signbit 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.

signbit — test sign


#include <math.h>

int signbit(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 signbit() macro shall determine whether the sign of its argument value is negative. NaNs, zeros, and infinities have a sign bit.

Return Value

The signbit() macro shall return a non-zero value if and only if the sign of its argument value is negative.


No errors are defined.

The following sections are informative.

See Also

fpclassify(), isfinite(), isinf(), isnan(), isnormal()

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


2013 IEEE/The Open Group POSIX Programmer's Manual