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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; 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, respec-
       tively.

       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 infin-
       ity, or (iv) a NAN (not-a-number).

       A decimal number consists of a non-empty sequence of decimal digits  possibly  con-
       taining  a  radix character (decimal point, locale-dependent, usually '.'), option-
       ally 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 non-empty sequence of
       decimal digits, and indicates multiplication by a power of 10.

       A hexadecimal number consists of a "0x" or "0X" followed by a non-empty 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 non-empty 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 char-
       acters, 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  pro-
       gram should set errno to 0 before the call, and then determine if an error occurred
       by checking whether errno has a non-zero 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 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2007-07-26                         STRTOD(3)

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