std::copysign, std::copysignf, std::copysignl
Header: <cmath>
1-3) Composes a floating point value with the magnitude of mag and the sign of sgn.The library provides overloads of std::copysign for all cv-unqualified floating-point types as the type of the parameters.(since C++23)
# Declarations
float copysign ( float mag, float sgn );
double copysign ( double mag, double sgn );
long double copysign ( long double mag, long double sgn );
(until C++23)
constexpr /*floating-point-type*/
copysign ( /*floating-point-type*/ mag,
/*floating-point-type*/ sgn );
(since C++23)
float copysignf( float mag, float sgn );
(since C++11) (constexpr since C++23)
long double copysignl( long double mag, long double sgn );
(since C++11) (constexpr since C++23)
SIMD overload (since C++26)
template< class V0, class V1 >
constexpr /*math-common-simd-t*/<V0, V1>
copysign ( const V0& v_mag, const V1& v_sgn );
(since C++26)
Additional overloads (since C++11)
template< class Integer >
double copysign ( Integer mag, Integer sgn );
(constexpr since C++23)
# Parameters
mag, sgn: floating-point or integer values
# Return value
If no errors occur, the floating point value with the magnitude of mag and the sign of sgn is returned.
# Notes
std::copysign is the only portable way to manipulate the sign of a NaN value (to examine the sign of a NaN, std::signbit may also be used).
The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their first argument num1 and second argument num2:
If num1 and num2 have arithmetic types, then std::copysign(num1, num2) has the same effect as std::copysign(static_cast</common-floating-point-type/>(num1),static_cast</common-floating-point-type/>(num2)), where /common-floating-point-type/ is the floating-point type with the greatest floating-point conversion rank and greatest floating-point conversion subrank between the types of num1 and num2, arguments of integer type are considered to have the same floating-point conversion rank as double.
If no such floating-point type with the greatest rank and subrank exists, then overload resolution does not result in a usable candidate from the overloads provided.
# Example
#include <cmath>
#include <iostream>
int main()
{
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';
}