# copysign man page

copysign, copysignf, copysignl — copy sign of a number

## Synopsis

#include <math.h>double copysign(doublex, doubley);float copysignf(floatx, floaty);long double copysignl(long doublex, long doubley);

`Link with `

*-lm*.

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 versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

## Description

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

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

No errors occur.

## Attributes

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

Interface | Attribute | Value |
---|---|---|

copysign(), copysignf(), copysignl() | Thread safety | MT-Safe |

## Conforming to

C99, POSIX.1-2001, POSIX.1-2008. This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).

## Notes

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

## See Also

## Colophon

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## Referenced By

copysignf(3) and copysignl(3) are aliases of copysign(3).