ISNAN(3) Library Functions Manual ISNAN(3)

isnan — test for a NaN

#include <math.h>

int isnan(real-floating x);

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 (“POSIX.1”) defers to the ISO C standard.

The isnan () macro shall determine 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.

The isnan () macro shall return a non-zero value if and only if its argument has a NaN value.

No errors are defined.

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None.

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fpclassify(3), isfinite(3), isinf(3), isnormal(3), signbit(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <math.h>

First released in Issue 3.

The DESCRIPTION is updated to indicate the return value when NaN is not supported. This text was previously published in the APPLICATION USAGE section.

Re-written for alignment with the ISO/IEC 9899:1999 (“ISO C99”) standard.

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January 1, 2004 posix.fail