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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 <&lt;stdlib.h>&gt;

       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, 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 non-empty 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 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  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
       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 deter-
       mine 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 3.05 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                             2007-07-26                         STRTOD(3)