atof


function
<cstdlib>
double atof ( const char * str );

Convert string to double

Parses the C string str interpreting its content as a floating point number and returns its value as a double.

The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes as many characters as possible that are valid following a syntax resembling that of floating point literals, and interprets them as a numerical value. The rest of the string after the last valid character is ignored and has no effect on the behavior of this function.

A valid floating point number for atof is formed by a succession of:
  • An optional plus or minus sign
  • A sequence of digits, optionally containing a decimal-point character
  • An optional exponent part, which itself consists on an 'e' or 'E' character followed by an optional sign and a sequence of digits.

If the first sequence of non-whitespace characters in str does not form a valid floating-point number as just defined, or if no such sequence exists because either str is empty or contains only whitespace characters, no conversion is performed.

Parameters

str
C string beginning with the representation of a floating-point number.


Return Value

On success, the function returns the converted floating point number as a double value.
If no valid conversion could be performed, or if the correct value would cause underflow, a zero value (0.0) is returned.
If the correct value is out of the range of representable values, a positive or negative HUGE_VAL is returned.

Example

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/* atof example: sine calculator */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main ()
{
  double n,m;
  double pi=3.1415926535;
  char szInput [256];
  printf ( "Enter degrees: " );
  gets ( szInput );
  n = atof ( szInput );
  m = sin (n*pi/180);
  printf ( "The sine of %f degrees is %f\n" , n, m );
  return 0;
}


Output:

Enter degrees: 45
The sine of 45.000000 degrees is 0.707101


See also