isfinite - Man Page

test for finite value


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 isfinite(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 isfinite() macro shall determine whether its argument has a finite value (zero, subnormal, or normal, and not infinite or 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 isfinite() macro shall return a non-zero value if and only if its argument has a finite value.


No errors are defined.

The following sections are informative.



Application Usage




Future Directions


See Also

fpclassify(), isinf(), isnan(), isnormal(), signbit()

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

Referenced By

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

2017 IEEE/The Open Group POSIX Programmer's Manual