STRTOD(3) Linux Programmer's Manual STRTOD(3) NAME strtod, strtof, strtold - convert ASCII string to floating-point number SYNOPSIS#include <stdlib.h>double strtod(const char *nptr, char **endptr);float strtof(const char *nptr, char **endptr);long double strtold(const char *nptr, char **endptr);Feature Test Macro Requirements for glibc (see feature_test_macros(7)):strtof(),strtold(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L DESCRIPTION Thestrtod(),strtof(), andstrtold() functions convert the initial portion of the string pointed to bynptrtodouble,float, andlongdoublerepresentation, respectively. The expected form of the (initial portion of the) string is optional leading white space as recognized by isspace(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 numberconsists 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 numberconsists 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. Aninfinityis either "INF" or "INFINITY", disregarding case. ANANis "NAN" (disregarding case) optionally followed by a string,(n-char-sequence), wheren-char-sequencespecifies in an implementation- dependent way the type of NAN (see NOTES). RETURN VALUE These functions return the converted value, if any. Ifendptris 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 (unlessendptris null) the value ofnptris 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. ERRORSERANGEOverflow or underflow occurred. ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ┌──────────────────────────────┬───────────────┬────────────────┐ │Interface│Attribute│Value│ ├──────────────────────────────┼───────────────┼────────────────┤ │strtod(),strtof(),strtold() │ Thread safety │ MT-Safe locale │ └──────────────────────────────┴───────────────┴────────────────┘ CONFORMING TO POSIX.1-2001, POSIX.1-2008, C99.strtod() was also described in C89. NOTES Since 0 can legitimately be returned on both success and failure, the calling program should seterrnoto 0 before the call, and then determine if an error occurred by checking whethererrnohas a nonzero value after the call. In the glibc implementation, then-char-sequencethat 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. EXAMPLES See the example on the strtol(3) manual page; the use of the functions described in this manual page is similar. SEE ALSO atof(3), atoi(3), atol(3), nan(3), nanf(3), nanl(3), strfromd(3), strtol(3), strtoul(3) COLOPHON This page is part of release 5.09 of the Linuxman-pagesproject. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2020-11-01 STRTOD(3)