isnan - test for a NaN
int isnan(real-floating x);
[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 IEEE Std 1003.1-2001 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.
fpclassify(), isfinite(), isinf(), isnormal(), signbit(), the Base Definitions volume of IEEE Std 1003.1-2001, <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 standard.