C in a Nutshell

Name

isfinite

Synopsis

Tests whether a given floating-point value is a finite number

#include <math.h>
intisfinite( float x );
int isfinite( double x );
int isfinite( long double x );

The macro isfinite() yields a nonzero value (that is, true) if its argument is not an infinite number and not a NaN. Otherwise, isfinite() yields 0. The argument must be a real floating-point type. The rule that floating-point types are promoted to at least double precision for mathematical calculations does not apply here; the argument’s properties are determined based on its representation in its actual semantic type.

Example

double vsum( int n, ... )
// n is the number of arguments in the list
{
  va_list argptr;
  double sum = 0.0, next = 0.0;
  va_start( argptr, n );
  while ( n− )
  {
    next = va_arg( argptr, double );
    sum += next;
    if (isfinite( sum ) == 0 )
      break;                        // If sum reaches infinity, stop adding.
  }
  va_end( argptr );
  return sum;
}

See Also

fpclassify(), isinf(), isnan(), isnormal(), signbit()