copysign(3) — Linux manual page

copysign(3)              Library Functions Manual             copysign(3)

NAME         top

       copysign, copysignf, copysignl - copy sign of a number

LIBRARY         top

       Math library (libm, -lm)

SYNOPSIS         top

       #include <math.h>

       double copysign(double x, double y);
       float copysignf(float x, float y);
       long double copysignl(long double x, long double y);

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       copysign(), copysignf(), copysignl():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION         top

       These functions return a value whose absolute value matches that
       of x, but whose sign bit matches that of y.

       For example, copysign(42.0, -1.0) and copysign(-42.0, -1.0) both
       return -42.0.

RETURN VALUE         top

       On success, these functions return a value whose magnitude is
       taken from x and whose sign is taken from y.

       If x is a NaN, a NaN with the sign bit of y is returned.

ERRORS         top

       No errors occur.

ATTRIBUTES         top

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

VERSIONS         top

       On architectures where the floating-point formats are not IEEE 754
       compliant, these functions may treat a negative zero as positive.

STANDARDS         top

       C11, POSIX.1-2008.

       This function is defined in IEC 559 (and the appendix with
       recommended functions in IEEE 754/IEEE 854).

HISTORY         top

       C99, POSIX.1-2001, 4.3BSD.

SEE ALSO         top

       signbit(3)

COLOPHON         top

       This page is part of the man-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 is not
       part of the original manual page), send a mail to
       man-pages@man7.org

Linux man-pages 6.15            2025-05-17                    copysign(3)

Pages that refer to this page: signbit(3)

HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.