C Reference function atof() convert a string to a double

This function of stdlib will convert a string to a double.

Usage of atof():

double atof ( const char * str );


C string str interpreting its content as a floating point number. White-spaces are discarded until the first non-whitespace character is found. A valid floating point number for atof is formed by: plus or minus sign, sequence of digits, decimal point and optional exponent part (character ‘e’ or ‘E’)

Return value:

The function returns the converted floating point number as a double value, if successful.
If no valid conversion could be performed then an zero value is returned.

Source code example of atof():


	int main ()
		double a,b;
		char buffer [256];
		printf ( "Input: " );
		gets (buffer);
		a = atof (buffer);
		b = a/2;
		printf ( "a= %f and b= %f\n" , a, b );
		return 0;

Output of the atof example program above:

	Input: 12
	a= 12.000000 and b= 6.000000

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  1. patadiya dharmesh on February 16th, 2012:

    Can you give some more examples? This has given me some idea but still has not cleared logic.