### atof -- Convert Character String to Float

Format

>     #include <stdlib.h>
>     double atof(const char *string);

Language Level: ANSI, POSIX, XPG4, Extension
atof converts a character string to a double-precision floating-point value.

The input string is a sequence of characters that can be interpreted as a numerical value of the specified return type. The function stops reading the input string at the first character that it cannot recognize as part of a number; this character can be the null character that ends the string.

atof expects a string in the following form:

The white space consists of the same characters for which the isspace function is true, such as spaces and tabs. atof ignores leading white-space characters.

For atof, digits is one or more decimal digits; if no digits appear before the decimal point, at least one digit must appear after the decimal point. The decimal digits can precede an exponent, introduced by the letter e or E. The exponent is a decimal integer, which may be signed.

atof will not fail if a character other than a digit follows an E or if e is read in as an exponent. For example, 100elf will be converted to the floating-point value 100.0. The accuracy is up to 17 significant character digits.

The string, on OS/2, can also be "infinity", "inf", or "nan" . These strings are case insensitive, and can be preceded by a unary minus (-). They are converted to infinity and NaN values.

Return Value
atof returns a double value produced by interpreting the input characters as a number. The return value is 0 if the function cannot convert the input to a value of that type. The return value is undefined in case of overflow.

Example
This example shows how to convert numbers stored as strings to numerical values using the atof function.

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

    int main(void)
    {
       double x;
       char *s;

       s = " -2309.12E-15";
       x = atof(s);                             /* x = -2309.12E-15 */
       printf("atof( %s ) = %G\n", s, x);
       return 0;

       /**************************************************************
          The output should be:

          atof(  -2309.12E-15 ) = -2.30912E-12
       **************************************************************/
    }

atoi -- Convert Character String to Integer
atol -- Convert Character String to Long Integer
_atold -- Convert Character String to Long Double
strtod -- Convert Character String to Double
strtol -- Convert Character String to Long Integer
strtold -- Convert String to Long Do uble
<stdlib.h>