).
21762 -- An lvalue does not designate an object when evaluated (6.3.2.1).
21763 -- A non-array lvalue with an incomplete type is used in a context that requires the value
21764 of the designated object (6.3.2.1).
21765 -- An lvalue designating an object of automatic storage duration that could have been
21766 declared with the register storage class is used in a context that requires the value
21767 of the designated object, but the object is uninitialized. (6.3.2.1).
21768 -- An lvalue having array type is converted to a pointer to the initial element of the
21769 array, and the array object has register storage class (6.3.2.1).
21770 -- An attempt is made to use the value of a void expression, or an implicit or explicit
21771 conversion (except to void) is applied to a void expression (6.3.2.2).
21772 -- Conversion of a pointer to an integer type produces a value outside the range that can
21773 be represented (6.3.2.3).
21774 -- Conversion between two pointer types produces a result that is incorrectly aligned
21776 -- A pointer is used to call a function whose type is not compatible with the referenced
21783 -- An unmatched ' or " character is encountered on a logical source line during
21784 tokenization (6.4).
21785 -- A reserved keyword token is used in translation phase 7 or 8 for some purpose other
21786 than as a keyword (6.4.1).
21787 -- A universal character name in an identifier does not designate a character whose
21788 encoding falls into one of the specified ranges (6.4.2.1).
21789 -- The initial character of an identifier is a universal character name designating a digit
21791 -- Two identifiers differ only in nonsignificant characters (6.4.2.1).
21792 -- The identifier __func__ is explicitly declared (6.4.2.2).
21793 -- The program attempts to modify a string literal (6.4.5).
21794 -- The characters ', \, ", //, or /* occur in the sequence between the < and >
21795 delimiters, or the characters ', \, //, or /* occur in the sequence between the "
21796 delimiters, in a header name preprocessing token (6.4.7).
21797 -- A side effect on a scalar object is unsequenced relative to either a different side effect
21798 on the same scalar object or a value computation using the value of the same scalar
21800 -- An exceptional condition occurs during the evaluation of an expression (6.5).
21801 -- An object has its stored value accessed other than by an lvalue of an allowable type
21803 -- For a call to a function without a function prototype in scope, the number of *
21804 arguments does not equal the number of parameters (6.5.2.2).
21805 -- For call to a function without a function prototype in scope where the function is
21806 defined with a function prototype, either the prototype ends with an ellipsis or the
21807 types of the arguments after promotion are not compatible with the types of the
21808 parameters (6.5.2.2).
21809 -- For a call to a function without a function prototype in scope where the function is not
21810 defined with a function prototype, the types of the arguments after promotion are not
21811 compatible with those of the parameters after promotion (with certain exceptions)
21813 -- A function is defined with a type that is not compatible with the type (of the
21814 expression) pointed to by the expression that denotes the called function (6.5.2.2).
21815 -- A member of an atomic structure or union is accessed (6.5.2.3).
21816 -- The operand of the unary * operator has an invalid value (6.5.3.2).
21821 -- A pointer is converted to other than an integer or pointer type (6.5.4).
21822 -- The value of the second operand of the / or % operator is zero (6.5.5).
21823 -- Addition or subtraction of a pointer into, or just beyond, an array object and an
21824 integer type produces a result that does not point into, or just beyond, the same array
21826 -- Addition or subtraction of a pointer into, or just beyond, an array object and an
21827 integer type produces a result that points just beyond the array object and is used as
21828 the operand of a unary * operator that is evaluated (6.5.6).
21829 -- Pointers that do not point into, or just beyond, the same array object are subtracted
21831 -- An array subscript is out of range, even if an object is apparently accessible with the
21832 given subscript (as in the lvalue expression a[1][7] given the declaration int
21834 -- The result of subtracting two pointers is not representable in an object of type
21836 -- An expression is shifted by a negative number or by an amount greater than or equal
21837 to the width of the promoted expression (6.5.7).
21838 -- An expression having signed promoted type is left-shifted and either the value of the
21839 expression is negative or the result of shifting would be not be representable in the
21840 promoted type (6.5.7).
21841 -- Pointers that do not point to the same aggregate or union (nor just beyond the same
21842 array object) are compared using relational operators (6.5.8).
21843 -- An object is assigned to an inexactly overlapping object or to an exactly overlapping
21844 object with incompatible type (6.5.16.1).
21845 -- An expression that is required to be an integer constant expression does not have an
21846 integer type; has operands that are not integer constants, enumeration constants,
21847 character constants, sizeof expressions whose results are integer constants, or
21848 immediately-cast floating constants; or contains casts (outside operands to sizeof
21849 operators) other than conversions of arithmetic types to integer types (6.6).
21850 -- A constant expression in an initializer is not, or does not evaluate to, one of the
21851 following: an arithmetic constant expression, a null pointer constant, an address
21852 constant, or an address constant for a complete object type plus or minus an integer
21853 constant expression (6.6).
21854 -- An arithmetic constant expression does not have arithmetic type; has operands that
21855 are not integer constants, floating constants, enumeration constants, character
21856 constants, or sizeof expressions; or contains casts (outside operands to sizeof
21860 operators) other than conversions of arithmetic types to arithmetic types (6.6).
21861 -- The value of an object is accessed by an array-subscript [], member-access . or ->,
21862 address &, or indirection * operator or a pointer cast in creating an address constant
21864 -- An identifier for an object is declared with no linkage and the type of the object is
21865 incomplete after its declarator, or after its init-declarator if it has an initializer (6.7).
21866 -- A function is declared at block scope with an explicit storage-class specifier other
21867 than extern (6.7.1).
21868 -- A structure or union is defined as containing no named members, no anonymous
21869 structures, and no anonymous unions (6.7.2.1).
21870 -- An attempt is made to access, or generate a pointer to just past, a flexible array
21871 member of a structure when the referenced object provides no elements for that array
21873 -- When the complete type is needed, an incomplete structure or union type is not
21874 completed in the same scope by another declaration of the tag that defines the content
21876 -- An attempt is made to modify an object defined with a const-qualified type through
21877 use of an lvalue with non-const-qualified type (6.7.3).
21878 -- An attempt is made to refer to an object defined with a volatile-qualified type through
21879 use of an lvalue with non-volatile-qualified type (6.7.3).
21880 -- The specification of a function type includes any type qualifiers (6.7.3). *
21881 -- Two qualified types that are required to be compatible do not have the identically
21882 qualified version of a compatible type (6.7.3).
21883 -- An object which has been modified is accessed through a restrict-qualified pointer to
21884 a const-qualified type, or through a restrict-qualified pointer and another pointer that
21885 are not both based on the same object (6.7.3.1).
21886 -- A restrict-qualified pointer is assigned a value based on another restricted pointer
21887 whose associated block neither began execution before the block associated with this
21888 pointer, nor ended before the assignment (6.7.3.1).
21889 -- A function with external linkage is declared with an inline function specifier, but is
21890 not also defined in the same translation unit (6.7.4).
21891 -- A function declared with a _Noreturn function specifier returns to its caller (6.7.4).
21892 -- The definition of an object has an alignment specifier and another declaration of that
21893 object has a different alignment specifier (6.7.5).
21898 -- Declarations of an object in different translation units have different alignment
21899 specifiers (6.7.5).
21900 -- Two pointer types that are required to be compatible are not identically qualified, or
21901 are not pointers to compatible types (6.7.6.1).
21902 -- The size expression in an array declaration is not a constant expression and evaluates
21903 at program execution time to a nonpositive value (6.7.6.2).
21904 -- In a context requiring two array types to be compatible, they do not have compatible
21905 element types, or their size specifiers evaluate to unequal values (6.7.6.2).
21906 -- A declaration of an array parameter includes the keyword static within the [ and
21907 ] and the corresponding argument does not provide access to the first element of an
21908 array with at least the specified number of elements (6.7.6.3).
21909 -- A storage-class specifier or type qualifier modifies the keyword void as a function
21910 parameter type list (6.7.6.3).
21911 -- In a context requiring two function types to be compatible, they do not have
21912 compatible return types, or their parameters disagree in use of the ellipsis terminator
21913 or the number and type of parameters (after default argument promotion, when there
21914 is no parameter type list or when one type is specified by a function definition with an
21915 identifier list) (6.7.6.3).
21916 -- The value of an unnamed member of a structure or union is used (6.7.9).
21917 -- The initializer for a scalar is neither a single expression nor a single expression
21918 enclosed in braces (6.7.9).
21919 -- The initializer for a structure or union object that has automatic storage duration is
21920 neither an initializer list nor a single expression that has compatible structure or union
21922 -- The initializer for an aggregate or union, other than an array initialized by a string
21923 literal, is not a brace-enclosed list of initializers for its elements or members (6.7.9).
21924 -- An identifier with external linkage is used, but in the program there does not exist
21925 exactly one external definition for the identifier, or the identifier is not used and there
21926 exist multiple external definitions for the identifier (6.9).
21927 -- A function definition includes an identifier list, but the types of the parameters are not
21928 declared in a following declaration list (6.9.1).
21929 -- An adjusted parameter type in a function definition is not a complete object type
21931 -- A function that accepts a variable number of arguments is defined without a
21932 parameter type list that ends with the ellipsis notation (6.9.1).
21936 -- The } that terminates a function is reached, and the value of the function call is used
21937 by the caller (6.9.1).
21938 -- An identifier for an object with internal linkage and an incomplete type is declared
21939 with a tentative definition (6.9.2).
21940 -- The token defined is generated during the expansion of a #if or #elif
21941 preprocessing directive, or the use of the defined unary operator does not match
21942 one of the two specified forms prior to macro replacement (6.10.1).
21943 -- The #include preprocessing directive that results after expansion does not match
21944 one of the two header name forms (6.10.2).
21945 -- The character sequence in an #include preprocessing directive does not start with a
21947 -- There are sequences of preprocessing tokens within the list of macro arguments that
21948 would otherwise act as preprocessing directives (6.10.3).
21949 -- The result of the preprocessing operator # is not a valid character string literal
21951 -- The result of the preprocessing operator ## is not a valid preprocessing token
21953 -- The #line preprocessing directive that results after expansion does not match one of
21954 the two well-defined forms, or its digit sequence specifies zero or a number greater
21955 than 2147483647 (6.10.4).
21956 -- A non-STDC #pragma preprocessing directive that is documented as causing
21957 translation failure or some other form of undefined behavior is encountered (6.10.6).
21958 -- A #pragma STDC preprocessing directive does not match one of the well-defined
21960 -- The name of a predefined macro, or the identifier defined, is the subject of a
21961 #define or #undef preprocessing directive (6.10.8).
21962 -- An attempt is made to copy an object to an overlapping object by use of a library
21963 function, other than as explicitly allowed (e.g., memmove) (clause 7).
21964 -- A file with the same name as one of the standard headers, not provided as part of the
21965 implementation, is placed in any of the standard places that are searched for included
21966 source files (7.1.2).
21967 -- A header is included within an external declaration or definition (7.1.2).
21968 -- A function, object, type, or macro that is specified as being declared or defined by
21969 some standard header is used before any header that declares or defines it is included
21974 -- A standard header is included while a macro is defined with the same name as a
21976 -- The program attempts to declare a library function itself, rather than via a standard
21977 header, but the declaration does not have external linkage (7.1.2).
21978 -- The program declares or defines a reserved identifier, other than as allowed by 7.1.4
21980 -- The program removes the definition of a macro whose name begins with an
21981 underscore and either an uppercase letter or another underscore (7.1.3).
21982 -- An argument to a library function has an invalid value or a type not expected by a
21983 function with variable number of arguments (7.1.4).
21984 -- The pointer passed to a library function array parameter does not have a value such
21985 that all address computations and object accesses are valid (7.1.4).
21986 -- The macro definition of assert is suppressed in order to access an actual function
21988 -- The argument to the assert macro does not have a scalar type (7.2).
21989 -- The CX_LIMITED_RANGE, FENV_ACCESS, or FP_CONTRACT pragma is used in
21990 any context other than outside all external declarations or preceding all explicit
21991 declarations and statements inside a compound statement (7.3.4, 7.6.1, 7.12.2).
21992 -- The value of an argument to a character handling function is neither equal to the value
21993 of EOF nor representable as an unsigned char (7.4).
21994 -- A macro definition of errno is suppressed in order to access an actual object, or the
21995 program defines an identifier with the name errno (7.5).
21996 -- Part of the program tests floating-point status flags, sets floating-point control modes,
21997 or runs under non-default mode settings, but was translated with the state for the
21998 FENV_ACCESS pragma ''off'' (7.6.1).
21999 -- The exception-mask argument for one of the functions that provide access to the
22000 floating-point status flags has a nonzero value not obtained by bitwise OR of the
22001 floating-point exception macros (7.6.2).
22002 -- The fesetexceptflag function is used to set floating-point status flags that were
22003 not specified in the call to the fegetexceptflag function that provided the value
22004 of the corresponding fexcept_t object (7.6.2.4).
22005 -- The argument to fesetenv or feupdateenv is neither an object set by a call to
22006 fegetenv or feholdexcept, nor is it an environment macro (7.6.4.3, 7.6.4.4).
22007 -- The value of the result of an integer arithmetic or conversion function cannot be
22008 represented (7.8.2.1, 7.8.2.2, 7.8.2.3, 7.8.2.4, 7.22.6.1, 7.22.6.2, 7.22.1).
22012 -- The program modifies the string pointed to by the value returned by the setlocale
22013 function (7.11.1.1).
22014 -- The program modifies the structure pointed to by the value returned by the
22015 localeconv function (7.11.2.1).
22016 -- A macro definition of math_errhandling is suppressed or the program defines
22017 an identifier with the name math_errhandling (7.12).
22018 -- An argument to a floating-point classification or comparison macro is not of real
22019 floating type (7.12.3, 7.12.14).
22020 -- A macro definition of setjmp is suppressed in order to access an actual function, or
22021 the program defines an external identifier with the name setjmp (7.13).
22022 -- An invocation of the setjmp macro occurs other than in an allowed context
22024 -- The longjmp function is invoked to restore a nonexistent environment (7.13.2.1).
22025 -- After a longjmp, there is an attempt to access the value of an object of automatic
22026 storage duration that does not have volatile-qualified type, local to the function
22027 containing the invocation of the corresponding setjmp macro, that was changed
22028 between the setjmp invocation and longjmp call (7.13.2.1).
22029 -- The program specifies an invalid pointer to a signal handler function (7.14.1.1).
22030 -- A signal handler returns when the signal corresponded to a computational exception
22032 -- A signal occurs as the result of calling the abort or raise function, and the signal
22033 handler calls the raise function (7.14.1.1).
22034 -- A signal occurs other than as the result of calling the abort or raise function, and
22035 the signal handler refers to an object with static or thread storage duration that is not a
22036 lock-free atomic object other than by assigning a value to an object declared as
22037 volatile sig_atomic_t, or calls any function in the standard library other
22038 than the abort function, the _Exit function, the quick_exit function, or the
22039 signal function (for the same signal number) (7.14.1.1).
22040 -- The value of errno is referred to after a signal occurred other than as the result of
22041 calling the abort or raise function and the corresponding signal handler obtained
22042 a SIG_ERR return from a call to the signal function (7.14.1.1).
22043 -- A signal is generated by an asynchronous signal handler (7.14.1.1).
22044 -- A function with a variable number of arguments attempts to access its varying
22045 arguments other than through a properly declared and initialized va_list object, or
22046 before the va_start macro is invoked (7.16, 7.16.1.1, 7.16.1.4).
22050 -- The macro va_arg is invoked using the parameter ap that was passed to a function
22051 that invoked the macro va_arg with the same parameter (7.16).
22052 -- A macro definition of va_start, va_arg, va_copy, or va_end is suppressed in
22053 order to access an actual function, or the program defines an external identifier with
22054 the name va_copy or va_end (7.16.1).
22055 -- The va_start or va_copy macro is invoked without a corresponding invocation
22056 of the va_end macro in the same function, or vice versa (7.16.1, 7.16.1.2, 7.16.1.3,
22058 -- The type parameter to the va_arg macro is not such that a pointer to an object of
22059 that type can be obtained simply by postfixing a * (7.16.1.1).
22060 -- The va_arg macro is invoked when there is no actual next argument, or with a
22061 specified type that is not compatible with the promoted type of the actual next
22062 argument, with certain exceptions (7.16.1.1).
22063 -- The va_copy or va_start macro is called to initialize a va_list that was
22064 previously initialized by either macro without an intervening invocation of the
22065 va_end macro for the same va_list (7.16.1.2, 7.16.1.4).
22066 -- The parameter parmN of a va_start macro is declared with the register
22067 storage class, with a function or array type, or with a type that is not compatible with
22068 the type that results after application of the default argument promotions (7.16.1.4).
22069 -- The member designator parameter of an offsetof macro is an invalid right
22070 operand of the . operator for the type parameter, or designates a bit-field (7.19).
22071 -- The argument in an instance of one of the integer-constant macros is not a decimal,
22072 octal, or hexadecimal constant, or it has a value that exceeds the limits for the
22073 corresponding type (7.20.4).
22074 -- A byte input/output function is applied to a wide-oriented stream, or a wide character
22075 input/output function is applied to a byte-oriented stream (7.21.2).
22076 -- Use is made of any portion of a file beyond the most recent wide character written to
22077 a wide-oriented stream (7.21.2).
22078 -- The value of a pointer to a FILE object is used after the associated file is closed
22080 -- The stream for the fflush function points to an input stream or to an update stream
22081 in which the most recent operation was input (7.21.5.2).
22082 -- The string pointed to by the mode argument in a call to the fopen function does not
22083 exactly match one of the specified character sequences (7.21.5.3).
22084 -- An output operation on an update stream is followed by an input operation without an
22085 intervening call to the fflush function or a file positioning function, or an input
22088 operation on an update stream is followed by an output operation with an intervening
22089 call to a file positioning function (7.21.5.3).
22090 -- An attempt is made to use the contents of the array that was supplied in a call to the
22091 setvbuf function (7.21.5.6).
22092 -- There are insufficient arguments for the format in a call to one of the formatted
22093 input/output functions, or an argument does not have an appropriate type (7.21.6.1,
22094 7.21.6.2, 7.28.2.1, 7.28.2.2).
22095 -- The format in a call to one of the formatted input/output functions or to the
22096 strftime or wcsftime function is not a valid multibyte character sequence that
22097 begins and ends in its initial shift state (7.21.6.1, 7.21.6.2, 7.26.3.5, 7.28.2.1, 7.28.2.2,
22099 -- In a call to one of the formatted output functions, a precision appears with a
22100 conversion specifier other than those described (7.21.6.1, 7.28.2.1).
22101 -- A conversion specification for a formatted output function uses an asterisk to denote
22102 an argument-supplied field width or precision, but the corresponding argument is not
22103 provided (7.21.6.1, 7.28.2.1).
22104 -- A conversion specification for a formatted output function uses a # or 0 flag with a
22105 conversion specifier other than those described (7.21.6.1, 7.28.2.1).
22106 -- A conversion specification for one of the formatted input/output functions uses a
22107 length modifier with a conversion specifier other than those described (7.21.6.1,
22108 7.21.6.2, 7.28.2.1, 7.28.2.2).
22109 -- An s conversion specifier is encountered by one of the formatted output functions,
22110 and the argument is missing the null terminator (unless a precision is specified that
22111 does not require null termination) (7.21.6.1, 7.28.2.1).
22112 -- An n conversion specification for one of the formatted input/output functions includes
22113 any flags, an assignment-suppressing character, a field width, or a precision (7.21.6.1,
22114 7.21.6.2, 7.28.2.1, 7.28.2.2).
22115 -- A % conversion specifier is encountered by one of the formatted input/output
22116 functions, but the complete conversion specification is not exactly %% (7.21.6.1,
22117 7.21.6.2, 7.28.2.1, 7.28.2.2).
22118 -- An invalid conversion specification is found in the format for one of the formatted
22119 input/output functions, or the strftime or wcsftime function (7.21.6.1, 7.21.6.2,
22120 7.26.3.5, 7.28.2.1, 7.28.2.2, 7.28.5.1).
22121 -- The number of characters transmitted by a formatted output function is greater than
22122 INT_MAX (7.21.6.1, 7.21.6.3, 7.21.6.8, 7.21.6.10).
22127 -- The result of a conversion by one of the formatted input functions cannot be
22128 represented in the corresponding object, or the receiving object does not have an
22129 appropriate type (7.21.6.2, 7.28.2.2).
22130 -- A c, s, or [ conversion specifier is encountered by one of the formatted input
22131 functions, and the array pointed to by the corresponding argument is not large enough
22132 to accept the input sequence (and a null terminator if the conversion specifier is s or
22133 [) (7.21.6.2, 7.28.2.2).
22134 -- A c, s, or [ conversion specifier with an l qualifier is encountered by one of the
22135 formatted input functions, but the input is not a valid multibyte character sequence
22136 that begins in the initial shift state (7.21.6.2, 7.28.2.2).
22137 -- The input item for a %p conversion by one of the formatted input functions is not a
22138 value converted earlier during the same program execution (7.21.6.2, 7.28.2.2).
22139 -- The vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf,
22140 vsscanf, vfwprintf, vfwscanf, vswprintf, vswscanf, vwprintf, or
22141 vwscanf function is called with an improperly initialized va_list argument, or
22142 the argument is used (other than in an invocation of va_end) after the function
22143 returns (7.21.6.8, 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
22144 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10).
22145 -- The contents of the array supplied in a call to the fgets or fgetws function are
22146 used after a read error occurred (7.21.7.2, 7.28.3.2).
22147 -- The file position indicator for a binary stream is used after a call to the ungetc
22148 function where its value was zero before the call (7.21.7.10).
22149 -- The file position indicator for a stream is used after an error occurred during a call to
22150 the fread or fwrite function (7.21.8.1, 7.21.8.2).
22151 -- A partial element read by a call to the fread function is used (7.21.8.1).
22152 -- The fseek function is called for a text stream with a nonzero offset and either the
22153 offset was not returned by a previous successful call to the ftell function on a
22154 stream associated with the same file or whence is not SEEK_SET (7.21.9.2).
22155 -- The fsetpos function is called to set a position that was not returned by a previous
22156 successful call to the fgetpos function on a stream associated with the same file
22158 -- A non-null pointer returned by a call to the calloc, malloc, or realloc function
22159 with a zero requested size is used to access an object (7.22.3).
22160 -- The value of a pointer that refers to space deallocated by a call to the free or
22161 realloc function is used (7.22.3).
22166 -- The alignment requested of the aligned_alloc function is not valid or not
22167 supported by the implementation, or the size requested is not an integral multiple of
22168 the alignment (7.22.3.1).
22169 -- The pointer argument to the free or realloc function does not match a pointer
22170 earlier returned by a memory management function, or the space has been deallocated
22171 by a call to free or realloc (7.22.3.3, 7.22.3.5).
22172 -- The value of the object allocated by the malloc function is used (7.22.3.4).
22173 -- The value of any bytes in a new object allocated by the realloc function beyond
22174 the size of the old object are used (7.22.3.5).
22175 -- The program calls the exit or quick_exit function more than once, or calls both
22176 functions (7.22.4.4, 7.22.4.7).
22177 -- During the call to a function registered with the atexit or at_quick_exit
22178 function, a call is made to the longjmp function that would terminate the call to the
22179 registered function (7.22.4.4, 7.22.4.7).
22180 -- The string set up by the getenv or strerror function is modified by the program
22181 (7.22.4.6, 7.23.6.2).
22182 -- A command is executed through the system function in a way that is documented as
22183 causing termination or some other form of undefined behavior (7.22.4.8).
22184 -- A searching or sorting utility function is called with an invalid pointer argument, even
22185 if the number of elements is zero (7.22.5).
22186 -- The comparison function called by a searching or sorting utility function alters the
22187 contents of the array being searched or sorted, or returns ordering values
22188 inconsistently (7.22.5).
22189 -- The array being searched by the bsearch function does not have its elements in
22190 proper order (7.22.5.1).
22191 -- The current conversion state is used by a multibyte/wide character conversion
22192 function after changing the LC_CTYPE category (7.22.7).
22193 -- A string or wide string utility function is instructed to access an array beyond the end
22194 of an object (7.23.1, 7.28.4).
22195 -- A string or wide string utility function is called with an invalid pointer argument, even
22196 if the length is zero (7.23.1, 7.28.4).
22197 -- The contents of the destination array are used after a call to the strxfrm,
22198 strftime, wcsxfrm, or wcsftime function in which the specified length was
22199 too small to hold the entire null-terminated result (7.23.4.5, 7.26.3.5, 7.28.4.4.4,
22204 -- The first argument in the very first call to the strtok or wcstok is a null pointer
22205 (7.23.5.8, 7.28.4.5.7).
22206 -- The type of an argument to a type-generic macro is not compatible with the type of
22207 the corresponding parameter of the selected function (7.24).
22208 -- A complex argument is supplied for a generic parameter of a type-generic macro that
22209 has no corresponding complex function (7.24).
22210 -- At least one field of the broken-down time passed to asctime contains a value
22211 outside its normal range, or the calculated year exceeds four digits or is less than the
22212 year 1000 (7.26.3.1).
22213 -- The argument corresponding to an s specifier without an l qualifier in a call to the
22214 fwprintf function does not point to a valid multibyte character sequence that
22215 begins in the initial shift state (7.28.2.11).
22216 -- In a call to the wcstok function, the object pointed to by ptr does not have the
22217 value stored by the previous call for the same wide string (7.28.4.5.7).
22218 -- An mbstate_t object is used inappropriately (7.28.6).
22219 -- The value of an argument of type wint_t to a wide character classification or case
22220 mapping function is neither equal to the value of WEOF nor representable as a
22222 -- The iswctype function is called using a different LC_CTYPE category from the
22223 one in effect for the call to the wctype function that returned the description
22225 -- The towctrans function is called using a different LC_CTYPE category from the
22226 one in effect for the call to the wctrans function that returned the description
22228 J.3 Implementation-defined behavior
22229 1 A conforming implementation is required to document its choice of behavior in each of
22230 the areas listed in this subclause. The following are implementation-defined:
22238 1 -- How a diagnostic is identified (3.10, 5.1.1.3).
22239 -- Whether each nonempty sequence of white-space characters other than new-line is
22240 retained or replaced by one space character in translation phase 3 (5.1.1.2).
22242 1 -- The mapping between physical source file multibyte characters and the source
22243 character set in translation phase 1 (5.1.1.2).
22244 -- The name and type of the function called at program startup in a freestanding
22245 environment (5.1.2.1).
22246 -- The effect of program termination in a freestanding environment (5.1.2.1).
22247 -- An alternative manner in which the main function may be defined (5.1.2.2.1).
22248 -- The values given to the strings pointed to by the argv argument to main (5.1.2.2.1).
22249 -- What constitutes an interactive device (5.1.2.3).
22250 -- Whether a program can have more than one thread of execution in a freestanding
22251 environment (5.1.2.4).
22252 -- The set of signals, their semantics, and their default handling (7.14).
22253 -- Signal values other than SIGFPE, SIGILL, and SIGSEGV that correspond to a
22254 computational exception (7.14.1.1).
22255 -- Signals for which the equivalent of signal(sig, SIG_IGN); is executed at
22256 program startup (7.14.1.1).
22257 -- The set of environment names and the method for altering the environment list used
22258 by the getenv function (7.22.4.6).
22259 -- The manner of execution of the string by the system function (7.22.4.8).
22261 1 -- Which additional multibyte characters may appear in identifiers and their
22262 correspondence to universal character names (6.4.2).
22263 -- The number of significant initial characters in an identifier (5.2.4.1, 6.4.2).
22271 1 -- The number of bits in a byte (3.6).
22272 -- The values of the members of the execution character set (5.2.1).
22273 -- The unique value of the member of the execution character set produced for each of
22274 the standard alphabetic escape sequences (5.2.2).
22275 -- The value of a char object into which has been stored any character other than a
22276 member of the basic execution character set (6.2.5).
22277 -- Which of signed char or unsigned char has the same range, representation,
22278 and behavior as ''plain'' char (6.2.5, 6.3.1.1).
22279 -- The mapping of members of the source character set (in character constants and string
22280 literals) to members of the execution character set (6.4.4.4, 5.1.1.2).
22281 -- The value of an integer character constant containing more than one character or
22282 containing a character or escape sequence that does not map to a single-byte
22283 execution character (6.4.4.4).
22284 -- The value of a wide character constant containing more than one multibyte character
22285 or a single multibyte character that maps to multiple members of the extended
22286 execution character set, or containing a multibyte character or escape sequence not
22287 represented in the extended execution character set (6.4.4.4).
22288 -- The current locale used to convert a wide character constant consisting of a single
22289 multibyte character that maps to a member of the extended execution character set
22290 into a corresponding wide character code (6.4.4.4).
22291 -- Whether differently-prefixed wide string literal tokens can be concatenated and, if so,
22292 the treatment of the resulting multibyte character sequence (6.4.5).
22293 -- The current locale used to convert a wide string literal into corresponding wide
22294 character codes (6.4.5).
22295 -- The value of a string literal containing a multibyte character or escape sequence not
22296 represented in the execution character set (6.4.5).
22297 -- The encoding of any of wchar_t, char16_t, and char32_t where the
22298 corresponding standard encoding macro (__STDC_ISO_10646__,
22299 __STDC_UTF_16__, or __STDC_UTF_32__) is not defined (6.10.8.2).
22307 1 -- Any extended integer types that exist in the implementation (6.2.5).
22308 -- Whether signed integer types are represented using sign and magnitude, two's
22309 complement, or ones' complement, and whether the extraordinary value is a trap
22310 representation or an ordinary value (6.2.6.2).
22311 -- The rank of any extended integer type relative to another extended integer type with
22312 the same precision (6.3.1.1).
22313 -- The result of, or the signal raised by, converting an integer to a signed integer type
22314 when the value cannot be represented in an object of that type (6.3.1.3).
22315 -- The results of some bitwise operations on signed integers (6.5).
22316 J.3.6 Floating point
22317 1 -- The accuracy of the floating-point operations and of the library functions in
22318 <math.h> and <complex.h> that return floating-point results (5.2.4.2.2).
22319 -- The accuracy of the conversions between floating-point internal representations and
22320 string representations performed by the library functions in <stdio.h>,
22321 <stdlib.h>, and <wchar.h> (5.2.4.2.2).
22322 -- The rounding behaviors characterized by non-standard values of FLT_ROUNDS
22324 -- The evaluation methods characterized by non-standard negative values of
22325 FLT_EVAL_METHOD (5.2.4.2.2).
22326 -- The direction of rounding when an integer is converted to a floating-point number that
22327 cannot exactly represent the original value (6.3.1.4).
22328 -- The direction of rounding when a floating-point number is converted to a narrower
22329 floating-point number (6.3.1.5).
22330 -- How the nearest representable value or the larger or smaller representable value
22331 immediately adjacent to the nearest representable value is chosen for certain floating
22332 constants (6.4.4.2).
22333 -- Whether and how floating expressions are contracted when not disallowed by the
22334 FP_CONTRACT pragma (6.5).
22335 -- The default state for the FENV_ACCESS pragma (7.6.1).
22336 -- Additional floating-point exceptions, rounding modes, environments, and
22337 classifications, and their macro names (7.6, 7.12).
22338 -- The default state for the FP_CONTRACT pragma (7.12.2).
22343 J.3.7 Arrays and pointers
22344 1 -- The result of converting a pointer to an integer or vice versa (6.3.2.3).
22345 -- The size of the result of subtracting two pointers to elements of the same array
22348 1 -- The extent to which suggestions made by using the register storage-class
22349 specifier are effective (6.7.1).
22350 -- The extent to which suggestions made by using the inline function specifier are
22352 J.3.9 Structures, unions, enumerations, and bit-fields
22353 1 -- Whether a ''plain'' int bit-field is treated as a signed int bit-field or as an
22354 unsigned int bit-field (6.7.2, 6.7.2.1).
22355 -- Allowable bit-field types other than _Bool, signed int, and unsigned int
22357 -- Whether atomic types are permitted for bit-fields (6.7.2.1).
22358 -- Whether a bit-field can straddle a storage-unit boundary (6.7.2.1).
22359 -- The order of allocation of bit-fields within a unit (6.7.2.1).
22360 -- The alignment of non-bit-field members of structures (6.7.2.1). This should present
22361 no problem unless binary data written by one implementation is read by another.
22362 -- The integer type compatible with each enumerated type (6.7.2.2).
22364 1 -- What constitutes an access to an object that has volatile-qualified type (6.7.3).
22365 J.3.11 Preprocessing directives
22366 1 -- The locations within #pragma directives where header name preprocessing tokens
22367 are recognized (6.4, 6.4.7).
22368 -- How sequences in both forms of header names are mapped to headers or external
22369 source file names (6.4.7).
22370 -- Whether the value of a character constant in a constant expression that controls
22371 conditional inclusion matches the value of the same character constant in the
22372 execution character set (6.10.1).
22373 -- Whether the value of a single-character character constant in a constant expression
22374 that controls conditional inclusion may have a negative value (6.10.1).
22379 -- The places that are searched for an included < > delimited header, and how the places
22380 are specified or the header is identified (6.10.2).
22381 -- How the named source file is searched for in an included " " delimited header
22383 -- The method by which preprocessing tokens (possibly resulting from macro
22384 expansion) in a #include directive are combined into a header name (6.10.2).
22385 -- The nesting limit for #include processing (6.10.2).
22386 -- Whether the # operator inserts a \ character before the \ character that begins a
22387 universal character name in a character constant or string literal (6.10.3.2).
22388 -- The behavior on each recognized non-STDC #pragma directive (6.10.6).
22389 -- The definitions for __DATE__ and __TIME__ when respectively, the date and
22390 time of translation are not available (6.10.8.1).
22391 J.3.12 Library functions
22392 1 -- Any library facilities available to a freestanding program, other than the minimal set
22393 required by clause 4 (5.1.2.1).
22394 -- The format of the diagnostic printed by the assert macro (7.2.1.1).
22395 -- The representation of the floating-point status flags stored by the
22396 fegetexceptflag function (7.6.2.2).
22397 -- Whether the feraiseexcept function raises the ''inexact'' floating-point
22398 exception in addition to the ''overflow'' or ''underflow'' floating-point exception
22400 -- Strings other than "C" and "" that may be passed as the second argument to the
22401 setlocale function (7.11.1.1).
22402 -- The types defined for float_t and double_t when the value of the
22403 FLT_EVAL_METHOD macro is less than 0 (7.12).
22404 -- Domain errors for the mathematics functions, other than those required by this
22405 International Standard (7.12.1).
22406 -- The values returned by the mathematics functions on domain errors or pole errors
22408 -- The values returned by the mathematics functions on underflow range errors, whether
22409 errno is set to the value of the macro ERANGE when the integer expression
22410 math_errhandling & MATH_ERRNO is nonzero, and whether the ''underflow''
22411 floating-point exception is raised when the integer expression math_errhandling
22412 & MATH_ERREXCEPT is nonzero. (7.12.1).
22416 -- Whether a domain error occurs or zero is returned when an fmod function has a
22417 second argument of zero (7.12.10.1).
22418 -- Whether a domain error occurs or zero is returned when a remainder function has
22419 a second argument of zero (7.12.10.2).
22420 -- The base-2 logarithm of the modulus used by the remquo functions in reducing the
22421 quotient (7.12.10.3).
22422 -- Whether a domain error occurs or zero is returned when a remquo function has a
22423 second argument of zero (7.12.10.3).
22424 -- Whether the equivalent of signal(sig, SIG_DFL); is executed prior to the call
22425 of a signal handler, and, if not, the blocking of signals that is performed (7.14.1.1).
22426 -- The null pointer constant to which the macro NULL expands (7.19).
22427 -- Whether the last line of a text stream requires a terminating new-line character
22429 -- Whether space characters that are written out to a text stream immediately before a
22430 new-line character appear when read in (7.21.2).
22431 -- The number of null characters that may be appended to data written to a binary
22433 -- Whether the file position indicator of an append-mode stream is initially positioned at
22434 the beginning or end of the file (7.21.3).
22435 -- Whether a write on a text stream causes the associated file to be truncated beyond that
22437 -- The characteristics of file buffering (7.21.3).
22438 -- Whether a zero-length file actually exists (7.21.3).
22439 -- The rules for composing valid file names (7.21.3).
22440 -- Whether the same file can be simultaneously open multiple times (7.21.3).
22441 -- The nature and choice of encodings used for multibyte characters in files (7.21.3).
22442 -- The effect of the remove function on an open file (7.21.4.1).
22443 -- The effect if a file with the new name exists prior to a call to the rename function
22445 -- Whether an open temporary file is removed upon abnormal program termination
22447 -- Which changes of mode are permitted (if any), and under what circumstances
22452 -- The style used to print an infinity or NaN, and the meaning of any n-char or n-wchar
22453 sequence printed for a NaN (7.21.6.1, 7.28.2.1).
22454 -- The output for %p conversion in the fprintf or fwprintf function (7.21.6.1,
22456 -- The interpretation of a - character that is neither the first nor the last character, nor
22457 the second where a ^ character is the first, in the scanlist for %[ conversion in the
22458 fscanf or fwscanf function (7.21.6.2, 7.28.2.1).
22459 -- The set of sequences matched by a %p conversion and the interpretation of the
22460 corresponding input item in the fscanf or fwscanf function (7.21.6.2, 7.28.2.2).
22461 -- The value to which the macro errno is set by the fgetpos, fsetpos, or ftell
22462 functions on failure (7.21.9.1, 7.21.9.3, 7.21.9.4).
22463 -- The meaning of any n-char or n-wchar sequence in a string representing a NaN that is
22464 converted by the strtod, strtof, strtold, wcstod, wcstof, or wcstold
22465 function (7.22.1.3, 7.28.4.1.1).
22466 -- Whether or not the strtod, strtof, strtold, wcstod, wcstof, or wcstold
22467 function sets errno to ERANGE when underflow occurs (7.22.1.3, 7.28.4.1.1).
22468 -- Whether the calloc, malloc, and realloc functions return a null pointer or a
22469 pointer to an allocated object when the size requested is zero (7.22.3).
22470 -- Whether open streams with unwritten buffered data are flushed, open streams are
22471 closed, or temporary files are removed when the abort or _Exit function is called
22472 (7.22.4.1, 7.22.4.5).
22473 -- The termination status returned to the host environment by the abort, exit,
22474 _Exit, or quick_exit function (7.22.4.1, 7.22.4.4, 7.22.4.5, 7.22.4.7).
22475 -- The value returned by the system function when its argument is not a null pointer
22477 -- The local time zone and Daylight Saving Time (7.26.1).
22478 -- The range and precision of times representable in clock_t and time_t (7.26).
22479 -- The era for the clock function (7.26.2.1).
22480 -- The replacement string for the %Z specifier to the strftime, and wcsftime
22481 functions in the "C" locale (7.26.3.5, 7.28.5.1).
22482 -- Whether the functions in <math.h> honor the rounding direction mode in an
22483 IEC 60559 conformant implementation, unless explicitly specified otherwise (F.10).
22490 J.3.13 Architecture
22491 1 -- The values or expressions assigned to the macros specified in the headers
22492 <float.h>, <limits.h>, and <stdint.h> (5.2.4.2, 7.20.2, 7.20.3).
22493 -- The result of attempting to indirectly access an object with automatic or thread
22494 storage duration from a thread other than the one with which it is associated (6.2.4).
22495 -- The number, order, and encoding of bytes in any object (when not explicitly specified
22496 in this International Standard) (6.2.6.1).
22497 -- Whether any extended alignments are supported and the contexts in which they are
22499 -- Valid alignment values other than those returned by an alignof expression for
22500 fundamental types, if any (6.2.8).
22501 -- The value of the result of the sizeof and alignof operators (6.5.3.4).
22502 J.4 Locale-specific behavior
22503 1 The following characteristics of a hosted environment are locale-specific and are required
22504 to be documented by the implementation:
22505 -- Additional members of the source and execution character sets beyond the basic
22506 character set (5.2.1).
22507 -- The presence, meaning, and representation of additional multibyte characters in the
22508 execution character set beyond the basic character set (5.2.1.2).
22509 -- The shift states used for the encoding of multibyte characters (5.2.1.2).
22510 -- The direction of writing of successive printing characters (5.2.2).
22511 -- The decimal-point character (7.1.1).
22512 -- The set of printing characters (7.4, 7.29.2).
22513 -- The set of control characters (7.4, 7.29.2).
22514 -- The sets of characters tested for by the isalpha, isblank, islower, ispunct,
22515 isspace, isupper, iswalpha, iswblank, iswlower, iswpunct,
22516 iswspace, or iswupper functions (7.4.1.2, 7.4.1.3, 7.4.1.7, 7.4.1.9, 7.4.1.10,
22517 7.4.1.11, 7.29.2.1.2, 7.29.2.1.3, 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, 7.29.2.1.11).
22518 -- The native environment (7.11.1.1).
22519 -- Additional subject sequences accepted by the numeric conversion functions (7.22.1,
22521 -- The collation sequence of the execution character set (7.23.4.3, 7.28.4.4.2).
22526 -- The contents of the error message strings set up by the strerror function
22528 -- The formats for time and date (7.26.3.5, 7.28.5.1).
22529 -- Character mappings that are supported by the towctrans function (7.29.1).
22530 -- Character classifications that are supported by the iswctype function (7.29.1).
22531 J.5 Common extensions
22532 1 The following extensions are widely used in many systems, but are not portable to all
22533 implementations. The inclusion of any extension that may cause a strictly conforming
22534 program to become invalid renders an implementation nonconforming. Examples of such
22535 extensions are new keywords, extra library functions declared in standard headers, or
22536 predefined macros with names that do not begin with an underscore.
22537 J.5.1 Environment arguments
22538 1 In a hosted environment, the main function receives a third argument, char *envp[],
22539 that points to a null-terminated array of pointers to char, each of which points to a string
22540 that provides information about the environment for this execution of the program
22542 J.5.2 Specialized identifiers
22543 1 Characters other than the underscore _, letters, and digits, that are not part of the basic
22544 source character set (such as the dollar sign $, or characters in national character sets)
22545 may appear in an identifier (6.4.2).
22546 J.5.3 Lengths and cases of identifiers
22547 1 All characters in identifiers (with or without external linkage) are significant (6.4.2).
22548 J.5.4 Scopes of identifiers
22549 1 A function identifier, or the identifier of an object the declaration of which contains the
22550 keyword extern, has file scope (6.2.1).
22551 J.5.5 Writable string literals
22552 1 String literals are modifiable (in which case, identical string literals should denote distinct
22560 J.5.6 Other arithmetic types
22561 1 Additional arithmetic types, such as __int128 or double double, and their
22562 appropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may have
22563 more range or precision than long double, may be used for evaluating expressions of
22564 other floating types, and may be used to define float_t or double_t.
22565 J.5.7 Function pointer casts
22566 1 A pointer to an object or to void may be cast to a pointer to a function, allowing data to
22567 be invoked as a function (6.5.4).
22568 2 A pointer to a function may be cast to a pointer to an object or to void, allowing a
22569 function to be inspected or modified (for example, by a debugger) (6.5.4).
22570 J.5.8 Extended bit-field types
22571 1 A bit-field may be declared with a type other than _Bool, unsigned int, or
22572 signed int, with an appropriate maximum width (6.7.2.1).
22573 J.5.9 The fortran keyword
22574 1 The fortran function specifier may be used in a function declaration to indicate that
22575 calls suitable for FORTRAN should be generated, or that a different representation for the
22576 external name is to be generated (6.7.4).
22577 J.5.10 The asm keyword
22578 1 The asm keyword may be used to insert assembly language directly into the translator
22579 output (6.8). The most common implementation is via a statement of the form:
22580 asm ( character-string-literal );
22581 J.5.11 Multiple external definitions
22582 1 There may be more than one external definition for the identifier of an object, with or
22583 without the explicit use of the keyword extern; if the definitions disagree, or more than
22584 one is initialized, the behavior is undefined (6.9.2).
22585 J.5.12 Predefined macro names
22586 1 Macro names that do not begin with an underscore, describing the translation and
22587 execution environments, are defined by the implementation before translation begins
22595 J.5.13 Floating-point status flags
22596 1 If any floating-point status flags are set on normal termination after all calls to functions
22597 registered by the atexit function have been made (see 7.22.4.4), the implementation
22598 writes some diagnostics indicating the fact to the stderr stream, if it is still open,
22599 J.5.14 Extra arguments for signal handlers
22600 1 Handlers for specific signals are called with extra arguments in addition to the signal
22602 J.5.15 Additional stream types and file-opening modes
22603 1 Additional mappings from files to streams are supported (7.21.2).
22604 2 Additional file-opening modes may be specified by characters appended to the mode
22605 argument of the fopen function (7.21.5.3).
22606 J.5.16 Defined file position indicator
22607 1 The file position indicator is decremented by each successful call to the ungetc or
22608 ungetwc function for a text stream, except if its value was zero before a call (7.21.7.10,
22610 J.5.17 Math error reporting
22611 1 Functions declared in <complex.h> and <math.h> raise SIGFPE to report errors
22612 instead of, or in addition to, setting errno or raising floating-point exceptions (7.3,
22622 Bounds-checking interfaces
22624 1 Traditionally, the C Library has contained many functions that trust the programmer to
22625 provide output character arrays big enough to hold the result being produced. Not only
22626 do these functions not check that the arrays are big enough, they frequently lack the
22627 information needed to perform such checks. While it is possible to write safe, robust, and
22628 error-free code using the existing library, the library tends to promote programming styles
22629 that lead to mysterious failures if a result is too big for the provided array.
22630 2 A common programming style is to declare character arrays large enough to handle most
22631 practical cases. However, if these arrays are not large enough to handle the resulting
22632 strings, data can be written past the end of the array overwriting other data and program
22633 structures. The program never gets any indication that a problem exists, and so never has
22634 a chance to recover or to fail gracefully.
22635 3 Worse, this style of programming has compromised the security of computers and
22636 networks. Buffer overflows can often be exploited to run arbitrary code with the
22637 permissions of the vulnerable (defective) program.
22638 4 If the programmer writes runtime checks to verify lengths before calling library
22639 functions, then those runtime checks frequently duplicate work done inside the library
22640 functions, which discover string lengths as a side effect of doing their job.
22641 5 This annex provides alternative library functions that promote safer, more secure
22642 programming. The alternative functions verify that output buffers are large enough for
22643 the intended result and return a failure indicator if they are not. Data is never written past
22644 the end of an array. All string results are null terminated.
22645 6 This annex also addresses another problem that complicates writing robust code:
22646 functions that are not reentrant because they return pointers to static objects owned by the
22647 function. Such functions can be troublesome since a previously returned result can
22648 change if the function is called again, perhaps by another thread.
22656 1 This annex specifies a series of optional extensions that can be useful in the mitigation of
22657 security vulnerabilities in programs, and comprise new functions, macros, and types
22658 declared or defined in existing standard headers.
22659 2 An implementation that defines __STDC_LIB_EXT1__ shall conform to the
22660 specifications in this annex.367)
22661 3 Subclause K.3 should be read as if it were merged into the parallel structure of named
22662 subclauses of clause 7.
22665 K.3.1.1 Standard headers
22666 1 The functions, macros, and types declared or defined in K.3 and its subclauses are not
22667 declared or defined by their respective headers if __STDC_WANT_LIB_EXT1__ is
22668 defined as a macro which expands to the integer constant 0 at the point in the source file
22669 where the appropriate header is first included.
22670 2 The functions, macros, and types declared or defined in K.3 and its subclauses are
22671 declared and defined by their respective headers if __STDC_WANT_LIB_EXT1__ is
22672 defined as a macro which expands to the integer constant 1 at the point in the source file
22673 where the appropriate header is first included.368)
22674 3 It is implementation-defined whether the functions, macros, and types declared or defined
22675 in K.3 and its subclauses are declared or defined by their respective headers if
22676 __STDC_WANT_LIB_EXT1__ is not defined as a macro at the point in the source file
22677 where the appropriate header is first included.369)
22678 4 Within a preprocessing translation unit, __STDC_WANT_LIB_EXT1__ shall be
22679 defined identically for all inclusions of any headers from subclause K.3. If
22680 __STDC_WANT_LIB_EXT1__ is defined differently for any such inclusion, the
22681 implementation shall issue a diagnostic as if a preprocessor error directive were used.
22684 367) Implementations that do not define __STDC_LIB_EXT1__ are not required to conform to these
22686 368) Future revisions of this International Standard may define meanings for other values of
22687 __STDC_WANT_LIB_EXT1__.
22688 369) Subclause 7.1.3 reserves certain names and patterns of names that an implementation may use in
22689 headers. All other names are not reserved, and a conforming implementation is not permitted to use
22690 them. While some of the names defined in K.3 and its subclauses are reserved, others are not. If an
22691 unreserved name is defined in a header when __STDC_WANT_LIB_EXT1__ is defined as 0, the
22692 implementation is not conforming.
22696 K.3.1.2 Reserved identifiers
22697 1 Each macro name in any of the following subclauses is reserved for use as specified if it
22698 is defined by any of its associated headers when included; unless explicitly stated
22699 otherwise (see 7.1.4).
22700 2 All identifiers with external linkage in any of the following subclauses are reserved for
22701 use as identifiers with external linkage if any of them are used by the program. None of
22702 them are reserved if none of them are used.
22703 3 Each identifier with file scope listed in any of the following subclauses is reserved for use
22704 as a macro name and as an identifier with file scope in the same name space if it is
22705 defined by any of its associated headers when included.
22706 K.3.1.3 Use of errno
22707 1 An implementation may set errno for the functions defined in this annex, but is not
22709 K.3.1.4 Runtime-constraint violations
22710 1 Most functions in this annex include as part of their specification a list of runtime-
22711 constraints. These runtime-constraints are requirements on the program using the
22713 2 Implementations shall verify that the runtime-constraints for a function are not violated
22714 by the program. If a runtime-constraint is violated, the implementation shall call the
22715 currently registered runtime-constraint handler (see set_constraint_handler_s
22716 in <stdlib.h>). Multiple runtime-constraint violations in the same call to a library
22717 function result in only one call to the runtime-constraint handler. It is unspecified which
22718 one of the multiple runtime-constraint violations cause the handler to be called.
22719 3 If the runtime-constraints section for a function states an action to be performed when a
22720 runtime-constraint violation occurs, the function shall perform the action before calling
22721 the runtime-constraint handler. If the runtime-constraints section lists actions that are
22722 prohibited when a runtime-constraint violation occurs, then such actions are prohibited to
22723 the function both before calling the handler and after the handler returns.
22724 4 The runtime-constraint handler might not return. If the handler does return, the library
22725 function whose runtime-constraint was violated shall return some indication of failure as
22726 given by the returns section in the function's specification.
22730 370) Although runtime-constraints replace many cases of undefined behavior, undefined behavior still
22731 exists in this annex. Implementations are free to detect any case of undefined behavior and treat it as a
22732 runtime-constraint violation by calling the runtime-constraint handler. This license comes directly
22733 from the definition of undefined behavior.
22737 K.3.2 Errors <errno.h>
22738 1 The header <errno.h> defines a type.
22741 which is type int.371)
22742 K.3.3 Common definitions <stddef.h>
22743 1 The header <stddef.h> defines a type.
22746 which is the type size_t.372)
22747 K.3.4 Integer types <stdint.h>
22748 1 The header <stdint.h> defines a macro.
22751 which expands to a value373) of type size_t. Functions that have parameters of type
22752 rsize_t consider it a runtime-constraint violation if the values of those parameters are
22753 greater than RSIZE_MAX.
22754 Recommended practice
22755 3 Extremely large object sizes are frequently a sign that an object's size was calculated
22756 incorrectly. For example, negative numbers appear as very large positive numbers when
22757 converted to an unsigned type like size_t. Also, some implementations do not support
22758 objects as large as the maximum value that can be represented by type size_t.
22759 4 For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect
22760 programming errors. For implementations targeting machines with large address spaces,
22761 it is recommended that RSIZE_MAX be defined as the smaller of the size of the largest
22762 object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of
22763 some legitimate, but very large, objects. Implementations targeting machines with small
22764 address spaces may wish to define RSIZE_MAX as SIZE_MAX, which means that there
22766 371) As a matter of programming style, errno_t may be used as the type of something that deals only
22767 with the values that might be found in errno. For example, a function which returns the value of
22768 errno might be declared as having the return type errno_t.
22769 372) See the description of the RSIZE_MAX macro in <stdint.h>.
22770 373) The macro RSIZE_MAX need not expand to a constant expression.
22774 is no object size that is considered a runtime-constraint violation.
22775 K.3.5 Input/output <stdio.h>
22776 1 The header <stdio.h> defines several macros and two types.
22779 which expands to an integer constant expression that is the size needed for an array of
22780 char large enough to hold a temporary file name string generated by the tmpnam_s
22783 which expands to an integer constant expression that is the maximum number of unique
22784 file names that can be generated by the tmpnam_s function.
22787 which is type int; and
22789 which is the type size_t.
22790 K.3.5.1 Operations on files
22791 K.3.5.1.1 The tmpfile_s function
22793 1 #define __STDC_WANT_LIB_EXT1__ 1
22795 errno_t tmpfile_s(FILE * restrict * restrict streamptr);
22796 Runtime-constraints
22797 2 streamptr shall not be a null pointer.
22798 3 If there is a runtime-constraint violation, tmpfile_s does not attempt to create a file.
22800 4 The tmpfile_s function creates a temporary binary file that is different from any other
22801 existing file and that will automatically be removed when it is closed or at program
22802 termination. If the program terminates abnormally, whether an open temporary file is
22803 removed is implementation-defined. The file is opened for update with "wb+" mode
22804 with the meaning that mode has in the fopen_s function (including the mode's effect
22805 on exclusive access and file permissions).
22810 5 If the file was created successfully, then the pointer to FILE pointed to by streamptr
22811 will be set to the pointer to the object controlling the opened file. Otherwise, the pointer
22812 to FILE pointed to by streamptr will be set to a null pointer.
22813 Recommended practice
22814 It should be possible to open at least TMP_MAX_S temporary files during the lifetime of
22815 the program (this limit may be shared with tmpnam_s) and there should be no limit on
22816 the number simultaneously open other than this limit and any limit on the number of open
22819 6 The tmpfile_s function returns zero if it created the file. If it did not create the file or
22820 there was a runtime-constraint violation, tmpfile_s returns a nonzero value.
22821 K.3.5.1.2 The tmpnam_s function
22823 1 #define __STDC_WANT_LIB_EXT1__ 1
22825 errno_t tmpnam_s(char *s, rsize_t maxsize);
22826 Runtime-constraints
22827 2 s shall not be a null pointer. maxsize shall be less than or equal to RSIZE_MAX.
22828 maxsize shall be greater than the length of the generated file name string.
22830 3 The tmpnam_s function generates a string that is a valid file name and that is not the
22831 same as the name of an existing file.374) The function is potentially capable of generating
22832 TMP_MAX_S different strings, but any or all of them may already be in use by existing
22833 files and thus not be suitable return values. The lengths of these strings shall be less than
22834 the value of the L_tmpnam_s macro.
22835 4 The tmpnam_s function generates a different string each time it is called.
22836 5 It is assumed that s points to an array of at least maxsize characters. This array will be
22837 set to generated string, as specified below.
22841 374) Files created using strings generated by the tmpnam_s function are temporary only in the sense that
22842 their names should not collide with those generated by conventional naming rules for the
22843 implementation. It is still necessary to use the remove function to remove such files when their use
22844 is ended, and before program termination. Implementations should take care in choosing the patterns
22845 used for names returned by tmpnam_s. For example, making a thread id part of the names avoids the
22846 race condition and possible conflict when multiple programs run simultaneously by the same user
22847 generate the same temporary file names.
22851 6 The implementation shall behave as if no library function except tmpnam calls the
22852 tmpnam_s function.375)
22853 Recommended practice
22854 7 After a program obtains a file name using the tmpnam_s function and before the
22855 program creates a file with that name, the possibility exists that someone else may create
22856 a file with that same name. To avoid this race condition, the tmpfile_s function
22857 should be used instead of tmpnam_s when possible. One situation that requires the use
22858 of the tmpnam_s function is when the program needs to create a temporary directory
22859 rather than a temporary file.
22861 8 If no suitable string can be generated, or if there is a runtime-constraint violation, the
22862 tmpnam_s function writes a null character to s[0] (only if s is not null and maxsize
22863 is greater than zero) and returns a nonzero value.
22864 9 Otherwise, the tmpnam_s function writes the string in the array pointed to by s and
22866 Environmental limits
22867 10 The value of the macro TMP_MAX_S shall be at least 25.
22868 K.3.5.2 File access functions
22869 K.3.5.2.1 The fopen_s function
22871 1 #define __STDC_WANT_LIB_EXT1__ 1
22873 errno_t fopen_s(FILE * restrict * restrict streamptr,
22874 const char * restrict filename,
22875 const char * restrict mode);
22876 Runtime-constraints
22877 2 None of streamptr, filename, or mode shall be a null pointer.
22878 3 If there is a runtime-constraint violation, fopen_s does not attempt to open a file.
22879 Furthermore, if streamptr is not a null pointer, fopen_s sets *streamptr to the
22885 375) An implementation may have tmpnam call tmpnam_s (perhaps so there is only one naming
22886 convention for temporary files), but this is not required.
22891 4 The fopen_s function opens the file whose name is the string pointed to by
22892 filename, and associates a stream with it.
22893 5 The mode string shall be as described for fopen, with the addition that modes starting
22894 with the character 'w' or 'a' may be preceded by the character 'u', see below:
22895 uw truncate to zero length or create text file for writing, default
22897 uwx create text file for writing, default permissions
22898 ua append; open or create text file for writing at end-of-file, default
22900 uwb truncate to zero length or create binary file for writing, default
22902 uwbx create binary file for writing, default permissions
22903 uab append; open or create binary file for writing at end-of-file, default
22905 uw+ truncate to zero length or create text file for update, default
22907 uw+x create text file for update, default permissions
22908 ua+ append; open or create text file for update, writing at end-of-file,
22909 default permissions
22910 uw+b or uwb+ truncate to zero length or create binary file for update, default
22912 uw+bx or uwb+x create binary file for update, default permissions
22913 ua+b or uab+ append; open or create binary file for update, writing at end-of-file,
22914 default permissions
22915 6 Opening a file with exclusive mode ('x' as the last character in the mode argument)
22916 fails if the file already exists or cannot be created.
22917 7 To the extent that the underlying system supports the concepts, files opened for writing
22918 shall be opened with exclusive (also known as non-shared) access. If the file is being
22919 created, and the first character of the mode string is not 'u', to the extent that the
22920 underlying system supports it, the file shall have a file permission that prevents other
22921 users on the system from accessing the file. If the file is being created and first character
22922 of the mode string is 'u', then by the time the file has been closed, it shall have the
22923 system default file access permissions.376)
22924 8 If the file was opened successfully, then the pointer to FILE pointed to by streamptr
22925 will be set to the pointer to the object controlling the opened file. Otherwise, the pointer
22928 376) These are the same permissions that the file would have been created with by fopen.
22932 to FILE pointed to by streamptr will be set to a null pointer.
22934 9 The fopen_s function returns zero if it opened the file. If it did not open the file or if
22935 there was a runtime-constraint violation, fopen_s returns a nonzero value.
22936 K.3.5.2.2 The freopen_s function
22938 1 #define __STDC_WANT_LIB_EXT1__ 1
22940 errno_t freopen_s(FILE * restrict * restrict newstreamptr,
22941 const char * restrict filename,
22942 const char * restrict mode,
22943 FILE * restrict stream);
22944 Runtime-constraints
22945 2 None of newstreamptr, mode, and stream shall be a null pointer.
22946 3 If there is a runtime-constraint violation, freopen_s neither attempts to close any file
22947 associated with stream nor attempts to open a file. Furthermore, if newstreamptr is
22948 not a null pointer, fopen_s sets *newstreamptr to the null pointer.
22950 4 The freopen_s function opens the file whose name is the string pointed to by
22951 filename and associates the stream pointed to by stream with it. The mode
22952 argument has the same meaning as in the fopen_s function (including the mode's effect
22953 on exclusive access and file permissions).
22954 5 If filename is a null pointer, the freopen_s function attempts to change the mode of
22955 the stream to that specified by mode, as if the name of the file currently associated with
22956 the stream had been used. It is implementation-defined which changes of mode are
22957 permitted (if any), and under what circumstances.
22958 6 The freopen_s function first attempts to close any file that is associated with stream.
22959 Failure to close the file is ignored. The error and end-of-file indicators for the stream are
22961 7 If the file was opened successfully, then the pointer to FILE pointed to by
22962 newstreamptr will be set to the value of stream. Otherwise, the pointer to FILE
22963 pointed to by newstreamptr will be set to a null pointer.
22965 8 The freopen_s function returns zero if it opened the file. If it did not open the file or
22966 there was a runtime-constraint violation, freopen_s returns a nonzero value.
22970 K.3.5.3 Formatted input/output functions
22971 1 Unless explicitly stated otherwise, if the execution of a function described in this
22972 subclause causes copying to take place between objects that overlap, the objects take on
22973 unspecified values.
22974 K.3.5.3.1 The fprintf_s function
22976 1 #define __STDC_WANT_LIB_EXT1__ 1
22978 int fprintf_s(FILE * restrict stream,
22979 const char * restrict format, ...);
22980 Runtime-constraints
22981 2 Neither stream nor format shall be a null pointer. The %n specifier377) (modified or
22982 not by flags, field width, or precision) shall not appear in the string pointed to by
22983 format. Any argument to fprintf_s corresponding to a %s specifier shall not be a
22985 3 If there is a runtime-constraint violation,378) the fprintf_s function does not attempt
22986 to produce further output, and it is unspecified to what extent fprintf_s produced
22987 output before discovering the runtime-constraint violation.
22989 4 The fprintf_s function is equivalent to the fprintf function except for the explicit
22990 runtime-constraints listed above.
22992 5 The fprintf_s function returns the number of characters transmitted, or a negative
22993 value if an output error, encoding error, or runtime-constraint violation occurred.
22998 377) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
22999 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23000 format string was %%n.
23001 378) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an
23002 implementation may treat any unsupported specifiers in the string pointed to by format as a runtime-
23003 constraint violation.
23007 K.3.5.3.2 The fscanf_s function
23009 1 #define __STDC_WANT_LIB_EXT1__ 1
23011 int fscanf_s(FILE * restrict stream,
23012 const char * restrict format, ...);
23013 Runtime-constraints
23014 2 Neither stream nor format shall be a null pointer. Any argument indirected though in
23015 order to store converted input shall not be a null pointer.
23016 3 If there is a runtime-constraint violation,379) the fscanf_s function does not attempt to
23017 perform further input, and it is unspecified to what extent fscanf_s performed input
23018 before discovering the runtime-constraint violation.
23020 4 The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion
23021 specifiers apply to a pair of arguments (unless assignment suppression is indicated by a
23022 *). The first of these arguments is the same as for fscanf. That argument is
23023 immediately followed in the argument list by the second argument, which has type
23024 rsize_t and gives the number of elements in the array pointed to by the first argument
23025 of the pair. If the first argument points to a scalar object, it is considered to be an array of
23027 5 A matching failure occurs if the number of elements in a receiving object is insufficient to
23028 hold the converted input (including any trailing null character).
23030 6 The fscanf_s function returns the value of the macro EOF if an input failure occurs
23031 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23033 379) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an
23034 implementation may treat any unsupported specifiers in the string pointed to by format as a runtime-
23035 constraint violation.
23036 380) If the format is known at translation time, an implementation may issue a diagnostic for any argument
23037 used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an
23038 argument of a type compatible with rsize_t. A limited amount of checking may be done if even if
23039 the format is not known at translation time. For example, an implementation may issue a diagnostic
23040 for each argument after format that has of type pointer to one of char, signed char,
23041 unsigned char, or void that is not followed by an argument of a type compatible with
23042 rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier
23043 using the hh length modifier, a length argument must follow the pointer argument. Another useful
23044 diagnostic could flag any non-pointer argument following format that did not have a type
23045 compatible with rsize_t.
23049 fscanf_s function returns the number of input items assigned, which can be fewer than
23050 provided for, or even zero, in the event of an early matching failure.
23051 7 EXAMPLE 1 The call:
23052 #define __STDC_WANT_LIB_EXT1__ 1
23055 int n, i; float x; char name[50];
23056 n = fscanf_s(stdin, "%d%f%s", &i, &x, name, (rsize_t) 50);
23057 with the input line:
23058 25 54.32E-1 thompson
23059 will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
23062 8 EXAMPLE 2 The call:
23063 #define __STDC_WANT_LIB_EXT1__ 1
23067 n = fscanf_s(stdin, "%s", s, sizeof s);
23068 with the input line:
23070 will assign to n the value 0 since a matching failure occurred because the sequence hello\0 requires an
23071 array of six characters to store it.
23073 K.3.5.3.3 The printf_s function
23075 1 #define __STDC_WANT_LIB_EXT1__ 1
23077 int printf_s(const char * restrict format, ...);
23078 Runtime-constraints
23079 2 format shall not be a null pointer. The %n specifier381) (modified or not by flags, field
23080 width, or precision) shall not appear in the string pointed to by format. Any argument
23081 to printf_s corresponding to a %s specifier shall not be a null pointer.
23082 3 If there is a runtime-constraint violation, the printf_s function does not attempt to
23083 produce further output, and it is unspecified to what extent printf_s produced output
23084 before discovering the runtime-constraint violation.
23087 381) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23088 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23089 format string was %%n.
23094 4 The printf_s function is equivalent to the printf function except for the explicit
23095 runtime-constraints listed above.
23097 5 The printf_s function returns the number of characters transmitted, or a negative
23098 value if an output error, encoding error, or runtime-constraint violation occurred.
23099 K.3.5.3.4 The scanf_s function
23101 1 #define __STDC_WANT_LIB_EXT1__ 1
23103 int scanf_s(const char * restrict format, ...);
23104 Runtime-constraints
23105 2 format shall not be a null pointer. Any argument indirected though in order to store
23106 converted input shall not be a null pointer.
23107 3 If there is a runtime-constraint violation, the scanf_s function does not attempt to
23108 perform further input, and it is unspecified to what extent scanf_s performed input
23109 before discovering the runtime-constraint violation.
23111 4 The scanf_s function is equivalent to fscanf_s with the argument stdin
23112 interposed before the arguments to scanf_s.
23114 5 The scanf_s function returns the value of the macro EOF if an input failure occurs
23115 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23116 scanf_s function returns the number of input items assigned, which can be fewer than
23117 provided for, or even zero, in the event of an early matching failure.
23118 K.3.5.3.5 The snprintf_s function
23120 1 #define __STDC_WANT_LIB_EXT1__ 1
23122 int snprintf_s(char * restrict s, rsize_t n,
23123 const char * restrict format, ...);
23124 Runtime-constraints
23125 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
23126 than RSIZE_MAX. The %n specifier382) (modified or not by flags, field width, or
23127 precision) shall not appear in the string pointed to by format. Any argument to
23130 snprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
23132 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
23133 than zero and less than RSIZE_MAX, then the snprintf_s function sets s[0] to the
23136 4 The snprintf_s function is equivalent to the snprintf function except for the
23137 explicit runtime-constraints listed above.
23138 5 The snprintf_s function, unlike sprintf_s, will truncate the result to fit within the
23139 array pointed to by s.
23141 6 The snprintf_s function returns the number of characters that would have been
23142 written had n been sufficiently large, not counting the terminating null character, or a
23143 negative value if a runtime-constraint violation occurred. Thus, the null-terminated
23144 output has been completely written if and only if the returned value is nonnegative and
23146 K.3.5.3.6 The sprintf_s function
23148 1 #define __STDC_WANT_LIB_EXT1__ 1
23150 int sprintf_s(char * restrict s, rsize_t n,
23151 const char * restrict format, ...);
23152 Runtime-constraints
23153 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
23154 than RSIZE_MAX. The number of characters (including the trailing null) required for the
23155 result to be written to the array pointed to by s shall not be greater than n. The %n
23156 specifier383) (modified or not by flags, field width, or precision) shall not appear in the
23157 string pointed to by format. Any argument to sprintf_s corresponding to a %s
23158 specifier shall not be a null pointer. No encoding error shall occur.
23162 382) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23163 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23164 format string was %%n.
23165 383) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23166 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23167 format string was %%n.
23171 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
23172 than zero and less than RSIZE_MAX, then the sprintf_s function sets s[0] to the
23175 4 The sprintf_s function is equivalent to the sprintf function except for the
23176 parameter n and the explicit runtime-constraints listed above.
23177 5 The sprintf_s function, unlike snprintf_s, treats a result too big for the array
23178 pointed to by s as a runtime-constraint violation.
23180 6 If no runtime-constraint violation occurred, the sprintf_s function returns the number
23181 of characters written in the array, not counting the terminating null character. If an
23182 encoding error occurred, sprintf_s returns a negative value. If any other runtime-
23183 constraint violation occurred, sprintf_s returns zero.
23184 K.3.5.3.7 The sscanf_s function
23186 1 #define __STDC_WANT_LIB_EXT1__ 1
23188 int sscanf_s(const char * restrict s,
23189 const char * restrict format, ...);
23190 Runtime-constraints
23191 2 Neither s nor format shall be a null pointer. Any argument indirected though in order
23192 to store converted input shall not be a null pointer.
23193 3 If there is a runtime-constraint violation, the sscanf_s function does not attempt to
23194 perform further input, and it is unspecified to what extent sscanf_s performed input
23195 before discovering the runtime-constraint violation.
23197 4 The sscanf_s function is equivalent to fscanf_s, except that input is obtained from
23198 a string (specified by the argument s) rather than from a stream. Reaching the end of the
23199 string is equivalent to encountering end-of-file for the fscanf_s function. If copying
23200 takes place between objects that overlap, the objects take on unspecified values.
23202 5 The sscanf_s function returns the value of the macro EOF if an input failure occurs
23203 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23204 sscanf_s function returns the number of input items assigned, which can be fewer than
23205 provided for, or even zero, in the event of an early matching failure.
23209 K.3.5.3.8 The vfprintf_s function
23211 1 #define __STDC_WANT_LIB_EXT1__ 1
23212 #include <stdarg.h>
23214 int vfprintf_s(FILE * restrict stream,
23215 const char * restrict format,
23217 Runtime-constraints
23218 2 Neither stream nor format shall be a null pointer. The %n specifier384) (modified or
23219 not by flags, field width, or precision) shall not appear in the string pointed to by
23220 format. Any argument to vfprintf_s corresponding to a %s specifier shall not be a
23222 3 If there is a runtime-constraint violation, the vfprintf_s function does not attempt to
23223 produce further output, and it is unspecified to what extent vfprintf_s produced
23224 output before discovering the runtime-constraint violation.
23226 4 The vfprintf_s function is equivalent to the vfprintf function except for the
23227 explicit runtime-constraints listed above.
23229 5 The vfprintf_s function returns the number of characters transmitted, or a negative
23230 value if an output error, encoding error, or runtime-constraint violation occurred.
23231 K.3.5.3.9 The vfscanf_s function
23233 1 #define __STDC_WANT_LIB_EXT1__ 1
23234 #include <stdarg.h>
23236 int vfscanf_s(FILE * restrict stream,
23237 const char * restrict format,
23243 384) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23244 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23245 format string was %%n.
23249 Runtime-constraints
23250 2 Neither stream nor format shall be a null pointer. Any argument indirected though in
23251 order to store converted input shall not be a null pointer.
23252 3 If there is a runtime-constraint violation, the vfscanf_s function does not attempt to
23253 perform further input, and it is unspecified to what extent vfscanf_s performed input
23254 before discovering the runtime-constraint violation.
23256 4 The vfscanf_s function is equivalent to fscanf_s, with the variable argument list
23257 replaced by arg, which shall have been initialized by the va_start macro (and
23258 possibly subsequent va_arg calls). The vfscanf_s function does not invoke the
23261 5 The vfscanf_s function returns the value of the macro EOF if an input failure occurs
23262 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23263 vfscanf_s function returns the number of input items assigned, which can be fewer
23264 than provided for, or even zero, in the event of an early matching failure.
23265 K.3.5.3.10 The vprintf_s function
23267 1 #define __STDC_WANT_LIB_EXT1__ 1
23268 #include <stdarg.h>
23270 int vprintf_s(const char * restrict format,
23272 Runtime-constraints
23273 2 format shall not be a null pointer. The %n specifier386) (modified or not by flags, field
23274 width, or precision) shall not appear in the string pointed to by format. Any argument
23275 to vprintf_s corresponding to a %s specifier shall not be a null pointer.
23276 3 If there is a runtime-constraint violation, the vprintf_s function does not attempt to
23277 produce further output, and it is unspecified to what extent vprintf_s produced output
23278 before discovering the runtime-constraint violation.
23280 385) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
23281 vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
23283 386) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23284 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23285 format string was %%n.
23290 4 The vprintf_s function is equivalent to the vprintf function except for the explicit
23291 runtime-constraints listed above.
23293 5 The vprintf_s function returns the number of characters transmitted, or a negative
23294 value if an output error, encoding error, or runtime-constraint violation occurred.
23295 K.3.5.3.11 The vscanf_s function
23297 1 #define __STDC_WANT_LIB_EXT1__ 1
23298 #include <stdarg.h>
23300 int vscanf_s(const char * restrict format,
23302 Runtime-constraints
23303 2 format shall not be a null pointer. Any argument indirected though in order to store
23304 converted input shall not be a null pointer.
23305 3 If there is a runtime-constraint violation, the vscanf_s function does not attempt to
23306 perform further input, and it is unspecified to what extent vscanf_s performed input
23307 before discovering the runtime-constraint violation.
23309 4 The vscanf_s function is equivalent to scanf_s, with the variable argument list
23310 replaced by arg, which shall have been initialized by the va_start macro (and
23311 possibly subsequent va_arg calls). The vscanf_s function does not invoke the
23314 5 The vscanf_s function returns the value of the macro EOF if an input failure occurs
23315 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23316 vscanf_s function returns the number of input items assigned, which can be fewer than
23317 provided for, or even zero, in the event of an early matching failure.
23322 387) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
23323 vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
23328 K.3.5.3.12 The vsnprintf_s function
23330 1 #define __STDC_WANT_LIB_EXT1__ 1
23331 #include <stdarg.h>
23333 int vsnprintf_s(char * restrict s, rsize_t n,
23334 const char * restrict format,
23336 Runtime-constraints
23337 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
23338 than RSIZE_MAX. The %n specifier388) (modified or not by flags, field width, or
23339 precision) shall not appear in the string pointed to by format. Any argument to
23340 vsnprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
23342 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
23343 than zero and less than RSIZE_MAX, then the vsnprintf_s function sets s[0] to the
23346 4 The vsnprintf_s function is equivalent to the vsnprintf function except for the
23347 explicit runtime-constraints listed above.
23348 5 The vsnprintf_s function, unlike vsprintf_s, will truncate the result to fit within
23349 the array pointed to by s.
23351 6 The vsnprintf_s function returns the number of characters that would have been
23352 written had n been sufficiently large, not counting the terminating null character, or a
23353 negative value if a runtime-constraint violation occurred. Thus, the null-terminated
23354 output has been completely written if and only if the returned value is nonnegative and
23360 388) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23361 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23362 format string was %%n.
23366 K.3.5.3.13 The vsprintf_s function
23368 1 #define __STDC_WANT_LIB_EXT1__ 1
23369 #include <stdarg.h>
23371 int vsprintf_s(char * restrict s, rsize_t n,
23372 const char * restrict format,
23374 Runtime-constraints
23375 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
23376 than RSIZE_MAX. The number of characters (including the trailing null) required for the
23377 result to be written to the array pointed to by s shall not be greater than n. The %n
23378 specifier389) (modified or not by flags, field width, or precision) shall not appear in the
23379 string pointed to by format. Any argument to vsprintf_s corresponding to a %s
23380 specifier shall not be a null pointer. No encoding error shall occur.
23381 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
23382 than zero and less than RSIZE_MAX, then the vsprintf_s function sets s[0] to the
23385 4 The vsprintf_s function is equivalent to the vsprintf function except for the
23386 parameter n and the explicit runtime-constraints listed above.
23387 5 The vsprintf_s function, unlike vsnprintf_s, treats a result too big for the array
23388 pointed to by s as a runtime-constraint violation.
23390 6 If no runtime-constraint violation occurred, the vsprintf_s function returns the
23391 number of characters written in the array, not counting the terminating null character. If
23392 an encoding error occurred, vsprintf_s returns a negative value. If any other
23393 runtime-constraint violation occurred, vsprintf_s returns zero.
23398 389) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
23399 at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
23400 format string was %%n.
23404 K.3.5.3.14 The vsscanf_s function
23406 1 #define __STDC_WANT_LIB_EXT1__ 1
23407 #include <stdarg.h>
23409 int vsscanf_s(const char * restrict s,
23410 const char * restrict format,
23412 Runtime-constraints
23413 2 Neither s nor format shall be a null pointer. Any argument indirected though in order
23414 to store converted input shall not be a null pointer.
23415 3 If there is a runtime-constraint violation, the vsscanf_s function does not attempt to
23416 perform further input, and it is unspecified to what extent vsscanf_s performed input
23417 before discovering the runtime-constraint violation.
23419 4 The vsscanf_s function is equivalent to sscanf_s, with the variable argument list
23420 replaced by arg, which shall have been initialized by the va_start macro (and
23421 possibly subsequent va_arg calls). The vsscanf_s function does not invoke the
23424 5 The vsscanf_s function returns the value of the macro EOF if an input failure occurs
23425 before any conversion or if there is a runtime-constraint violation. Otherwise, the
23426 vscanf_s function returns the number of input items assigned, which can be fewer than
23427 provided for, or even zero, in the event of an early matching failure.
23428 K.3.5.4 Character input/output functions
23429 K.3.5.4.1 The gets_s function
23431 1 #define __STDC_WANT_LIB_EXT1__ 1
23433 char *gets_s(char *s, rsize_t n);
23438 390) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
23439 vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
23444 Runtime-constraints
23445 2 s shall not be a null pointer. n shall neither be equal to zero nor be greater than
23446 RSIZE_MAX. A new-line character, end-of-file, or read error shall occur within reading
23447 n-1 characters from stdin.391)
23448 3 If there is a runtime-constraint violation, s[0] is set to the null character, and characters
23449 are read and discarded from stdin until a new-line character is read, or end-of-file or a
23452 4 The gets_s function reads at most one less than the number of characters specified by n
23453 from the stream pointed to by stdin, into the array pointed to by s. No additional
23454 characters are read after a new-line character (which is discarded) or after end-of-file.
23455 The discarded new-line character does not count towards number of characters read. A
23456 null character is written immediately after the last character read into the array.
23457 5 If end-of-file is encountered and no characters have been read into the array, or if a read
23458 error occurs during the operation, then s[0] is set to the null character, and the other
23459 elements of s take unspecified values.
23460 Recommended practice
23461 6 The fgets function allows properly-written programs to safely process input lines too
23462 long to store in the result array. In general this requires that callers of fgets pay
23463 attention to the presence or absence of a new-line character in the result array. Consider
23464 using fgets (along with any needed processing based on new-line characters) instead of
23467 7 The gets_s function returns s if successful. If there was a runtime-constraint violation,
23468 or if end-of-file is encountered and no characters have been read into the array, or if a
23469 read error occurs during the operation, then a null pointer is returned.
23474 391) The gets_s function, unlike the historical gets function, makes it a runtime-constraint violation for
23475 a line of input to overflow the buffer to store it. Unlike the fgets function, gets_s maintains a
23476 one-to-one relationship between input lines and successful calls to gets_s. Programs that use gets
23477 expect such a relationship.
23481 K.3.6 General utilities <stdlib.h>
23482 1 The header <stdlib.h> defines three types.
23485 which is type int; and
23487 which is the type size_t; and
23488 constraint_handler_t
23489 which has the following definition
23490 typedef void (*constraint_handler_t)(
23491 const char * restrict msg,
23492 void * restrict ptr,
23494 K.3.6.1 Runtime-constraint handling
23495 K.3.6.1.1 The set_constraint_handler_s function
23497 1 #define __STDC_WANT_LIB_EXT1__ 1
23498 #include <stdlib.h>
23499 constraint_handler_t set_constraint_handler_s(
23500 constraint_handler_t handler);
23502 2 The set_constraint_handler_s function sets the runtime-constraint handler to
23503 be handler. The runtime-constraint handler is the function to be called when a library
23504 function detects a runtime-constraint violation. Only the most recent handler registered
23505 with set_constraint_handler_s is called when a runtime-constraint violation
23507 3 When the handler is called, it is passed the following arguments in the following order:
23508 1. A pointer to a character string describing the runtime-constraint violation.
23509 2. A null pointer or a pointer to an implementation defined object.
23510 3. If the function calling the handler has a return type declared as errno_t, the
23511 return value of the function is passed. Otherwise, a positive value of type
23518 4 The implementation has a default constraint handler that is used if no calls to the
23519 set_constraint_handler_s function have been made. The behavior of the
23520 default handler is implementation-defined, and it may cause the program to exit or abort.
23521 5 If the handler argument to set_constraint_handler_s is a null pointer, the
23522 implementation default handler becomes the current constraint handler.
23524 6 The set_constraint_handler_s function returns a pointer to the previously
23525 registered handler.392)
23526 K.3.6.1.2 The abort_handler_s function
23528 1 #define __STDC_WANT_LIB_EXT1__ 1
23529 #include <stdlib.h>
23530 void abort_handler_s(
23531 const char * restrict msg,
23532 void * restrict ptr,
23535 2 A pointer to the abort_handler_s function shall be a suitable argument to the
23536 set_constraint_handler_s function.
23537 3 The abort_handler_s function writes a message on the standard error stream in an
23538 implementation-defined format. The message shall include the string pointed to by msg.
23539 The abort_handler_s function then calls the abort function.393)
23541 4 The abort_handler_s function does not return to its caller.
23546 392) If the previous handler was registered by calling set_constraint_handler_s with a null
23547 pointer argument, a pointer to the implementation default handler is returned (not NULL).
23548 393) Many implementations invoke a debugger when the abort function is called.
23552 K.3.6.1.3 The ignore_handler_s function
23554 1 #define __STDC_WANT_LIB_EXT1__ 1
23555 #include <stdlib.h>
23556 void ignore_handler_s(
23557 const char * restrict msg,
23558 void * restrict ptr,
23561 2 A pointer to the ignore_handler_s function shall be a suitable argument to the
23562 set_constraint_handler_s function.
23563 3 The ignore_handler_s function simply returns to its caller.394)
23565 4 The ignore_handler_s function returns no value.
23566 K.3.6.2 Communication with the environment
23567 K.3.6.2.1 The getenv_s function
23569 1 #define __STDC_WANT_LIB_EXT1__ 1
23570 #include <stdlib.h>
23571 errno_t getenv_s(size_t * restrict len,
23572 char * restrict value, rsize_t maxsize,
23573 const char * restrict name);
23574 Runtime-constraints
23575 2 name shall not be a null pointer. maxsize shall neither equal zero nor be greater than
23576 RSIZE_MAX. If maxsize is not equal to zero, then value shall not be a null pointer.
23577 3 If there is a runtime-constraint violation, the integer pointed to by len is set to 0 (if len
23578 is not null), and the environment list is not searched.
23580 4 The getenv_s function searches an environment list, provided by the host environment,
23581 for a string that matches the string pointed to by name.
23584 394) If the runtime-constraint handler is set to the ignore_handler_s function, any library function in
23585 which a runtime-constraint violation occurs will return to its caller. The caller can determine whether
23586 a runtime-constraint violation occurred based on the library function's specification (usually, the
23587 library function returns a nonzero errno_t).
23591 5 If that name is found then getenv_s performs the following actions. If len is not a
23592 null pointer, the length of the string associated with the matched list member is stored in
23593 the integer pointed to by len. If the length of the associated string is less than maxsize,
23594 then the associated string is copied to the array pointed to by value.
23595 6 If that name is not found then getenv_s performs the following actions. If len is not
23596 a null pointer, zero is stored in the integer pointed to by len. If maxsize is greater than
23597 zero, then value[0] is set to the null character.
23598 7 The set of environment names and the method for altering the environment list are
23599 implementation-defined.
23601 8 The getenv_s function returns zero if the specified name is found and the associated
23602 string was successfully stored in value. Otherwise, a nonzero value is returned.
23603 K.3.6.3 Searching and sorting utilities
23604 1 These utilities make use of a comparison function to search or sort arrays of unspecified
23605 type. Where an argument declared as size_t nmemb specifies the length of the array
23606 for a function, if nmemb has the value zero on a call to that function, then the comparison
23607 function is not called, a search finds no matching element, sorting performs no
23608 rearrangement, and the pointer to the array may be null.
23609 2 The implementation shall ensure that the second argument of the comparison function
23610 (when called from bsearch_s), or both arguments (when called from qsort_s), are
23611 pointers to elements of the array.395) The first argument when called from bsearch_s
23613 3 The comparison function shall not alter the contents of either the array or search key. The
23614 implementation may reorder elements of the array between calls to the comparison
23615 function, but shall not otherwise alter the contents of any individual element.
23616 4 When the same objects (consisting of size bytes, irrespective of their current positions
23617 in the array) are passed more than once to the comparison function, the results shall be
23618 consistent with one another. That is, for qsort_s they shall define a total ordering on
23619 the array, and for bsearch_s the same object shall always compare the same way with
23625 395) That is, if the value passed is p, then the following expressions are always valid and nonzero:
23626 ((char *)p - (char *)base) % size == 0
23627 (char *)p >= (char *)base
23628 (char *)p < (char *)base + nmemb * size
23633 5 A sequence point occurs immediately before and immediately after each call to the
23634 comparison function, and also between any call to the comparison function and any
23635 movement of the objects passed as arguments to that call.
23636 K.3.6.3.1 The bsearch_s function
23638 1 #define __STDC_WANT_LIB_EXT1__ 1
23639 #include <stdlib.h>
23640 void *bsearch_s(const void *key, const void *base,
23641 rsize_t nmemb, rsize_t size,
23642 int (*compar)(const void *k, const void *y,
23645 Runtime-constraints
23646 2 Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to
23647 zero, then none of key, base, or compar shall be a null pointer.
23648 3 If there is a runtime-constraint violation, the bsearch_s function does not search the
23651 4 The bsearch_s function searches an array of nmemb objects, the initial element of
23652 which is pointed to by base, for an element that matches the object pointed to by key.
23653 The size of each element of the array is specified by size.
23654 5 The comparison function pointed to by compar is called with three arguments. The first
23655 two point to the key object and to an array element, in that order. The function shall
23656 return an integer less than, equal to, or greater than zero if the key object is considered,
23657 respectively, to be less than, to match, or to be greater than the array element. The array
23658 shall consist of: all the elements that compare less than, all the elements that compare
23659 equal to, and all the elements that compare greater than the key object, in that order.396)
23660 The third argument to the comparison function is the context argument passed to
23661 bsearch_s. The sole use of context by bsearch_s is to pass it to the comparison
23667 396) In practice, this means that the entire array has been sorted according to the comparison function.
23668 397) The context argument is for the use of the comparison function in performing its duties. For
23669 example, it might specify a collating sequence used by the comparison function.
23674 6 The bsearch_s function returns a pointer to a matching element of the array, or a null
23675 pointer if no match is found or there is a runtime-constraint violation. If two elements
23676 compare as equal, which element is matched is unspecified.
23677 K.3.6.3.2 The qsort_s function
23679 1 #define __STDC_WANT_LIB_EXT1__ 1
23680 #include <stdlib.h>
23681 errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size,
23682 int (*compar)(const void *x, const void *y,
23685 Runtime-constraints
23686 2 Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to
23687 zero, then neither base nor compar shall be a null pointer.
23688 3 If there is a runtime-constraint violation, the qsort_s function does not sort the array.
23690 4 The qsort_s function sorts an array of nmemb objects, the initial element of which is
23691 pointed to by base. The size of each object is specified by size.
23692 5 The contents of the array are sorted into ascending order according to a comparison
23693 function pointed to by compar, which is called with three arguments. The first two
23694 point to the objects being compared. The function shall return an integer less than, equal
23695 to, or greater than zero if the first argument is considered to be respectively less than,
23696 equal to, or greater than the second. The third argument to the comparison function is the
23697 context argument passed to qsort_s. The sole use of context by qsort_s is to
23698 pass it to the comparison function.398)
23699 6 If two elements compare as equal, their relative order in the resulting sorted array is
23702 7 The qsort_s function returns zero if there was no runtime-constraint violation.
23703 Otherwise, a nonzero value is returned.
23708 398) The context argument is for the use of the comparison function in performing its duties. For
23709 example, it might specify a collating sequence used by the comparison function.
23713 K.3.6.4 Multibyte/wide character conversion functions
23714 1 The behavior of the multibyte character functions is affected by the LC_CTYPE category
23715 of the current locale. For a state-dependent encoding, each function is placed into its
23716 initial conversion state by a call for which its character pointer argument, s, is a null
23717 pointer. Subsequent calls with s as other than a null pointer cause the internal conversion
23718 state of the function to be altered as necessary. A call with s as a null pointer causes
23719 these functions to set the int pointed to by their status argument to a nonzero value if
23720 encodings have state dependency, and zero otherwise.399) Changing the LC_CTYPE
23721 category causes the conversion state of these functions to be indeterminate.
23722 K.3.6.4.1 The wctomb_s function
23724 1 #define __STDC_WANT_LIB_EXT1__ 1
23725 #include <stdlib.h>
23726 errno_t wctomb_s(int * restrict status,
23730 Runtime-constraints
23731 2 Let n denote the number of bytes needed to represent the multibyte character
23732 corresponding to the wide character given by wc (including any shift sequences).
23733 3 If s is not a null pointer, then smax shall not be less than n, and smax shall not be
23734 greater than RSIZE_MAX. If s is a null pointer, then smax shall equal zero.
23735 4 If there is a runtime-constraint violation, wctomb_s does not modify the int pointed to
23736 by status, and if s is not a null pointer, no more than smax elements in the array
23737 pointed to by s will be accessed.
23739 5 The wctomb_s function determines n and stores the multibyte character representation
23740 of wc in the array whose first element is pointed to by s (if s is not a null pointer). The
23741 number of characters stored never exceeds MB_CUR_MAX or smax. If wc is a null wide
23742 character, a null byte is stored, preceded by any shift sequence needed to restore the
23743 initial shift state, and the function is left in the initial conversion state.
23744 6 The implementation shall behave as if no library function calls the wctomb_s function.
23749 399) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
23750 character codes, but are grouped with an adjacent multibyte character.
23754 7 If s is a null pointer, the wctomb_s function stores into the int pointed to by status a
23755 nonzero or zero value, if multibyte character encodings, respectively, do or do not have
23756 state-dependent encodings.
23757 8 If s is not a null pointer, the wctomb_s function stores into the int pointed to by
23758 status either n or -1 if wc, respectively, does or does not correspond to a valid
23759 multibyte character.
23760 9 In no case will the int pointed to by status be set to a value greater than the
23763 10 The wctomb_s function returns zero if successful, and a nonzero value if there was a
23764 runtime-constraint violation or wc did not correspond to a valid multibyte character.
23765 K.3.6.5 Multibyte/wide string conversion functions
23766 1 The behavior of the multibyte string functions is affected by the LC_CTYPE category of
23767 the current locale.
23768 K.3.6.5.1 The mbstowcs_s function
23770 1 #include <stdlib.h>
23771 errno_t mbstowcs_s(size_t * restrict retval,
23772 wchar_t * restrict dst, rsize_t dstmax,
23773 const char * restrict src, rsize_t len);
23774 Runtime-constraints
23775 2 Neither retval nor src shall be a null pointer. If dst is not a null pointer, then
23776 neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer,
23777 then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal
23778 zero. If dst is not a null pointer and len is not less than dstmax, then a null character
23779 shall occur within the first dstmax multibyte characters of the array pointed to by src.
23780 3 If there is a runtime-constraint violation, then mbstowcs_s does the following. If
23781 retval is not a null pointer, then mbstowcs_s sets *retval to (size_t)(-1). If
23782 dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
23783 then mbstowcs_s sets dst[0] to the null wide character.
23785 4 The mbstowcs_s function converts a sequence of multibyte characters that begins in
23786 the initial shift state from the array pointed to by src into a sequence of corresponding
23787 wide characters. If dst is not a null pointer, the converted characters are stored into the
23788 array pointed to by dst. Conversion continues up to and including a terminating null
23789 character, which is also stored. Conversion stops earlier in two cases: when a sequence of
23792 bytes is encountered that does not form a valid multibyte character, or (if dst is not a
23793 null pointer) when len wide characters have been stored into the array pointed to by
23794 dst.400) If dst is not a null pointer and no null wide character was stored into the array
23795 pointed to by dst, then dst[len] is set to the null wide character. Each conversion
23796 takes place as if by a call to the mbrtowc function.
23797 5 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
23798 sequence of bytes that do not form a valid multibyte character, an encoding error occurs:
23799 the mbstowcs_s function stores the value (size_t)(-1) into *retval.
23800 Otherwise, the mbstowcs_s function stores into *retval the number of multibyte
23801 characters successfully converted, not including the terminating null character (if any).
23802 6 All elements following the terminating null wide character (if any) written by
23803 mbstowcs_s in the array of dstmax wide characters pointed to by dst take
23804 unspecified values when mbstowcs_s returns.401)
23805 7 If copying takes place between objects that overlap, the objects take on unspecified
23808 8 The mbstowcs_s function returns zero if no runtime-constraint violation and no
23809 encoding error occurred. Otherwise, a nonzero value is returned.
23810 K.3.6.5.2 The wcstombs_s function
23812 1 #include <stdlib.h>
23813 errno_t wcstombs_s(size_t * restrict retval,
23814 char * restrict dst, rsize_t dstmax,
23815 const wchar_t * restrict src, rsize_t len);
23816 Runtime-constraints
23817 2 Neither retval nor src shall be a null pointer. If dst is not a null pointer, then
23818 neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer,
23819 then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal
23820 zero. If dst is not a null pointer and len is not less than dstmax, then the conversion
23821 shall have been stopped (see below) because a terminating null wide character was
23822 reached or because an encoding error occurred.
23827 400) Thus, the value of len is ignored if dst is a null pointer.
23828 401) This allows an implementation to attempt converting the multibyte string before discovering a
23829 terminating null character did not occur where required.
23833 3 If there is a runtime-constraint violation, then wcstombs_s does the following. If
23834 retval is not a null pointer, then wcstombs_s sets *retval to (size_t)(-1). If
23835 dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
23836 then wcstombs_s sets dst[0] to the null character.
23838 4 The wcstombs_s function converts a sequence of wide characters from the array
23839 pointed to by src into a sequence of corresponding multibyte characters that begins in
23840 the initial shift state. If dst is not a null pointer, the converted characters are then stored
23841 into the array pointed to by dst. Conversion continues up to and including a terminating
23842 null wide character, which is also stored. Conversion stops earlier in two cases:
23843 -- when a wide character is reached that does not correspond to a valid multibyte
23845 -- (if dst is not a null pointer) when the next multibyte character would exceed the
23846 limit of n total bytes to be stored into the array pointed to by dst. If the wide
23847 character being converted is the null wide character, then n is the lesser of len or
23848 dstmax. Otherwise, n is the lesser of len or dstmax-1.
23849 If the conversion stops without converting a null wide character and dst is not a null
23850 pointer, then a null character is stored into the array pointed to by dst immediately
23851 following any multibyte characters already stored. Each conversion takes place as if by a
23852 call to the wcrtomb function.402)
23853 5 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
23854 wide character that does not correspond to a valid multibyte character, an encoding error
23855 occurs: the wcstombs_s function stores the value (size_t)(-1) into *retval.
23856 Otherwise, the wcstombs_s function stores into *retval the number of bytes in the
23857 resulting multibyte character sequence, not including the terminating null character (if
23859 6 All elements following the terminating null character (if any) written by wcstombs_s
23860 in the array of dstmax elements pointed to by dst take unspecified values when
23861 wcstombs_s returns.403)
23862 7 If copying takes place between objects that overlap, the objects take on unspecified
23866 402) If conversion stops because a terminating null wide character has been reached, the bytes stored
23867 include those necessary to reach the initial shift state immediately before the null byte. However, if
23868 the conversion stops before a terminating null wide character has been reached, the result will be null
23869 terminated, but might not end in the initial shift state.
23870 403) When len is not less than dstmax, the implementation might fill the array before discovering a
23871 runtime-constraint violation.
23876 8 The wcstombs_s function returns zero if no runtime-constraint violation and no
23877 encoding error occurred. Otherwise, a nonzero value is returned.
23878 K.3.7 String handling <string.h>
23879 1 The header <string.h> defines two types.
23882 which is type int; and
23884 which is the type size_t.
23885 K.3.7.1 Copying functions
23886 K.3.7.1.1 The memcpy_s function
23888 1 #define __STDC_WANT_LIB_EXT1__ 1
23889 #include <string.h>
23890 errno_t memcpy_s(void * restrict s1, rsize_t s1max,
23891 const void * restrict s2, rsize_t n);
23892 Runtime-constraints
23893 2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
23894 RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between
23895 objects that overlap.
23896 3 If there is a runtime-constraint violation, the memcpy_s function stores zeros in the first
23897 s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is
23898 not greater than RSIZE_MAX.
23900 4 The memcpy_s function copies n characters from the object pointed to by s2 into the
23901 object pointed to by s1.
23903 5 The memcpy_s function returns zero if there was no runtime-constraint violation.
23904 Otherwise, a nonzero value is returned.
23911 K.3.7.1.2 The memmove_s function
23913 1 #define __STDC_WANT_LIB_EXT1__ 1
23914 #include <string.h>
23915 errno_t memmove_s(void *s1, rsize_t s1max,
23916 const void *s2, rsize_t n);
23917 Runtime-constraints
23918 2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
23919 RSIZE_MAX. n shall not be greater than s1max.
23920 3 If there is a runtime-constraint violation, the memmove_s function stores zeros in the
23921 first s1max characters of the object pointed to by s1 if s1 is not a null pointer and
23922 s1max is not greater than RSIZE_MAX.
23924 4 The memmove_s function copies n characters from the object pointed to by s2 into the
23925 object pointed to by s1. This copying takes place as if the n characters from the object
23926 pointed to by s2 are first copied into a temporary array of n characters that does not
23927 overlap the objects pointed to by s1 or s2, and then the n characters from the temporary
23928 array are copied into the object pointed to by s1.
23930 5 The memmove_s function returns zero if there was no runtime-constraint violation.
23931 Otherwise, a nonzero value is returned.
23932 K.3.7.1.3 The strcpy_s function
23934 1 #define __STDC_WANT_LIB_EXT1__ 1
23935 #include <string.h>
23936 errno_t strcpy_s(char * restrict s1,
23938 const char * restrict s2);
23939 Runtime-constraints
23940 2 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
23941 s1max shall not equal zero. s1max shall be greater than strnlen_s(s2, s1max).
23942 Copying shall not take place between objects that overlap.
23943 3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
23944 greater than zero and not greater than RSIZE_MAX, then strcpy_s sets s1[0] to the
23950 4 The strcpy_s function copies the string pointed to by s2 (including the terminating
23951 null character) into the array pointed to by s1.
23952 5 All elements following the terminating null character (if any) written by strcpy_s in
23953 the array of s1max characters pointed to by s1 take unspecified values when
23954 strcpy_s returns.404)
23956 6 The strcpy_s function returns zero405) if there was no runtime-constraint violation.
23957 Otherwise, a nonzero value is returned.
23958 K.3.7.1.4 The strncpy_s function
23960 1 #define __STDC_WANT_LIB_EXT1__ 1
23961 #include <string.h>
23962 errno_t strncpy_s(char * restrict s1,
23964 const char * restrict s2,
23966 Runtime-constraints
23967 2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
23968 RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max
23969 shall be greater than strnlen_s(s2, s1max). Copying shall not take place between
23970 objects that overlap.
23971 3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
23972 greater than zero and not greater than RSIZE_MAX, then strncpy_s sets s1[0] to the
23975 4 The strncpy_s function copies not more than n successive characters (characters that
23976 follow a null character are not copied) from the array pointed to by s2 to the array
23977 pointed to by s1. If no null character was copied from s2, then s1[n] is set to a null
23981 404) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if
23982 any of those characters are null. Such an approach might write a character to every element of s1
23983 before discovering that the first element should be set to the null character.
23984 405) A zero return value implies that all of the requested characters from the string pointed to by s2 fit
23985 within the array pointed to by s1 and that the result in s1 is null terminated.
23989 5 All elements following the terminating null character (if any) written by strncpy_s in
23990 the array of s1max characters pointed to by s1 take unspecified values when
23991 strncpy_s returns.406)
23993 6 The strncpy_s function returns zero407) if there was no runtime-constraint violation.
23994 Otherwise, a nonzero value is returned.
23995 7 EXAMPLE 1 The strncpy_s function can be used to copy a string without the danger that the result
23996 will not be null terminated or that characters will be written past the end of the destination array.
23997 #define __STDC_WANT_LIB_EXT1__ 1
23998 #include <string.h>
24000 char src1[100] = "hello";
24001 char src2[7] = {'g', 'o', 'o', 'd', 'b', 'y', 'e'};
24002 char dst1[6], dst2[5], dst3[5];
24004 r1 = strncpy_s(dst1, 6, src1, 100);
24005 r2 = strncpy_s(dst2, 5, src2, 7);
24006 r3 = strncpy_s(dst3, 5, src2, 4);
24007 The first call will assign to r1 the value zero and to dst1 the sequence hello\0.
24008 The second call will assign to r2 a nonzero value and to dst2 the sequence \0.
24009 The third call will assign to r3 the value zero and to dst3 the sequence good\0.
24011 K.3.7.2 Concatenation functions
24012 K.3.7.2.1 The strcat_s function
24014 1 #define __STDC_WANT_LIB_EXT1__ 1
24015 #include <string.h>
24016 errno_t strcat_s(char * restrict s1,
24018 const char * restrict s2);
24019 Runtime-constraints
24020 2 Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to
24026 406) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if
24027 any of those characters are null. Such an approach might write a character to every element of s1
24028 before discovering that the first element should be set to the null character.
24029 407) A zero return value implies that all of the requested characters from the string pointed to by s2 fit
24030 within the array pointed to by s1 and that the result in s1 is null terminated.
24034 3 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
24035 s1max shall not equal zero. m shall not equal zero.408) m shall be greater than
24036 strnlen_s(s2, m). Copying shall not take place between objects that overlap.
24037 4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
24038 greater than zero and not greater than RSIZE_MAX, then strcat_s sets s1[0] to the
24041 5 The strcat_s function appends a copy of the string pointed to by s2 (including the
24042 terminating null character) to the end of the string pointed to by s1. The initial character
24043 from s2 overwrites the null character at the end of s1.
24044 6 All elements following the terminating null character (if any) written by strcat_s in
24045 the array of s1max characters pointed to by s1 take unspecified values when
24046 strcat_s returns.409)
24048 7 The strcat_s function returns zero410) if there was no runtime-constraint violation.
24049 Otherwise, a nonzero value is returned.
24050 K.3.7.2.2 The strncat_s function
24052 1 #define __STDC_WANT_LIB_EXT1__ 1
24053 #include <string.h>
24054 errno_t strncat_s(char * restrict s1,
24056 const char * restrict s2,
24058 Runtime-constraints
24059 2 Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to
24061 3 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
24062 RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.411) If n is not less
24065 408) Zero means that s1 was not null terminated upon entry to strcat_s.
24066 409) This allows an implementation to append characters from s2 to s1 while simultaneously checking if
24067 any of those characters are null. Such an approach might write a character to every element of s1
24068 before discovering that the first element should be set to the null character.
24069 410) A zero return value implies that all of the requested characters from the string pointed to by s2 were
24070 appended to the string pointed to by s1 and that the result in s1 is null terminated.
24074 than m, then m shall be greater than strnlen_s(s2, m). Copying shall not take
24075 place between objects that overlap.
24076 4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
24077 greater than zero and not greater than RSIZE_MAX, then strncat_s sets s1[0] to the
24080 5 The strncat_s function appends not more than n successive characters (characters
24081 that follow a null character are not copied) from the array pointed to by s2 to the end of
24082 the string pointed to by s1. The initial character from s2 overwrites the null character at
24083 the end of s1. If no null character was copied from s2, then s1[s1max-m+n] is set to
24085 6 All elements following the terminating null character (if any) written by strncat_s in
24086 the array of s1max characters pointed to by s1 take unspecified values when
24087 strncat_s returns.412)
24089 7 The strncat_s function returns zero413) if there was no runtime-constraint violation.
24090 Otherwise, a nonzero value is returned.
24091 8 EXAMPLE 1 The strncat_s function can be used to copy a string without the danger that the result
24092 will not be null terminated or that characters will be written past the end of the destination array.
24093 #define __STDC_WANT_LIB_EXT1__ 1
24094 #include <string.h>
24096 char s1[100] = "good";
24097 char s2[6] = "hello";
24098 char s3[6] = "hello";
24099 char s4[7] = "abc";
24100 char s5[1000] = "bye";
24101 int r1, r2, r3, r4;
24102 r1 = strncat_s(s1, 100, s5, 1000);
24103 r2 = strncat_s(s2, 6, "", 1);
24104 r3 = strncat_s(s3, 6, "X", 2);
24105 r4 = strncat_s(s4, 7, "defghijklmn", 3);
24106 After the first call r1 will have the value zero and s1 will contain the sequence goodbye\0.
24110 411) Zero means that s1 was not null terminated upon entry to strncat_s.
24111 412) This allows an implementation to append characters from s2 to s1 while simultaneously checking if
24112 any of those characters are null. Such an approach might write a character to every element of s1
24113 before discovering that the first element should be set to the null character.
24114 413) A zero return value implies that all of the requested characters from the string pointed to by s2 were
24115 appended to the string pointed to by s1 and that the result in s1 is null terminated.
24119 After the second call r2 will have the value zero and s2 will contain the sequence hello\0.
24120 After the third call r3 will have a nonzero value and s3 will contain the sequence \0.
24121 After the fourth call r4 will have the value zero and s4 will contain the sequence abcdef\0.
24123 K.3.7.3 Search functions
24124 K.3.7.3.1 The strtok_s function
24126 1 #define __STDC_WANT_LIB_EXT1__ 1
24127 #include <string.h>
24128 char *strtok_s(char * restrict s1,
24129 rsize_t * restrict s1max,
24130 const char * restrict s2,
24131 char ** restrict ptr);
24132 Runtime-constraints
24133 2 None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr
24134 shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX.
24135 The end of the token found shall occur within the first *s1max characters of s1 for the
24136 first call, and shall occur within the first *s1max characters of where searching resumes
24137 on subsequent calls.
24138 3 If there is a runtime-constraint violation, the strtok_s function does not indirect
24139 through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr.
24141 4 A sequence of calls to the strtok_s function breaks the string pointed to by s1 into a
24142 sequence of tokens, each of which is delimited by a character from the string pointed to
24143 by s2. The fourth argument points to a caller-provided char pointer into which the
24144 strtok_s function stores information necessary for it to continue scanning the same
24146 5 The first call in a sequence has a non-null first argument and s1max points to an object
24147 whose value is the number of elements in the character array pointed to by the first
24148 argument. The first call stores an initial value in the object pointed to by ptr and
24149 updates the value pointed to by s1max to reflect the number of elements that remain in
24150 relation to ptr. Subsequent calls in the sequence have a null first argument and the
24151 objects pointed to by s1max and ptr are required to have the values stored by the
24152 previous call in the sequence, which are then updated. The separator string pointed to by
24153 s2 may be different from call to call.
24154 6 The first call in the sequence searches the string pointed to by s1 for the first character
24155 that is not contained in the current separator string pointed to by s2. If no such character
24156 is found, then there are no tokens in the string pointed to by s1 and the strtok_s
24157 function returns a null pointer. If such a character is found, it is the start of the first token.
24160 7 The strtok_s function then searches from there for the first character in s1 that is
24161 contained in the current separator string. If no such character is found, the current token
24162 extends to the end of the string pointed to by s1, and subsequent searches in the same
24163 string for a token return a null pointer. If such a character is found, it is overwritten by a
24164 null character, which terminates the current token.
24165 8 In all cases, the strtok_s function stores sufficient information in the pointer pointed
24166 to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
24167 value for ptr, shall start searching just past the element overwritten by a null character
24170 9 The strtok_s function returns a pointer to the first character of a token, or a null
24171 pointer if there is no token or there is a runtime-constraint violation.
24173 #define __STDC_WANT_LIB_EXT1__ 1
24174 #include <string.h>
24175 static char str1[] = "?a???b,,,#c";
24176 static char str2[] = "\t \t";
24177 char *t, *ptr1, *ptr2;
24178 rsize_t max1 = sizeof(str1);
24179 rsize_t max2 = sizeof(str2);
24180 t = strtok_s(str1, &max1, "?", &ptr1); // t points to the token "a"
24181 t = strtok_s(NULL, &max1, ",", &ptr1); // t points to the token "??b"
24182 t = strtok_s(str2, &max2, " \t", &ptr2); // t is a null pointer
24183 t = strtok_s(NULL, &max1, "#,", &ptr1); // t points to the token "c"
24184 t = strtok_s(NULL, &max1, "?", &ptr1); // t is a null pointer
24186 K.3.7.4 Miscellaneous functions
24187 K.3.7.4.1 The memset_s function
24189 1 #define __STDC_WANT_LIB_EXT1__ 1
24190 #include <string.h>
24191 errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
24192 Runtime-constraints
24193 2 s shall not be a null pointer. Neither smax nor n shall be greater than RSIZE_MAX. n
24194 shall not be greater than smax.
24195 3 If there is a runtime-constraint violation, then if s is not a null pointer and smax is not
24196 greater than RSIZE_MAX, the memset_s function stores the value of c (converted to an
24197 unsigned char) into each of the first smax characters of the object pointed to by s.
24204 4 The memset_s function copies the value of c (converted to an unsigned char) into
24205 each of the first n characters of the object pointed to by s. Unlike memset, any call to
24206 the memset_s function shall be evaluated strictly according to the rules of the abstract
24207 machine as described in (5.1.2.3). That is, any call to the memset_s function shall
24208 assume that the memory indicated by s and n may be accessible in the future and thus
24209 must contain the values indicated by c.
24211 5 The memset_s function returns zero if there was no runtime-constraint violation.
24212 Otherwise, a nonzero value is returned.
24213 K.3.7.4.2 The strerror_s function
24215 1 #define __STDC_WANT_LIB_EXT1__ 1
24216 #include <string.h>
24217 errno_t strerror_s(char *s, rsize_t maxsize,
24219 Runtime-constraints
24220 2 s shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX.
24221 maxsize shall not equal zero.
24222 3 If there is a runtime-constraint violation, then the array (if any) pointed to by s is not
24225 4 The strerror_s function maps the number in errnum to a locale-specific message
24226 string. Typically, the values for errnum come from errno, but strerror_s shall
24227 map any value of type int to a message.
24228 5 If the length of the desired string is less than maxsize, then the string is copied to the
24229 array pointed to by s.
24230 6 Otherwise, if maxsize is greater than zero, then maxsize-1 characters are copied
24231 from the string to the array pointed to by s and then s[maxsize-1] is set to the null
24232 character. Then, if maxsize is greater than 3, then s[maxsize-2],
24233 s[maxsize-3], and s[maxsize-4] are set to the character period (.).
24235 7 The strerror_s function returns zero if the length of the desired string was less than
24236 maxsize and there was no runtime-constraint violation. Otherwise, the strerror_s
24237 function returns a nonzero value.
24241 K.3.7.4.3 The strerrorlen_s function
24243 1 #define __STDC_WANT_LIB_EXT1__ 1
24244 #include <string.h>
24245 size_t strerrorlen_s(errno_t errnum);
24247 2 The strerrorlen_s function calculates the length of the (untruncated) locale-specific
24248 message string that the strerror_s function maps to errnum.
24250 3 The strerrorlen_s function returns the number of characters (not including the null
24251 character) in the full message string.
24252 K.3.7.4.4 The strnlen_s function
24254 1 #define __STDC_WANT_LIB_EXT1__ 1
24255 #include <string.h>
24256 size_t strnlen_s(const char *s, size_t maxsize);
24258 2 The strnlen_s function computes the length of the string pointed to by s.
24260 3 If s is a null pointer,414) then the strnlen_s function returns zero.
24261 4 Otherwise, the strnlen_s function returns the number of characters that precede the
24262 terminating null character. If there is no null character in the first maxsize characters of
24263 s then strnlen_s returns maxsize. At most the first maxsize characters of s shall
24264 be accessed by strnlen_s.
24269 414) Note that the strnlen_s function has no runtime-constraints. This lack of runtime-constraints
24270 along with the values returned for a null pointer or an unterminated string argument make
24271 strnlen_s useful in algorithms that gracefully handle such exceptional data.
24275 K.3.8 Date and time <time.h>
24276 1 The header <time.h> defines two types.
24279 which is type int; and
24281 which is the type size_t.
24282 K.3.8.1 Components of time
24283 1 A broken-down time is normalized if the values of the members of the tm structure are in
24284 their normal rages.415)
24285 K.3.8.2 Time conversion functions
24286 1 Like the strftime function, the asctime_s and ctime_s functions do not return a
24287 pointer to a static object, and other library functions are permitted to call them.
24288 K.3.8.2.1 The asctime_s function
24290 1 #define __STDC_WANT_LIB_EXT1__ 1
24292 errno_t asctime_s(char *s, rsize_t maxsize,
24293 const struct tm *timeptr);
24294 Runtime-constraints
24295 2 Neither s nor timeptr shall be a null pointer. maxsize shall not be less than 26 and
24296 shall not be greater than RSIZE_MAX. The broken-down time pointed to by timeptr
24297 shall be normalized. The calendar year represented by the broken-down time pointed to
24298 by timeptr shall not be less than calendar year 0 and shall not be greater than calendar
24300 3 If there is a runtime-constraint violation, there is no attempt to convert the time, and
24301 s[0] is set to a null character if s is not a null pointer and maxsize is not zero and is
24302 not greater than RSIZE_MAX.
24304 4 The asctime_s function converts the normalized broken-down time in the structure
24305 pointed to by timeptr into a 26 character (including the null character) string in the
24308 415) The normal ranges are defined in 7.26.1.
24313 Sun Sep 16 01:03:52 1973\n\0
24314 The fields making up this string are (in order):
24315 1. The name of the day of the week represented by timeptr->tm_wday using the
24316 following three character weekday names: Sun, Mon, Tue, Wed, Thu, Fri, and Sat.
24317 2. The character space.
24318 3. The name of the month represented by timeptr->tm_mon using the following
24319 three character month names: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct,
24321 4. The character space.
24322 5. The value of timeptr->tm_mday as if printed using the fprintf format
24324 6. The character space.
24325 7. The value of timeptr->tm_hour as if printed using the fprintf format
24327 8. The character colon.
24328 9. The value of timeptr->tm_min as if printed using the fprintf format
24330 10. The character colon.
24331 11. The value of timeptr->tm_sec as if printed using the fprintf format
24333 12. The character space.
24334 13. The value of timeptr->tm_year + 1900 as if printed using the fprintf
24336 14. The character new line.
24337 15. The null character.
24338 Recommended practice
24339 The strftime function allows more flexible formatting and supports locale-specific
24340 behavior. If you do not require the exact form of the result string produced by the
24341 asctime_s function, consider using the strftime function instead.
24343 5 The asctime_s function returns zero if the time was successfully converted and stored
24344 into the array pointed to by s. Otherwise, it returns a nonzero value.
24347 K.3.8.2.2 The ctime_s function
24349 1 #define __STDC_WANT_LIB_EXT1__ 1
24351 errno_t ctime_s(char *s, rsize_t maxsize,
24352 const time_t *timer);
24353 Runtime-constraints
24354 2 Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and
24355 shall not be greater than RSIZE_MAX.
24356 3 If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null
24357 pointer and maxsize is not equal zero and is not greater than RSIZE_MAX.
24359 4 The ctime_s function converts the calendar time pointed to by timer to local time in
24360 the form of a string. It is equivalent to
24361 asctime_s(s, maxsize, localtime_s(timer))
24362 Recommended practice
24363 The strftime function allows more flexible formatting and supports locale-specific
24364 behavior. If you do not require the exact form of the result string produced by the
24365 ctime_s function, consider using the strftime function instead.
24367 5 The ctime_s function returns zero if the time was successfully converted and stored
24368 into the array pointed to by s. Otherwise, it returns a nonzero value.
24369 K.3.8.2.3 The gmtime_s function
24371 1 #define __STDC_WANT_LIB_EXT1__ 1
24373 struct tm *gmtime_s(const time_t * restrict timer,
24374 struct tm * restrict result);
24375 Runtime-constraints
24376 2 Neither timer nor result shall be a null pointer.
24377 3 If there is a runtime-constraint violation, there is no attempt to convert the time.
24379 4 The gmtime_s function converts the calendar time pointed to by timer into a broken-
24380 down time, expressed as UTC. The broken-down time is stored in the structure pointed
24385 5 The gmtime_s function returns result, or a null pointer if the specified time cannot
24386 be converted to UTC or there is a runtime-constraint violation.
24387 K.3.8.2.4 The localtime_s function
24389 1 #define __STDC_WANT_LIB_EXT1__ 1
24391 struct tm *localtime_s(const time_t * restrict timer,
24392 struct tm * restrict result);
24393 Runtime-constraints
24394 2 Neither timer nor result shall be a null pointer.
24395 3 If there is a runtime-constraint violation, there is no attempt to convert the time.
24397 4 The localtime_s function converts the calendar time pointed to by timer into a
24398 broken-down time, expressed as local time. The broken-down time is stored in the
24399 structure pointed to by result.
24401 5 The localtime_s function returns result, or a null pointer if the specified time
24402 cannot be converted to local time or there is a runtime-constraint violation.
24403 K.3.9 Extended multibyte and wide character utilities <wchar.h>
24404 1 The header <wchar.h> defines two types.
24407 which is type int; and
24409 which is the type size_t.
24410 3 Unless explicitly stated otherwise, if the execution of a function described in this
24411 subclause causes copying to take place between objects that overlap, the objects take on
24412 unspecified values.
24419 K.3.9.1 Formatted wide character input/output functions
24420 K.3.9.1.1 The fwprintf_s function
24422 1 #define __STDC_WANT_LIB_EXT1__ 1
24424 int fwprintf_s(FILE * restrict stream,
24425 const wchar_t * restrict format, ...);
24426 Runtime-constraints
24427 2 Neither stream nor format shall be a null pointer. The %n specifier416) (modified or
24428 not by flags, field width, or precision) shall not appear in the wide string pointed to by
24429 format. Any argument to fwprintf_s corresponding to a %s specifier shall not be a
24431 3 If there is a runtime-constraint violation, the fwprintf_s function does not attempt to
24432 produce further output, and it is unspecified to what extent fwprintf_s produced
24433 output before discovering the runtime-constraint violation.
24435 4 The fwprintf_s function is equivalent to the fwprintf function except for the
24436 explicit runtime-constraints listed above.
24438 5 The fwprintf_s function returns the number of wide characters transmitted, or a
24439 negative value if an output error, encoding error, or runtime-constraint violation occurred.
24440 K.3.9.1.2 The fwscanf_s function
24442 1 #define __STDC_WANT_LIB_EXT1__ 1
24445 int fwscanf_s(FILE * restrict stream,
24446 const wchar_t * restrict format, ...);
24447 Runtime-constraints
24448 2 Neither stream nor format shall be a null pointer. Any argument indirected though in
24449 order to store converted input shall not be a null pointer.
24452 416) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24453 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24454 example, if the entire format string was L"%%n".
24458 3 If there is a runtime-constraint violation, the fwscanf_s function does not attempt to
24459 perform further input, and it is unspecified to what extent fwscanf_s performed input
24460 before discovering the runtime-constraint violation.
24462 4 The fwscanf_s function is equivalent to fwscanf except that the c, s, and [
24463 conversion specifiers apply to a pair of arguments (unless assignment suppression is
24464 indicated by a *). The first of these arguments is the same as for fwscanf. That
24465 argument is immediately followed in the argument list by the second argument, which has
24466 type size_t and gives the number of elements in the array pointed to by the first
24467 argument of the pair. If the first argument points to a scalar object, it is considered to be
24468 an array of one element.417)
24469 5 A matching failure occurs if the number of elements in a receiving object is insufficient to
24470 hold the converted input (including any trailing null character).
24472 6 The fwscanf_s function returns the value of the macro EOF if an input failure occurs
24473 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24474 fwscanf_s function returns the number of input items assigned, which can be fewer
24475 than provided for, or even zero, in the event of an early matching failure.
24476 K.3.9.1.3 The snwprintf_s function
24478 1 #define __STDC_WANT_LIB_EXT1__ 1
24480 int snwprintf_s(wchar_t * restrict s,
24482 const wchar_t * restrict format, ...);
24483 Runtime-constraints
24484 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
24485 than RSIZE_MAX. The %n specifier418) (modified or not by flags, field width, or
24487 417) If the format is known at translation time, an implementation may issue a diagnostic for any argument
24488 used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an
24489 argument of a type compatible with rsize_t. A limited amount of checking may be done if even if
24490 the format is not known at translation time. For example, an implementation may issue a diagnostic
24491 for each argument after format that has of type pointer to one of char, signed char,
24492 unsigned char, or void that is not followed by an argument of a type compatible with
24493 rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier
24494 using the hh length modifier, a length argument must follow the pointer argument. Another useful
24495 diagnostic could flag any non-pointer argument following format that did not have a type
24496 compatible with rsize_t.
24500 precision) shall not appear in the wide string pointed to by format. Any argument to
24501 snwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
24503 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
24504 than zero and less than RSIZE_MAX, then the snwprintf_s function sets s[0] to the
24505 null wide character.
24507 4 The snwprintf_s function is equivalent to the swprintf function except for the
24508 explicit runtime-constraints listed above.
24509 5 The snwprintf_s function, unlike swprintf_s, will truncate the result to fit within
24510 the array pointed to by s.
24512 6 The snwprintf_s function returns the number of wide characters that would have
24513 been written had n been sufficiently large, not counting the terminating wide null
24514 character, or a negative value if a runtime-constraint violation occurred. Thus, the null-
24515 terminated output has been completely written if and only if the returned value is
24516 nonnegative and less than n.
24517 K.3.9.1.4 The swprintf_s function
24519 1 #define __STDC_WANT_LIB_EXT1__ 1
24521 int swprintf_s(wchar_t * restrict s, rsize_t n,
24522 const wchar_t * restrict format, ...);
24523 Runtime-constraints
24524 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
24525 than RSIZE_MAX. The number of wide characters (including the trailing null) required
24526 for the result to be written to the array pointed to by s shall not be greater than n. The %n
24527 specifier419) (modified or not by flags, field width, or precision) shall not appear in the
24528 wide string pointed to by format. Any argument to swprintf_s corresponding to a
24529 %s specifier shall not be a null pointer. No encoding error shall occur.
24532 418) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24533 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24534 example, if the entire format string was L"%%n".
24535 419) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24536 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24537 example, if the entire format string was L"%%n".
24541 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
24542 than zero and less than RSIZE_MAX, then the swprintf_s function sets s[0] to the
24543 null wide character.
24545 4 The swprintf_s function is equivalent to the swprintf function except for the
24546 explicit runtime-constraints listed above.
24547 5 The swprintf_s function, unlike snwprintf_s, treats a result too big for the array
24548 pointed to by s as a runtime-constraint violation.
24550 6 If no runtime-constraint violation occurred, the swprintf_s function returns the
24551 number of wide characters written in the array, not counting the terminating null wide
24552 character. If an encoding error occurred or if n or more wide characters are requested to
24553 be written, swprintf_s returns a negative value. If any other runtime-constraint
24554 violation occurred, swprintf_s returns zero.
24555 K.3.9.1.5 The swscanf_s function
24557 1 #define __STDC_WANT_LIB_EXT1__ 1
24559 int swscanf_s(const wchar_t * restrict s,
24560 const wchar_t * restrict format, ...);
24561 Runtime-constraints
24562 2 Neither s nor format shall be a null pointer. Any argument indirected though in order
24563 to store converted input shall not be a null pointer.
24564 3 If there is a runtime-constraint violation, the swscanf_s function does not attempt to
24565 perform further input, and it is unspecified to what extent swscanf_s performed input
24566 before discovering the runtime-constraint violation.
24568 4 The swscanf_s function is equivalent to fwscanf_s, except that the argument s
24569 specifies a wide string from which the input is to be obtained, rather than from a stream.
24570 Reaching the end of the wide string is equivalent to encountering end-of-file for the
24571 fwscanf_s function.
24573 5 The swscanf_s function returns the value of the macro EOF if an input failure occurs
24574 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24575 swscanf_s function returns the number of input items assigned, which can be fewer
24576 than provided for, or even zero, in the event of an early matching failure.
24579 K.3.9.1.6 The vfwprintf_s function
24581 1 #define __STDC_WANT_LIB_EXT1__ 1
24582 #include <stdarg.h>
24585 int vfwprintf_s(FILE * restrict stream,
24586 const wchar_t * restrict format,
24588 Runtime-constraints
24589 2 Neither stream nor format shall be a null pointer. The %n specifier420) (modified or
24590 not by flags, field width, or precision) shall not appear in the wide string pointed to by
24591 format. Any argument to vfwprintf_s corresponding to a %s specifier shall not be
24593 3 If there is a runtime-constraint violation, the vfwprintf_s function does not attempt
24594 to produce further output, and it is unspecified to what extent vfwprintf_s produced
24595 output before discovering the runtime-constraint violation.
24597 4 The vfwprintf_s function is equivalent to the vfwprintf function except for the
24598 explicit runtime-constraints listed above.
24600 5 The vfwprintf_s function returns the number of wide characters transmitted, or a
24601 negative value if an output error, encoding error, or runtime-constraint violation occurred.
24602 K.3.9.1.7 The vfwscanf_s function
24604 1 #define __STDC_WANT_LIB_EXT1__ 1
24605 #include <stdarg.h>
24608 int vfwscanf_s(FILE * restrict stream,
24609 const wchar_t * restrict format, va_list arg);
24613 420) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24614 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24615 example, if the entire format string was L"%%n".
24619 Runtime-constraints
24620 2 Neither stream nor format shall be a null pointer. Any argument indirected though in
24621 order to store converted input shall not be a null pointer.
24622 3 If there is a runtime-constraint violation, the vfwscanf_s function does not attempt to
24623 perform further input, and it is unspecified to what extent vfwscanf_s performed input
24624 before discovering the runtime-constraint violation.
24626 4 The vfwscanf_s function is equivalent to fwscanf_s, with the variable argument
24627 list replaced by arg, which shall have been initialized by the va_start macro (and
24628 possibly subsequent va_arg calls). The vfwscanf_s function does not invoke the
24631 5 The vfwscanf_s function returns the value of the macro EOF if an input failure occurs
24632 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24633 vfwscanf_s function returns the number of input items assigned, which can be fewer
24634 than provided for, or even zero, in the event of an early matching failure.
24635 K.3.9.1.8 The vsnwprintf_s function
24637 1 #define __STDC_WANT_LIB_EXT1__ 1
24638 #include <stdarg.h>
24640 int vsnwprintf_s(wchar_t * restrict s,
24642 const wchar_t * restrict format,
24644 Runtime-constraints
24645 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
24646 than RSIZE_MAX. The %n specifier422) (modified or not by flags, field width, or
24647 precision) shall not appear in the wide string pointed to by format. Any argument to
24648 vsnwprintf_s corresponding to a %s specifier shall not be a null pointer. No
24649 encoding error shall occur.
24651 421) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
24652 value of arg after the return is indeterminate.
24653 422) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24654 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24655 example, if the entire format string was L"%%n".
24659 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
24660 than zero and less than RSIZE_MAX, then the vsnwprintf_s function sets s[0] to
24661 the null wide character.
24663 4 The vsnwprintf_s function is equivalent to the vswprintf function except for the
24664 explicit runtime-constraints listed above.
24665 5 The vsnwprintf_s function, unlike vswprintf_s, will truncate the result to fit
24666 within the array pointed to by s.
24668 6 The vsnwprintf_s function returns the number of wide characters that would have
24669 been written had n been sufficiently large, not counting the terminating null character, or
24670 a negative value if a runtime-constraint violation occurred. Thus, the null-terminated
24671 output has been completely written if and only if the returned value is nonnegative and
24673 K.3.9.1.9 The vswprintf_s function
24675 1 #define __STDC_WANT_LIB_EXT1__ 1
24676 #include <stdarg.h>
24678 int vswprintf_s(wchar_t * restrict s,
24680 const wchar_t * restrict format,
24682 Runtime-constraints
24683 2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
24684 than RSIZE_MAX. The number of wide characters (including the trailing null) required
24685 for the result to be written to the array pointed to by s shall not be greater than n. The %n
24686 specifier423) (modified or not by flags, field width, or precision) shall not appear in the
24687 wide string pointed to by format. Any argument to vswprintf_s corresponding to a
24688 %s specifier shall not be a null pointer. No encoding error shall occur.
24689 3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
24690 than zero and less than RSIZE_MAX, then the vswprintf_s function sets s[0] to the
24691 null wide character.
24693 423) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24694 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24695 example, if the entire format string was L"%%n".
24700 4 The vswprintf_s function is equivalent to the vswprintf function except for the
24701 explicit runtime-constraints listed above.
24702 5 The vswprintf_s function, unlike vsnwprintf_s, treats a result too big for the
24703 array pointed to by s as a runtime-constraint violation.
24705 6 If no runtime-constraint violation occurred, the vswprintf_s function returns the
24706 number of wide characters written in the array, not counting the terminating null wide
24707 character. If an encoding error occurred or if n or more wide characters are requested to
24708 be written, vswprintf_s returns a negative value. If any other runtime-constraint
24709 violation occurred, vswprintf_s returns zero.
24710 K.3.9.1.10 The vswscanf_s function
24712 1 #define __STDC_WANT_LIB_EXT1__ 1
24713 #include <stdarg.h>
24715 int vswscanf_s(const wchar_t * restrict s,
24716 const wchar_t * restrict format,
24718 Runtime-constraints
24719 2 Neither s nor format shall be a null pointer. Any argument indirected though in order
24720 to store converted input shall not be a null pointer.
24721 3 If there is a runtime-constraint violation, the vswscanf_s function does not attempt to
24722 perform further input, and it is unspecified to what extent vswscanf_s performed input
24723 before discovering the runtime-constraint violation.
24725 4 The vswscanf_s function is equivalent to swscanf_s, with the variable argument
24726 list replaced by arg, which shall have been initialized by the va_start macro (and
24727 possibly subsequent va_arg calls). The vswscanf_s function does not invoke the
24733 424) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
24734 value of arg after the return is indeterminate.
24739 5 The vswscanf_s function returns the value of the macro EOF if an input failure occurs
24740 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24741 vswscanf_s function returns the number of input items assigned, which can be fewer
24742 than provided for, or even zero, in the event of an early matching failure.
24743 K.3.9.1.11 The vwprintf_s function
24745 1 #define __STDC_WANT_LIB_EXT1__ 1
24746 #include <stdarg.h>
24748 int vwprintf_s(const wchar_t * restrict format,
24750 Runtime-constraints
24751 2 format shall not be a null pointer. The %n specifier425) (modified or not by flags, field
24752 width, or precision) shall not appear in the wide string pointed to by format. Any
24753 argument to vwprintf_s corresponding to a %s specifier shall not be a null pointer.
24754 3 If there is a runtime-constraint violation, the vwprintf_s function does not attempt to
24755 produce further output, and it is unspecified to what extent vwprintf_s produced
24756 output before discovering the runtime-constraint violation.
24758 4 The vwprintf_s function is equivalent to the vwprintf function except for the
24759 explicit runtime-constraints listed above.
24761 5 The vwprintf_s function returns the number of wide characters transmitted, or a
24762 negative value if an output error, encoding error, or runtime-constraint violation occurred.
24767 425) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24768 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24769 example, if the entire format string was L"%%n".
24773 K.3.9.1.12 The vwscanf_s function
24775 1 #define __STDC_WANT_LIB_EXT1__ 1
24776 #include <stdarg.h>
24778 int vwscanf_s(const wchar_t * restrict format,
24780 Runtime-constraints
24781 2 format shall not be a null pointer. Any argument indirected though in order to store
24782 converted input shall not be a null pointer.
24783 3 If there is a runtime-constraint violation, the vwscanf_s function does not attempt to
24784 perform further input, and it is unspecified to what extent vwscanf_s performed input
24785 before discovering the runtime-constraint violation.
24787 4 The vwscanf_s function is equivalent to wscanf_s, with the variable argument list
24788 replaced by arg, which shall have been initialized by the va_start macro (and
24789 possibly subsequent va_arg calls). The vwscanf_s function does not invoke the
24792 5 The vwscanf_s function returns the value of the macro EOF if an input failure occurs
24793 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24794 vwscanf_s function returns the number of input items assigned, which can be fewer
24795 than provided for, or even zero, in the event of an early matching failure.
24796 K.3.9.1.13 The wprintf_s function
24798 1 #define __STDC_WANT_LIB_EXT1__ 1
24800 int wprintf_s(const wchar_t * restrict format, ...);
24801 Runtime-constraints
24802 2 format shall not be a null pointer. The %n specifier427) (modified or not by flags, field
24804 426) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
24805 value of arg after the return is indeterminate.
24806 427) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
24807 string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
24808 example, if the entire format string was L"%%n".
24812 width, or precision) shall not appear in the wide string pointed to by format. Any
24813 argument to wprintf_s corresponding to a %s specifier shall not be a null pointer.
24814 3 If there is a runtime-constraint violation, the wprintf_s function does not attempt to
24815 produce further output, and it is unspecified to what extent wprintf_s produced output
24816 before discovering the runtime-constraint violation.
24818 4 The wprintf_s function is equivalent to the wprintf function except for the explicit
24819 runtime-constraints listed above.
24821 5 The wprintf_s function returns the number of wide characters transmitted, or a
24822 negative value if an output error, encoding error, or runtime-constraint violation occurred.
24823 K.3.9.1.14 The wscanf_s function
24825 1 #define __STDC_WANT_LIB_EXT1__ 1
24827 int wscanf_s(const wchar_t * restrict format, ...);
24828 Runtime-constraints
24829 2 format shall not be a null pointer. Any argument indirected though in order to store
24830 converted input shall not be a null pointer.
24831 3 If there is a runtime-constraint violation, the wscanf_s function does not attempt to
24832 perform further input, and it is unspecified to what extent wscanf_s performed input
24833 before discovering the runtime-constraint violation.
24835 4 The wscanf_s function is equivalent to fwscanf_s with the argument stdin
24836 interposed before the arguments to wscanf_s.
24838 5 The wscanf_s function returns the value of the macro EOF if an input failure occurs
24839 before any conversion or if there is a runtime-constraint violation. Otherwise, the
24840 wscanf_s function returns the number of input items assigned, which can be fewer than
24841 provided for, or even zero, in the event of an early matching failure.
24848 K.3.9.2 General wide string utilities
24849 K.3.9.2.1 Wide string copying functions
24850 K.3.9.2.1.1 The wcscpy_s function
24852 1 #define __STDC_WANT_LIB_EXT1__ 1
24854 errno_t wcscpy_s(wchar_t * restrict s1,
24856 const wchar_t * restrict s2);
24857 Runtime-constraints
24858 2 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
24859 s1max shall not equal zero. s1max shall be greater than wcsnlen_s(s2, s1max).
24860 Copying shall not take place between objects that overlap.
24861 3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
24862 greater than zero and not greater than RSIZE_MAX, then wcscpy_s sets s1[0] to the
24863 null wide character.
24865 4 The wcscpy_s function copies the wide string pointed to by s2 (including the
24866 terminating null wide character) into the array pointed to by s1.
24867 5 All elements following the terminating null wide character (if any) written by
24868 wcscpy_s in the array of s1max wide characters pointed to by s1 take unspecified
24869 values when wcscpy_s returns.428)
24871 6 The wcscpy_s function returns zero429) if there was no runtime-constraint violation.
24872 Otherwise, a nonzero value is returned.
24877 428) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking
24878 if any of those wide characters are null. Such an approach might write a wide character to every
24879 element of s1 before discovering that the first element should be set to the null wide character.
24880 429) A zero return value implies that all of the requested wide characters from the string pointed to by s2
24881 fit within the array pointed to by s1 and that the result in s1 is null terminated.
24885 K.3.9.2.1.2 The wcsncpy_s function
24887 7 #define __STDC_WANT_LIB_EXT1__ 1
24889 errno_t wcsncpy_s(wchar_t * restrict s1,
24891 const wchar_t * restrict s2,
24893 Runtime-constraints
24894 8 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
24895 RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max
24896 shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between
24897 objects that overlap.
24898 9 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
24899 greater than zero and not greater than RSIZE_MAX, then wcsncpy_s sets s1[0] to the
24900 null wide character.
24902 10 The wcsncpy_s function copies not more than n successive wide characters (wide
24903 characters that follow a null wide character are not copied) from the array pointed to by
24904 s2 to the array pointed to by s1. If no null wide character was copied from s2, then
24905 s1[n] is set to a null wide character.
24906 11 All elements following the terminating null wide character (if any) written by
24907 wcsncpy_s in the array of s1max wide characters pointed to by s1 take unspecified
24908 values when wcsncpy_s returns.430)
24910 12 The wcsncpy_s function returns zero431) if there was no runtime-constraint violation.
24911 Otherwise, a nonzero value is returned.
24912 13 EXAMPLE 1 The wcsncpy_s function can be used to copy a wide string without the danger that the
24913 result will not be null terminated or that wide characters will be written past the end of the destination
24919 430) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking
24920 if any of those wide characters are null. Such an approach might write a wide character to every
24921 element of s1 before discovering that the first element should be set to the null wide character.
24922 431) A zero return value implies that all of the requested wide characters from the string pointed to by s2
24923 fit within the array pointed to by s1 and that the result in s1 is null terminated.
24927 #define __STDC_WANT_LIB_EXT1__ 1
24930 wchar_t src1[100] = L"hello";
24931 wchar_t src2[7] = {L'g', L'o', L'o', L'd', L'b', L'y', L'e'};
24932 wchar_t dst1[6], dst2[5], dst3[5];
24934 r1 = wcsncpy_s(dst1, 6, src1, 100);
24935 r2 = wcsncpy_s(dst2, 5, src2, 7);
24936 r3 = wcsncpy_s(dst3, 5, src2, 4);
24937 The first call will assign to r1 the value zero and to dst1 the sequence of wide characters hello\0.
24938 The second call will assign to r2 a nonzero value and to dst2 the sequence of wide characters \0.
24939 The third call will assign to r3 the value zero and to dst3 the sequence of wide characters good\0.
24941 K.3.9.2.1.3 The wmemcpy_s function
24943 14 #define __STDC_WANT_LIB_EXT1__ 1
24945 errno_t wmemcpy_s(wchar_t * restrict s1,
24947 const wchar_t * restrict s2,
24949 Runtime-constraints
24950 15 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
24951 RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between
24952 objects that overlap.
24953 16 If there is a runtime-constraint violation, the wmemcpy_s function stores zeros in the
24954 first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and
24955 s1max is not greater than RSIZE_MAX.
24957 17 The wmemcpy_s function copies n successive wide characters from the object pointed
24958 to by s2 into the object pointed to by s1.
24960 18 The wmemcpy_s function returns zero if there was no runtime-constraint violation.
24961 Otherwise, a nonzero value is returned.
24968 K.3.9.2.1.4 The wmemmove_s function
24970 19 #define __STDC_WANT_LIB_EXT1__ 1
24972 errno_t wmemmove_s(wchar_t *s1, rsize_t s1max,
24973 const wchar_t *s2, rsize_t n);
24974 Runtime-constraints
24975 20 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
24976 RSIZE_MAX. n shall not be greater than s1max.
24977 21 If there is a runtime-constraint violation, the wmemmove_s function stores zeros in the
24978 first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and
24979 s1max is not greater than RSIZE_MAX.
24981 22 The wmemmove_s function copies n successive wide characters from the object pointed
24982 to by s2 into the object pointed to by s1. This copying takes place as if the n wide
24983 characters from the object pointed to by s2 are first copied into a temporary array of n
24984 wide characters that does not overlap the objects pointed to by s1 or s2, and then the n
24985 wide characters from the temporary array are copied into the object pointed to by s1.
24987 23 The wmemmove_s function returns zero if there was no runtime-constraint violation.
24988 Otherwise, a nonzero value is returned.
24989 K.3.9.2.2 Wide string concatenation functions
24990 K.3.9.2.2.1 The wcscat_s function
24992 1 #define __STDC_WANT_LIB_EXT1__ 1
24994 errno_t wcscat_s(wchar_t * restrict s1,
24996 const wchar_t * restrict s2);
24997 Runtime-constraints
24998 2 Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to
25000 3 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
25001 s1max shall not equal zero. m shall not equal zero.432) m shall be greater than
25002 wcsnlen_s(s2, m). Copying shall not take place between objects that overlap.
25006 4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
25007 greater than zero and not greater than RSIZE_MAX, then wcscat_s sets s1[0] to the
25008 null wide character.
25010 5 The wcscat_s function appends a copy of the wide string pointed to by s2 (including
25011 the terminating null wide character) to the end of the wide string pointed to by s1. The
25012 initial wide character from s2 overwrites the null wide character at the end of s1.
25013 6 All elements following the terminating null wide character (if any) written by
25014 wcscat_s in the array of s1max wide characters pointed to by s1 take unspecified
25015 values when wcscat_s returns.433)
25017 7 The wcscat_s function returns zero434) if there was no runtime-constraint violation.
25018 Otherwise, a nonzero value is returned.
25019 K.3.9.2.2.2 The wcsncat_s function
25021 8 #define __STDC_WANT_LIB_EXT1__ 1
25023 errno_t wcsncat_s(wchar_t * restrict s1,
25025 const wchar_t * restrict s2,
25027 Runtime-constraints
25028 9 Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to
25030 10 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
25031 RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.435) If n is not less
25032 than m, then m shall be greater than wcsnlen_s(s2, m). Copying shall not take
25033 place between objects that overlap.
25036 432) Zero means that s1 was not null terminated upon entry to wcscat_s.
25037 433) This allows an implementation to append wide characters from s2 to s1 while simultaneously
25038 checking if any of those wide characters are null. Such an approach might write a wide character to
25039 every element of s1 before discovering that the first element should be set to the null wide character.
25040 434) A zero return value implies that all of the requested wide characters from the wide string pointed to by
25041 s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated.
25042 435) Zero means that s1 was not null terminated upon entry to wcsncat_s.
25046 11 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
25047 greater than zero and not greater than RSIZE_MAX, then wcsncat_s sets s1[0] to the
25048 null wide character.
25050 12 The wcsncat_s function appends not more than n successive wide characters (wide
25051 characters that follow a null wide character are not copied) from the array pointed to by
25052 s2 to the end of the wide string pointed to by s1. The initial wide character from s2
25053 overwrites the null wide character at the end of s1. If no null wide character was copied
25054 from s2, then s1[s1max-m+n] is set to a null wide character.
25055 13 All elements following the terminating null wide character (if any) written by
25056 wcsncat_s in the array of s1max wide characters pointed to by s1 take unspecified
25057 values when wcsncat_s returns.436)
25059 14 The wcsncat_s function returns zero437) if there was no runtime-constraint violation.
25060 Otherwise, a nonzero value is returned.
25061 15 EXAMPLE 1 The wcsncat_s function can be used to copy a wide string without the danger that the
25062 result will not be null terminated or that wide characters will be written past the end of the destination
25064 #define __STDC_WANT_LIB_EXT1__ 1
25067 wchar_t s1[100] = L"good";
25068 wchar_t s2[6] = L"hello";
25069 wchar_t s3[6] = L"hello";
25070 wchar_t s4[7] = L"abc";
25071 wchar_t s5[1000] = L"bye";
25072 int r1, r2, r3, r4;
25073 r1 = wcsncat_s(s1, 100, s5, 1000);
25074 r2 = wcsncat_s(s2, 6, L"", 1);
25075 r3 = wcsncat_s(s3, 6, L"X", 2);
25076 r4 = wcsncat_s(s4, 7, L"defghijklmn", 3);
25077 After the first call r1 will have the value zero and s1 will be the wide character sequence goodbye\0.
25078 After the second call r2 will have the value zero and s2 will be the wide character sequence hello\0.
25079 After the third call r3 will have a nonzero value and s3 will be the wide character sequence \0.
25080 After the fourth call r4 will have the value zero and s4 will be the wide character sequence abcdef\0.
25085 436) This allows an implementation to append wide characters from s2 to s1 while simultaneously
25086 checking if any of those wide characters are null. Such an approach might write a wide character to
25087 every element of s1 before discovering that the first element should be set to the null wide character.
25088 437) A zero return value implies that all of the requested wide characters from the wide string pointed to by
25089 s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated.
25093 K.3.9.2.3 Wide string search functions
25094 K.3.9.2.3.1 The wcstok_s function
25096 1 #define __STDC_WANT_LIB_EXT1__ 1
25098 wchar_t *wcstok_s(wchar_t * restrict s1,
25099 rsize_t * restrict s1max,
25100 const wchar_t * restrict s2,
25101 wchar_t ** restrict ptr);
25102 Runtime-constraints
25103 2 None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr
25104 shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX.
25105 The end of the token found shall occur within the first *s1max wide characters of s1 for
25106 the first call, and shall occur within the first *s1max wide characters of where searching
25107 resumes on subsequent calls.
25108 3 If there is a runtime-constraint violation, the wcstok_s function does not indirect
25109 through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr.
25111 4 A sequence of calls to the wcstok_s function breaks the wide string pointed to by s1
25112 into a sequence of tokens, each of which is delimited by a wide character from the wide
25113 string pointed to by s2. The fourth argument points to a caller-provided wchar_t
25114 pointer into which the wcstok_s function stores information necessary for it to
25115 continue scanning the same wide string.
25116 5 The first call in a sequence has a non-null first argument and s1max points to an object
25117 whose value is the number of elements in the wide character array pointed to by the first
25118 argument. The first call stores an initial value in the object pointed to by ptr and
25119 updates the value pointed to by s1max to reflect the number of elements that remain in
25120 relation to ptr. Subsequent calls in the sequence have a null first argument and the
25121 objects pointed to by s1max and ptr are required to have the values stored by the
25122 previous call in the sequence, which are then updated. The separator wide string pointed
25123 to by s2 may be different from call to call.
25124 6 The first call in the sequence searches the wide string pointed to by s1 for the first wide
25125 character that is not contained in the current separator wide string pointed to by s2. If no
25126 such wide character is found, then there are no tokens in the wide string pointed to by s1
25127 and the wcstok_s function returns a null pointer. If such a wide character is found, it is
25128 the start of the first token.
25133 7 The wcstok_s function then searches from there for the first wide character in s1 that
25134 is contained in the current separator wide string. If no such wide character is found, the
25135 current token extends to the end of the wide string pointed to by s1, and subsequent
25136 searches in the same wide string for a token return a null pointer. If such a wide character
25137 is found, it is overwritten by a null wide character, which terminates the current token.
25138 8 In all cases, the wcstok_s function stores sufficient information in the pointer pointed
25139 to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
25140 value for ptr, shall start searching just past the element overwritten by a null wide
25141 character (if any).
25143 9 The wcstok_s function returns a pointer to the first wide character of a token, or a null
25144 pointer if there is no token or there is a runtime-constraint violation.
25146 #define __STDC_WANT_LIB_EXT1__ 1
25148 static wchar_t str1[] = L"?a???b,,,#c";
25149 static wchar_t str2[] = L"\t \t";
25150 wchar_t *t, *ptr1, *ptr2;
25151 rsize_t max1 = wcslen(str1)+1;
25152 rsize_t max2 = wcslen(str2)+1;
25153 t = wcstok_s(str1, &max1, "?", &ptr1); // t points to the token "a"
25154 t = wcstok_s(NULL, &max1, ",", &ptr1); // t points to the token "??b"
25155 t = wcstok_s(str2, &max2, " \t", &ptr2); // t is a null pointer
25156 t = wcstok_s(NULL, &max1, "#,", &ptr1); // t points to the token "c"
25157 t = wcstok_s(NULL, &max1, "?", &ptr1); // t is a null pointer
25159 K.3.9.2.4 Miscellaneous functions
25160 K.3.9.2.4.1 The wcsnlen_s function
25162 1 #define __STDC_WANT_LIB_EXT1__ 1
25164 size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
25166 2 The wcsnlen_s function computes the length of the wide string pointed to by s.
25168 3 If s is a null pointer,438) then the wcsnlen_s function returns zero.
25169 4 Otherwise, the wcsnlen_s function returns the number of wide characters that precede
25170 the terminating null wide character. If there is no null wide character in the first
25171 maxsize wide characters of s then wcsnlen_s returns maxsize. At most the first
25175 maxsize wide characters of s shall be accessed by wcsnlen_s.
25176 K.3.9.3 Extended multibyte/wide character conversion utilities
25177 K.3.9.3.1 Restartable multibyte/wide character conversion functions
25178 1 Unlike wcrtomb, wcrtomb_s does not permit the ps parameter (the pointer to the
25179 conversion state) to be a null pointer.
25180 K.3.9.3.1.1 The wcrtomb_s function
25182 2 #include <wchar.h>
25183 errno_t wcrtomb_s(size_t * restrict retval,
25184 char * restrict s, rsize_t smax,
25185 wchar_t wc, mbstate_t * restrict ps);
25186 Runtime-constraints
25187 3 Neither retval nor ps shall be a null pointer. If s is not a null pointer, then smax
25188 shall not equal zero and shall not be greater than RSIZE_MAX. If s is not a null pointer,
25189 then smax shall be not be less than the number of bytes to be stored in the array pointed
25190 to by s. If s is a null pointer, then smax shall equal zero.
25191 4 If there is a runtime-constraint violation, then wcrtomb_s does the following. If s is
25192 not a null pointer and smax is greater than zero and not greater than RSIZE_MAX, then
25193 wcrtomb_s sets s[0] to the null character. If retval is not a null pointer, then
25194 wcrtomb_s sets *retval to (size_t)(-1).
25196 5 If s is a null pointer, the wcrtomb_s function is equivalent to the call
25197 wcrtomb_s(&retval, buf, sizeof buf, L'\0', ps)
25198 where retval and buf are internal variables of the appropriate types, and the size of
25199 buf is greater than MB_CUR_MAX.
25200 6 If s is not a null pointer, the wcrtomb_s function determines the number of bytes
25201 needed to represent the multibyte character that corresponds to the wide character given
25202 by wc (including any shift sequences), and stores the multibyte character representation
25203 in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are
25204 stored. If wc is a null wide character, a null byte is stored, preceded by any shift
25205 sequence needed to restore the initial shift state; the resulting state described is the initial
25208 438) Note that the wcsnlen_s function has no runtime-constraints. This lack of runtime-constraints
25209 along with the values returned for a null pointer or an unterminated wide string argument make
25210 wcsnlen_s useful in algorithms that gracefully handle such exceptional data.
25214 7 If wc does not correspond to a valid multibyte character, an encoding error occurs: the
25215 wcrtomb_s function stores the value (size_t)(-1) into *retval and the
25216 conversion state is unspecified. Otherwise, the wcrtomb_s function stores into
25217 *retval the number of bytes (including any shift sequences) stored in the array pointed
25220 8 The wcrtomb_s function returns zero if no runtime-constraint violation and no
25221 encoding error occurred. Otherwise, a nonzero value is returned.
25222 K.3.9.3.2 Restartable multibyte/wide string conversion functions
25223 1 Unlike mbsrtowcs and wcsrtombs, mbsrtowcs_s and wcsrtombs_s do not
25224 permit the ps parameter (the pointer to the conversion state) to be a null pointer.
25225 K.3.9.3.2.1 The mbsrtowcs_s function
25227 2 #include <wchar.h>
25228 errno_t mbsrtowcs_s(size_t * restrict retval,
25229 wchar_t * restrict dst, rsize_t dstmax,
25230 const char ** restrict src, rsize_t len,
25231 mbstate_t * restrict ps);
25232 Runtime-constraints
25233 3 None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer,
25234 then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null
25235 pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall
25236 not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null
25237 character shall occur within the first dstmax multibyte characters of the array pointed to
25239 4 If there is a runtime-constraint violation, then mbsrtowcs_s does the following. If
25240 retval is not a null pointer, then mbsrtowcs_s sets *retval to (size_t)(-1).
25241 If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
25242 then mbsrtowcs_s sets dst[0] to the null wide character.
25244 5 The mbsrtowcs_s function converts a sequence of multibyte characters that begins in
25245 the conversion state described by the object pointed to by ps, from the array indirectly
25246 pointed to by src into a sequence of corresponding wide characters. If dst is not a null
25247 pointer, the converted characters are stored into the array pointed to by dst. Conversion
25248 continues up to and including a terminating null character, which is also stored.
25249 Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
25250 not form a valid multibyte character, or (if dst is not a null pointer) when len wide
25253 characters have been stored into the array pointed to by dst.439) If dst is not a null
25254 pointer and no null wide character was stored into the array pointed to by dst, then
25255 dst[len] is set to the null wide character. Each conversion takes place as if by a call
25256 to the mbrtowc function.
25257 6 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
25258 pointer (if conversion stopped due to reaching a terminating null character) or the address
25259 just past the last multibyte character converted (if any). If conversion stopped due to
25260 reaching a terminating null character and if dst is not a null pointer, the resulting state
25261 described is the initial conversion state.
25262 7 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
25263 sequence of bytes that do not form a valid multibyte character, an encoding error occurs:
25264 the mbsrtowcs_s function stores the value (size_t)(-1) into *retval and the
25265 conversion state is unspecified. Otherwise, the mbsrtowcs_s function stores into
25266 *retval the number of multibyte characters successfully converted, not including the
25267 terminating null character (if any).
25268 8 All elements following the terminating null wide character (if any) written by
25269 mbsrtowcs_s in the array of dstmax wide characters pointed to by dst take
25270 unspecified values when mbsrtowcs_s returns.440)
25271 9 If copying takes place between objects that overlap, the objects take on unspecified
25274 10 The mbsrtowcs_s function returns zero if no runtime-constraint violation and no
25275 encoding error occurred. Otherwise, a nonzero value is returned.
25276 K.3.9.3.2.2 The wcsrtombs_s function
25278 11 #include <wchar.h>
25279 errno_t wcsrtombs_s(size_t * restrict retval,
25280 char * restrict dst, rsize_t dstmax,
25281 const wchar_t ** restrict src, rsize_t len,
25282 mbstate_t * restrict ps);
25287 439) Thus, the value of len is ignored if dst is a null pointer.
25288 440) This allows an implementation to attempt converting the multibyte string before discovering a
25289 terminating null character did not occur where required.
25293 Runtime-constraints
25294 12 None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer,
25295 then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null
25296 pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall
25297 not equal zero. If dst is not a null pointer and len is not less than dstmax, then the
25298 conversion shall have been stopped (see below) because a terminating null wide character
25299 was reached or because an encoding error occurred.
25300 13 If there is a runtime-constraint violation, then wcsrtombs_s does the following. If
25301 retval is not a null pointer, then wcsrtombs_s sets *retval to (size_t)(-1).
25302 If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
25303 then wcsrtombs_s sets dst[0] to the null character.
25305 14 The wcsrtombs_s function converts a sequence of wide characters from the array
25306 indirectly pointed to by src into a sequence of corresponding multibyte characters that
25307 begins in the conversion state described by the object pointed to by ps. If dst is not a
25308 null pointer, the converted characters are then stored into the array pointed to by dst.
25309 Conversion continues up to and including a terminating null wide character, which is also
25310 stored. Conversion stops earlier in two cases:
25311 -- when a wide character is reached that does not correspond to a valid multibyte
25313 -- (if dst is not a null pointer) when the next multibyte character would exceed the
25314 limit of n total bytes to be stored into the array pointed to by dst. If the wide
25315 character being converted is the null wide character, then n is the lesser of len or
25316 dstmax. Otherwise, n is the lesser of len or dstmax-1.
25317 If the conversion stops without converting a null wide character and dst is not a null
25318 pointer, then a null character is stored into the array pointed to by dst immediately
25319 following any multibyte characters already stored. Each conversion takes place as if by a
25320 call to the wcrtomb function.441)
25321 15 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
25322 pointer (if conversion stopped due to reaching a terminating null wide character) or the
25323 address just past the last wide character converted (if any). If conversion stopped due to
25324 reaching a terminating null wide character, the resulting state described is the initial
25328 441) If conversion stops because a terminating null wide character has been reached, the bytes stored
25329 include those necessary to reach the initial shift state immediately before the null byte. However, if
25330 the conversion stops before a terminating null wide character has been reached, the result will be null
25331 terminated, but might not end in the initial shift state.
25335 16 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
25336 wide character that does not correspond to a valid multibyte character, an encoding error
25337 occurs: the wcsrtombs_s function stores the value (size_t)(-1) into *retval
25338 and the conversion state is unspecified. Otherwise, the wcsrtombs_s function stores
25339 into *retval the number of bytes in the resulting multibyte character sequence, not
25340 including the terminating null character (if any).
25341 17 All elements following the terminating null character (if any) written by wcsrtombs_s
25342 in the array of dstmax elements pointed to by dst take unspecified values when
25343 wcsrtombs_s returns.442)
25344 18 If copying takes place between objects that overlap, the objects take on unspecified
25347 19 The wcsrtombs_s function returns zero if no runtime-constraint violation and no
25348 encoding error occurred. Otherwise, a nonzero value is returned.
25353 442) When len is not less than dstmax, the implementation might fill the array before discovering a
25354 runtime-constraint violation.
25362 1 This annex specifies optional behavior that can aid in the analyzability of C programs.
25363 2 An implementation that defines __STDC_ANALYZABLE__ shall conform to the
25364 specifications in this annex.443)
25367 1 out-of-bounds store
25368 an (attempted) access (3.1) that, at run time, for a given computational state, would
25369 modify (or, for an object declared volatile, fetch) one or more bytes that lie outside
25370 the bounds permitted by this Standard.
25372 1 bounded undefined behavior
25373 undefined behavior (3.4.3) that does not perform an out-of-bounds store.
25374 2 NOTE 1 The behavior might perform a trap.
25376 3 NOTE 2 Any values produced or stored might be indeterminate values.
25379 1 critical undefined behavior
25380 undefined behavior that is not bounded undefined behavior.
25381 2 NOTE The behavior might perform an out-of-bounds store or perform a trap.
25386 443) Implementations that do not define __STDC_ANALYZABLE__ are not required to conform to these
25392 1 If the program performs a trap (3.19.5), the implementation is permitted to invoke a
25393 runtime-constraint handler. Any such semantics are implementation-defined.
25394 2 All undefined behavior shall be limited to bounded undefined behavior, except for the
25395 following which are permitted to result in critical undefined behavior:
25396 -- An object is referred to outside of its lifetime (6.2.4).
25397 -- An lvalue does not designate an object when evaluated (6.3.2.1).
25398 -- A pointer is used to call a function whose type is not compatible with the referenced
25400 -- The operand of the unary * operator has an invalid value (6.5.3.2).
25401 -- Addition or subtraction of a pointer into, or just beyond, an array object and an
25402 integer type produces a result that points just beyond the array object and is used as
25403 the operand of a unary * operator that is evaluated (6.5.6).
25404 -- An argument to a library function has an invalid value or a type not expected by a
25405 function with variable number of arguments (7.1.4).
25406 -- The value of a pointer that refers to space deallocated by a call to the free or realloc
25407 function is used (7.22.3).
25408 -- A string or wide string utility function is instructed to access an array beyond the end
25409 of an object (7.23.1, 7.28.4).
25418 1. ''The C Reference Manual'' by Dennis M. Ritchie, a version of which was
25419 published in The C Programming Language by Brian W. Kernighan and Dennis
25420 M. Ritchie, Prentice-Hall, Inc., (1978). Copyright owned by AT&T.
25421 2. 1984 /usr/group Standard by the /usr/group Standards Committee, Santa Clara,
25422 California, USA, November 1984.
25423 3. ANSI X3/TR-1-82 (1982), American National Dictionary for Information
25424 Processing Systems, Information Processing Systems Technical Report.
25425 4. ANSI/IEEE 754-1985, American National Standard for Binary Floating-Point
25427 5. ANSI/IEEE 854-1988, American National Standard for Radix-Independent
25428 Floating-Point Arithmetic.
25429 6. IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems,
25430 second edition (previously designated IEC 559:1989).
25431 7. ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and
25432 symbols for use in the physical sciences and technology.
25433 8. ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for
25434 information interchange.
25435 9. ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1:
25437 10. ISO 4217:1995, Codes for the representation of currencies and funds.
25438 11. ISO 8601:1988, Data elements and interchange formats -- Information
25439 interchange -- Representation of dates and times.
25440 12. ISO/IEC 9899:1990, Programming languages -- C.
25441 13. ISO/IEC 9899/COR1:1994, Technical Corrigendum 1.
25442 14. ISO/IEC 9899/COR2:1996, Technical Corrigendum 2.
25443 15. ISO/IEC 9899/AMD1:1995, Amendment 1 to ISO/IEC 9899:1990 C Integrity.
25444 16. ISO/IEC 9899:1999, Programming languages -- C.
25445 17. ISO/IEC 9899:1999/Cor.1:2001, Technical Corrigendum 1.
25446 18. ISO/IEC 9899:1999/Cor.2:2004, Technical Corrigendum 2.
25447 19. ISO/IEC 9899:1999/Cor.3:2007, Technical Corrigendum 3.
25453 20. ISO/IEC 9945-2:1993, Information technology -- Portable Operating System
25454 Interface (POSIX) -- Part 2: Shell and Utilities.
25455 21. ISO/IEC TR 10176:1998, Information technology -- Guidelines for the
25456 preparation of programming language standards.
25457 22. ISO/IEC 10646-1:1993, Information technology -- Universal Multiple-Octet
25458 Coded Character Set (UCS) -- Part 1: Architecture and Basic Multilingual Plane.
25459 23. ISO/IEC 10646-1/COR1:1996, Technical Corrigendum 1 to
25460 ISO/IEC 10646-1:1993.
25461 24. ISO/IEC 10646-1/COR2:1998, Technical Corrigendum 2 to
25462 ISO/IEC 10646-1:1993.
25463 25. ISO/IEC 10646-1/AMD1:1996, Amendment 1 to ISO/IEC 10646-1:1993
25464 Transformation Format for 16 planes of group 00 (UTF-16).
25465 26. ISO/IEC 10646-1/AMD2:1996, Amendment 2 to ISO/IEC 10646-1:1993 UCS
25466 Transformation Format 8 (UTF-8).
25467 27. ISO/IEC 10646-1/AMD3:1996, Amendment 3 to ISO/IEC 10646-1:1993.
25468 28. ISO/IEC 10646-1/AMD4:1996, Amendment 4 to ISO/IEC 10646-1:1993.
25469 29. ISO/IEC 10646-1/AMD5:1998, Amendment 5 to ISO/IEC 10646-1:1993 Hangul
25471 30. ISO/IEC 10646-1/AMD6:1997, Amendment 6 to ISO/IEC 10646-1:1993
25473 31. ISO/IEC 10646-1/AMD7:1997, Amendment 7 to ISO/IEC 10646-1:1993 33
25474 additional characters.
25475 32. ISO/IEC 10646-1/AMD8:1997, Amendment 8 to ISO/IEC 10646-1:1993.
25476 33. ISO/IEC 10646-1/AMD9:1997, Amendment 9 to ISO/IEC 10646-1:1993
25477 Identifiers for characters.
25478 34. ISO/IEC 10646-1/AMD10:1998, Amendment 10 to ISO/IEC 10646-1:1993
25480 35. ISO/IEC 10646-1/AMD11:1998, Amendment 11 to ISO/IEC 10646-1:1993
25481 Unified Canadian Aboriginal Syllabics.
25482 36. ISO/IEC 10646-1/AMD12:1998, Amendment 12 to ISO/IEC 10646-1:1993
25484 37. ISO/IEC 10967-1:1994, Information technology -- Language independent
25485 arithmetic -- Part 1: Integer and floating point arithmetic.
25490 38. ISO/IEC TR 19769:2004, Information technology -- Programming languages,
25491 their environments and system software interfaces -- Extensions for the
25492 programming language C to support new character data types.
25493 39. ISO/IEC TR 24731-1:2007, Information technology -- Programming languages,
25494 their environments and system software interfaces -- Extensions to the C library
25495 -- Part 1: Bounds-checking interfaces.
25504 [^ x ^], 3.20 , (comma operator), 5.1.2.4, 6.5.17
25505 , (comma punctuator), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2,
25506 [_ x _], 3.21 6.7.2.3, 6.7.9
25507 ! (logical negation operator), 6.5.3.3 - (subtraction operator), 6.2.6.2, 6.5.6, F.3, G.5.2
25508 != (inequality operator), 6.5.9 - (unary minus operator), 6.5.3.3, F.3
25509 # operator, 6.10.3.2 -- (postfix decrement operator), 6.3.2.1, 6.5.2.4
25510 # preprocessing directive, 6.10.7 -- (prefix decrement operator), 6.3.2.1, 6.5.3.1
25511 # punctuator, 6.10 -= (subtraction assignment operator), 6.5.16.2
25512 ## operator, 6.10.3.3 -> (structure/union pointer operator), 6.5.2.3
25513 #define preprocessing directive, 6.10.3 . (structure/union member operator), 6.3.2.1,
25514 #elif preprocessing directive, 6.10.1 6.5.2.3
25515 #else preprocessing directive, 6.10.1 . punctuator, 6.7.9
25516 #endif preprocessing directive, 6.10.1 ... (ellipsis punctuator), 6.5.2.2, 6.7.6.3, 6.10.3
25517 #error preprocessing directive, 4, 6.10.5 / (division operator), 6.2.6.2, 6.5.5, F.3, G.5.1
25518 #if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2, /* */ (comment delimiters), 6.4.9
25519 6.10.1, 7.1.4 // (comment delimiter), 6.4.9
25520 #ifdef preprocessing directive, 6.10.1 /= (division assignment operator), 6.5.16.2
25521 #ifndef preprocessing directive, 6.10.1 : (colon punctuator), 6.7.2.1
25522 #include preprocessing directive, 5.1.1.2, :> (alternative spelling of ]), 6.4.6
25523 6.10.2 ; (semicolon punctuator), 6.7, 6.7.2.1, 6.8.3,
25524 #line preprocessing directive, 6.10.4 6.8.5, 6.8.6
25525 #pragma preprocessing directive, 6.10.6 < (less-than operator), 6.5.8
25526 #undef preprocessing directive, 6.10.3.5, 7.1.3, <% (alternative spelling of {), 6.4.6
25527 7.1.4 <: (alternative spelling of [), 6.4.6
25528 % (remainder operator), 6.2.6.2, 6.5.5 << (left-shift operator), 6.2.6.2, 6.5.7
25529 %: (alternative spelling of #), 6.4.6 <<= (left-shift assignment operator), 6.5.16.2
25530 %:%: (alternative spelling of ##), 6.4.6 <= (less-than-or-equal-to operator), 6.5.8
25531 %= (remainder assignment operator), 6.5.16.2 <assert.h> header, 7.2
25532 %> (alternative spelling of }), 6.4.6 <complex.h> header, 5.2.4.2.2, 6.10.8.3, 7.1.2,
25533 & (address operator), 6.3.2.1, 6.5.3.2 7.3, 7.24, 7.30.1, G.6, J.5.17
25534 & (bitwise AND operator), 6.2.6.2, 6.5.10 <ctype.h> header, 7.4, 7.30.2
25535 && (logical AND operator), 5.1.2.4, 6.5.13 <errno.h> header, 7.5, 7.30.3, K.3.2
25536 &= (bitwise AND assignment operator), 6.5.16.2 <fenv.h> header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F,
25537 ' ' (space character), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3, H
25538 7.4.1.10, 7.29.2.1.3 <float.h> header, 4, 5.2.4.2.2, 7.7, 7.22.1.3,
25539 ( ) (cast operator), 6.5.4 7.28.4.1.1
25540 ( ) (function-call operator), 6.5.2.2 <inttypes.h> header, 7.8, 7.30.4
25541 ( ) (parentheses punctuator), 6.7.6.3, 6.8.4, 6.8.5 <iso646.h> header, 4, 7.9
25542 ( ){ } (compound-literal operator), 6.5.2.5 <limits.h> header, 4, 5.2.4.2.1, 6.2.5, 7.10
25543 * (asterisk punctuator), 6.7.6.1, 6.7.6.2 <locale.h> header, 7.11, 7.30.5
25544 * (indirection operator), 6.5.2.1, 6.5.3.2 <math.h> header, 5.2.4.2.2, 6.5, 7.12, 7.24, F,
25545 * (multiplication operator), 6.2.6.2, 6.5.5, F.3, F.10, J.5.17
25546 G.5.1 <setjmp.h> header, 7.13
25547 *= (multiplication assignment operator), 6.5.16.2 <signal.h> header, 7.14, 7.30.6
25548 + (addition operator), 6.2.6.2, 6.5.2.1, 6.5.3.2, <stdalign.h> header, 4, 7.15
25549 6.5.6, F.3, G.5.2 <stdarg.h> header, 4, 6.7.6.3, 7.16
25550 + (unary plus operator), 6.5.3.3 <stdatomic.h> header, 6.10.8.3, 7.1.2, 7.17
25551 ++ (postfix increment operator), 6.3.2.1, 6.5.2.4 <stdbool.h> header, 4, 7.18, 7.30.7, H
25552 ++ (prefix increment operator), 6.3.2.1, 6.5.3.1 <stddef.h> header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
25553 += (addition assignment operator), 6.5.16.2
25556 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 \x hexadecimal digits (hexadecimal-character
25557 <stdint.h> header, 4, 5.2.4.2, 6.10.1, 7.8, escape sequence), 6.4.4.4
25558 7.20, 7.30.8, K.3.3, K.3.4 ^ (bitwise exclusive OR operator), 6.2.6.2, 6.5.11
25559 <stdio.h> header, 5.2.4.2.2, 7.21, 7.30.9, F, ^= (bitwise exclusive OR assignment operator),
25561 <stdlib.h> header, 5.2.4.2.2, 7.22, 7.30.10, F, __alignas_is_defined macro, 7.15
25562 K.3.1.4, K.3.6 __bool_true_false_are_defined
25563 <string.h> header, 7.23, 7.30.11, K.3.7 macro, 7.18
25564 <tgmath.h> header, 7.24, G.7 __cplusplus macro, 6.10.8
25565 <threads.h> header, 6.10.8.3, 7.1.2, 7.25 __DATE__ macro, 6.10.8.1
25566 <time.h> header, 7.26, K.3.8 __FILE__ macro, 6.10.8.1, 7.2.1.1
25567 <uchar.h> header, 6.4.4.4, 6.4.5, 7.27 __func__ identifier, 6.4.2.2, 7.2.1.1
25568 <wchar.h> header, 5.2.4.2.2, 7.21.1, 7.28, __LINE__ macro, 6.10.8.1, 7.2.1.1
25569 7.30.12, F, K.3.9 __STDC_, 6.11.9
25570 <wctype.h> header, 7.29, 7.30.13 __STDC__ macro, 6.10.8.1
25571 = (equal-sign punctuator), 6.7, 6.7.2.2, 6.7.9 __STDC_ANALYZABLE__ macro, 6.10.8.3, L.1
25572 = (simple assignment operator), 6.5.16.1 __STDC_HOSTED__ macro, 6.10.8.1
25573 == (equality operator), 6.5.9 __STDC_IEC_559__ macro, 6.10.8.3, F.1
25574 > (greater-than operator), 6.5.8 __STDC_IEC_559_COMPLEX__ macro,
25575 >= (greater-than-or-equal-to operator), 6.5.8 6.10.8.3, G.1
25576 >> (right-shift operator), 6.2.6.2, 6.5.7 __STDC_ISO_10646__ macro, 6.10.8.2
25577 >>= (right-shift assignment operator), 6.5.16.2 __STDC_LIB_EXT1__ macro, 6.10.8.3, K.2
25578 ? : (conditional operator), 5.1.2.4, 6.5.15 __STDC_MB_MIGHT_NEQ_WC__ macro,
25579 ?? (trigraph sequences), 5.2.1.1 6.10.8.2, 7.19
25580 [ ] (array subscript operator), 6.5.2.1, 6.5.3.2 __STDC_NO_COMPLEX__ macro, 6.10.8.3,
25581 [ ] (brackets punctuator), 6.7.6.2, 6.7.9 7.3.1
25582 \ (backslash character), 5.1.1.2, 5.2.1, 6.4.4.4 __STDC_NO_THREADS__ macro, 6.10.8.3,
25583 \ (escape character), 6.4.4.4 7.17.1, 7.25.1
25584 \" (double-quote escape sequence), 6.4.4.4, __STDC_NO_VLA__ macro, 6.10.8.3
25585 6.4.5, 6.10.9 __STDC_UTF_16__ macro, 6.10.8.2
25586 \\ (backslash escape sequence), 6.4.4.4, 6.10.9 __STDC_UTF_32__ macro, 6.10.8.2
25587 \' (single-quote escape sequence), 6.4.4.4, 6.4.5 __STDC_VERSION__ macro, 6.10.8.1
25588 \0 (null character), 5.2.1, 6.4.4.4, 6.4.5 __STDC_WANT_LIB_EXT1__ macro, K.3.1.1
25589 padding of binary stream, 7.21.2 __TIME__ macro, 6.10.8.1
25590 \? (question-mark escape sequence), 6.4.4.4 __VA_ARGS__ identifier, 6.10.3, 6.10.3.1
25591 \a (alert escape sequence), 5.2.2, 6.4.4.4 _Alignas, 6.7.5
25592 \b (backspace escape sequence), 5.2.2, 6.4.4.4 _Atomic type qualifier, 6.7.3
25593 \f (form-feed escape sequence), 5.2.2, 6.4.4.4, _Bool type, 6.2.5, 6.3.1.1, 6.3.1.2, 6.7.2, 7.17.1,
25595 \n (new-line escape sequence), 5.2.2, 6.4.4.4, _Bool type conversions, 6.3.1.2
25596 7.4.1.10 _Complex types, 6.2.5, 6.7.2, 7.3.1, G
25597 \octal digits (octal-character escape sequence), _Complex_I macro, 7.3.1
25598 6.4.4.4 _Exit function, 7.22.4.5, 7.22.4.7
25599 \r (carriage-return escape sequence), 5.2.2, _Imaginary keyword, G.2
25600 6.4.4.4, 7.4.1.10 _Imaginary types, 7.3.1, G
25601 \t (horizontal-tab escape sequence), 5.2.2, _Imaginary_I macro, 7.3.1, G.6
25602 6.4.4.4, 7.4.1.3, 7.4.1.10, 7.29.2.1.3 _IOFBF macro, 7.21.1, 7.21.5.5, 7.21.5.6
25603 \U (universal character names), 6.4.3 _IOLBF macro, 7.21.1, 7.21.5.6
25604 \u (universal character names), 6.4.3 _IONBF macro, 7.21.1, 7.21.5.5, 7.21.5.6
25605 \v (vertical-tab escape sequence), 5.2.2, 6.4.4.4, _Noreturn, 6.7.4
25606 7.4.1.10 _Pragma operator, 5.1.1.2, 6.10.9
25610 _Static_assert, 6.7.10, 7.2 allocated storage, order and contiguity, 7.22.3
25611 _Thread_local storage-class specifier, 6.2.4, and macro, 7.9
25612 6.7.1 AND operators
25613 { } (braces punctuator), 6.7.2.2, 6.7.2.3, 6.7.9, bitwise (&), 6.2.6.2, 6.5.10
25614 6.8.2 bitwise assignment (&=), 6.5.16.2
25615 { } (compound-literal operator), 6.5.2.5 logical (&&), 5.1.2.4, 6.5.13
25616 | (bitwise inclusive OR operator), 6.2.6.2, 6.5.12 and_eq macro, 7.9
25617 |= (bitwise inclusive OR assignment operator), anonymous structure, 6.7.2.1
25618 6.5.16.2 anonymous union, 6.7.2.1
25619 || (logical OR operator), 5.1.2.4, 6.5.14 ANSI/IEEE 754, F.1
25620 ~ (bitwise complement operator), 6.2.6.2, 6.5.3.3 ANSI/IEEE 854, F.1
25621 argc (main function parameter), 5.1.2.2.1
25622 abort function, 7.2.1.1, 7.14.1.1, 7.21.3, argument, 3.3
25623 7.22.4.1, 7.25.3.6, K.3.6.1.2 array, 6.9.1
25624 abort_handler_s function, K.3.6.1.2 default promotions, 6.5.2.2
25625 abs function, 7.22.6.1 function, 6.5.2.2, 6.9.1
25626 absolute-value functions macro, substitution, 6.10.3.1
25627 complex, 7.3.8, G.6.4 argument, complex, 7.3.9.1
25628 integer, 7.8.2.1, 7.22.6.1 argv (main function parameter), 5.1.2.2.1
25629 real, 7.12.7, F.10.4 arithmetic constant expression, 6.6
25630 abstract declarator, 6.7.7 arithmetic conversions, usual, see usual arithmetic
25631 abstract machine, 5.1.2.3 conversions
25632 access, 3.1, 6.7.3, L.2.1 arithmetic operators
25633 accuracy, see floating-point accuracy additive, 6.2.6.2, 6.5.6, G.5.2
25634 acos functions, 7.12.4.1, F.10.1.1 bitwise, 6.2.6.2, 6.5.3.3, 6.5.10, 6.5.11, 6.5.12
25635 acos type-generic macro, 7.24 increment and decrement, 6.5.2.4, 6.5.3.1
25636 acosh functions, 7.12.5.1, F.10.2.1 multiplicative, 6.2.6.2, 6.5.5, G.5.1
25637 acosh type-generic macro, 7.24 shift, 6.2.6.2, 6.5.7
25638 acquire fence, 7.17.4 unary, 6.5.3.3
25639 acquire operation, 5.1.2.4 arithmetic types, 6.2.5
25640 active position, 5.2.2 arithmetic, pointer, 6.5.6
25641 actual argument, 3.3 array
25642 actual parameter (deprecated), 3.3 argument, 6.9.1
25643 addition assignment operator (+=), 6.5.16.2 declarator, 6.7.6.2
25644 addition operator (+), 6.2.6.2, 6.5.2.1, 6.5.3.2, initialization, 6.7.9
25645 6.5.6, F.3, G.5.2 multidimensional, 6.5.2.1
25646 additive expressions, 6.5.6, G.5.2 parameter, 6.9.1
25647 address constant, 6.6 storage order, 6.5.2.1
25648 address operator (&), 6.3.2.1, 6.5.3.2 subscript operator ([ ]), 6.5.2.1, 6.5.3.2
25649 address-free, 7.17.5 subscripting, 6.5.2.1
25650 aggregate initialization, 6.7.9 type, 6.2.5
25651 aggregate types, 6.2.5 type conversion, 6.3.2.1
25652 alert escape sequence (\a), 5.2.2, 6.4.4.4 variable length, 6.7.6, 6.7.6.2, 6.10.8.3
25653 aliasing, 6.5 arrow operator (->), 6.5.2.3
25654 alignas macro, 7.15 as-if rule, 5.1.2.3
25655 aligned_alloc function, 7.22.3, 7.22.3.1 ASCII code set, 5.2.1.1
25656 alignment, 3.2, 6.2.8, 7.22.3.1 asctime function, 7.26.3.1
25657 pointer, 6.2.5, 6.3.2.3 asctime_s function, K.3.8.2, K.3.8.2.1
25658 structure/union member, 6.7.2.1 asin functions, 7.12.4.2, F.10.1.2
25659 alignment specifier, 6.7.5 asin type-generic macro, 7.24, G.7
25660 alignof operator, 6.5.3, 6.5.3.4 asinh functions, 7.12.5.2, F.10.2.2
25664 asinh type-generic macro, 7.24, G.7 atomic_is_lock_free generic function,
25665 asm keyword, J.5.10 7.17.5.1
25666 assert macro, 7.2.1.1 ATOMIC_LLONG_LOCK_FREE macro, 7.17.1
25667 assert.h header, 7.2 atomic_load generic functions, 7.17.7.2
25668 assignment ATOMIC_LONG_LOCK_FREE macro, 7.17.1
25669 compound, 6.5.16.2 ATOMIC_SHORT_LOCK_FREE macro, 7.17.1
25670 conversion, 6.5.16.1 atomic_signal_fence function, 7.17.4.2
25671 expression, 6.5.16 atomic_store generic functions, 7.17.7.1
25672 operators, 6.3.2.1, 6.5.16 atomic_thread_fence function, 7.17.4.1
25673 simple, 6.5.16.1 ATOMIC_VAR_INIT macro, 7.17.2.1
25674 associativity of operators, 6.5 ATOMIC_WCHAR_T_LOCK_FREE macro, 7.17.1
25675 asterisk punctuator (*), 6.7.6.1, 6.7.6.2 atomics header, 7.17
25676 at_quick_exit function, 7.22.4.2, 7.22.4.3, auto storage-class specifier, 6.7.1, 6.9
25677 7.22.4.4, 7.22.4.5, 7.22.4.7 automatic storage duration, 5.2.3, 6.2.4
25678 atan functions, 7.12.4.3, F.10.1.3
25679 atan type-generic macro, 7.24, G.7 backslash character (\), 5.1.1.2, 5.2.1, 6.4.4.4
25680 atan2 functions, 7.12.4.4, F.10.1.4 backslash escape sequence (\\), 6.4.4.4, 6.10.9
25681 atan2 type-generic macro, 7.24 backspace escape sequence (\b), 5.2.2, 6.4.4.4
25682 atanh functions, 7.12.5.3, F.10.2.3 basic character set, 3.6, 3.7.2, 5.2.1
25683 atanh type-generic macro, 7.24, G.7 basic types, 6.2.5
25684 atexit function, 7.22.4.2, 7.22.4.3, 7.22.4.4, behavior, 3.4
25685 7.22.4.5, 7.22.4.7, J.5.13 binary streams, 7.21.2, 7.21.7.10, 7.21.9.2,
25686 atof function, 7.22.1, 7.22.1.1 7.21.9.4
25687 atoi function, 7.22.1, 7.22.1.2 bit, 3.5
25688 atol function, 7.22.1, 7.22.1.2 high order, 3.6
25689 atoll function, 7.22.1, 7.22.1.2 low order, 3.6
25690 atomic lock-free macros, 7.17.1, 7.17.5 bit-field, 6.7.2.1
25691 atomic operations, 5.1.2.4 bitand macro, 7.9
25692 atomic types, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, bitor macro, 7.9
25693 6.5.2.3, 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, bitwise operators, 6.5
25694 7.17.6 AND, 6.2.6.2, 6.5.10
25695 atomic_address type, 7.17.1, 7.17.6 AND assignment (&=), 6.5.16.2
25696 ATOMIC_ADDRESS_LOCK_FREE macro, 7.17.1 complement (~), 6.2.6.2, 6.5.3.3
25697 atomic_bool type, 7.17.1, 7.17.6 exclusive OR, 6.2.6.2, 6.5.11
25698 ATOMIC_CHAR16_T_LOCK_FREE macro, exclusive OR assignment (^=), 6.5.16.2
25699 7.17.1 inclusive OR, 6.2.6.2, 6.5.12
25700 ATOMIC_CHAR32_T_LOCK_FREE macro, inclusive OR assignment (|=), 6.5.16.2
25701 7.17.1 shift, 6.2.6.2, 6.5.7
25702 ATOMIC_CHAR_LOCK_FREE macro, 7.17.1 blank character, 7.4.1.3
25703 atomic_compare_exchange generic block, 6.8, 6.8.2, 6.8.4, 6.8.5
25704 functions, 7.17.7.4 block scope, 6.2.1
25705 atomic_exchange generic functions, 7.17.7.3 block structure, 6.2.1
25706 atomic_fetch and modify generic functions, bold type convention, 6.1
25707 7.17.7.5 bool macro, 7.18
25708 atomic_flag type, 7.17.1, 7.17.8 boolean type, 6.3.1.2
25709 atomic_flag_clear functions, 7.17.8.2 boolean type conversion, 6.3.1.1, 6.3.1.2
25710 ATOMIC_FLAG_INIT macro, 7.17.1, 7.17.8 bounded undefined behavior, L.2.2
25711 atomic_flag_test_and_set functions, braces punctuator ({ }), 6.7.2.2, 6.7.2.3, 6.7.9,
25713 atomic_init generic function, 7.17.2.2 brackets operator ([ ]), 6.5.2.1, 6.5.3.2
25714 ATOMIC_INT_LOCK_FREE macro, 7.17.1 brackets punctuator ([ ]), 6.7.6.2, 6.7.9
25718 branch cuts, 7.3.3 type-generic macro for, 7.24
25719 break statement, 6.8.6.3 ccosh functions, 7.3.6.4, G.6.2.4
25720 broken-down time, 7.26.1, 7.26.2.3, 7.26.3, type-generic macro for, 7.24
25721 7.26.3.1, 7.26.3.3, 7.26.3.4, 7.26.3.5, ceil functions, 7.12.9.1, F.10.6.1
25722 K.3.8.2.1, K.3.8.2.3, K.3.8.2.4 ceil type-generic macro, 7.24
25723 bsearch function, 7.22.5, 7.22.5.1 cerf function, 7.30.1
25724 bsearch_s function, K.3.6.3, K.3.6.3.1 cerfc function, 7.30.1
25725 btowc function, 7.28.6.1.1 cexp functions, 7.3.7.1, G.6.3.1
25726 BUFSIZ macro, 7.21.1, 7.21.2, 7.21.5.5 type-generic macro for, 7.24
25727 byte, 3.6, 6.5.3.4 cexp2 function, 7.30.1
25728 byte input/output functions, 7.21.1 cexpm1 function, 7.30.1
25729 byte-oriented stream, 7.21.2 char type, 6.2.5, 6.3.1.1, 6.7.2, K.3.5.3.2,
25731 C program, 5.1.1.1 char type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
25732 c16rtomb function, 7.27.1.2 6.3.1.8
25733 c32rtomb function, 7.27.1.4 char16_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27
25734 cabs functions, 7.3.8.1, G.6 char32_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27
25735 type-generic macro for, 7.24 CHAR_BIT macro, 5.2.4.2.1, 6.7.2.1
25736 cacos functions, 7.3.5.1, G.6.1.1 CHAR_MAX macro, 5.2.4.2.1, 7.11.2.1
25737 type-generic macro for, 7.24 CHAR_MIN macro, 5.2.4.2.1
25738 cacosh functions, 7.3.6.1, G.6.2.1 character, 3.7, 3.7.1
25739 type-generic macro for, 7.24 character array initialization, 6.7.9
25740 calendar time, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4, character case mapping functions, 7.4.2
25741 7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2, wide character, 7.29.3.1
25742 K.3.8.2.3, K.3.8.2.4 extensible, 7.29.3.2
25743 call by value, 6.5.2.2 character classification functions, 7.4.1
25744 call_once function, 7.25.1, 7.25.2.1 wide character, 7.29.2.1
25745 calloc function, 7.22.3, 7.22.3.2 extensible, 7.29.2.2
25746 carg functions, 7.3.9.1, G.6 character constant, 5.1.1.2, 5.2.1, 6.4.4.4
25747 carg type-generic macro, 7.24, G.7 character display semantics, 5.2.2
25748 carriage-return escape sequence (\r), 5.2.2, character handling header, 7.4, 7.11.1.1
25749 6.4.4.4, 7.4.1.10 character input/output functions, 7.21.7, K.3.5.4
25750 carries a dependency, 5.1.2.4 wide character, 7.28.3
25751 case label, 6.8.1, 6.8.4.2 character sets, 5.2.1
25752 case mapping functions character string literal, see string literal
25753 character, 7.4.2 character type conversion, 6.3.1.1
25754 wide character, 7.29.3.1 character types, 6.2.5, 6.7.9
25755 extensible, 7.29.3.2 cimag functions, 7.3.9.2, 7.3.9.5, G.6
25756 casin functions, 7.3.5.2, G.6 cimag type-generic macro, 7.24, G.7
25757 type-generic macro for, 7.24 cis function, G.6
25758 casinh functions, 7.3.6.2, G.6.2.2 classification functions
25759 type-generic macro for, 7.24 character, 7.4.1
25760 cast expression, 6.5.4 floating-point, 7.12.3
25761 cast operator (( )), 6.5.4 wide character, 7.29.2.1
25762 catan functions, 7.3.5.3, G.6 extensible, 7.29.2.2
25763 type-generic macro for, 7.24 clearerr function, 7.21.10.1
25764 catanh functions, 7.3.6.3, G.6.2.3 clgamma function, 7.30.1
25765 type-generic macro for, 7.24 clock function, 7.26.2.1
25766 cbrt functions, 7.12.7.1, F.10.4.1 clock_t type, 7.26.1, 7.26.2.1
25767 cbrt type-generic macro, 7.24 CLOCKS_PER_SEC macro, 7.26.1, 7.26.2.1
25768 ccos functions, 7.3.5.4, G.6 clog functions, 7.3.7.2, G.6.3.2
25772 type-generic macro for, 7.24 string, 7.23.3, K.3.7.2
25773 clog10 function, 7.30.1 wide string, 7.28.4.3, K.3.9.2.2
25774 clog1p function, 7.30.1 concatenation, preprocessing, see preprocessing
25775 clog2 function, 7.30.1 concatenation
25776 CMPLX macros, 7.3.9.3 conceptual models, 5.1
25777 cnd_broadcast function, 7.25.3.1, 7.25.3.5, conditional features, 4, 6.2.5, 6.7.6.2, 6.10.8.3,
25778 7.25.3.6 7.1.2, F.1, G.1, K.2, L.1
25779 cnd_destroy function, 7.25.3.2 conditional inclusion, 6.10.1
25780 cnd_init function, 7.25.3.3 conditional operator (? :), 5.1.2.4, 6.5.15
25781 cnd_signal function, 7.25.3.4, 7.25.3.5, conflict, 5.1.2.4
25782 7.25.3.6 conformance, 4
25783 cnd_t type, 7.25.1 conj functions, 7.3.9.4, G.6
25784 cnd_timedwait function, 7.25.3.5 conj type-generic macro, 7.24
25785 cnd_wait function, 7.25.3.3, 7.25.3.6 const type qualifier, 6.7.3
25786 collating sequences, 5.2.1 const-qualified type, 6.2.5, 6.3.2.1, 6.7.3
25787 colon punctuator (:), 6.7.2.1 constant expression, 6.6, F.8.4
25788 comma operator (,), 5.1.2.4, 6.5.17 constants, 6.4.4
25789 comma punctuator (,), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, as primary expression, 6.5.1
25790 6.7.2.3, 6.7.9 character, 6.4.4.4
25791 command processor, 7.22.4.8 enumeration, 6.2.1, 6.4.4.3
25792 comment delimiters (/* */ and //), 6.4.9 floating, 6.4.4.2
25793 comments, 5.1.1.2, 6.4, 6.4.9 hexadecimal, 6.4.4.1
25794 common extensions, J.5 integer, 6.4.4.1
25795 common initial sequence, 6.5.2.3 octal, 6.4.4.1
25796 common real type, 6.3.1.8 constraint, 3.8, 4
25797 common warnings, I constraint_handler_t type, K.3.6
25798 comparison functions, 7.22.5, 7.22.5.1, 7.22.5.2, consume operation, 5.1.2.4
25799 K.3.6.3, K.3.6.3.1, K.3.6.3.2 content of structure/union/enumeration, 6.7.2.3
25800 string, 7.23.4 contiguity of allocated storage, 7.22.3
25801 wide string, 7.28.4.4 continue statement, 6.8.6.2
25802 comparison macros, 7.12.14 contracted expression, 6.5, 7.12.2, F.7
25803 comparison, pointer, 6.5.8 control character, 5.2.1, 7.4
25804 compatible type, 6.2.7, 6.7.2, 6.7.3, 6.7.6 control wide character, 7.29.2
25805 compl macro, 7.9 conversion, 6.3
25806 complement operator (~), 6.2.6.2, 6.5.3.3 arithmetic operands, 6.3.1
25807 complete type, 6.2.5 array argument, 6.9.1
25808 complex macro, 7.3.1 array parameter, 6.9.1
25809 complex numbers, 6.2.5, G arrays, 6.3.2.1
25810 complex type conversion, 6.3.1.6, 6.3.1.7 boolean, 6.3.1.2
25811 complex type domain, 6.2.5 boolean, characters, and integers, 6.3.1.1
25812 complex types, 6.2.5, 6.7.2, 6.10.8.3, G by assignment, 6.5.16.1
25813 complex.h header, 5.2.4.2.2, 6.10.8.3, 7.1.2, by return statement, 6.8.6.4
25814 7.3, 7.24, 7.30.1, G.6, J.5.17 complex types, 6.3.1.6
25815 compliance, see conformance explicit, 6.3
25816 components of time, 7.26.1, K.3.8.1 function, 6.3.2.1
25817 composite type, 6.2.7 function argument, 6.5.2.2, 6.9.1
25818 compound assignment, 6.5.16.2 function designators, 6.3.2.1
25819 compound literals, 6.5.2.5 function parameter, 6.9.1
25820 compound statement, 6.8.2 imaginary, G.4.1
25821 compound-literal operator (( ){ }), 6.5.2.5 imaginary and complex, G.4.3
25822 concatenation functions implicit, 6.3
25826 lvalues, 6.3.2.1 csinh functions, 7.3.6.5, G.6.2.5
25827 pointer, 6.3.2.1, 6.3.2.3 type-generic macro for, 7.24
25828 real and complex, 6.3.1.7 csqrt functions, 7.3.8.3, G.6.4.2
25829 real and imaginary, G.4.2 type-generic macro for, 7.24
25830 real floating and integer, 6.3.1.4, F.3, F.4 ctan functions, 7.3.5.6, G.6
25831 real floating types, 6.3.1.5, F.3 type-generic macro for, 7.24
25832 signed and unsigned integers, 6.3.1.3 ctanh functions, 7.3.6.6, G.6.2.6
25833 usual arithmetic, see usual arithmetic type-generic macro for, 7.24
25834 conversions ctgamma function, 7.30.1
25835 void type, 6.3.2.2 ctime function, 7.26.3.2
25836 conversion functions ctime_s function, K.3.8.2, K.3.8.2.2
25837 multibyte/wide character, 7.22.7, K.3.6.4 ctype.h header, 7.4, 7.30.2
25838 extended, 7.28.6, K.3.9.3 current object, 6.7.9
25839 restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 CX_LIMITED_RANGE pragma, 6.10.6, 7.3.4
25840 multibyte/wide string, 7.22.8, K.3.6.5
25841 restartable, 7.28.6.4, K.3.9.3.2 data race, 5.1.2.4, 7.1.4, 7.22.2.1, 7.22.4.6,
25842 numeric, 7.8.2.3, 7.22.1 7.23.5.8, 7.23.6.2, 7.26.3, 7.27.1, 7.28.6.3,
25843 wide string, 7.8.2.4, 7.28.4.1 7.28.6.4
25844 single byte/wide character, 7.28.6.1 data stream, see streams
25845 time, 7.26.3, K.3.8.2 date and time header, 7.26, K.3.8
25846 wide character, 7.28.5 Daylight Saving Time, 7.26.1
25847 conversion specifier, 7.21.6.1, 7.21.6.2, 7.28.2.1, DBL_DECIMAL_DIG macro, 5.2.4.2.2
25848 7.28.2.2 DBL_DIG macro, 5.2.4.2.2
25849 conversion state, 7.22.7, 7.27.1, 7.27.1.1, DBL_EPSILON macro, 5.2.4.2.2
25850 7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.6, DBL_HAS_SUBNORM macro, 5.2.4.2.2
25851 7.28.6.2.1, 7.28.6.3, 7.28.6.3.2, 7.28.6.3.3, DBL_MANT_DIG macro, 5.2.4.2.2
25852 7.28.6.4, 7.28.6.4.1, 7.28.6.4.2, K.3.6.4, DBL_MAX macro, 5.2.4.2.2
25853 K.3.9.3.1, K.3.9.3.1.1, K.3.9.3.2, K.3.9.3.2.1, DBL_MAX_10_EXP macro, 5.2.4.2.2
25854 K.3.9.3.2.2 DBL_MAX_EXP macro, 5.2.4.2.2
25855 conversion state functions, 7.28.6.2 DBL_MIN macro, 5.2.4.2.2
25856 copying functions DBL_MIN_10_EXP macro, 5.2.4.2.2
25857 string, 7.23.2, K.3.7.1 DBL_MIN_EXP macro, 5.2.4.2.2
25858 wide string, 7.28.4.2, K.3.9.2.1 DBL_TRUE_MIN macro, 5.2.4.2.2
25859 copysign functions, 7.3.9.5, 7.12.11.1, F.3, decimal constant, 6.4.4.1
25860 F.10.8.1 decimal digit, 5.2.1
25861 copysign type-generic macro, 7.24 decimal-point character, 7.1.1, 7.11.2.1
25862 correctly rounded result, 3.9 DECIMAL_DIG macro, 5.2.4.2.2, 7.21.6.1,
25863 corresponding real type, 6.2.5 7.22.1.3, 7.28.2.1, 7.28.4.1.1, F.5
25864 cos functions, 7.12.4.5, F.10.1.5 declaration specifiers, 6.7
25865 cos type-generic macro, 7.24, G.7 declarations, 6.7
25866 cosh functions, 7.12.5.4, F.10.2.4 function, 6.7.6.3
25867 cosh type-generic macro, 7.24, G.7 pointer, 6.7.6.1
25868 cpow functions, 7.3.8.2, G.6.4.1 structure/union, 6.7.2.1
25869 type-generic macro for, 7.24 typedef, 6.7.8
25870 cproj functions, 7.3.9.5, G.6 declarator, 6.7.6
25871 cproj type-generic macro, 7.24 abstract, 6.7.7
25872 creal functions, 7.3.9.6, G.6 declarator type derivation, 6.2.5, 6.7.6
25873 creal type-generic macro, 7.24, G.7 decrement operators, see arithmetic operators,
25874 critical undefined behavior, L.2.3 increment and decrement
25875 csin functions, 7.3.5.5, G.6 default argument promotions, 6.5.2.2
25876 type-generic macro for, 7.24 default initialization, 6.7.9
25880 default label, 6.8.1, 6.8.4.2 elif preprocessing directive, 6.10.1
25881 define preprocessing directive, 6.10.3 ellipsis punctuator (...), 6.5.2.2, 6.7.6.3, 6.10.3
25882 defined operator, 6.10.1, 6.10.8 else preprocessing directive, 6.10.1
25883 definition, 6.7 else statement, 6.8.4.1
25884 function, 6.9.1 empty statement, 6.8.3
25885 dependency-ordered before, 5.1.2.4 encoding error, 7.21.3, 7.27.1.1, 7.27.1.2,
25886 derived declarator types, 6.2.5 7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3,
25887 derived types, 6.2.5 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2,
25888 designated initializer, 6.7.9 K.3.6.5.1, K.3.6.5.2, K.3.9.3.1.1, K.3.9.3.2.1,
25889 destringizing, 6.10.9 K.3.9.3.2.2
25890 device input/output, 5.1.2.3 end-of-file, 7.28.1
25891 diagnostic message, 3.10, 5.1.1.3 end-of-file indicator, 7.21.1, 7.21.5.3, 7.21.7.1,
25892 diagnostics, 5.1.1.3 7.21.7.5, 7.21.7.6, 7.21.7.10, 7.21.9.2,
25893 diagnostics header, 7.2 7.21.9.3, 7.21.10.1, 7.21.10.2, 7.28.3.1,
25894 difftime function, 7.26.2.2 7.28.3.10
25895 digit, 5.2.1, 7.4 end-of-file macro, see EOF macro
25896 digraphs, 6.4.6 end-of-line indicator, 5.2.1
25897 direct input/output functions, 7.21.8 endif preprocessing directive, 6.10.1
25898 display device, 5.2.2 enum type, 6.2.5, 6.7.2, 6.7.2.2
25899 div function, 7.22.6.2 enumerated type, 6.2.5
25900 div_t type, 7.22 enumeration, 6.2.5, 6.7.2.2
25901 division assignment operator (/=), 6.5.16.2 enumeration constant, 6.2.1, 6.4.4.3
25902 division operator (/), 6.2.6.2, 6.5.5, F.3, G.5.1 enumeration content, 6.7.2.3
25903 do statement, 6.8.5.2 enumeration members, 6.7.2.2
25904 documentation of implementation, 4 enumeration specifiers, 6.7.2.2
25905 domain error, 7.12.1, 7.12.4.1, 7.12.4.2, 7.12.4.4, enumeration tag, 6.2.3, 6.7.2.3
25906 7.12.5.1, 7.12.5.3, 7.12.6.5, 7.12.6.7, enumerator, 6.7.2.2
25907 7.12.6.8, 7.12.6.9, 7.12.6.10, 7.12.6.11, environment, 5
25908 7.12.7.4, 7.12.7.5, 7.12.8.4, 7.12.9.5, environment functions, 7.22.4, K.3.6.2
25909 7.12.9.7, 7.12.10.1, 7.12.10.2, 7.12.10.3 environment list, 7.22.4.6, K.3.6.2.1
25910 dot operator (.), 6.5.2.3 environmental considerations, 5.2
25911 double _Complex type, 6.2.5 environmental limits, 5.2.4, 7.13.1.1, 7.21.2,
25912 double _Complex type conversion, 6.3.1.6, 7.21.3, 7.21.4.4, 7.21.6.1, 7.22.2.1, 7.22.4.2,
25913 6.3.1.7, 6.3.1.8 7.22.4.3, 7.28.2.1, K.3.5.1.2
25914 double _Imaginary type, G.2 EOF macro, 7.4, 7.21.1, 7.21.5.1, 7.21.5.2,
25915 double type, 6.2.5, 6.4.4.2, 6.7.2, 7.21.6.2, 7.21.6.2, 7.21.6.7, 7.21.6.9, 7.21.6.11,
25916 7.28.2.2, F.2 7.21.6.14, 7.21.7.1, 7.21.7.3, 7.21.7.4,
25917 double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, 7.21.7.5, 7.21.7.6, 7.21.7.8, 7.21.7.9,
25918 6.3.1.8 7.21.7.10, 7.28.1, 7.28.2.2, 7.28.2.4,
25919 double-precision arithmetic, 5.1.2.3 7.28.2.6, 7.28.2.8, 7.28.2.10, 7.28.2.12,
25920 double-quote escape sequence (\"), 6.4.4.4, 7.28.3.4, 7.28.6.1.1, 7.28.6.1.2, K.3.5.3.7,
25921 6.4.5, 6.10.9 K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.2,
25922 double_t type, 7.12, J.5.6 K.3.9.1.5, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12,
25924 EDOM macro, 7.5, 7.12.1, see also domain error equal-sign punctuator (=), 6.7, 6.7.2.2, 6.7.9
25925 effective type, 6.5 equal-to operator, see equality operator
25926 EILSEQ macro, 7.5, 7.21.3, 7.27.1.1, 7.27.1.2, equality expressions, 6.5.9
25927 7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3, equality operator (==), 6.5.9
25928 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, ERANGE macro, 7.5, 7.8.2.3, 7.8.2.4, 7.12.1,
25929 see also encoding error 7.22.1.3, 7.22.1.4, 7.28.4.1.1, 7.28.4.1.2, see
25930 element type, 6.2.5 also range error, pole error
25934 erf functions, 7.12.8.1, F.10.5.1 exp2 functions, 7.12.6.2, F.10.3.2
25935 erf type-generic macro, 7.24 exp2 type-generic macro, 7.24
25936 erfc functions, 7.12.8.2, F.10.5.2 explicit conversion, 6.3
25937 erfc type-generic macro, 7.24 expm1 functions, 7.12.6.3, F.10.3.3
25938 errno macro, 7.1.3, 7.3.2, 7.5, 7.8.2.3, 7.8.2.4, expm1 type-generic macro, 7.24
25939 7.12.1, 7.14.1.1, 7.21.3, 7.21.9.3, 7.21.10.4, exponent part, 6.4.4.2
25940 7.22.1, 7.22.1.3, 7.22.1.4, 7.23.6.2, 7.27.1.1, exponential functions
25941 7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.3.1, complex, 7.3.7, G.6.3
25942 7.28.3.3, 7.28.4.1.1, 7.28.4.1.2, 7.28.6.3.2, real, 7.12.6, F.10.3
25943 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, J.5.17, expression, 6.5
25944 K.3.1.3, K.3.7.4.2 assignment, 6.5.16
25945 errno.h header, 7.5, 7.30.3, K.3.2 cast, 6.5.4
25946 errno_t type, K.3.2, K.3.5, K.3.6, K.3.6.1.1, constant, 6.6
25947 K.3.7, K.3.8, K.3.9 evaluation, 5.1.2.3
25949 domain, see domain error order of evaluation, see order of evaluation
25950 encoding, see encoding error parenthesized, 6.5.1
25951 pole, see pole error primary, 6.5.1
25952 range, see range error unary, 6.5.3
25953 error conditions, 7.12.1 expression statement, 6.8.3
25954 error functions, 7.12.8, F.10.5 extended alignment, 6.2.8
25955 error indicator, 7.21.1, 7.21.5.3, 7.21.7.1, extended character set, 3.7.2, 5.2.1, 5.2.1.2
25956 7.21.7.3, 7.21.7.5, 7.21.7.6, 7.21.7.7, extended characters, 5.2.1
25957 7.21.7.8, 7.21.9.2, 7.21.10.1, 7.21.10.3, extended integer types, 6.2.5, 6.3.1.1, 6.4.4.1,
25958 7.28.3.1, 7.28.3.3 7.20
25959 error preprocessing directive, 4, 6.10.5 extended multibyte/wide character conversion
25960 error-handling functions, 7.21.10, 7.23.6.2, utilities, 7.28.6, K.3.9.3
25961 K.3.7.4.2, K.3.7.4.3 extensible wide character case mapping functions,
25962 escape character (\), 6.4.4.4 7.29.3.2
25963 escape sequences, 5.2.1, 5.2.2, 6.4.4.4, 6.11.4 extensible wide character classification functions,
25964 evaluation format, 5.2.4.2.2, 6.4.4.2, 7.12 7.29.2.2
25965 evaluation method, 5.2.4.2.2, 6.5, F.8.5 extern storage-class specifier, 6.2.2, 6.7.1
25966 evaluation of expression, 5.1.2.3 external definition, 6.9
25967 evaluation order, see order of evaluation external identifiers, underscore, 7.1.3
25968 exceptional condition, 6.5 external linkage, 6.2.2
25969 excess precision, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 external name, 6.4.2.1
25970 excess range, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 external object definitions, 6.9.2
25971 exclusive OR operators
25972 bitwise (^), 6.2.6.2, 6.5.11 fabs functions, 7.12.7.2, F.3, F.10.4.2
25973 bitwise assignment (^=), 6.5.16.2 fabs type-generic macro, 7.24, G.7
25974 executable program, 5.1.1.1 false macro, 7.18
25975 execution character set, 5.2.1 fclose function, 7.21.5.1
25976 execution environment, 5, 5.1.2, see also fdim functions, 7.12.12.1, F.10.9.1
25977 environmental limits fdim type-generic macro, 7.24
25978 execution sequence, 5.1.2.3, 6.8 FE_ALL_EXCEPT macro, 7.6
25979 exit function, 5.1.2.2.3, 7.21.3, 7.22, 7.22.4.4, FE_DFL_ENV macro, 7.6
25980 7.22.4.5, 7.22.4.7 FE_DIVBYZERO macro, 7.6, 7.12, F.3
25981 EXIT_FAILURE macro, 7.22, 7.22.4.4 FE_DOWNWARD macro, 7.6, F.3
25982 EXIT_SUCCESS macro, 7.22, 7.22.4.4 FE_INEXACT macro, 7.6, F.3
25983 exp functions, 7.12.6.1, F.10.3.1 FE_INVALID macro, 7.6, 7.12, F.3
25984 exp type-generic macro, 7.24 FE_OVERFLOW macro, 7.6, 7.12, F.3
25988 FE_TONEAREST macro, 7.6, F.3 float _Complex type conversion, 6.3.1.6,
25989 FE_TOWARDZERO macro, 7.6, F.3 6.3.1.7, 6.3.1.8
25990 FE_UNDERFLOW macro, 7.6, F.3 float _Imaginary type, G.2
25991 FE_UPWARD macro, 7.6, F.3 float type, 6.2.5, 6.4.4.2, 6.7.2, F.2
25992 feclearexcept function, 7.6.2, 7.6.2.1, F.3 float type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
25993 fegetenv function, 7.6.4.1, 7.6.4.3, 7.6.4.4, F.3 6.3.1.8
25994 fegetexceptflag function, 7.6.2, 7.6.2.2, F.3 float.h header, 4, 5.2.4.2.2, 7.7, 7.22.1.3,
25995 fegetround function, 7.6, 7.6.3.1, F.3 7.28.4.1.1
25996 feholdexcept function, 7.6.4.2, 7.6.4.3, float_t type, 7.12, J.5.6
25997 7.6.4.4, F.3 floating constant, 6.4.4.2
25998 fence, 5.1.2.4 floating suffix, f or F, 6.4.4.2
25999 fences, 7.17.4 floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
26000 fenv.h header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H F.3, F.4
26001 FENV_ACCESS pragma, 6.10.6, 7.6.1, F.8, F.9, floating types, 6.2.5, 6.11.1
26002 F.10 floating-point accuracy, 5.2.4.2.2, 6.4.4.2, 6.5,
26003 fenv_t type, 7.6 7.22.1.3, F.5, see also contracted expression
26004 feof function, 7.21.10.2 floating-point arithmetic functions, 7.12, F.10
26005 feraiseexcept function, 7.6.2, 7.6.2.3, F.3 floating-point classification functions, 7.12.3
26006 ferror function, 7.21.10.3 floating-point control mode, 7.6, F.8.6
26007 fesetenv function, 7.6.4.3, F.3 floating-point environment, 7.6, F.8, F.8.6
26008 fesetexceptflag function, 7.6.2, 7.6.2.4, F.3 floating-point exception, 7.6, 7.6.2, F.10
26009 fesetround function, 7.6, 7.6.3.2, F.3 floating-point number, 5.2.4.2.2, 6.2.5
26010 fetestexcept function, 7.6.2, 7.6.2.5, F.3 floating-point rounding mode, 5.2.4.2.2
26011 feupdateenv function, 7.6.4.2, 7.6.4.4, F.3 floating-point status flag, 7.6, F.8.6
26012 fexcept_t type, 7.6, F.3 floor functions, 7.12.9.2, F.10.6.2
26013 fflush function, 7.21.5.2, 7.21.5.3 floor type-generic macro, 7.24
26014 fgetc function, 7.21.1, 7.21.3, 7.21.7.1, FLT_DECIMAL_DIG macro, 5.2.4.2.2
26015 7.21.7.5, 7.21.8.1 FLT_DIG macro, 5.2.4.2.2
26016 fgetpos function, 7.21.2, 7.21.9.1, 7.21.9.3 FLT_EPSILON macro, 5.2.4.2.2
26017 fgets function, 7.21.1, 7.21.7.2, K.3.5.4.1 FLT_EVAL_METHOD macro, 5.2.4.2.2, 6.6, 7.12,
26018 fgetwc function, 7.21.1, 7.21.3, 7.28.3.1, F.10.11
26019 7.28.3.6 FLT_HAS_SUBNORM macro, 5.2.4.2.2
26020 fgetws function, 7.21.1, 7.28.3.2 FLT_MANT_DIG macro, 5.2.4.2.2
26021 field width, 7.21.6.1, 7.28.2.1 FLT_MAX macro, 5.2.4.2.2
26022 file, 7.21.3 FLT_MAX_10_EXP macro, 5.2.4.2.2
26023 access functions, 7.21.5, K.3.5.2 FLT_MAX_EXP macro, 5.2.4.2.2
26024 name, 7.21.3 FLT_MIN macro, 5.2.4.2.2
26025 operations, 7.21.4, K.3.5.1 FLT_MIN_10_EXP macro, 5.2.4.2.2
26026 position indicator, 7.21.1, 7.21.2, 7.21.3, FLT_MIN_EXP macro, 5.2.4.2.2
26027 7.21.5.3, 7.21.7.1, 7.21.7.3, 7.21.7.10, FLT_RADIX macro, 5.2.4.2.2, 7.21.6.1, 7.22.1.3,
26028 7.21.8.1, 7.21.8.2, 7.21.9.1, 7.21.9.2, 7.28.2.1, 7.28.4.1.1
26029 7.21.9.3, 7.21.9.4, 7.21.9.5, 7.28.3.1, FLT_ROUNDS macro, 5.2.4.2.2, 7.6, F.3
26030 7.28.3.3, 7.28.3.10 FLT_TRUE_MIN macro, 5.2.4.2.2
26031 positioning functions, 7.21.9 fma functions, 7.12, 7.12.13.1, F.10.10.1
26032 file scope, 6.2.1, 6.9 fma type-generic macro, 7.24
26033 FILE type, 7.21.1, 7.21.3 fmax functions, 7.12.12.2, F.10.9.2
26034 FILENAME_MAX macro, 7.21.1 fmax type-generic macro, 7.24
26035 flags, 7.21.6.1, 7.28.2.1, see also floating-point fmin functions, 7.12.12.3, F.10.9.3
26036 status flag fmin type-generic macro, 7.24
26037 flexible array member, 6.7.2.1 fmod functions, 7.12.10.1, F.10.7.1
26038 float _Complex type, 6.2.5 fmod type-generic macro, 7.24
26042 fopen function, 7.21.5.3, 7.21.5.4, K.3.5.2.1 K.3.5.3.7, K.3.5.3.9
26043 FOPEN_MAX macro, 7.21.1, 7.21.3, 7.21.4.3, fseek function, 7.21.1, 7.21.5.3, 7.21.7.10,
26044 K.3.5.1.1 7.21.9.2, 7.21.9.4, 7.21.9.5, 7.28.3.10
26045 fopen_s function, K.3.5.1.1, K.3.5.2.1, fsetpos function, 7.21.2, 7.21.5.3, 7.21.7.10,
26046 K.3.5.2.2 7.21.9.1, 7.21.9.3, 7.28.3.10
26047 for statement, 6.8.5, 6.8.5.3 ftell function, 7.21.9.2, 7.21.9.4
26048 form-feed character, 5.2.1, 6.4 full declarator, 6.7.6
26049 form-feed escape sequence (\f), 5.2.2, 6.4.4.4, full expression, 6.8
26050 7.4.1.10 fully buffered stream, 7.21.3
26051 formal argument (deprecated), 3.16 function
26052 formal parameter, 3.16 argument, 6.5.2.2, 6.9.1
26053 formatted input/output functions, 7.11.1.1, 7.21.6, body, 6.9.1
26054 K.3.5.3 call, 6.5.2.2
26055 wide character, 7.28.2, K.3.9.1 library, 7.1.4
26056 fortran keyword, J.5.9 declarator, 6.7.6.3, 6.11.6
26057 forward reference, 3.11 definition, 6.7.6.3, 6.9.1, 6.11.7
26058 FP_CONTRACT pragma, 6.5, 6.10.6, 7.12.2, see designator, 6.3.2.1
26059 also contracted expression image, 5.2.3
26060 FP_FAST_FMA macro, 7.12 inline, 6.7.4
26061 FP_FAST_FMAF macro, 7.12 library, 5.1.1.1, 7.1.4
26062 FP_FAST_FMAL macro, 7.12 name length, 5.2.4.1, 6.4.2.1, 6.11.3
26063 FP_ILOGB0 macro, 7.12, 7.12.6.5 no-return, 6.7.4
26064 FP_ILOGBNAN macro, 7.12, 7.12.6.5 parameter, 5.1.2.2.1, 6.5.2.2, 6.7, 6.9.1
26065 FP_INFINITE macro, 7.12, F.3 prototype, 5.1.2.2.1, 6.2.1, 6.2.7, 6.5.2.2, 6.7,
26066 FP_NAN macro, 7.12, F.3 6.7.6.3, 6.9.1, 6.11.6, 6.11.7, 7.1.2, 7.12
26067 FP_NORMAL macro, 7.12, F.3 prototype scope, 6.2.1, 6.7.6.2
26068 FP_SUBNORMAL macro, 7.12, F.3 recursive call, 6.5.2.2
26069 FP_ZERO macro, 7.12, F.3 return, 6.8.6.4, F.6
26070 fpclassify macro, 7.12.3.1, F.3 scope, 6.2.1
26071 fpos_t type, 7.21.1, 7.21.2 type, 6.2.5
26072 fprintf function, 7.8.1, 7.21.1, 7.21.6.1, type conversion, 6.3.2.1
26073 7.21.6.2, 7.21.6.3, 7.21.6.5, 7.21.6.6, function specifiers, 6.7.4
26074 7.21.6.8, 7.28.2.2, F.3, K.3.5.3.1 function type, 6.2.5
26075 fprintf_s function, K.3.5.3.1 function-call operator (( )), 6.5.2.2
26076 fputc function, 5.2.2, 7.21.1, 7.21.3, 7.21.7.3, function-like macro, 6.10.3
26077 7.21.7.7, 7.21.8.2 fundamental alignment, 6.2.8
26078 fputs function, 7.21.1, 7.21.7.4 future directions
26079 fputwc function, 7.21.1, 7.21.3, 7.28.3.3, language, 6.11
26080 7.28.3.8 library, 7.30
26081 fputws function, 7.21.1, 7.28.3.4 fwide function, 7.21.2, 7.28.3.5
26082 fread function, 7.21.1, 7.21.8.1 fwprintf function, 7.8.1, 7.21.1, 7.21.6.2,
26083 free function, 7.22.3.3, 7.22.3.5 7.28.2.1, 7.28.2.2, 7.28.2.3, 7.28.2.5,
26084 freestanding execution environment, 4, 5.1.2, 7.28.2.11, K.3.9.1.1
26085 5.1.2.1 fwprintf_s function, K.3.9.1.1
26086 freopen function, 7.21.2, 7.21.5.4 fwrite function, 7.21.1, 7.21.8.2
26087 freopen_s function, K.3.5.2.2 fwscanf function, 7.8.1, 7.21.1, 7.28.2.2,
26088 frexp functions, 7.12.6.4, F.10.3.4 7.28.2.4, 7.28.2.6, 7.28.2.12, 7.28.3.10,
26089 frexp type-generic macro, 7.24 K.3.9.1.2
26090 fscanf function, 7.8.1, 7.21.1, 7.21.6.2, fwscanf_s function, K.3.9.1.2, K.3.9.1.5,
26091 7.21.6.4, 7.21.6.7, 7.21.6.9, F.3, K.3.5.3.2 K.3.9.1.7, K.3.9.1.14
26092 fscanf_s function, K.3.5.3.2, K.3.5.3.4,
26096 gamma functions, 7.12.8, F.10.5 name spaces, 6.2.3
26097 general utilities, 7.22, K.3.6 reserved, 6.4.1, 7.1.3, K.3.1.2
26098 wide string, 7.28.4, K.3.9.2 scope, 6.2.1
26099 general wide string utilities, 7.28.4, K.3.9.2 type, 6.2.5
26100 generic parameters, 7.24 identifier list, 6.7.6
26101 generic selection, 6.5.1.1 identifier nondigit, 6.4.2.1
26102 getc function, 7.21.1, 7.21.7.5, 7.21.7.6 IEC 559, F.1
26103 getchar function, 7.21.1, 7.21.7.6 IEC 60559, 2, 5.1.2.3, 5.2.4.2.2, 6.10.8.3, 7.3.3,
26104 getenv function, 7.22.4.6 7.6, 7.6.4.2, 7.12.1, 7.12.10.2, 7.12.14, F, G,
26105 getenv_s function, K.3.6.2.1 H.1
26106 gets function, K.3.5.4.1 IEEE 754, F.1
26107 gets_s function, K.3.5.4.1 IEEE 854, F.1
26108 getwc function, 7.21.1, 7.28.3.6, 7.28.3.7 IEEE floating-point arithmetic standard, see
26109 getwchar function, 7.21.1, 7.28.3.7 IEC 60559, ANSI/IEEE 754,
26110 gmtime function, 7.26.3.3 ANSI/IEEE 854
26111 gmtime_s function, K.3.8.2.3 if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2,
26112 goto statement, 6.2.1, 6.8.1, 6.8.6.1 6.10.1, 7.1.4
26113 graphic characters, 5.2.1 if statement, 6.8.4.1
26114 greater-than operator (>), 6.5.8 ifdef preprocessing directive, 6.10.1
26115 greater-than-or-equal-to operator (>=), 6.5.8 ifndef preprocessing directive, 6.10.1
26116 ignore_handler_s function, K.3.6.1.3
26117 happens before, 5.1.2.4 ilogb functions, 7.12, 7.12.6.5, F.10.3.5
26118 header, 5.1.1.1, 7.1.2, see also standard headers ilogb type-generic macro, 7.24
26119 header names, 6.4, 6.4.7, 6.10.2 imaginary macro, 7.3.1, G.6
26120 hexadecimal constant, 6.4.4.1 imaginary numbers, G
26121 hexadecimal digit, 6.4.4.1, 6.4.4.2, 6.4.4.4 imaginary type domain, G.2
26122 hexadecimal prefix, 6.4.4.1 imaginary types, G
26123 hexadecimal-character escape sequence imaxabs function, 7.8.2.1
26124 (\x hexadecimal digits), 6.4.4.4 imaxdiv function, 7.8, 7.8.2.2
26125 high-order bit, 3.6 imaxdiv_t type, 7.8
26126 horizontal-tab character, 5.2.1, 6.4 implementation, 3.12
26127 horizontal-tab escape sequence (\r), 7.29.2.1.3 implementation limit, 3.13, 4, 5.2.4.2, 6.4.2.1,
26128 horizontal-tab escape sequence (\t), 5.2.2, 6.7.6, 6.8.4.2, E, see also environmental
26129 6.4.4.4, 7.4.1.3, 7.4.1.10 limits
26130 hosted execution environment, 4, 5.1.2, 5.1.2.2 implementation-defined behavior, 3.4.1, 4, J.3
26131 HUGE_VAL macro, 7.12, 7.12.1, 7.22.1.3, implementation-defined value, 3.19.1
26132 7.28.4.1.1, F.10 implicit conversion, 6.3
26133 HUGE_VALF macro, 7.12, 7.12.1, 7.22.1.3, implicit initialization, 6.7.9
26134 7.28.4.1.1, F.10 include preprocessing directive, 5.1.1.2, 6.10.2
26135 HUGE_VALL macro, 7.12, 7.12.1, 7.22.1.3, inclusive OR operators
26136 7.28.4.1.1, F.10 bitwise (|), 6.2.6.2, 6.5.12
26137 hyperbolic functions bitwise assignment (|=), 6.5.16.2
26138 complex, 7.3.6, G.6.2 incomplete type, 6.2.5
26139 real, 7.12.5, F.10.2 increment operators, see arithmetic operators,
26140 hypot functions, 7.12.7.3, F.10.4.3 increment and decrement
26141 hypot type-generic macro, 7.24 indeterminate value, 3.19.2
26142 indeterminately sequenced, 5.1.2.3, 6.5.2.2,
26143 I macro, 7.3.1, 7.3.9.5, G.6 6.5.2.4, 6.5.16.2, see also sequenced before,
26144 identifier, 6.4.2.1, 6.5.1 unsequenced
26145 linkage, see linkage indirection operator (*), 6.5.2.1, 6.5.3.2
26146 maximum length, 6.4.2.1 inequality operator (!=), 6.5.9
26150 infinitary, 7.12.1 extended, 6.2.5, 6.3.1.1, 6.4.4.1, 7.20
26151 INFINITY macro, 7.3.9.5, 7.12, F.2.1 inter-thread happens before, 5.1.2.4
26152 initial position, 5.2.2 interactive device, 5.1.2.3, 7.21.3, 7.21.5.3
26153 initial shift state, 5.2.1.2 internal linkage, 6.2.2
26154 initialization, 5.1.2, 6.2.4, 6.3.2.1, 6.5.2.5, 6.7.9, internal name, 6.4.2.1
26155 F.8.5 interrupt, 5.2.3
26156 in blocks, 6.8 INTMAX_C macro, 7.20.4.2
26157 initializer, 6.7.9 INTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
26158 permitted form, 6.6 INTMAX_MIN macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
26159 string literal, 6.3.2.1 intmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2,
26160 inline, 6.7.4 7.28.2.1, 7.28.2.2
26161 inner scope, 6.2.1 INTN_C macros, 7.20.4.1
26162 input failure, 7.28.2.6, 7.28.2.8, 7.28.2.10, INTN_MAX macros, 7.20.2.1
26163 K.3.5.3.2, K.3.5.3.4, K.3.5.3.7, K.3.5.3.9, INTN_MIN macros, 7.20.2.1
26164 K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, K.3.9.1.5, intN_t types, 7.20.1.1
26165 K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, K.3.9.1.14 INTPTR_MAX macro, 7.20.2.4
26166 input/output functions INTPTR_MIN macro, 7.20.2.4
26167 character, 7.21.7, K.3.5.4 intptr_t type, 7.20.1.4
26168 direct, 7.21.8 inttypes.h header, 7.8, 7.30.4
26169 formatted, 7.21.6, K.3.5.3 isalnum function, 7.4.1.1, 7.4.1.9, 7.4.1.10
26170 wide character, 7.28.2, K.3.9.1 isalpha function, 7.4.1.1, 7.4.1.2
26171 wide character, 7.28.3 isblank function, 7.4.1.3
26172 formatted, 7.28.2, K.3.9.1 iscntrl function, 7.4.1.2, 7.4.1.4, 7.4.1.7,
26173 input/output header, 7.21, K.3.5 7.4.1.11
26174 input/output, device, 5.1.2.3 isdigit function, 7.4.1.1, 7.4.1.2, 7.4.1.5,
26175 int type, 6.2.5, 6.3.1.1, 6.3.1.3, 6.4.4.1, 6.7.2 7.4.1.7, 7.4.1.11, 7.11.1.1
26176 int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, isfinite macro, 7.12.3.2, F.3
26177 6.3.1.8 isgraph function, 7.4.1.6
26178 INT_FASTN_MAX macros, 7.20.2.3 isgreater macro, 7.12.14.1, F.3
26179 INT_FASTN_MIN macros, 7.20.2.3 isgreaterequal macro, 7.12.14.2, F.3
26180 int_fastN_t types, 7.20.1.3 isinf macro, 7.12.3.3
26181 INT_LEASTN_MAX macros, 7.20.2.2 isless macro, 7.12.14.3, F.3
26182 INT_LEASTN_MIN macros, 7.20.2.2 islessequal macro, 7.12.14.4, F.3
26183 int_leastN_t types, 7.20.1.2 islessgreater macro, 7.12.14.5, F.3
26184 INT_MAX macro, 5.2.4.2.1, 7.12, 7.12.6.5 islower function, 7.4.1.2, 7.4.1.7, 7.4.2.1,
26185 INT_MIN macro, 5.2.4.2.1, 7.12 7.4.2.2
26186 integer arithmetic functions, 7.8.2.1, 7.8.2.2, isnan macro, 7.12.3.4, F.3
26187 7.22.6 isnormal macro, 7.12.3.5
26188 integer character constant, 6.4.4.4 ISO 31-11, 2, 3
26189 integer constant, 6.4.4.1 ISO 4217, 2, 7.11.2.1
26190 integer constant expression, 6.3.2.3, 6.6, 6.7.2.1, ISO 8601, 2, 7.26.3.5
26191 6.7.2.2, 6.7.6.2, 6.7.9, 6.7.10, 6.8.4.2, 6.10.1, ISO/IEC 10646, 2, 6.4.2.1, 6.4.3, 6.10.8.2
26192 7.1.4 ISO/IEC 10976-1, H.1
26193 integer conversion rank, 6.3.1.1 ISO/IEC 2382-1, 2, 3
26194 integer promotions, 5.1.2.3, 5.2.4.2.1, 6.3.1.1, ISO/IEC 646, 2, 5.2.1.1
26195 6.5.2.2, 6.5.3.3, 6.5.7, 6.8.4.2, 7.20.2, 7.20.3, ISO/IEC 9945-2, 7.11
26196 7.21.6.1, 7.28.2.1 iso646.h header, 4, 7.9 *
26197 integer suffix, 6.4.4.1 isprint function, 5.2.2, 7.4.1.8
26198 integer type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, ispunct function, 7.4.1.2, 7.4.1.7, 7.4.1.9,
26200 integer types, 6.2.5, 7.20 isspace function, 7.4.1.2, 7.4.1.7, 7.4.1.9,
26204 7.4.1.10, 7.4.1.11, 7.21.6.2, 7.22.1.3, LC_ALL macro, 7.11, 7.11.1.1, 7.11.2.1
26205 7.22.1.4, 7.28.2.2 LC_COLLATE macro, 7.11, 7.11.1.1, 7.23.4.3,
26206 isunordered macro, 7.12.14.6, F.3 7.28.4.4.2
26207 isupper function, 7.4.1.2, 7.4.1.11, 7.4.2.1, LC_CTYPE macro, 7.11, 7.11.1.1, 7.22, 7.22.7,
26208 7.4.2.2 7.22.8, 7.28.6, 7.29.1, 7.29.2.2.1, 7.29.2.2.2,
26209 iswalnum function, 7.29.2.1.1, 7.29.2.1.9, 7.29.3.2.1, 7.29.3.2.2, K.3.6.4, K.3.6.5
26210 7.29.2.1.10, 7.29.2.2.1 LC_MONETARY macro, 7.11, 7.11.1.1, 7.11.2.1
26211 iswalpha function, 7.29.2.1.1, 7.29.2.1.2, LC_NUMERIC macro, 7.11, 7.11.1.1, 7.11.2.1
26212 7.29.2.2.1 LC_TIME macro, 7.11, 7.11.1.1, 7.26.3.5
26213 iswblank function, 7.29.2.1.3, 7.29.2.2.1 lconv structure type, 7.11
26214 iswcntrl function, 7.29.2.1.2, 7.29.2.1.4, LDBL_DECIMAL_DIG macro, 5.2.4.2.2
26215 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1 LDBL_DIG macro, 5.2.4.2.2
26216 iswctype function, 7.29.2.2.1, 7.29.2.2.2 LDBL_EPSILON macro, 5.2.4.2.2
26217 iswdigit function, 7.29.2.1.1, 7.29.2.1.2, LDBL_HAS_SUBNORM macro, 5.2.4.2.2
26218 7.29.2.1.5, 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1 LDBL_MANT_DIG macro, 5.2.4.2.2
26219 iswgraph function, 7.29.2.1, 7.29.2.1.6, LDBL_MAX macro, 5.2.4.2.2
26220 7.29.2.1.10, 7.29.2.2.1 LDBL_MAX_10_EXP macro, 5.2.4.2.2
26221 iswlower function, 7.29.2.1.2, 7.29.2.1.7, LDBL_MAX_EXP macro, 5.2.4.2.2
26222 7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2 LDBL_MIN macro, 5.2.4.2.2
26223 iswprint function, 7.29.2.1.6, 7.29.2.1.8, LDBL_MIN_10_EXP macro, 5.2.4.2.2
26224 7.29.2.2.1 LDBL_MIN_EXP macro, 5.2.4.2.2
26225 iswpunct function, 7.29.2.1, 7.29.2.1.2, LDBL_TRUE_MIN macro, 5.2.4.2.2
26226 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, ldexp functions, 7.12.6.6, F.10.3.6
26227 7.29.2.1.11, 7.29.2.2.1 ldexp type-generic macro, 7.24
26228 iswspace function, 7.21.6.2, 7.28.2.2, ldiv function, 7.22.6.2
26229 7.28.4.1.1, 7.28.4.1.2, 7.29.2.1.2, 7.29.2.1.6, ldiv_t type, 7.22
26230 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, leading underscore in identifiers, 7.1.3
26231 7.29.2.1.11, 7.29.2.2.1 left-shift assignment operator (<<=), 6.5.16.2
26232 iswupper function, 7.29.2.1.2, 7.29.2.1.11, left-shift operator (<<), 6.2.6.2, 6.5.7
26233 7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2 length
26234 iswxdigit function, 7.29.2.1.12, 7.29.2.2.1 external name, 5.2.4.1, 6.4.2.1, 6.11.3
26235 isxdigit function, 7.4.1.12, 7.11.1.1 function name, 5.2.4.1, 6.4.2.1, 6.11.3
26236 italic type convention, 3, 6.1 identifier, 6.4.2.1
26237 iteration statements, 6.8.5 internal name, 5.2.4.1, 6.4.2.1
26238 length function, 7.22.7.1, 7.23.6.3, 7.28.4.6.1,
26239 jmp_buf type, 7.13 7.28.6.3.1, K.3.7.4.4, K.3.9.2.4.1
26240 jump statements, 6.8.6 length modifier, 7.21.6.1, 7.21.6.2, 7.28.2.1,
26242 keywords, 6.4.1, G.2, J.5.9, J.5.10 less-than operator (<), 6.5.8
26243 kill_dependency macro, 5.1.2.4, 7.17.3.1 less-than-or-equal-to operator (<=), 6.5.8
26244 known constant size, 6.2.5 letter, 5.2.1, 7.4
26245 lexical elements, 5.1.1.2, 6.4
26246 L_tmpnam macro, 7.21.1, 7.21.4.4 lgamma functions, 7.12.8.3, F.10.5.3
26247 L_tmpnam_s macro, K.3.5, K.3.5.1.2 lgamma type-generic macro, 7.24
26248 label name, 6.2.1, 6.2.3 library, 5.1.1.1, 7, K.3
26249 labeled statement, 6.8.1 future directions, 7.30
26250 labs function, 7.22.6.1 summary, B
26251 language, 6 terms, 7.1.1
26252 future directions, 6.11 use of functions, 7.1.4
26253 syntax summary, A lifetime, 6.2.4
26254 Latin alphabet, 5.2.1, 6.4.2.1 limits
26258 environmental, see environmental limits 6.3.1.6, 6.3.1.7, 6.3.1.8
26259 implementation, see implementation limits long double _Imaginary type, G.2
26260 numerical, see numerical limits long double suffix, l or L, 6.4.4.2
26261 translation, see translation limits long double type, 6.2.5, 6.4.4.2, 6.7.2,
26262 limits.h header, 4, 5.2.4.2.1, 6.2.5, 7.10 7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2, F.2
26263 line buffered stream, 7.21.3 long double type conversion, 6.3.1.4, 6.3.1.5,
26264 line number, 6.10.4, 6.10.8.1 6.3.1.7, 6.3.1.8
26265 line preprocessing directive, 6.10.4 long int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1,
26266 lines, 5.1.1.2, 7.21.2 7.21.6.2, 7.28.2.1, 7.28.2.2
26267 preprocessing directive, 6.10 long int type conversion, 6.3.1.1, 6.3.1.3,
26268 linkage, 6.2.2, 6.7, 6.7.4, 6.7.6.2, 6.9, 6.9.2, 6.3.1.4, 6.3.1.8
26269 6.11.2 long integer suffix, l or L, 6.4.4.1
26270 llabs function, 7.22.6.1 long long int type, 6.2.5, 6.3.1.1, 6.7.2,
26271 lldiv function, 7.22.6.2 7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2
26272 lldiv_t type, 7.22 long long int type conversion, 6.3.1.1,
26273 LLONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 6.3.1.3, 6.3.1.4, 6.3.1.8
26274 7.28.4.1.2 long long integer suffix, ll or LL, 6.4.4.1
26275 LLONG_MIN macro, 5.2.4.2.1, 7.22.1.4, LONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2
26276 7.28.4.1.2 LONG_MIN macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2
26277 llrint functions, 7.12.9.5, F.3, F.10.6.5 longjmp function, 7.13.1.1, 7.13.2.1, 7.22.4.4,
26278 llrint type-generic macro, 7.24 7.22.4.7
26279 llround functions, 7.12.9.7, F.10.6.7 loop body, 6.8.5
26280 llround type-generic macro, 7.24 low-order bit, 3.6
26281 local time, 7.26.1 lowercase letter, 5.2.1
26282 locale, 3.4.2 lrint functions, 7.12.9.5, F.3, F.10.6.5
26283 locale-specific behavior, 3.4.2, J.4 lrint type-generic macro, 7.24
26284 locale.h header, 7.11, 7.30.5 lround functions, 7.12.9.7, F.10.6.7
26285 localeconv function, 7.11.1.1, 7.11.2.1 lround type-generic macro, 7.24
26286 localization, 7.11 lvalue, 6.3.2.1, 6.5.1, 6.5.2.4, 6.5.3.1, 6.5.16,
26287 localtime function, 7.26.3.4 6.7.2.4
26288 localtime_s function, K.3.8.2.4 lvalue conversion, 6.3.2.1, 6.5.16, 6.5.16.1,
26289 log functions, 7.12.6.7, F.10.3.7 6.5.16.2
26290 log type-generic macro, 7.24
26291 log10 functions, 7.12.6.8, F.10.3.8 macro argument substitution, 6.10.3.1
26292 log10 type-generic macro, 7.24 macro definition
26293 log1p functions, 7.12.6.9, F.10.3.9 library function, 7.1.4
26294 log1p type-generic macro, 7.24 macro invocation, 6.10.3
26295 log2 functions, 7.12.6.10, F.10.3.10 macro name, 6.10.3
26296 log2 type-generic macro, 7.24 length, 5.2.4.1
26297 logarithmic functions predefined, 6.10.8, 6.11.9
26298 complex, 7.3.7, G.6.3 redefinition, 6.10.3
26299 real, 7.12.6, F.10.3 scope, 6.10.3.5
26300 logb functions, 7.12.6.11, F.3, F.10.3.11 macro parameter, 6.10.3
26301 logb type-generic macro, 7.24 macro preprocessor, 6.10
26302 logical operators macro replacement, 6.10.3
26303 AND (&&), 5.1.2.4, 6.5.13 magnitude, complex, 7.3.8.1
26304 negation (!), 6.5.3.3 main function, 5.1.2.2.1, 5.1.2.2.3, 6.7.3.1, 6.7.4,
26305 OR (||), 5.1.2.4, 6.5.14 7.21.3
26306 logical source lines, 5.1.1.2 malloc function, 7.22.3, 7.22.3.4, 7.22.3.5
26307 long double _Complex type, 6.2.5 manipulation functions
26308 long double _Complex type conversion, complex, 7.3.9
26312 real, 7.12.11, F.10.8 modf functions, 7.12.6.12, F.10.3.12
26313 matching failure, 7.28.2.6, 7.28.2.8, 7.28.2.10, modifiable lvalue, 6.3.2.1
26314 K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 modification order, 5.1.2.4
26315 math.h header, 5.2.4.2.2, 6.5, 7.12, 7.24, F, modulus functions, 7.12.6.12
26316 F.10, J.5.17 modulus, complex, 7.3.8.1
26317 MATH_ERREXCEPT macro, 7.12, F.10 mtx_destroy function, 7.25.4.1
26318 math_errhandling macro, 7.1.3, 7.12, F.10 mtx_init function, 7.25.1, 7.25.4.2
26319 MATH_ERRNO macro, 7.12 mtx_lock function, 7.25.4.3
26320 max_align_t type, 7.19 mtx_t type, 7.25.1
26321 maximum functions, 7.12.12, F.10.9 mtx_timedlock function, 7.25.4.4
26322 MB_CUR_MAX macro, 7.1.1, 7.22, 7.22.7.2, mtx_trylock function, 7.25.4.5
26323 7.22.7.3, 7.27.1.2, 7.27.1.4, 7.28.6.3.3, mtx_unlock function, 7.25.4.3, 7.25.4.4,
26324 K.3.6.4.1, K.3.9.3.1.1 7.25.4.5, 7.25.4.6
26325 MB_LEN_MAX macro, 5.2.4.2.1, 7.1.1, 7.22 multibyte character, 3.7.2, 5.2.1.2, 6.4.4.4
26326 mblen function, 7.22.7.1, 7.28.6.3 multibyte conversion functions
26327 mbrlen function, 7.28.6.3.1 wide character, 7.22.7, K.3.6.4
26328 mbrtoc16 function, 6.4.4.4, 6.4.5, 7.27.1.1 extended, 7.28.6, K.3.9.3
26329 mbrtoc32 function, 6.4.4.4, 6.4.5, 7.27.1.3 restartable, 7.27.1, 7.28.6.3, K.3.9.3.1
26330 mbrtowc function, 7.21.3, 7.21.6.1, 7.21.6.2, wide string, 7.22.8, K.3.6.5
26331 7.28.2.1, 7.28.2.2, 7.28.6.3.1, 7.28.6.3.2, restartable, 7.28.6.4, K.3.9.3.2
26332 7.28.6.4.1, K.3.6.5.1, K.3.9.3.2.1 multibyte string, 7.1.1
26333 mbsinit function, 7.28.6.2.1 multibyte/wide character conversion functions,
26334 mbsrtowcs function, 7.28.6.4.1, K.3.9.3.2 7.22.7, K.3.6.4
26335 mbsrtowcs_s function, K.3.9.3.2, K.3.9.3.2.1 extended, 7.28.6, K.3.9.3
26336 mbstate_t type, 7.21.2, 7.21.3, 7.21.6.1, restartable, 7.27.1, 7.28.6.3, K.3.9.3.1
26337 7.21.6.2, 7.27, 7.27.1, 7.28.1, 7.28.2.1, multibyte/wide string conversion functions,
26338 7.28.2.2, 7.28.6, 7.28.6.2.1, 7.28.6.3, 7.22.8, K.3.6.5
26339 7.28.6.3.1, 7.28.6.4 restartable, 7.28.6.4, K.3.9.3.2
26340 mbstowcs function, 6.4.5, 7.22.8.1, 7.28.6.4 multidimensional array, 6.5.2.1
26341 mbstowcs_s function, K.3.6.5.1 multiplication assignment operator (*=), 6.5.16.2
26342 mbtowc function, 6.4.4.4, 7.22.7.1, 7.22.7.2, multiplication operator (*), 6.2.6.2, 6.5.5, F.3,
26343 7.22.8.1, 7.28.6.3 G.5.1
26344 member access operators (. and ->), 6.5.2.3 multiplicative expressions, 6.5.5, G.5.1
26345 member alignment, 6.7.2.1
26346 memchr function, 7.23.5.1 n-char sequence, 7.22.1.3
26347 memcmp function, 7.23.4, 7.23.4.1 n-wchar sequence, 7.28.4.1.1
26348 memcpy function, 7.23.2.1 name
26349 memcpy_s function, K.3.7.1.1 external, 5.2.4.1, 6.4.2.1, 6.11.3
26350 memmove function, 7.23.2.2 file, 7.21.3
26351 memmove_s function, K.3.7.1.2 internal, 5.2.4.1, 6.4.2.1
26352 memory location, 3.14 label, 6.2.3
26353 memory management functions, 7.22.3 structure/union member, 6.2.3
26354 memory_order type, 7.17.1, 7.17.3 name spaces, 6.2.3
26355 memset function, 7.23.6.1, K.3.7.4.1 named label, 6.8.1
26356 memset_s function, K.3.7.4.1 NaN, 5.2.4.2.2
26357 minimum functions, 7.12.12, F.10.9 nan functions, 7.12.11.2, F.2.1, F.10.8.2
26358 minus operator, unary, 6.5.3.3 NAN macro, 7.12, F.2.1
26359 miscellaneous functions NDEBUG macro, 7.2
26360 string, 7.23.6, K.3.7.4 nearbyint functions, 7.12.9.3, 7.12.9.4, F.3,
26361 wide string, 7.28.4.6, K.3.9.2.4 F.10.6.3
26362 mktime function, 7.26.2.3 nearbyint type-generic macro, 7.24
26366 nearest integer functions, 7.12.9, F.10.6 operating system, 5.1.2.1, 7.22.4.8
26367 negation operator (!), 6.5.3.3 operations on files, 7.21.4, K.3.5.1
26368 negative zero, 6.2.6.2, 7.12.11.1 operator, 6.4.6
26369 new-line character, 5.1.1.2, 5.2.1, 6.4, 6.10, 6.10.4 operators, 6.5
26370 new-line escape sequence (\n), 5.2.2, 6.4.4.4, additive, 6.2.6.2, 6.5.6
26371 7.4.1.10 alignof, 6.5.3.4
26372 nextafter functions, 7.12.11.3, 7.12.11.4, F.3, assignment, 6.5.16
26373 F.10.8.3 associativity, 6.5
26374 nextafter type-generic macro, 7.24 equality, 6.5.9
26375 nexttoward functions, 7.12.11.4, F.3, F.10.8.4 multiplicative, 6.2.6.2, 6.5.5, G.5.1
26376 nexttoward type-generic macro, 7.24 postfix, 6.5.2
26377 no linkage, 6.2.2 precedence, 6.5
26378 no-return function, 6.7.4 preprocessing, 6.10.1, 6.10.3.2, 6.10.3.3, 6.10.9
26379 non-stop floating-point control mode, 7.6.4.2 relational, 6.5.8
26380 nongraphic characters, 5.2.2, 6.4.4.4 shift, 6.5.7
26381 nonlocal jumps header, 7.13 sizeof, 6.5.3.4
26382 norm, complex, 7.3.8.1 unary, 6.5.3
26383 normalized broken-down time, K.3.8.1, K.3.8.2.1 unary arithmetic, 6.5.3.3
26384 not macro, 7.9 optional features, see conditional features
26385 not-equal-to operator, see inequality operator or macro, 7.9
26386 not_eq macro, 7.9 OR operators
26387 null character (\0), 5.2.1, 6.4.4.4, 6.4.5 bitwise exclusive (^), 6.2.6.2, 6.5.11
26388 padding of binary stream, 7.21.2 bitwise exclusive assignment (^=), 6.5.16.2
26389 NULL macro, 7.11, 7.19, 7.21.1, 7.22, 7.23.1, bitwise inclusive (|), 6.2.6.2, 6.5.12
26390 7.26.1, 7.28.1 bitwise inclusive assignment (|=), 6.5.16.2
26391 null pointer, 6.3.2.3 logical (||), 5.1.2.4, 6.5.14
26392 null pointer constant, 6.3.2.3 or_eq macro, 7.9
26393 null preprocessing directive, 6.10.7 order of allocated storage, 7.22.3
26394 null statement, 6.8.3 order of evaluation, 6.5, 6.5.16, 6.10.3.2, 6.10.3.3,
26395 null wide character, 7.1.1 see also sequence points
26396 number classification macros, 7.12, 7.12.3.1 ordinary identifier name space, 6.2.3
26397 numeric conversion functions, 7.8.2.3, 7.22.1 orientation of stream, 7.21.2, 7.28.3.5
26398 wide string, 7.8.2.4, 7.28.4.1 out-of-bounds store, L.2.1
26399 numerical limits, 5.2.4.2 outer scope, 6.2.1
26400 over-aligned, 6.2.8
26402 object representation, 6.2.6.1 padding
26403 object type, 6.2.5 binary stream, 7.21.2
26404 object-like macro, 6.10.3 bits, 6.2.6.2, 7.20.1.1
26405 observable behavior, 5.1.2.3 structure/union, 6.2.6.1, 6.7.2.1
26406 obsolescence, 6.11, 7.30 parameter, 3.16
26407 octal constant, 6.4.4.1 array, 6.9.1
26408 octal digit, 6.4.4.1, 6.4.4.4 ellipsis, 6.7.6.3, 6.10.3
26409 octal-character escape sequence (\octal digits), function, 6.5.2.2, 6.7, 6.9.1
26410 6.4.4.4 macro, 6.10.3
26411 offsetof macro, 7.19 main function, 5.1.2.2.1
26412 on-off switch, 6.10.6 program, 5.1.2.2.1
26413 once_flag type, 7.25.1 parameter type list, 6.7.6.3
26414 ONCE_FLAG_INIT macro, 7.25.1 parentheses punctuator (( )), 6.7.6.3, 6.8.4, 6.8.5
26415 ones' complement, 6.2.6.2 parenthesized expression, 6.5.1
26416 operand, 6.4.6, 6.5 parse state, 7.21.2
26420 perform a trap, 3.19.5 preprocessor, 6.10
26421 permitted form of initializer, 6.6 PRIcFASTN macros, 7.8.1
26422 perror function, 7.21.10.4 PRIcLEASTN macros, 7.8.1
26423 phase angle, complex, 7.3.9.1 PRIcMAX macros, 7.8.1
26424 physical source lines, 5.1.1.2 PRIcN macros, 7.8.1
26425 placemarker, 6.10.3.3 PRIcPTR macros, 7.8.1
26426 plus operator, unary, 6.5.3.3 primary expression, 6.5.1
26427 pointer arithmetic, 6.5.6 printf function, 7.21.1, 7.21.6.3, 7.21.6.10,
26428 pointer comparison, 6.5.8 K.3.5.3.3
26429 pointer declarator, 6.7.6.1 printf_s function, K.3.5.3.3
26430 pointer operator (->), 6.5.2.3 printing character, 5.2.2, 7.4, 7.4.1.8
26431 pointer to function, 6.5.2.2 printing wide character, 7.29.2
26432 pointer type, 6.2.5 program diagnostics, 7.2.1
26433 pointer type conversion, 6.3.2.1, 6.3.2.3 program execution, 5.1.2.2.2, 5.1.2.3
26434 pointer, null, 6.3.2.3 program file, 5.1.1.1
26435 pole error, 7.12.1, 7.12.5.3, 7.12.6.7, 7.12.6.8, program image, 5.1.1.2
26436 7.12.6.9, 7.12.6.10, 7.12.6.11, 7.12.7.4, program name (argv[0]), 5.1.2.2.1
26437 7.12.8.3, 7.12.8.4 program parameters, 5.1.2.2.1
26438 portability, 4, J program startup, 5.1.2, 5.1.2.1, 5.1.2.2.1
26439 position indicator, file, see file position indicator program structure, 5.1.1.1
26440 positive difference, 7.12.12.1 program termination, 5.1.2, 5.1.2.1, 5.1.2.2.3,
26441 positive difference functions, 7.12.12, F.10.9 5.1.2.3
26442 postfix decrement operator (--), 6.3.2.1, 6.5.2.4 program, conforming, 4
26443 postfix expressions, 6.5.2 program, strictly conforming, 4
26444 postfix increment operator (++), 6.3.2.1, 6.5.2.4 promotions
26445 pow functions, 7.12.7.4, F.10.4.4 default argument, 6.5.2.2
26446 pow type-generic macro, 7.24 integer, 5.1.2.3, 6.3.1.1
26447 power functions prototype, see function prototype
26448 complex, 7.3.8, G.6.4 pseudo-random sequence functions, 7.22.2
26449 real, 7.12.7, F.10.4 PTRDIFF_MAX macro, 7.20.3
26450 pp-number, 6.4.8 PTRDIFF_MIN macro, 7.20.3
26451 pragma operator, 6.10.9 ptrdiff_t type, 7.17.1, 7.19, 7.20.3, 7.21.6.1,
26452 pragma preprocessing directive, 6.10.6, 6.11.8 7.21.6.2, 7.28.2.1, 7.28.2.2
26453 precedence of operators, 6.5 punctuators, 6.4.6
26454 precedence of syntax rules, 5.1.1.2 putc function, 7.21.1, 7.21.7.7, 7.21.7.8
26455 precision, 6.2.6.2, 6.3.1.1, 7.21.6.1, 7.28.2.1 putchar function, 7.21.1, 7.21.7.8
26456 excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 puts function, 7.21.1, 7.21.7.9
26457 predefined macro names, 6.10.8, 6.11.9 putwc function, 7.21.1, 7.28.3.8, 7.28.3.9
26458 prefix decrement operator (--), 6.3.2.1, 6.5.3.1 putwchar function, 7.21.1, 7.28.3.9
26459 prefix increment operator (++), 6.3.2.1, 6.5.3.1
26460 preprocessing concatenation, 6.10.3.3 qsort function, 7.22.5, 7.22.5.2
26461 preprocessing directives, 5.1.1.2, 6.10 qsort_s function, K.3.6.3, K.3.6.3.2
26462 preprocessing file, 5.1.1.1, 6.10 qualified types, 6.2.5
26463 preprocessing numbers, 6.4, 6.4.8 qualified version of type, 6.2.5
26464 preprocessing operators question-mark escape sequence (\?), 6.4.4.4
26465 #, 6.10.3.2 quick_exit function, 7.22.4.3, 7.22.4.4,
26466 ##, 6.10.3.3 7.22.4.7
26467 _Pragma, 5.1.1.2, 6.10.9 quiet NaN, 5.2.4.2.2
26469 preprocessing tokens, 5.1.1.2, 6.4, 6.10 raise function, 7.14, 7.14.1.1, 7.14.2.1, 7.22.4.1
26470 preprocessing translation unit, 5.1.1.1 rand function, 7.22, 7.22.2.1, 7.22.2.2
26474 RAND_MAX macro, 7.22, 7.22.2.1 restrict-qualified type, 6.2.5, 6.7.3
26475 range return statement, 6.8.6.4, F.6
26476 excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 rewind function, 7.21.5.3, 7.21.7.10, 7.21.9.5,
26477 range error, 7.12.1, 7.12.5.4, 7.12.5.5, 7.12.6.1, 7.28.3.10
26478 7.12.6.2, 7.12.6.3, 7.12.6.5, 7.12.6.6, right-shift assignment operator (>>=), 6.5.16.2
26479 7.12.6.13, 7.12.7.3, 7.12.7.4, 7.12.8.2, right-shift operator (>>), 6.2.6.2, 6.5.7
26480 7.12.8.3, 7.12.8.4, 7.12.9.5, 7.12.9.7, rint functions, 7.12.9.4, F.3, F.10.6.4
26481 7.12.11.3, 7.12.12.1, 7.12.13.1 rint type-generic macro, 7.24
26482 rank, see integer conversion rank round functions, 7.12.9.6, F.10.6.6
26483 read-modify-write operations, 5.1.2.4 round type-generic macro, 7.24
26484 real floating type conversion, 6.3.1.4, 6.3.1.5, rounding mode, floating point, 5.2.4.2.2
26485 6.3.1.7, F.3, F.4 RSIZE_MAX macro, K.3.3, K.3.4, K.3.5.1.2,
26486 real floating types, 6.2.5 K.3.5.3.5, K.3.5.3.6, K.3.5.3.12, K.3.5.3.13,
26487 real type domain, 6.2.5 K.3.5.4.1, K.3.6.2.1, K.3.6.3.1, K.3.6.3.2,
26488 real types, 6.2.5 K.3.6.4.1, K.3.6.5.1, K.3.6.5.2, K.3.7.1.1,
26489 real-floating, 7.12.3 K.3.7.1.2, K.3.7.1.3, K.3.7.1.4, K.3.7.2.1,
26490 realloc function, 7.22.3, 7.22.3.5 K.3.7.2.2, K.3.7.3.1, K.3.7.4.1, K.3.7.4.2,
26491 recommended practice, 3.17 K.3.8.2.1, K.3.8.2.2, K.3.9.1.3, K.3.9.1.4,
26492 recursion, 6.5.2.2 K.3.9.1.8, K.3.9.1.9, K.3.9.2.1.1, K.3.9.2.1.2,
26493 recursive function call, 6.5.2.2 K.3.9.2.1.3, K.3.9.2.1.4, K.3.9.2.2.1,
26494 redefinition of macro, 6.10.3 K.3.9.2.2.2, K.3.9.2.3.1, K.3.9.3.1.1,
26495 reentrancy, 5.1.2.3, 5.2.3 K.3.9.3.2.1, K.3.9.3.2.2
26496 library functions, 7.1.4 rsize_t type, K.3.3, K.3.4, K.3.5, K.3.5.3.2,
26497 referenced type, 6.2.5 K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2
26498 register storage-class specifier, 6.7.1, 6.9 runtime-constraint, 3.18
26499 relational expressions, 6.5.8 Runtime-constraint handling functions, K.3.6.1
26500 relaxed atomic operations, 5.1.2.4 rvalue, 6.3.2.1
26501 release fence, 7.17.4
26502 release operation, 5.1.2.4 same scope, 6.2.1
26503 release sequence, 5.1.2.4 save calling environment function, 7.13.1
26504 reliability of data, interrupted, 5.1.2.3 scalar types, 6.2.5
26505 remainder assignment operator (%=), 6.5.16.2 scalbln function, 7.12.6.13, F.3, F.10.3.13
26506 remainder functions, 7.12.10, F.10.7 scalbln type-generic macro, 7.24
26507 remainder functions, 7.12.10.2, 7.12.10.3, F.3, scalbn function, 7.12.6.13, F.3, F.10.3.13
26508 F.10.7.2 scalbn type-generic macro, 7.24
26509 remainder operator (%), 6.2.6.2, 6.5.5 scanf function, 7.21.1, 7.21.6.4, 7.21.6.11
26510 remainder type-generic macro, 7.24 scanf_s function, K.3.5.3.4, K.3.5.3.11
26511 remove function, 7.21.4.1, 7.21.4.4, K.3.5.1.2 scanlist, 7.21.6.2, 7.28.2.2
26512 remquo functions, 7.12.10.3, F.3, F.10.7.3 scanset, 7.21.6.2, 7.28.2.2
26513 remquo type-generic macro, 7.24 SCHAR_MAX macro, 5.2.4.2.1
26514 rename function, 7.21.4.2 SCHAR_MIN macro, 5.2.4.2.1
26515 representations of types, 6.2.6 SCNcFASTN macros, 7.8.1
26516 pointer, 6.2.5 SCNcLEASTN macros, 7.8.1
26517 rescanning and replacement, 6.10.3.4 SCNcMAX macros, 7.8.1
26518 reserved identifiers, 6.4.1, 7.1.3, K.3.1.2 SCNcN macros, 7.8.1
26519 restartable multibyte/wide character conversion SCNcPTR macros, 7.8.1
26520 functions, 7.27.1, 7.28.6.3, K.3.9.3.1 scope of identifier, 6.2.1, 6.9.2
26521 restartable multibyte/wide string conversion search functions
26522 functions, 7.28.6.4, K.3.9.3.2 string, 7.23.5, K.3.7.3
26523 restore calling environment function, 7.13.2 utility, 7.22.5, K.3.6.3
26524 restrict type qualifier, 6.7.3, 6.7.3.1 wide string, 7.28.4.5, K.3.9.2.3
26528 SEEK_CUR macro, 7.21.1, 7.21.9.2 sign and magnitude, 6.2.6.2
26529 SEEK_END macro, 7.21.1, 7.21.9.2 sign bit, 6.2.6.2
26530 SEEK_SET macro, 7.21.1, 7.21.9.2 signal function, 7.14.1.1, 7.22.4.5, 7.22.4.7
26531 selection statements, 6.8.4 signal handler, 5.1.2.3, 5.2.3, 7.14.1.1, 7.14.2.1
26532 self-referential structure, 6.7.2.3 signal handling functions, 7.14.1
26533 semicolon punctuator (;), 6.7, 6.7.2.1, 6.8.3, signal.h header, 7.14, 7.30.6
26534 6.8.5, 6.8.6 signaling NaN, 5.2.4.2.2, F.2.1
26535 separate compilation, 5.1.1.1 signals, 5.1.2.3, 5.2.3, 7.14.1
26536 separate translation, 5.1.1.1 signbit macro, 7.12.3.6, F.3
26537 sequence points, 5.1.2.3, 6.5.2.2, 6.5.13, 6.5.14, signed char type, 6.2.5, 7.21.6.1, 7.21.6.2,
26538 6.5.15, 6.5.17, 6.7.3, 6.7.3.1, 6.7.6, 6.8, 7.28.2.1, 7.28.2.2, K.3.5.3.2, K.3.9.1.2
26539 7.1.4, 7.21.6, 7.22.5, 7.28.2, C, K.3.6.3 signed character, 6.3.1.1
26540 sequenced after, see sequenced before signed integer types, 6.2.5, 6.3.1.3, 6.4.4.1
26541 sequenced before, 5.1.2.3, 6.5, 6.5.2.2, 6.5.2.4, signed type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
26542 6.5.16, see also indeterminately sequenced, 6.3.1.8
26543 unsequenced signed types, 6.2.5, 6.7.2
26544 sequencing of statements, 6.8 significand part, 6.4.4.2
26545 set_constraint_handler_s function, SIGSEGV macro, 7.14, 7.14.1.1
26546 K.3.1.4, K.3.6.1.1, K.3.6.1.2, K.3.6.1.3 SIGTERM macro, 7.14
26547 setbuf function, 7.21.3, 7.21.5.1, 7.21.5.5 simple assignment operator (=), 6.5.16.1
26548 setjmp macro, 7.1.3, 7.13.1.1, 7.13.2.1 sin functions, 7.12.4.6, F.10.1.6
26549 setjmp.h header, 7.13 sin type-generic macro, 7.24, G.7
26550 setlocale function, 7.11.1.1, 7.11.2.1 single-byte character, 3.7.1, 5.2.1.2
26551 setvbuf function, 7.21.1, 7.21.3, 7.21.5.1, single-byte/wide character conversion functions,
26552 7.21.5.5, 7.21.5.6 7.28.6.1
26553 shall, 4 single-precision arithmetic, 5.1.2.3
26554 shift expressions, 6.5.7 single-quote escape sequence (\'), 6.4.4.4, 6.4.5
26555 shift sequence, 7.1.1 singularity, 7.12.1
26556 shift states, 5.2.1.2 sinh functions, 7.12.5.5, F.10.2.5
26557 short identifier, character, 5.2.4.1, 6.4.3 sinh type-generic macro, 7.24, G.7
26558 short int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1, SIZE_MAX macro, 7.20.3
26559 7.21.6.2, 7.28.2.1, 7.28.2.2 size_t type, 6.2.8, 6.5.3.4, 7.19, 7.20.3, 7.21.1,
26560 short int type conversion, 6.3.1.1, 6.3.1.3, 7.21.6.1, 7.21.6.2, 7.22, 7.23.1, 7.26.1, 7.27,
26561 6.3.1.4, 6.3.1.8 7.28.1, 7.28.2.1, 7.28.2.2, K.3.3, K.3.4,
26562 SHRT_MAX macro, 5.2.4.2.1 K.3.5, K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2
26563 SHRT_MIN macro, 5.2.4.2.1 sizeof operator, 6.3.2.1, 6.5.3, 6.5.3.4
26564 side effects, 5.1.2.3, 6.2.6.1, 6.3.2.2, 6.5, 6.5.2.4, snprintf function, 7.21.6.5, 7.21.6.12,
26565 6.5.16, 6.7.9, 6.8.3, 7.6, 7.6.1, 7.21.7.5, K.3.5.3.5
26566 7.21.7.7, 7.28.3.6, 7.28.3.8, F.8.1, F.9.1, snprintf_s function, K.3.5.3.5, K.3.5.3.6
26567 F.9.3 snwprintf_s function, K.3.9.1.3, K.3.9.1.4
26568 SIG_ATOMIC_MAX macro, 7.20.3 sorting utility functions, 7.22.5, K.3.6.3
26569 SIG_ATOMIC_MIN macro, 7.20.3 source character set, 5.1.1.2, 5.2.1
26570 sig_atomic_t type, 5.1.2.3, 7.14, 7.14.1.1, source file, 5.1.1.1
26571 7.20.3 name, 6.10.4, 6.10.8.1
26572 SIG_DFL macro, 7.14, 7.14.1.1 source file inclusion, 6.10.2
26573 SIG_ERR macro, 7.14, 7.14.1.1 source lines, 5.1.1.2
26574 SIG_IGN macro, 7.14, 7.14.1.1 source text, 5.1.1.2
26575 SIGABRT macro, 7.14, 7.22.4.1 space character (' '), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3,
26576 SIGFPE macro, 7.12.1, 7.14, 7.14.1.1, J.5.17 7.4.1.10, 7.29.2.1.3
26577 SIGILL macro, 7.14, 7.14.1.1 sprintf function, 7.21.6.6, 7.21.6.13, K.3.5.3.6
26578 SIGINT macro, 7.14 sprintf_s function, K.3.5.3.5, K.3.5.3.6
26582 sqrt functions, 7.12.7.5, F.3, F.10.4.5 do, 6.8.5.2
26583 sqrt type-generic macro, 7.24 else, 6.8.4.1
26584 srand function, 7.22.2.2 expression, 6.8.3
26585 sscanf function, 7.21.6.7, 7.21.6.14 for, 6.8.5.3
26586 sscanf_s function, K.3.5.3.7, K.3.5.3.14 goto, 6.8.6.1
26587 standard error stream, 7.21.1, 7.21.3, 7.21.10.4 if, 6.8.4.1
26588 standard headers, 4, 7.1.2 iteration, 6.8.5
26589 <assert.h>, 7.2 jump, 6.8.6
26590 <complex.h>, 5.2.4.2.2, 6.10.8.3, 7.1.2, 7.3, labeled, 6.8.1
26591 7.24, 7.30.1, G.6, J.5.17 null, 6.8.3
26592 <ctype.h>, 7.4, 7.30.2 return, 6.8.6.4, F.6
26593 <errno.h>, 7.5, 7.30.3, K.3.2 selection, 6.8.4
26594 <fenv.h>, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H sequencing, 6.8
26595 <float.h>, 4, 5.2.4.2.2, 7.7, 7.22.1.3, switch, 6.8.4.2
26596 7.28.4.1.1 while, 6.8.5.1
26597 <inttypes.h>, 7.8, 7.30.4 static assertions, 6.7.10
26598 <iso646.h>, 4, 7.9 static storage duration, 6.2.4
26599 <limits.h>, 4, 5.2.4.2.1, 6.2.5, 7.10 static storage-class specifier, 6.2.2, 6.2.4, 6.7.1
26600 <locale.h>, 7.11, 7.30.5 static, in array declarators, 6.7.6.2, 6.7.6.3
26601 <math.h>, 5.2.4.2.2, 6.5, 7.12, 7.24, F, F.10, static_assert declaration, 6.7.10
26602 J.5.17 static_assert macro, 7.2
26603 <setjmp.h>, 7.13 stdalign.h header, 4, 7.15
26604 <signal.h>, 7.14, 7.30.6 stdarg.h header, 4, 6.7.6.3, 7.16
26605 <stdalign.h>, 4, 7.15 stdatomic.h header, 6.10.8.3, 7.1.2, 7.17
26606 <stdarg.h>, 4, 6.7.6.3, 7.16 stdbool.h header, 4, 7.18, 7.30.7, H
26607 <stdatomic.h>, 6.10.8.3, 7.1.2, 7.17 STDC, 6.10.6, 6.11.8
26608 <stdbool.h>, 4, 7.18, 7.30.7, H stddef.h header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
26609 <stddef.h>, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3
26610 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 stderr macro, 7.21.1, 7.21.2, 7.21.3
26611 <stdint.h>, 4, 5.2.4.2, 6.10.1, 7.8, 7.20, stdin macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.4,
26612 7.30.8, K.3.3, K.3.4 7.21.7.6, 7.28.2.12, 7.28.3.7, K.3.5.3.4,
26613 <stdio.h>, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5 K.3.5.4.1, K.3.9.1.14
26614 <stdlib.h>, 5.2.4.2.2, 7.22, 7.30.10, F, stdint.h header, 4, 5.2.4.2, 6.10.1, 7.8, 7.20,
26615 K.3.1.4, K.3.6 7.30.8, K.3.3, K.3.4
26616 <string.h>, 7.23, 7.30.11, K.3.7 stdio.h header, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5
26617 <tgmath.h>, 7.24, G.7 stdlib.h header, 5.2.4.2.2, 7.22, 7.30.10, F,
26618 <threads.h>, 6.10.8.3, 7.1.2, 7.25 K.3.1.4, K.3.6
26619 <time.h>, 7.26, K.3.8 stdout macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.3,
26620 <uchar.h>, 6.4.4.4, 6.4.5, 7.27 7.21.7.8, 7.21.7.9, 7.28.2.11, 7.28.3.9
26621 <wchar.h>, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12, storage duration, 6.2.4
26622 F, K.3.9 storage order of array, 6.5.2.1
26623 <wctype.h>, 7.29, 7.30.13 storage unit (bit-field), 6.2.6.1, 6.7.2.1
26624 standard input stream, 7.21.1, 7.21.3 storage-class specifiers, 6.7.1, 6.11.5
26625 standard integer types, 6.2.5 strcat function, 7.23.3.1
26626 standard output stream, 7.21.1, 7.21.3 strcat_s function, K.3.7.2.1
26627 standard signed integer types, 6.2.5 strchr function, 7.23.5.2
26628 state-dependent encoding, 5.2.1.2, 7.22.7, K.3.6.4 strcmp function, 7.23.4, 7.23.4.2
26629 statements, 6.8 strcoll function, 7.11.1.1, 7.23.4.3, 7.23.4.5
26630 break, 6.8.6.3 strcpy function, 7.23.2.3
26631 compound, 6.8.2 strcpy_s function, K.3.7.1.3
26632 continue, 6.8.6.2 strcspn function, 7.23.5.3
26636 streams, 7.21.2, 7.22.4.4 7.22.1.4, 7.28.2.2
26637 fully buffered, 7.21.3 strtoull function, 7.8.2.3, 7.22.1.2, 7.22.1.4
26638 line buffered, 7.21.3 strtoumax function, 7.8.2.3
26639 orientation, 7.21.2 struct hack, see flexible array member
26640 standard error, 7.21.1, 7.21.3 struct lconv, 7.11
26641 standard input, 7.21.1, 7.21.3 struct tm, 7.26.1
26642 standard output, 7.21.1, 7.21.3 structure
26643 unbuffered, 7.21.3 arrow operator (->), 6.5.2.3
26644 strerror function, 7.21.10.4, 7.23.6.2 content, 6.7.2.3
26645 strerror_s function, K.3.7.4.2, K.3.7.4.3 dot operator (.), 6.5.2.3
26646 strerrorlen_s function, K.3.7.4.3 initialization, 6.7.9
26647 strftime function, 7.11.1.1, 7.26.3, 7.26.3.5, member alignment, 6.7.2.1
26648 7.28.5.1, K.3.8.2, K.3.8.2.1, K.3.8.2.2 member name space, 6.2.3
26649 stricter, 6.2.8 member operator (.), 6.3.2.1, 6.5.2.3
26650 strictly conforming program, 4 pointer operator (->), 6.5.2.3
26651 string, 7.1.1 specifier, 6.7.2.1
26652 comparison functions, 7.23.4 tag, 6.2.3, 6.7.2.3
26653 concatenation functions, 7.23.3, K.3.7.2 type, 6.2.5, 6.7.2.1
26654 conversion functions, 7.11.1.1 strxfrm function, 7.11.1.1, 7.23.4.5
26655 copying functions, 7.23.2, K.3.7.1 subnormal floating-point numbers, 5.2.4.2.2
26656 library function conventions, 7.23.1 subscripting, 6.5.2.1
26657 literal, 5.1.1.2, 5.2.1, 6.3.2.1, 6.4.5, 6.5.1, 6.7.9 subtraction assignment operator (-=), 6.5.16.2
26658 miscellaneous functions, 7.23.6, K.3.7.4 subtraction operator (-), 6.2.6.2, 6.5.6, F.3, G.5.2
26659 numeric conversion functions, 7.8.2.3, 7.22.1 suffix
26660 search functions, 7.23.5, K.3.7.3 floating constant, 6.4.4.2
26661 string handling header, 7.23, K.3.7 integer constant, 6.4.4.1
26662 string.h header, 7.23, 7.30.11, K.3.7 switch body, 6.8.4.2
26663 stringizing, 6.10.3.2, 6.10.9 switch case label, 6.8.1, 6.8.4.2
26664 strlen function, 7.23.6.3 switch default label, 6.8.1, 6.8.4.2
26665 strncat function, 7.23.3.2 switch statement, 6.8.1, 6.8.4.2
26666 strncat_s function, K.3.7.2.2 swprintf function, 7.28.2.3, 7.28.2.7,
26667 strncmp function, 7.23.4, 7.23.4.4 K.3.9.1.3, K.3.9.1.4
26668 strncpy function, 7.23.2.4 swprintf_s function, K.3.9.1.3, K.3.9.1.4
26669 strncpy_s function, K.3.7.1.4 swscanf function, 7.28.2.4, 7.28.2.8
26670 strnlen_s function, K.3.7.4.4 swscanf_s function, K.3.9.1.5, K.3.9.1.10
26671 stronger, 6.2.8 symbols, 3
26672 strpbrk function, 7.23.5.4 synchronization operation, 5.1.2.4
26673 strrchr function, 7.23.5.5 synchronize with, 5.1.2.4
26674 strspn function, 7.23.5.6 syntactic categories, 6.1
26675 strstr function, 7.23.5.7 syntax notation, 6.1
26676 strtod function, 7.12.11.2, 7.21.6.2, 7.22.1.3, syntax rule precedence, 5.1.1.2
26677 7.28.2.2, F.3 syntax summary, language, A
26678 strtof function, 7.12.11.2, 7.22.1.3, F.3 system function, 7.22.4.8
26679 strtoimax function, 7.8.2.3
26680 strtok function, 7.23.5.8 tab characters, 5.2.1, 6.4
26681 strtok_s function, K.3.7.3.1 tag compatibility, 6.2.7
26682 strtol function, 7.8.2.3, 7.21.6.2, 7.22.1.2, tag name space, 6.2.3
26683 7.22.1.4, 7.28.2.2 tags, 6.7.2.3
26684 strtold function, 7.12.11.2, 7.22.1.3, F.3 tan functions, 7.12.4.7, F.10.1.7
26685 strtoll function, 7.8.2.3, 7.22.1.2, 7.22.1.4 tan type-generic macro, 7.24, G.7
26686 strtoul function, 7.8.2.3, 7.21.6.2, 7.22.1.2, tanh functions, 7.12.5.6, F.10.2.6
26690 tanh type-generic macro, 7.24, G.7 toupper function, 7.4.2.2
26691 temporary lifetime, 6.2.4 towctrans function, 7.29.3.2.1, 7.29.3.2.2
26692 tentative definition, 6.9.2 towlower function, 7.29.3.1.1, 7.29.3.2.1
26693 terms, 3 towupper function, 7.29.3.1.2, 7.29.3.2.1
26694 text streams, 7.21.2, 7.21.7.10, 7.21.9.2, 7.21.9.4 translation environment, 5, 5.1.1
26695 tgamma functions, 7.12.8.4, F.10.5.4 translation limits, 5.2.4.1
26696 tgamma type-generic macro, 7.24 translation phases, 5.1.1.2
26697 tgmath.h header, 7.24, G.7 translation unit, 5.1.1.1, 6.9
26698 thrd_create function, 7.25.1, 7.25.5.1 trap, see perform a trap
26699 thrd_current function, 7.25.5.2 trap representation, 3.19.4, 6.2.6.1, 6.2.6.2,
26700 thrd_detach function, 7.25.5.3 6.3.2.3, 6.5.2.3
26701 thrd_equal function, 7.25.5.4 trigonometric functions
26702 thrd_exit function, 7.25.5.5 complex, 7.3.5, G.6.1
26703 thrd_join function, 7.25.5.6 real, 7.12.4, F.10.1
26704 thrd_sleep function, 7.25.5.7 trigraph sequences, 5.1.1.2, 5.2.1.1
26705 thrd_start_t type, 7.25.1 true macro, 7.18
26706 thrd_t type, 7.25.1 trunc functions, 7.12.9.8, F.10.6.8
26707 thrd_yield function, 7.25.5.8 trunc type-generic macro, 7.24
26708 thread of execution, 5.1.2.4, 7.1.4, 7.6, 7.22.4.6 truncation, 6.3.1.4, 7.12.9.8, 7.21.3, 7.21.5.3
26709 thread storage duration, 6.2.4, 7.6 truncation toward zero, 6.5.5
26710 threads header, 7.25 tss_create function, 7.25.6.1
26711 threads.h header, 6.10.8.3, 7.1.2, 7.25 tss_delete function, 7.25.6.2
26712 time TSS_DTOR_ITERATIONS macro, 7.25.1
26713 broken down, 7.26.1, 7.26.2.3, 7.26.3, 7.26.3.1, tss_dtor_t type, 7.25.1
26714 7.26.3.3, 7.26.3.4, 7.26.3.5, K.3.8.2.1, tss_get function, 7.25.6.3
26715 K.3.8.2.3, K.3.8.2.4 tss_set function, 7.25.6.4
26716 calendar, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4, tss_t type, 7.25.1
26717 7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2, two's complement, 6.2.6.2, 7.20.1.1
26718 K.3.8.2.3, K.3.8.2.4 type category, 6.2.5
26719 components, 7.26.1, K.3.8.1 type conversion, 6.3
26720 conversion functions, 7.26.3, K.3.8.2 type definitions, 6.7.8
26721 wide character, 7.28.5 type domain, 6.2.5, G.2
26722 local, 7.26.1 type names, 6.7.7
26723 manipulation functions, 7.26.2 type punning, 6.5.2.3
26724 normalized broken down, K.3.8.1, K.3.8.2.1 type qualifiers, 6.7.3
26725 time function, 7.26.2.4 type specifiers, 6.7.2
26726 time.h header, 7.26, K.3.8 type-generic macro, 7.24, G.7
26727 time_t type, 7.26.1 typedef declaration, 6.7.8
26728 TIME_UTC macro, 7.25.7.1 typedef storage-class specifier, 6.7.1, 6.7.8
26729 tm structure type, 7.26.1, 7.28.1, K.3.8.1 types, 6.2.5
26730 TMP_MAX macro, 7.21.1, 7.21.4.3, 7.21.4.4 atomic, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, 6.5.2.3,
26731 TMP_MAX_S macro, K.3.5, K.3.5.1.1, K.3.5.1.2 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, 7.17.6
26732 tmpfile function, 7.21.4.3, 7.22.4.4 character, 6.7.9
26733 tmpfile_s function, K.3.5.1.1, K.3.5.1.2 compatible, 6.2.7, 6.7.2, 6.7.3, 6.7.6
26734 tmpnam function, 7.21.1, 7.21.4.3, 7.21.4.4, complex, 6.2.5, G
26735 K.3.5.1.2 composite, 6.2.7
26736 tmpnam_s function, K.3.5, K.3.5.1.1, K.3.5.1.2 const qualified, 6.7.3
26737 token, 5.1.1.2, 6.4, see also preprocessing tokens conversions, 6.3
26738 token concatenation, 6.10.3.3 imaginary, G
26739 token pasting, 6.10.3.3 restrict qualified, 6.7.3
26740 tolower function, 7.4.2.1 volatile qualified, 6.7.3
26744 uchar.h header, 6.4.4.4, 6.4.5, 7.27 universal character name, 6.4.3
26745 UCHAR_MAX macro, 5.2.4.2.1 unnormalized floating-point numbers, 5.2.4.2.2
26746 UINT_FASTN_MAX macros, 7.20.2.3 unqualified type, 6.2.5
26747 uint_fastN_t types, 7.20.1.3 unqualified version of type, 6.2.5
26748 uint_least16_t type, 7.27 unsequenced, 5.1.2.3, 6.5, 6.5.16, see also
26749 uint_least32_t type, 7.27 indeterminately sequenced, sequenced
26750 UINT_LEASTN_MAX macros, 7.20.2.2 before
26751 uint_leastN_t types, 7.20.1.2 unsigned char type, K.3.5.3.2, K.3.9.1.2
26752 UINT_MAX macro, 5.2.4.2.1 unsigned integer suffix, u or U, 6.4.4.1
26753 UINTMAX_C macro, 7.20.4.2 unsigned integer types, 6.2.5, 6.3.1.3, 6.4.4.1
26754 UINTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 unsigned type conversion, 6.3.1.1, 6.3.1.3,
26755 uintmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2, 6.3.1.4, 6.3.1.8
26756 7.28.2.1, 7.28.2.2 unsigned types, 6.2.5, 6.7.2, 7.21.6.1, 7.21.6.2,
26757 UINTN_C macros, 7.20.4.1 7.28.2.1, 7.28.2.2
26758 UINTN_MAX macros, 7.20.2.1 unspecified behavior, 3.4.4, 4, J.1
26759 uintN_t types, 7.20.1.1 unspecified value, 3.19.3
26760 UINTPTR_MAX macro, 7.20.2.4 uppercase letter, 5.2.1
26761 uintptr_t type, 7.20.1.4 use of library functions, 7.1.4
26762 ULLONG_MAX macro, 5.2.4.2.1, 7.22.1.4, USHRT_MAX macro, 5.2.4.2.1
26763 7.28.4.1.2 usual arithmetic conversions, 6.3.1.8, 6.5.5, 6.5.6,
26764 ULONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 6.5.8, 6.5.9, 6.5.10, 6.5.11, 6.5.12, 6.5.15
26765 7.28.4.1.2 UTF-16, 6.10.8.2
26766 unary arithmetic operators, 6.5.3.3 UTF-32, 6.10.8.2
26767 unary expression, 6.5.3 UTF-8 string literal, see string literal
26768 unary minus operator (-), 6.5.3.3, F.3 utilities, general, 7.22, K.3.6
26769 unary operators, 6.5.3 wide string, 7.28.4, K.3.9.2
26770 unary plus operator (+), 6.5.3.3
26771 unbuffered stream, 7.21.3 va_arg macro, 7.16, 7.16.1, 7.16.1.1, 7.16.1.2,
26772 undef preprocessing directive, 6.10.3.5, 7.1.3, 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10,
26773 7.1.4 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
26774 undefined behavior, 3.4.3, 4, J.2 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8,
26775 underscore character, 6.4.2.1 7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11,
26776 underscore, leading, in identifier, 7.1.3 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12
26777 ungetc function, 7.21.1, 7.21.7.10, 7.21.9.2, va_copy macro, 7.1.3, 7.16, 7.16.1, 7.16.1.1,
26778 7.21.9.3 7.16.1.2, 7.16.1.3
26779 ungetwc function, 7.21.1, 7.28.3.10 va_end macro, 7.1.3, 7.16, 7.16.1, 7.16.1.3,
26780 Unicode, 7.27, see also char16_t type, 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10,
26781 char32_t type, wchar_t type 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
26782 Unicode required set, 6.10.8.2 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8,
26783 union 7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11,
26784 arrow operator (->), 6.5.2.3 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12
26785 content, 6.7.2.3 va_list type, 7.16, 7.16.1.3
26786 dot operator (.), 6.5.2.3 va_start macro, 7.16, 7.16.1, 7.16.1.1,
26787 initialization, 6.7.9 7.16.1.2, 7.16.1.3, 7.16.1.4, 7.21.6.8,
26788 member alignment, 6.7.2.1 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12,
26789 member name space, 6.2.3 7.21.6.13, 7.21.6.14, 7.28.2.5, 7.28.2.6,
26790 member operator (.), 6.3.2.1, 6.5.2.3 7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10,
26791 pointer operator (->), 6.5.2.3 K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.7,
26792 specifier, 6.7.2.1 K.3.9.1.10, K.3.9.1.12
26793 tag, 6.2.3, 6.7.2.3 value, 3.19
26794 type, 6.2.5, 6.7.2.1 value bits, 6.2.6.2
26798 variable arguments, 6.10.3, 7.16 vswscanf function, 7.28.2.8
26799 variable arguments header, 7.16 vswscanf_s function, K.3.9.1.10
26800 variable length array, 6.7.6, 6.7.6.2, 6.10.8.3 vwprintf function, 7.21.1, 7.28.2.9, K.3.9.1.11
26801 variably modified type, 6.7.6, 6.7.6.2, 6.10.8.3 vwprintf_s function, K.3.9.1.11
26802 vertical-tab character, 5.2.1, 6.4 vwscanf function, 7.21.1, 7.28.2.10, 7.28.3.10
26803 vertical-tab escape sequence (\v), 5.2.2, 6.4.4.4, vwscanf_s function, K.3.9.1.12
26805 vfprintf function, 7.21.1, 7.21.6.8, K.3.5.3.8 warnings, I
26806 vfprintf_s function, K.3.5.3.8, K.3.5.3.9, wchar.h header, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12,
26807 K.3.5.3.11, K.3.5.3.14 F, K.3.9
26808 vfscanf function, 7.21.1, 7.21.6.8, 7.21.6.9 WCHAR_MAX macro, 7.20.3, 7.28.1
26809 vfscanf_s function, K.3.5.3.9, K.3.5.3.11, WCHAR_MIN macro, 7.20.3, 7.28.1
26810 K.3.5.3.14 wchar_t type, 3.7.3, 6.4.5, 6.7.9, 6.10.8.2, 7.19,
26811 vfwprintf function, 7.21.1, 7.28.2.5, K.3.9.1.6 7.20.3, 7.21.6.1, 7.21.6.2, 7.22, 7.28.1,
26812 vfwprintf_s function, K.3.9.1.6 7.28.2.1, 7.28.2.2
26813 vfwscanf function, 7.21.1, 7.28.2.6, 7.28.3.10 wcrtomb function, 7.21.3, 7.21.6.2, 7.28.2.2,
26814 vfwscanf_s function, K.3.9.1.7 7.28.6.3.3, 7.28.6.4.2, K.3.6.5.2, K.3.9.3.1,
26815 visibility of identifier, 6.2.1 K.3.9.3.2.2
26816 visible sequence of side effects, 5.1.2.4 wcrtomb_s function, K.3.9.3.1, K.3.9.3.1.1
26817 visible side effect, 5.1.2.4 wcscat function, 7.28.4.3.1
26818 VLA, see variable length array wcscat_s function, K.3.9.2.2.1
26819 void expression, 6.3.2.2 wcschr function, 7.28.4.5.1
26820 void function parameter, 6.7.6.3 wcscmp function, 7.28.4.4.1, 7.28.4.4.4
26821 void type, 6.2.5, 6.3.2.2, 6.7.2, K.3.5.3.2, wcscoll function, 7.28.4.4.2, 7.28.4.4.4
26822 K.3.9.1.2 wcscpy function, 7.28.4.2.1
26823 void type conversion, 6.3.2.2 wcscpy_s function, K.3.9.2.1.1
26824 volatile storage, 5.1.2.3 wcscspn function, 7.28.4.5.2
26825 volatile type qualifier, 6.7.3 wcsftime function, 7.11.1.1, 7.28.5.1
26826 volatile-qualified type, 6.2.5, 6.7.3 wcslen function, 7.28.4.6.1
26827 vprintf function, 7.21.1, 7.21.6.8, 7.21.6.10, wcsncat function, 7.28.4.3.2
26828 K.3.5.3.10 wcsncat_s function, K.3.9.2.2.2
26829 vprintf_s function, K.3.5.3.9, K.3.5.3.10, wcsncmp function, 7.28.4.4.3
26830 K.3.5.3.11, K.3.5.3.14 wcsncpy function, 7.28.4.2.2
26831 vscanf function, 7.21.1, 7.21.6.8, 7.21.6.11 wcsncpy_s function, K.3.9.2.1.2
26832 vscanf_s function, K.3.5.3.9, K.3.5.3.11, wcsnlen_s function, K.3.9.2.4.1
26833 K.3.5.3.14 wcspbrk function, 7.28.4.5.3
26834 vsnprintf function, 7.21.6.8, 7.21.6.12, wcsrchr function, 7.28.4.5.4
26835 K.3.5.3.12 wcsrtombs function, 7.28.6.4.2, K.3.9.3.2
26836 vsnprintf_s function, K.3.5.3.9, K.3.5.3.11, wcsrtombs_s function, K.3.9.3.2, K.3.9.3.2.2
26837 K.3.5.3.12, K.3.5.3.13, K.3.5.3.14 wcsspn function, 7.28.4.5.5
26838 vsnwprintf_s function, K.3.9.1.8, K.3.9.1.9 wcsstr function, 7.28.4.5.6
26839 vsprintf function, 7.21.6.8, 7.21.6.13, wcstod function, 7.21.6.2, 7.28.2.2
26840 K.3.5.3.13 wcstod function, 7.28.4.1.1
26841 vsprintf_s function, K.3.5.3.9, K.3.5.3.11, wcstof function, 7.28.4.1.1
26842 K.3.5.3.12, K.3.5.3.13, K.3.5.3.14 wcstoimax function, 7.8.2.4
26843 vsscanf function, 7.21.6.8, 7.21.6.14 wcstok function, 7.28.4.5.7
26844 vsscanf_s function, K.3.5.3.9, K.3.5.3.11, wcstok_s function, K.3.9.2.3.1
26845 K.3.5.3.14 wcstol function, 7.8.2.4, 7.21.6.2, 7.28.2.2,
26846 vswprintf function, 7.28.2.7, K.3.9.1.8, 7.28.4.1.2
26847 K.3.9.1.9 wcstold function, 7.28.4.1.1
26848 vswprintf_s function, K.3.9.1.8, K.3.9.1.9 wcstoll function, 7.8.2.4, 7.28.4.1.2
26852 wcstombs function, 7.22.8.2, 7.28.6.4 7.29.1
26853 wcstombs_s function, K.3.6.5.2 wmemchr function, 7.28.4.5.8
26854 wcstoul function, 7.8.2.4, 7.21.6.2, 7.28.2.2, wmemcmp function, 7.28.4.4.5
26855 7.28.4.1.2 wmemcpy function, 7.28.4.2.3
26856 wcstoull function, 7.8.2.4, 7.28.4.1.2 wmemcpy_s function, K.3.9.2.1.3
26857 wcstoumax function, 7.8.2.4 wmemmove function, 7.28.4.2.4
26858 wcsxfrm function, 7.28.4.4.4 wmemmove_s function, K.3.9.2.1.4
26859 wctob function, 7.28.6.1.2, 7.29.2.1 wmemset function, 7.28.4.6.2
26860 wctomb function, 7.22.7.3, 7.22.8.2, 7.28.6.3 wprintf function, 7.21.1, 7.28.2.9, 7.28.2.11,
26861 wctomb_s function, K.3.6.4.1 K.3.9.1.13
26862 wctrans function, 7.29.3.2.1, 7.29.3.2.2 wprintf_s function, K.3.9.1.13
26863 wctrans_t type, 7.29.1, 7.29.3.2.2 wscanf function, 7.21.1, 7.28.2.10, 7.28.2.12,
26864 wctype function, 7.29.2.2.1, 7.29.2.2.2 7.28.3.10
26865 wctype.h header, 7.29, 7.30.13 wscanf_s function, K.3.9.1.12, K.3.9.1.14
26866 wctype_t type, 7.29.1, 7.29.2.2.2
26867 weaker, 6.2.8 xor macro, 7.9
26868 WEOF macro, 7.28.1, 7.28.3.1, 7.28.3.3, 7.28.3.6, xor_eq macro, 7.9
26869 7.28.3.7, 7.28.3.8, 7.28.3.9, 7.28.3.10, xtime type, 7.25.1, 7.25.3.5, 7.25.4.4, 7.25.5.7,
26870 7.28.6.1.1, 7.29.1 7.25.7.1
26871 while statement, 6.8.5.1 xtime_get function, 7.25.7.1
26872 white space, 5.1.1.2, 6.4, 6.10, 7.4.1.10,
26874 white-space characters, 6.4
26875 wide character, 3.7.3
26876 case mapping functions, 7.29.3.1
26877 extensible, 7.29.3.2
26878 classification functions, 7.29.2.1
26879 extensible, 7.29.2.2
26881 formatted input/output functions, 7.28.2,
26883 input functions, 7.21.1
26884 input/output functions, 7.21.1, 7.28.3
26885 output functions, 7.21.1
26886 single-byte conversion functions, 7.28.6.1
26888 wide string comparison functions, 7.28.4.4
26889 wide string concatenation functions, 7.28.4.3,
26891 wide string copying functions, 7.28.4.2, K.3.9.2.1
26892 wide string literal, see string literal
26893 wide string miscellaneous functions, 7.28.4.6,
26895 wide string numeric conversion functions, 7.8.2.4,
26897 wide string search functions, 7.28.4.5, K.3.9.2.3
26898 wide-oriented stream, 7.21.2
26900 WINT_MAX macro, 7.20.3
26901 WINT_MIN macro, 7.20.3
26902 wint_t type, 7.20.3, 7.21.6.1, 7.28.1, 7.28.2.1,
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