copysign, copysignf, copysignl - copy sign of a number

```
#include <math.h>
double copysign(double x, double y);
float copysignf(float x, float y);
long double copysignl(long double x, long double y);
```

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
```

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 |

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).

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

signbit(3)

This page is part of release 4.15 of the Linux `man-pages`

project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.