isnan

- test for NaN

Synopsis

cc [ flag... ] file... -lm [ library... ]
#include <math.h>

int isnan(double x);

c99 [ flag... ] file... -lm [ library... ]
#include <math.h>

int isnan(real—floating x);

Description

In C90 mode, the isnan() function tests whether x is NaN.

In C99 mode, the isnan() macro determines whether its argument value is NaN. First, an argument represented in a format wider than its semantic type is converted to its semantic type. The determination is then based on the type of the argument.

Return Values

Both the isnan() function and macro return non-zero if and only if x is NaN.

Errors

No errors are defined.

Warnings

In C99 mode, the practice of explicitly supplying a prototype for isnan() after the line

#include <math.h>

is obsolete and will no longer work.

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

fpclassify(3M), isfinite(3M), isinf(3M), isnormal(3M), math.h(3HEAD), signbit(3M), attributes(5), standards(5)