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signbit(3) — Linux manual page

NAME \|LIBRARY \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|ATTRIBUTES \|STANDARDS \|HISTORY \|SEE ALSO \|COLOPHON

signbit(3)               Library Functions Manualsignbit(3)

NAME top

       signbit - test sign of a real floating-point number

LIBRARY top

       Math library (libm,-lm)

SYNOPSIS top

#include <math.h>int signbit(x);   Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):signbit():           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION top

signbit() is a generic macro which can work on all real floating-       point types.  It returns a nonzero value if the value ofx has its       sign bit set.       This is not the same asx < 0.0, because IEEE 754 floating point       allows zero to be signed.  The comparison-0.0 < 0.0 is false, butsignbit(-0.0) will return a nonzero value.       NaNs and infinities have a sign bit.

RETURN VALUE top

       Thesignbit() macro returns nonzero if the sign ofx is negative;       otherwise it returns zero.

ERRORS top

       No errors occur.

ATTRIBUTES top

       For an explanation of the terms used in this section, seeattributes(7).       ┌──────────────────────────────────────┬───────────────┬─────────┐       │Interface│Attribute│Value│       ├──────────────────────────────────────┼───────────────┼─────────┤       │signbit()                            │ Thread safety │ MT-Safe │       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

       C11, POSIX.1-2008.

HISTORY top

       POSIX.1-2001, C99.       This function is defined in IEC 559 (and the appendix with       recommended functions in IEEE 754/IEEE 854).

COLOPHON top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17signbit(3)

Pages that refer to this page:copysign(3), fpclassify(3)

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