7.12.3.4 The isnan macro

Synopsis

1

#include <math.h>
int isnan(real-floating x);

Description

2

The isnan macro determines whether its argument value is a NaN. First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then determination is based on the type of the argument.[1]

Returns

3

The isnan macro returns a nonzero value if and only if its argument has a NaN value.

Footnotes

[1]

For the isnan macro, the type for determination does not matter unless the implementation supports NaNs in the evaluation type but not in the semantic type.