NAME¶

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

Synopsis¶

Defined in header <cmath>
float copysign ( float mag, float sgn );

double copysign ( double mag, double sgn ); (until C++23)

long double copysign ( long double mag, long double
sgn );
constexpr /* floating-point-type */

copysign ( /* floating-point-type */
mag, (since C++23)
(1)
/* floating-point-type */ sgn
);
float copysignf( float mag, float sgn ); (2) (since C++11)
(constexpr since C++23)
long double copysignl( long double mag, long double (3) (since C++11)
sgn ); (constexpr since C++23)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer > (A) (constexpr since C++23)
double copysign ( Integer mag, Integer sgn );

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)

A) Additional overloads are provided for all integer types, which are (since C++11)
treated as double.

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 (A). 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 (until C++23)
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)).
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, (since C++23)
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¶

// Run this code

#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';
}

Output:¶

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

See also¶

abs(float)
fabs
fabsf absolute value of a floating point value (\(\small{|x|}\)|x|)
fabsl (function)
(C++11)
(C++11)
signbit checks if the given number is negative
(C++11) (function)
C documentation for
copysign