The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
A newer edition of this document exists here

NAME

isnan - test for a NaN

SYNOPSIS

#include <math.h>

int isnan(real-floating x);

DESCRIPTION

[CX] [Option Start] 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 defers to the ISO C standard. [Option End]

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.

RETURN VALUE

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

ERRORS

No errors are defined.

The following sections are informative.

EXAMPLES

None.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

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

CHANGE HISTORY

First released in Issue 3.

Issue 5

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

Issue 6

Re-written for alignment with the ISO/IEC 9899:1999 standard.

End of informative text.
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