std::copysign,std::copysignf,std::copysignl (3) - Linux Manuals

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


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


Defined in header <cmath>
float copysign ( float x, float y ); (1) (since C++11)
float copysignf( float x, float y );
double copysign ( double x, double y ); (2) (since C++11)
long double copysign ( long double x, long double y ); (3) (since C++11)
long double copysignl( long double x, long double y );
Promoted copysign ( Arithmetic1 x, Arithmetic2 y ); (4) (since C++11)

1-3) Composes a floating point value with the magnitude of x and the sign of y.
4) A set of overloads or a function template for all combinations of arguments of arithmetic type not covered by (1-3). 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.


x, y - floating point values

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.

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.


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)


// Run this code

  #include <iostream>
  #include <cmath>

  int main(void)
      std::cout << "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

See also

fabsl absolute value of a floating point value (|x|)


signbit checks if the given number is negative