11620 strtod man page typo equence
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All Rights Reserved. 45 .\" Portions Copyright (c) 2006, Sun Microsystems, Inc. All Rights Reserved. 46 .\" 47 .TH STRTOD 3C "Nov 1, 2003" 48 .SH NAME 49 strtod, strtof, strtold, atof \- convert string to floating-point number 50 .SH SYNOPSIS 51 .LP 52 .nf 53 #include <stdlib.h> 54 55 \fBdouble\fR \fBstrtod\fR(\fBconst char *restrict\fR \fInptr\fR, \fBchar **restrict\fR \fIendptr\fR); 56 .fi 57 58 .LP 59 .nf 60 \fBfloat\fR \fBstrtof\fR(\fBconst char *restrict\fR \fInptr\fR, \fBchar **restrict\fR \fIendptr\fR); 61 .fi 62 63 .LP 64 .nf 65 \fBlong double\fR \fBstrtold\fR(\fBconst char *restrict\fR \fInptr\fR, \fBchar **restrict\fR \fIendptr\fR); 66 .fi 67 68 .LP 69 .nf 70 \fBdouble\fR \fBatof\fR(\fBconst char *\fR\fIstr\fR); 71 .fi 72 73 .SH DESCRIPTION 74 .sp 75 .LP 76 The \fBstrtod()\fR, \fBstrtof()\fR, and \fBstrtold()\fR functions convert the 77 initial portion of the string pointed to by \fInptr\fR to \fBdouble\fR, 78 \fBfloat\fR, and \fBlong double\fR representation, respectively. First they 79 decompose the input string into three parts: 80 .RS +4 81 .TP 82 1. 83 An initial, possibly empty, sequence of white-space characters (as specified 84 by \fBisspace\fR(3C)) 85 .RE 86 .RS +4 87 .TP 88 2. 89 A subject sequence interpreted as a floating-point constant or representing 90 infinity or NaN 91 .RE 92 .RS +4 93 .TP 94 3. 95 A final string of one or more unrecognized characters, including the 96 terminating null byte of the input string. 97 .RE 98 .sp 99 .LP 100 Then they attempt to convert the subject sequence to a floating-point number, 101 and return the result. 102 .sp 103 .LP 104 The expected form of the subject sequence is an optional plus or minus sign, 105 then one of the following: 106 .RS +4 107 .TP 108 .ie t \(bu 109 .el o 110 A non-empty sequence of digits optionally containing a radix character, then an 111 optional exponent part 112 .RE 113 .RS +4 114 .TP 115 .ie t \(bu 116 .el o 117 A 0x or 0X, then a non-empty sequence of hexadecimal digits optionally 118 containing a radix character, then an optional binary exponent part 119 .RE 120 .RS +4 121 .TP 122 .ie t \(bu 123 .el o 124 One of INF or INFINITY, ignoring case 125 .RE 126 .RS +4 127 .TP 128 .ie t \(bu 129 .el o 130 One of NAN or NAN(\fIn-char-sequence\fR(\fIopt\fR)), ignoring case in the NAN 131 part, where: 132 .sp 133 .in +2 134 .nf 135 n-char-sequence: 136 digit 137 nondigit 138 n-char-sequence digit 139 n-char-sequence nondigit 140 .fi 141 .in -2 142 143 .RE 144 .sp 145 .LP 146 In default mode for \fBstrtod()\fR, only decimal, INF/INFINITY, and 147 NAN/NAN(\fIn-char-sequence\fR) forms are recognized. In C99/SUSv3 mode, 148 hexadecimal strings are also recognized. 149 .sp 150 .LP 151 In default mode for \fBstrtod()\fR, the \fIn-char-sequence\fR in the 152 NAN(\fIn-char-equence\fR) form can contain any character except ')' (right 153 parenthesis) or '\e0' (null). In C99/SUSv3 mode, the \fIn-char-sequence\fR can 154 contain only upper and lower case letters, digits, and '_' (underscore). 155 .sp 156 .LP 157 The \fBstrtof()\fR and \fBstrtold()\fR functions always function in 158 C99/SUSv3-conformant mode. 159 .sp 160 .LP 161 The subject sequence is defined as the longest initial subsequence of the input 162 string, starting with the first non-white-space character, that is of the 163 expected form. The subject sequence contains no characters if the input string 164 is not of the expected form. 165 .sp 166 .LP 167 If the subject sequence has the expected form for a floating-point number, the 168 sequence of characters starting with the first digit or the decimal-point 169 character (whichever occurs first) is interpreted as a floating constant of the 170 C language, except that the radix character is used in place of a period, and 171 that if neither an exponent part nor a radix character appears in a decimal 172 floating-point number, or if a binary exponent part does not appear in a 173 hexadecimal floating-point number, an exponent part of the appropriate type 174 with value zero is assumed to follow the last digit in the string. If the 175 subject sequence begins with a minus sign, the sequence is interpreted as 176 negated. A character sequence INF or INFINITY is interpreted as an infinity. A 177 character sequence NAN or NAN(\fIn-char-sequence\fR(\fIopt\fR)) is interpreted 178 as a quiet NaN. A pointer to the final string is stored in the object pointed 179 to by \fIendptr\fR, provided that \fIendptr\fR is not a null pointer. 180 .sp 181 .LP 182 If the subject sequence has either the decimal or hexadecimal form, the value 183 resulting from the conversion is rounded correctly according to the prevailing 184 floating point rounding direction mode. The conversion also raises floating 185 point inexact, underflow, or overflow exceptions as appropriate. 186 .sp 187 .LP 188 The radix character is defined in the program's locale (category 189 \fBLC_NUMERIC\fR). In the POSIX locale, or in a locale where the radix 190 character is not defined, the radix character defaults to a period ('.'). 191 .sp 192 .LP 193 If the subject sequence is empty or does not have the expected form, no 194 conversion is performed; the value of \fInptr\fR is stored in the object 195 pointed to by \fIendptr\fR, provided that \fIendptr\fR is not a null pointer. 196 .sp 197 .LP 198 The \fBstrtod()\fR function does not change the setting of \fBerrno\fR if 199 successful. 200 .sp 201 .LP 202 The \fBatof(\fR\fIstr\fR\fB)\fR function call is equivalent to 203 \fBstrtod(\fR\fInptr\fR\fB, (char **)NULL)\fR. 204 .SH RETURN VALUES 205 .sp 206 .LP 207 Upon successful completion, these functions return the converted value. If no 208 conversion could be performed, \fB0\fR is returned. 209 .sp 210 .LP 211 If the correct value is outside the range of representable values, 212 \fB\(+-HUGE_VAL\fR, \fB\(+-HUGE_VALF\fR, or \fB\(+-HUGE_VALL\fR is returned 213 (according to the sign of the value), a floating point overflow exception is 214 raised, and \fBerrno\fR is set to \fBERANGE\fR. 215 .sp 216 .LP 217 If the correct value would cause an underflow, the correctly rounded result 218 (which may be normal, subnormal, or zero) is returned, a floating point 219 underflow exception is raised, and \fBerrno\fR is set to \fBERANGE\fR. 220 .SH ERRORS 221 .sp 222 .LP 223 These functions will fail if: 224 .sp 225 .ne 2 226 .na 227 \fB\fBERANGE\fR\fR 228 .ad 229 .RS 10n 230 The value to be returned would cause overflow or underflow 231 .RE 232 233 .sp 234 .LP 235 These functions may fail if: 236 .sp 237 .ne 2 238 .na 239 \fB\fBEINVAL\fR\fR 240 .ad 241 .RS 10n 242 No conversion could be performed. 243 .RE 244 245 .SH USAGE 246 .sp 247 .LP 248 Since 0 is returned on error and is also a valid return on success, an 249 application wishing to check for error situations should set \fBerrno\fR to 0, 250 then call \fBstrtod()\fR, \fBstrtof()\fR, or \fBstrtold()\fR, then check 251 \fBerrno\fR. 252 .sp 253 .LP 254 The changes to \fBstrtod()\fR introduced by the ISO/IEC 9899: 1999 standard can 255 alter the behavior of well-formed applications complying with the ISO/IEC 9899: 256 1990 standard and thus earlier versions of IEEE Std 1003.1-200x. One such 257 example would be: 258 .sp 259 .in +2 260 .nf 261 int 262 what_kind_of_number (char *s) 263 { 264 char *endp; 265 double d; 266 long l; 267 d = strtod(s, &endp); 268 if (s != endp && *endp == '\e0') 269 printf("It's a float with value %g\en", d); 270 else 271 { 272 l = strtol(s, &endp, 0); 273 if (s != endp && *endp == '\e0') 274 printf("It's an integer with value %ld\en", 1); 275 else 276 return 1; 277 } 278 return 0; 279 } 280 .fi 281 .in -2 282 283 .sp 284 .LP 285 If the function is called with: 286 .sp 287 .in +2 288 .nf 289 what_kind_of_number ("0x10") 290 .fi 291 .in -2 292 293 .sp 294 .LP 295 an ISO/IEC 9899: 1990 standard-compliant library will result in the function 296 printing: 297 .sp 298 .in +2 299 .nf 300 It's an integer with value 16 301 .fi 302 .in -2 303 304 .sp 305 .LP 306 With the ISO/IEC 9899: 1999 standard, the result is: 307 .sp 308 .in +2 309 .nf 310 It's a float with value 16 311 .fi 312 .in -2 313 314 .sp 315 .LP 316 The change in behavior is due to the inclusion of floating-point numbers in 317 hexadecimal notation without requiring that either a decimal point or the 318 binary exponent be present. 319 .SH ATTRIBUTES 320 .sp 321 .LP 322 See \fBattributes\fR(5) for descriptions of the following attributes: 323 .sp 324 325 .sp 326 .TS 327 box; 328 c | c 329 l | l . 330 ATTRIBUTE TYPE ATTRIBUTE VALUE 331 _ 332 CSI Enabled 333 _ 334 Interface Stability Standard 335 _ 336 MT-Level MT-Safe with exceptions 337 .TE 338 339 .SH SEE ALSO 340 .sp 341 .LP 342 \fBisspace\fR(3C), \fBlocaleconv\fR(3C), \fBscanf\fR(3C), \fBsetlocale\fR(3C), 343 \fBstrtol\fR(3C), \fBattributes\fR(5), \fBstandards\fR(5) 344 .SH NOTES 345 .sp 346 .LP 347 The \fBstrtod()\fR and \fBatof()\fR functions can be used safely in 348 multithreaded applications, as long as \fBsetlocale\fR(3C) is not called to 349 change the locale. 350 .sp 351 .LP 352 The DESCRIPTION and RETURN VALUES sections above are very similar to the 353 wording used by the Single UNIX Specification version 2 (SUSv2) and the 1989 C 354 Standard to describe the behavior of the \fBstrtod()\fR function. Since some 355 users have reported that they find the description confusing, the following 356 notes might be helpful. 357 .RS +4 358 .TP 359 1. 360 The \fBstrtod()\fR function does not modify the string pointed to by 361 \fIstr\fR and does not \fBmalloc()\fR space to hold the decomposed portions of 362 the input string. 363 .RE 364 .RS +4 365 .TP 366 2. 367 If \fIendptr\fR is not \fB(char **)NULL\fR, \fBstrtod()\fR will set the 368 pointer pointed to by \fIendptr\fR to the first byte of the "final string of 369 unrecognized characters". (If all input characters were processed, the pointer 370 pointed to by \fIendptr\fR will be set to point to the null character at the 371 end of the input string.) 372 .RE 373 .RS +4 374 .TP 375 3. 376 If \fBstrtod()\fR returns 0.0, one of the following occurred: 377 .RS +4 378 .TP 379 a. 380 The "subject sequence" was not an empty string, but evaluated to 0.0. (In 381 this case, \fBerrno\fR will be left unchanged.) 382 .RE 383 .RS +4 384 .TP 385 b. 386 The "subject sequence" was an empty string . In this case, \fBerrno\fR will 387 be left unchanged. (The Single UNIX Specification version 2 allows \fBerrno\fR 388 to be set to \fBEINVAL\fR or to be left unchanged. The C Standard does not 389 specify any specific behavior in this case.) 390 .RE 391 .RS +4 392 .TP 393 c. 394 The "subject sequence" specified a numeric value whose conversion resulted 395 in a floating point underflow. In this case, an underflow exception is raised 396 and \fBerrno\fR is set to \fBERANGE\fR. 397 .RE 398 Note that the standards do not require that implementations distinguish between 399 these three cases. An application can determine case (b) by making sure that 400 there are no leading white-space characters in the string pointed to by 401 \fIstr\fR and giving \fBstrtod()\fR an \fIendptr\fR that is not \fB(char 402 **)NULL\fR. If \fIendptr\fR points to the first character of \fIstr\fR when 403 \fBstrtod()\fR returns, you have detected case (b). Case (c) can be detected 404 by examining the underflow flag or by looking for a non-zero digit before the 405 exponent part of the "subject sequence". Note, however, that the decimal-point 406 character is locale-dependent. 407 .RE 408 .RS +4 409 .TP 410 4. 411 If \fBstrtod()\fR returns \fB+HUGE_VAL\fR or \fB\(miHUGE_VAL\fR, one of the 412 following occurred: 413 .RS +4 414 .TP 415 a. 416 If \fB+HUGE_VAL\fR is returned and \fBerrno\fR is set to \fBERANGE\fR, a 417 floating point overflow occurred while processing a positive value, causing a 418 floating point overflow exception to be raised. 419 .RE 420 .RS +4 421 .TP 422 b. 423 If \fB\(miHUGE_VAL\fR is returned and \fBerrno\fR is set to \fBERANGE\fR, a 424 floating point overflow occurred while processing a negative value, causing a 425 floating point overflow exception to be raised. 426 .RE 427 .RS +4 428 .TP 429 c. 430 If \fBstrtod()\fR does not set \fBerrno\fR to \fBERANGE\fR, the value 431 specified by the "subject string" converted to \fB+HUGE_VAL\fR or 432 \fB\(miHUGE_VAL\fR, respectively. 433 .RE 434 Note that if \fBerrno\fR is set to \fBERANGE\fR when \fBstrtod()\fR is called, 435 case (c) can be distinguished from cases (a) and (b) by examining either 436 \fBERANGE\fR or the overflow flag. 437 .RE --- EOF ---