SAS/C Library Reference, Vol. 1

strtod -- Convert a String to Double

SYNOPSIS

 #include <stdlib.h>

 double strtod(const char *str, char **end);

DESCRIPTION

strtod expects 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.

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 returns the double value 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 370 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: %sn", input);

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

     printf("Extra characters after value ignored: %sn", stopchar);
     printf("The entered string was converted to: %gn", number);
  }

RELATED FUNCTIONS

strtol