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.
NAME
isnan - test for a NaN
SYNOPSIS
#include <math.h>
int isnan(real-floating x);
DESCRIPTION
[CX] ![[Option Start]](../images/opt-start.gif)
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]](../images/opt-end.gif)
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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