Movatterモバイル変換

strtod(3) — Linux manual page

NAME \|LIBRARY \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|ATTRIBUTES \|VERSIONS \|STANDARDS \|HISTORY \|CAVEATS \|EXAMPLES \|SEE ALSO \|COLOPHON

strtod(3)                Library Functions Manualstrtod(3)

NAME top

       strtod, strtof, strtold - convert ASCII string to floating-point       number

LIBRARY top

       Standard C library (libc,-lc)

SYNOPSIS top

#include <stdlib.h>double strtod(const char *restrictnptr,char **_Nullable restrictendptr);float strtof(const char *restrictnptr,char **_Nullable restrictendptr);long double strtold(const char *restrictnptr,char **_Nullable restrictendptr);   Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):strtof(),strtold():           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION top

       Thestrtod(),strtof(), andstrtold() functions convert the       initial portion of the string pointed to bynptr todouble,float,       andlong double representation, respectively.       The expected form of the (initial portion of the) string is       optional leading white space as recognized byisspace(3), an       optional plus ('+') or minus sign ('-') and then either (i) a       decimal number, or (ii) a hexadecimal number, or (iii) an       infinity, or (iv) a NAN (not-a-number).       Adecimal number consists of a nonempty sequence of decimal digits       possibly containing a radix character (decimal point, locale-       dependent, usually '.'), optionally followed by a decimal       exponent.  A decimal exponent consists of an 'E' or 'e', followed       by an optional plus or minus sign, followed by a nonempty sequence       of decimal digits, and indicates multiplication by a power of 10.       Ahexadecimal number consists of a "0x" or "0X" followed by a       nonempty sequence of hexadecimal digits possibly containing a       radix character, optionally followed by a binary exponent.  A       binary exponent consists of a 'P' or 'p', followed by an optional       plus or minus sign, followed by a nonempty sequence of decimal       digits, and indicates multiplication by a power of 2.  At least       one of radix character and binary exponent must be present.       Aninfinity is either "INF" or "INFINITY", disregarding case.       ANAN is "NAN" (disregarding case) optionally followed by a       string,(n-char-sequence), wheren-char-sequence specifies in an       implementation-dependent way the type of NAN (see VERSIONS).

RETURN VALUE top

       These functions return the converted value, if any.       Ifendptr is not NULL, a pointer to the character after the last       character used in the conversion is stored in the location       referenced byendptr.       If no conversion is performed, zero is returned and (unlessendptr       is null) the value ofnptr is stored in the location referenced byendptr.       If the correct value would cause overflow, plus or minusHUGE_VAL,HUGE_VALF, orHUGE_VALLis returned (according to the return type       and sign of the value), andERANGEis stored inerrno.       If the correct value would cause underflow, a value with magnitude       no larger thanDBL_MIN,FLT_MIN, orLDBL_MINis returned andERANGEis stored inerrno.

ERRORS top

ERANGEOverflow or underflow occurred.

ATTRIBUTES top

       For an explanation of the terms used in this section, seeattributes(7).       ┌───────────────────────────────┬───────────────┬────────────────┐       │Interface│Attribute│Value│       ├───────────────────────────────┼───────────────┼────────────────┤       │strtod(),strtof(),strtold() │ Thread safety │ MT-Safe locale │       └───────────────────────────────┴───────────────┴────────────────┘

VERSIONS top

       In the glibc implementation, then-char-sequence that optionally       follows "NAN" is interpreted as an integer number (with an       optional '0' or '0x' prefix to select base 8 or 16) that is to be       placed in the mantissa component of the returned value.

STANDARDS top

       C11, POSIX.1-2008.

HISTORY top

strtod()              C89, POSIX.1-2001.strtof()strtold()              C99, POSIX.1-2001.

CAVEATS top

       Since 0 can legitimately be returned on both success and failure,       the calling program should seterrno to 0 before the call, and       then determine if an error occurred by checking whethererrno has       a nonzero value after the call.

EXAMPLES top

       See the example on thestrtol(3) manual page; the use of the       functions described in this manual page is similar.

COLOPHON top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17strtod(3)

Pages that refer to this page:gawk(1), pcpintro(1), pmstore(1), strace(1), atof(3), atoi(3), nan(3), sscanf(3), strfromd(3), strtol(3), strtoul(3), locale(7)