strtod, strtof, strtold

strtod, strtof, strtold

Convert a String to Double

Portability: ISO/ANSI C conforming, UNIX compatible

SYNOPSIS
DESCRIPTION
RETURN VALUE
DIAGNOSTICS
EXAMPLE
RELATED FUNCTIONS
SEE ALSO

SYNOPSIS

#include <stdlib.h>
double strtod(const char *str, char **end);
float strtof(const char *str, char **end);
long double strtold(const char *str, char **end);

DESCRIPTION

strtod, strtof, and strtold, expect a floating-point number in C syntax, with these specifications:

a decimal point may be omitted
a + or - sign may precede the number
no type suffix (F or L) is allowed
can include one of the character sequences INF or INFINITY, ignoring case
can include one of the character sequences NAN or NAN(character sequence), ignoring case in the NAN part. See the nan function description for information about character sequence.

If the end value is not NULL, *end is modified to address the first character of the string that is not consistent with the floating-point syntax above. However, if no initial segment of the string can be interpreted as a floating-point number, str is assigned to *end.

RETURN VALUE

strtod, strtof, and strtold functions return the floating-point value (double, float, and long double) represented by the character string up to the first unrecognized character. If no initial segment of the string can be interpreted as a floating-point number, 0.0 is returned.

DIAGNOSTICS

If the floating-point value is outside the range of valid floating-point numbers, errno is set to ERANGE. In this case, ±HUGE_VAL (defined in <math.h>) is returned if the correct value is too large, or 0.0 if the correct value is too close to 0.

EXAMPLE

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

main()
{
   double number;
   char *input, *stopchar;
   char string[20];

   puts("Enter a string to be converted to double:");
   input = gets(string);

      /* Skip space characters.            */
   while(isspace(*input)) ++input;

      /* Convert from character to double. */
   number = strtod(input, &stopchar);
      /* Determine if string is valid.     */
   if (stopchar == input)
      printf("Invalid float number: %s\n", input);

      /* Check for characters afterwards.  */
   else if (*stopchar && !isspace(*stopchar))

   printf("Extra characters after value ignored: %s\n", stopchar);
   printf("The entered string was converted to: %g\n", number);
}

RELATED FUNCTIONS

nan, strtol

SEE ALSO

"String Utility Functions" in Chapter 2, "Function Categories."

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