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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():
           _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 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).

       A decimal 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 mul-
       tiplication by a power of 10.

       A hexadecimal number consists of a "0x" or "0X" followed by a nonempty sequence of hexa-
       decimal 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 multiplica-
       tion 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 specifies 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 character 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 is stored in the
       location referenced by endptr.

       If the correct value would cause overflow, plus or minus HUGE_VAL (HUGE_VALF, HUGE_VALL)
       is returned (according to the sign of the value), and ERANGE is stored in errno.  If the
       correct value would cause underflow, zero is returned and ERANGE is stored in errno.

ERRORS
       ERANGE Overflow or underflow occurred.

CONFORMING TO
       C89 describes strtod(), C99 describes the other two functions.

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 determine if an error occurred by checking
       whether errno has a nonzero value after the call.

EXAMPLE
       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), strtol(3), strtoul(3)

COLOPHON
       This page is part of release 3.53 of the Linux man-pages project.  A description of the
       project, and information about reporting bugs, can be found at
       http://www.kernel.org/doc/man-pages/.



Linux                                       2010-09-20                                  STRTOD(3)

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