fpclassify - Man Page

classify real floating type


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <math.h>

int fpclassify(real-floating x);


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 fpclassify() macro shall classify its argument value as NaN, infinite, normal, subnormal, zero, or into another implementation-defined category. First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then classification is based on the type of the argument.

Return Value

The fpclassify() macro shall return the value of the number classification macro appropriate to the value of its argument.


No errors are defined.

The following sections are informative.



Application Usage




Future Directions


See Also

isfinite(), isinf(), isnan(), isnormal(), signbit()

The Base Definitions volume of POSIX.1-2017, <math.h>

Referenced By

isfinite(3p), isinf(3p), isnan(3p), isnormal(3p), math.h(0p), signbit(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual