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 (seefeature_test_macros(7)): strtof(), strtold(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99 DESCRIPTION The strtod(), strtof(), and strtold() functions convert the initial portion of the string pointed to by nptr to double, float, and long 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). A decimal number consists of a nonempty sequence of decimal digits pos- sibly 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. A hexadecimal 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. An infinity is either "INF" or "INFINITY", disregarding case. A NAN is "NAN" (disregarding case) optionally followed by '(', a sequence of characters, followed by ')'. The character string speci- fies in an implementation-dependent way the type of NAN. RETURN VALUE These functions return the converted value, if any. If endptr is not NULL, a pointer to the character after the last char- acter used in the conversion is stored in the location referenced by endptr. If no conversion is performed, zero is returned and the value of nptr NOTES Since 0 can legitimately be returned on both success and failure, the calling program should set errno to 0 before the call, and then deter- mine if an error occurred by checking whether errno has a nonzero value after the call. EXAMPLE See the example on thestrtol(3)manual page; the use of the functions described in this manual page is similar. SEE ALSOatof(3),atoi(3),atol(3),strtol(3),strtoul(3)COLOPHON This page is part of release 3.35 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://man7.org/linux/man-pages/. Linux 2010-09-20STRTOD(3)