Copysign
Defined in header <cmath>
.
Description
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 mag
and sgn
(od C++23).
Additional Overloads are provided for all other combinations of arithmetic types.
Declarations
- C++23
- C++11
// 1)
constexpr /* floating-point-type */
copysign ( /* floating-point-type */ mag,
/* floating-point-type */ sgn );
// 2)
constexpr float copysignf( float mag, float sgn );
// 3)
constexpr long double copysignl( long double mag, long double sgn );
// 4)
template< class Arithmetic1, class Arithmetic2 >
constexpr /* common-floating-point-type */
copysign( Arithmetic1 mag, Arithmetic2 sgn );
// 1)
float copysign ( float mag, float sgn );
// 2)
double copysign ( double mag, double sgn );
// 3)
long double copysign ( long double mag, long double sgn );
// 4)
float copysignf( float mag, float sgn );
// 5)
long double copysignl( long double mag, long double sgn );
// 6)
template< class Arithmetic1, class Arithmetic2 >
/* common-floating-point-type */
copysign( Arithmetic1 mag, Arithmetic2 sgn );
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.
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, std::signbit
may also be used).
The additional overloads are not required to be provided exactly as Additional Overloads.
They only need to be sufficient to ensure that for their first argument num1
and second argument num2
:
If num1
or num2
has type long double, then
std::copysign(num1, num2)
has the same effect as
std::copysign(static_cast<long double>(num1), static_cast<long double>(num2))
.
Otherwise, if num1
and/or num2
has type double or an integer type, then
std::copysign(num1, num2)
has the same effect as
std::copysign(static_cast<double>(num1), static_cast<double>(num2))
.
Otherwise, if num1
or num2
has type float, then
std::copysign(num1, num2)
has the same effect as
std::copysign(static_cast<float>(num1), static_cast<float>(num2))
. (do C++23)
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.
Examples
#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';
}
copysign(1.0,+2.0) = +1
copysign(1.0,-2.0) = -1
copysign(inf,-2.0) = -inf
copysign(NaN,-2.0) = -nan