strtod, wcstod

Convert strings to a double-precision value.

double strtod( const char *nptr, char **endptr );

double wcstod( const wchar_t *nptr, wchar_t **endptr );

Each of these functions converts the input string nptr to a double.

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

strtod returns the value of the floating-point number, except when the representation would cause an overflow, in which case the function returns +/–HUGE_VAL. The sign of HUGE_VAL matches the sign of the value that cannot be represented. strtod returns 0 if no conversion can be performed or an underflow occurs.

wcstod returns values analogously to strtod. For both functions, errno is set to ERANGE if overflow or underflow occurs.

Parameters

nptr

Null-terminated string to convert

endptr

Pointer to character that stops scan

Remarks

The strtod function converts nptr to a double-precision value. strtod stops reading the string nptr at the first character it cannot recognize as part of a number. This may be the terminating null character. wcstod is a wide-character version of strtod; its nptr argument is a wide-character string. Otherwise these functions behave identically.

Generic-Text Routine Mappings

The LC_NUMERIC category setting of the current locale determines recognition of the radix character in nptr; for more information, see setlocale. If endptr is not NULL, a pointer to the character that stopped the scan is stored at the location pointed to by endptr. If no conversion can be performed (no valid digits were found or an invalid base was specified), the value of nptr is stored at the location pointed to by endptr.

strtod expects nptr to point to a string of the following form:

[whitespace] [sign] [digits] [.digits] [ {d | D | e | E}[sign]digits]

A whitespace may consist of space and tab characters, which are ignored; sign is either plus (+) or minus (–); and digits are one or more decimal digits. If no digits appear before the radix character, at least one must appear after the radix character. The decimal digits can be followed by an exponent, which consists of an introductory letter (d, D, e, or E) and an optionally signed integer. If neither an exponent part nor a radix character appears, a radix character is assumed to follow the last digit in the string. The first character that does not fit this form stops the scan.

Example

/* STRTOD.C: This program uses strtod to convert a
 * string to a double-precision value; strtol to
 * convert a string to long integer values; and strtoul
 * to convert a string to unsigned long-integer values.
 */

#include <stdlib.h>
#include <stdio.h>

void main( void )
{
   char   *string, *stopstring;
   double x;
   long   l;
   int    base;
   unsigned long ul;
   string = "3.1415926This stopped it";
   x = strtod( string, &stopstring );
   printf( "string = %s\n", string );
   printf("   strtod = %f\n", x );
   printf("   Stopped scan at: %s\n\n", stopstring );
   string = "-10110134932This stopped it";
   l = strtol( string, &stopstring, 10 );
   printf( "string = %s", string );
   printf("   strtol = %ld", l );
   printf("   Stopped scan at: %s", stopstring );
   string = "10110134932";
   printf( "string = %s\n", string );
   /* Convert string using base 2, 4, and 8: */
   for( base = 2; base <= 8; base *= 2 )
   {
      /* Convert the string: */
      ul = strtoul( string, &stopstring, base );
      printf( "   strtol = %ld (base %d)\n", ul, base );
      printf( "   Stopped scan at: %s\n", stopstring );
   }
}

Output

string = 3.1415926This stopped it
   strtod = 3.141593
   Stopped scan at: This stopped it

string = -10110134932This stopped it   strtol = -2147483647   Stopped scan at: This stopped itstring = 10110134932
   strtol = 45 (base 2)
   Stopped scan at: 34932
   strtol = 4423 (base 4)
   Stopped scan at: 4932
   strtol = 2134108 (base 8)
   Stopped scan at: 932

Data Conversion Routines |  Floating-Point Support Routines |  Locale Routines |  strtod Functions Overview

See Also   strtol, strtoul, atof, localeconv, setlocale