C in a Nutshell

Name

isinf

Synopsis

Tests whether a given floating point value is an infinity

#include <math.h>
intisinf( float x );
int isinf( double x );
int isinf( long double x );

The macro isinf() yields a nonzero value (that is, true) if its argument is a positive or negative infinity. Otherwise, isinf() 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

This function takes a short cut if it encounters an infinite addend:

double vsum( int n, va_list argptr )
{
  double sum = 0.0, next = 0.0;
  va_start( argptr, n );

  for ( int i = 0; i < n; i ++ )
  {
    next = va_arg( argptr, double );
    if (isinf( next ) )
      return next;
    sum += next;
  }
  va_end( argptr );
  return sum;
}

See Also

fpclassify(), isfinite(), isnan(), isnormal(), signbit()