function

atof

<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, the function returns zero (0.0).
There is no standard specification on what happens when the converted value would be out of the range of representable values by a double. See strtod for a more robust cross-platform alternative when this is a possibility.


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

strtod
Convert string to double (function )
atoi
Convert string to integer (function )
atol
Convert string to long integer (function )