NAME
isnan — test for a
NaN
SYNOPSIS
#include
<math.h>
int isnan(real-floating x);
DESCRIPTION
[CX] 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.
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.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
fpclassify(3), isfinite(3), isinf(3), isnormal(3), signbit(3)
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 (“ISO C99”) standard.