copysign(3) Library Functions Manual copysign(3)

copysign, copysignf, copysignl - copy sign of a number

Math library (libm, -lm)

#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

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.

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.

No errors occur.

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
copysign (), copysignf (), copysignl () Thread safety MT-Safe

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

C11, POSIX.1-2008.

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

C99, POSIX.1-2001, 4.3BSD.


2023-10-31 Linux man-pages 6.7