The Open Group Base Specifications Issue 7, 2018 edition
IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)
Copyright © 2001-2018 IEEE and The Open GroupA 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]](../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 POSIX.1-2017 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
XBD <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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