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 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.
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
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.
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