isnan

Determines if the given floating-point number arg is a not-a-number (NaN) value. The macro returns an integral value.

FLT_EVAL_METHOD

Parameters

Return value

Nonzero integral value if arg is a NaN, ​0​ otherwise.

Notes

There are many different NaN values with different sign bits and payloads, see nan.

NaN values never compare equal to themselves or to other NaN values. Copying a NaN may change its bit pattern.

Another way to test if a floating-point value is NaN is to compare it with itself: bool is_nan( double x) { return x ! = x; }

Example

#include <float.h>
#include <math.h>
#include <stdio.h>
 
int main(void)
{
    printf("isnan(NAN)         = %d\n", isnan(NAN));
    printf("isnan(INFINITY)    = %d\n", isnan(INFINITY));
    printf("isnan(0.0)         = %d\n", isnan(0.0));
    printf("isnan(DBL_MIN/2.0) = %d\n", isnan(DBL_MIN / 2.0));
    printf("isnan(0.0 / 0.0)   = %d\n", isnan(0.0 / 0.0));
    printf("isnan(Inf - Inf)   = %d\n", isnan(INFINITY - INFINITY));
}

isnan(NAN)         = 1
isnan(INFINITY)    = 0
isnan(0.0)         = 0
isnan(DBL_MIN/2.0) = 0
isnan(0.0 / 0.0)   = 1
isnan(Inf - Inf)   = 1

References

See also