isinf man page


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.

isinf — test for infinity


#include <math.h>

int isinf(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.1‐2008 defers to the ISO C standard.

The isinf() macro shall determine whether its argument value is an infinity (positive or negative). 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 isinf() macro shall return a non-zero value if and only if its argument has an infinite value.


No errors are defined.

The following sections are informative.

See Also

fpclassify(), isfinite(), isnan(), isnormal(), signbit()

The Base Definitions volume of POSIX.1‐2008, <math.h>


2013 IEEE/The Open Group POSIX Programmer's Manual