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# copysign, copysignf, copysignl

From cppreference.com
< c‎ | numeric‎ | math

Defined in header `<math.h>` |  |
float copysignf( float x, float y ); | (1) | (since C99)
double copysign( double x, double y ); | (2) | (since C99)
long double copysignl( long double x, long double y ); | (3) | (since C99)
Defined in header `<tgmath.h>` |  |
#define copysign(from, to) | (7) | (since C99)

1-3) Composes a floating point value with the magnitude of `x` and the sign of `y`.
4) Type-generic macro: If any argument has type long double, `copysignl` is called. Otherwise, if any argument has integer type or has type double, `copysign` is called. Otherwise, `copysignf` is called.

### [edit] Parameters

x, y | - | floating point values

### [edit] Return value

If no errors occur, the floating point value with the magnitude of `x` and the sign of `y` is returned.

If `x` is NaN, then NaN with the sign of `y` is returned.

If `y` is -0, the result is only negative if the implementation supports the signed zero consistently in arithmetic operations.

### [edit] Error handling

This function is not subject to any errors specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

- The returned value is exact (FE_INEXACT is never raised) and independent of the current rounding mode.

### [edit] Notes

`copysign` is the only portable way to manipulate the sign of a NaN value (to examine the sign of a NaN, signbit may also be used).

### [edit] Example

Run this code

    #include <stdio.h>
    #include <math.h>

    int main(void)
    {
        printf("copysign(1.0,+2.0)      = %+.1f\n", copysign(1.0,+2.0));
        printf("copysign(1.0,-2.0)      = %+.1f\n", copysign(1.0,-2.0));
        printf("copysign(INFINITY,-2.0) = %f\n",    copysign(INFINITY,-2.0));
        printf("copysign(NAN,-2.0)      = %f\n",    copysign(NAN,-2.0));
    }

Possible output:

    copysign(1.0,+2.0)      = +1.0
    copysign(1.0,-2.0)      = -1.0
    copysign(INFINITY,-2.0) = -inf
    copysign(NAN,-2.0)      = -nan

### [edit] References

- C11 standard (ISO/IEC 9899:2011):

  - 7.12.11.1 The copysign functions (p: 255)

  - 7.25 Type-generic math <tgmath.h> (p: 373-375)

  - F.10.8.1 The copysign functions (p: 529)

- C99 standard (ISO/IEC 9899:1999):

  - 7.12.11.1 The copysign functions (p: 236)

  - 7.22 Type-generic math <tgmath.h> (p: 335-337)

  - F.9.8.1 The copysign functions (p: 465)

### [edit] See also

fabs fabsf fabsl (C99)(C99) | computes absolute value of a floating-point value (|x|) (function) [edit]
signbit (C99) | checks if the given number is negative (function) [edit]
C++ documentation for copysign

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