Determines whether its argument value is a NaN.

[Classification]

Mathematical library

[Syntax]

#include <math.h>

int isnan(real-floating x); (C99)

[Return value]

If the argument is NaN, a value other than 0 is returned.

In other cases, 0 is returned.

[Description]

This macro determines whether its argument value is a NaN.

If a type other than the floating-point type is passed to the argument, correct operation is not guaranteed.