Not a Number (NAN) Items
The Visual C++ compiler supports comparisons of not a number (NAN) items in an IEEE-compliant manner. If x is NAN and y is not NAN:
(x != x) == true
(x == x) == false
(y > x) == false
(y < x) == false
NAN ordering tests always return false: NAN [<, <=, >, >=] [any_number] will be false.
The following code shows how NANs in Visual C++ cannot be compared successfully to a floating-point number:
#include <math.h>
#include <stdio.h>
#include <float.h>
int main( void ) {
unsigned long nan[2]={0xffffffff, 0x7fffffff};
double g = *( double* )nan;
if ( g <= 3.0 )
printf( "g( %g ) <= 3.0\n", g );
else if ( g > 3.0)
printf( "g( %g ) > 3.0\n", g );
else
printf( "g( %g ) is NaN\n", g );
}