| Skip Navigation Links | |
| Exit Print View | |
 | man pages section 3: Basic Library Functions Oracle Solaris 11 Information Library |
| Skip Navigation Links | |
| Exit Print View | |
| man pages section 3: Basic Library Functions Oracle Solaris 11 Information Library |
enable_extended_FILE_stdio(3C)
posix_spawnattr_getschedparam(3C)
posix_spawnattr_getschedpolicy(3C)
posix_spawnattr_getsigdefault(3C)
posix_spawnattr_getsigignore_np(3C)
posix_spawnattr_getsigmask(3C)
posix_spawnattr_setschedparam(3C)
posix_spawnattr_setschedpolicy(3C)
posix_spawnattr_setsigdefault(3C)
posix_spawnattr_setsigignore_np(3C)
posix_spawnattr_setsigmask(3C)
posix_spawn_file_actions_addclose(3C)
posix_spawn_file_actions_addclosefrom_np(3C)
posix_spawn_file_actions_adddup2(3C)
posix_spawn_file_actions_addopen(3C)
posix_spawn_file_actions_destroy(3C)
posix_spawn_file_actions_init(3C)
pthread_attr_getdetachstate(3C)
pthread_attr_getinheritsched(3C)
pthread_attr_getschedparam(3C)
pthread_attr_getschedpolicy(3C)
pthread_attr_setdetachstate(3C)
pthread_attr_setinheritsched(3C)
pthread_attr_setschedparam(3C)
pthread_attr_setschedpolicy(3C)
pthread_barrierattr_destroy(3C)
pthread_barrierattr_getpshared(3C)
pthread_barrierattr_setpshared(3C)
pthread_condattr_getpshared(3C)
pthread_condattr_setpshared(3C)
pthread_cond_reltimedwait_np(3C)
pthread_key_create_once_np(3C)
pthread_mutexattr_getprioceiling(3C)
pthread_mutexattr_getprotocol(3C)
pthread_mutexattr_getpshared(3C)
pthread_mutexattr_getrobust(3C)
pthread_mutexattr_setprioceiling(3C)
pthread_mutexattr_setprotocol(3C)
pthread_mutexattr_setpshared(3C)
pthread_mutexattr_setrobust(3C)
pthread_mutex_getprioceiling(3C)
pthread_mutex_reltimedlock_np(3C)
pthread_mutex_setprioceiling(3C)
pthread_rwlockattr_destroy(3C)
pthread_rwlockattr_getpshared(3C)
pthread_rwlockattr_setpshared(3C)
pthread_rwlock_reltimedrdlock_np(3C)
pthread_rwlock_reltimedwrlock_np(3C)
pthread_rwlock_timedrdlock(3C)
pthread_rwlock_timedwrlock(3C)
rctlblk_get_enforced_value(3C)
- convert string to floating-point number
#include <stdlib.h>doublestrtod(const char *restrictnptr,char **restrictendptr);
floatstrtof(const char *restrictnptr,char **restrictendptr);
long doublestrtold(const char *restrictnptr,char **restrictendptr);
doubleatof(const char *str);
Thestrtod(),strtof(), andstrtold() functions convert the initial portion of thestring pointed to bynptr todouble,float, andlong double representation, respectively. Firstthey decompose the input string into three parts:
An initial, possibly empty, sequence of white-space characters (as specified byisspace(3C))
A subject sequence interpreted as a floating-point constant or representing infinity or NaN
A final string of one or more unrecognized characters, including the terminating null byte of the input string.
Then they attempt to convert the subject sequence to a floating-point number,and return the result.
The expected form of the subject sequence is an optional plus orminus sign, then one of the following:
A non-empty sequence of digits optionally containing a radix character, then an optional exponent part
A 0x or 0X, then a non-empty sequence of hexadecimal digits optionally containing a radix character, then an optional binary exponent part
One of INF or INFINITY, ignoring case
One of NAN or NAN(n-char-sequenceopt), ignoring case in the NAN part, where:
n-char-sequence: digit nondigit n-char-sequence digit n-char-sequence nondigit
In default mode forstrtod(), only decimal, INF/INFINITY, and NAN/NAN(n-char-sequence) forms arerecognized. In C99/SUSv3 mode, hexadecimal strings are also recognized.
In default mode forstrtod(), then-char-sequence in the NAN(n-char-equence) form cancontain any character except ')' (right parenthesis) or '\0' (null). InC99/SUSv3 mode, then-char-sequence can contain only upper and lower case letters, digits,and '_' (underscore).
Thestrtof() andstrtold() functions always function in C99/SUSv3-conformant mode.
The subject sequence is defined as the longest initial subsequence of theinput string, starting with the first non-white-space character, that is of theexpected form. The subject sequence contains no characters if the input stringis not of the expected form.
If the subject sequence has the expected form for a floating-point number,the sequence of characters starting with the first digit or the decimal-pointcharacter (whichever occurs first) is interpreted as a floating constant of theC language, except that the radix character is used in place of aperiod, and that if neither an exponent part nor a radix characterappears in a decimal floating-point number, or if a binary exponent partdoes not appear in a hexadecimal floating-point number, an exponent part ofthe appropriate type with value zero is assumed to follow the lastdigit in the string. If the subject sequence begins with a minus sign,the sequence is interpreted as negated. A character sequence INF or INFINITYis interpreted as an infinity. A character sequence NAN or NAN(n-char-sequenceopt) isinterpreted as a quiet NaN. A pointer to the final string is storedin the object pointed to byendptr, provided thatendptr is nota null pointer.
If the subject sequence has either the decimal or hexadecimal form, thevalue resulting from the conversion is rounded correctly according to the prevailingfloating point rounding direction mode. The conversion also raises floating point inexact,underflow, or overflow exceptions as appropriate.
The radix character is defined in the program's locale (categoryLC_NUMERIC). Inthe POSIX locale, or in a locale where the radix character isnot defined, the radix character defaults to a period ('.').
If the subject sequence is empty or does not have the expectedform, no conversion is performed; the value ofnptr is stored inthe object pointed to byendptr, provided thatendptr is not anull pointer.
Thestrtod() function does not change the setting oferrno if successful.
Theatof(str) function call is equivalent tostrtod(nptr, (char **)NULL).
Upon successful completion, these functions return the converted value. If no conversioncould be performed,0 is returned.
If the correct value is outside the range of representable values,±HUGE_VAL,±HUGE_VALF, or±HUGE_VALL is returned (according to the sign of the value),a floating point overflow exception is raised, anderrno is set toERANGE.
If the correct value would cause an underflow, the correctly rounded result(which may be normal, subnormal, or zero) is returned, a floating pointunderflow exception is raised, anderrno is set toERANGE.
These functions will fail if:
The value to be returned would cause overflow or underflow
These functions may fail if:
No conversion could be performed.
Since 0 is returned on error and is also a valid returnon success, an application wishing to check for error situations should seterrno to 0, then callstrtod(),strtof(), orstrtold(), then checkerrno.
The changes tostrtod() introduced by the ISO/IEC 9899: 1999 standard canalter the behavior of well-formed applications complying with the ISO/IEC 9899: 1990standard and thus earlier versions of IEEE Std 1003.1-200x. One such examplewould be:
intwhat_kind_of_number (char *s){ char *endp; double d; long l; d = strtod(s, &endp); if (s != endp && *endp == `\\0') printf("It's a float with value %g\n", d); else { l = strtol(s, &endp, 0); if (s != endp && *endp == `\0') printf("It's an integer with value %ld\n", 1); else return 1; } return 0;}If the function is called with:
what_kind_of_number ("0x10")an ISO/IEC 9899: 1990 standard-compliant library will result in the function printing:
It's an integer with value 16
With the ISO/IEC 9899: 1999 standard, the result is:
It's a float with value 16
The change in behavior is due to the inclusion of floating-point numbersin hexadecimal notation without requiring that either a decimal point or thebinary exponent be present.
Seeattributes(5) for descriptions of the following attributes:
|
isspace(3C),localeconv(3C),scanf(3C),setlocale(3C),strtol(3C),attributes(5),standards(5)
Thestrtod() andatof() functions can be used safely in multithreaded applications,as long assetlocale(3C) is not called to change the locale.
The DESCRIPTION and RETURN VALUES sections above are very similar to thewording used by the Single UNIX Specification version 2 (SUSv2) and the1989 C Standard to describe the behavior of thestrtod() function. Since some users have reported that they find the description confusing, the followingnotes might be helpful.
Thestrtod() function does not modify the string pointed to bystr and does notmalloc() space to hold the decomposed portions of the input string.
Ifendptr is not(char **)NULL,strtod() will set the pointer pointed to byendptr to the first byte of the “final string of unrecognized characters”. (If all input characters were processed, the pointer pointed to byendptr will be set to point to the null character at the end of the input string.)
Ifstrtod() returns 0.0, one of the following occurred:
The “subject sequence” was not an empty string, but evaluated to 0.0. (In this case,errno will be left unchanged.)
The “subject sequence” was an empty string . In this case,errno will be left unchanged. (The Single UNIX Specification version 2 allowserrno to be set toEINVAL or to be left unchanged. The C Standard does not specify any specific behavior in this case.)
The “subject sequence” specified a numeric value whose conversion resulted in a floating point underflow. In this case, an underflow exception is raised anderrno is set toERANGE.
Note that the standards do not require that implementations distinguish between these three cases. An application can determine case (b) by making sure that there are no leading white-space characters in the string pointed to bystr and givingstrtod() anendptr that is not(char **)NULL. Ifendptr points to the first character ofstr whenstrtod() returns, you have detected case (b). Case (c) can be detected by examining the underflow flag or by looking for a non-zero digit before the exponent part of the “subject sequence”. Note, however, that the decimal-point character is locale-dependent.
Ifstrtod() returns+HUGE_VAL or-HUGE_VAL, one of the following occurred:
If+HUGE_VAL is returned anderrno is set toERANGE, a floating point overflow occurred while processing a positive value, causing a floating point overflow exception to be raised.
If-HUGE_VAL is returned anderrno is set toERANGE, a floating point overflow occurred while processing a negative value, causing a floating point overflow exception to be raised.
Ifstrtod() does not seterrno toERANGE, the value specified by the “subject string” converted to+HUGE_VAL or-HUGE_VAL, respectively.
Note that iferrno is set toERANGE whenstrtod() is called, case (c) can be distinguished from cases (a) and (b) by examining eitherERANGE or the overflow flag.
Copyright © 2011, Oracle and/or its affiliates. All rights reserved.Legal Notices |   |