NAME

std::copysign,std::copysignf,std::copysignl - std::copysign,std::copysignf,std::copysignl

Synopsis

Defined in header <cmath>
float copysign ( float mag, float sgn ); (1) (since C++11)
(constexpr since C++23)
float copysignf( float mag, float sgn ); (2) (since C++11)
(constexpr since C++23)
double copysign ( double mag, double sgn ); (3) (since C++11)
(constexpr since C++23)
long double copysign ( long double mag, long double sgn (4) (since C++11)
); (constexpr since C++23)
long double copysignl( long double mag, long double sgn (5) (since C++11)
); (constexpr since C++23)
Promoted copysign ( Arithmetic1 mag, Arithmetic2 sgn ); (6) (since C++11)
(constexpr since C++23)

1-5) Composes a floating point value with the magnitude of mag and the sign of sgn.
6) A set of overloads or a function template for all combinations of arguments of
arithmetic type not covered by (1-5). If any argument has integral type, it is cast
to double. If any argument is long double, then the return type Promoted is also
long double, otherwise the return type is always double.

Parameters

mag, sgn - floating point values

Return value

If no errors occur, the floating point value with the magnitude of mag and the sign
of sgn is returned.

If mag is NaN, then NaN with the sign of sgn is returned.

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

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.

Notes

std::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)

Example

// Run this code

#include <iostream>
#include <cmath>

int main(void)
{
std::cout << std::showpos
<< "copysign(1.0,+2.0) = " << std::copysign(1.0,+2.0) << '\n'
<< "copysign(1.0,-2.0) = " << std::copysign(1.0,-2.0) << '\n'
<< "copysign(inf,-2.0) = " << std::copysign(INFINITY,-2.0) << '\n'
<< "copysign(NaN,-2.0) = " << std::copysign(NAN,-2.0) << '\n';
}

Output:

copysign(1.0,+2.0) = +1
copysign(1.0,-2.0) = -1
copysign(inf,-2.0) = -inf
copysign(NaN,-2.0) = -nan