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

 

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Common mathematical functions

Functions
Basic operations
abs(int)labsllabsimaxabs (C++11) abs(float)fabs divldivlldivimaxdiv (C++11) fmod	remainder (C++11) remquo (C++11) fma (C++11) fmax (C++11) fmin (C++11) fdim (C++11) nannanfnanl (C++11)(C++11)(C++11)
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ceil floor roundlroundllround (C++11)(C++11)(C++11)	trunc (C++11) nearbyint (C++11) rintlrintllrint (C++11)(C++11)(C++11)
Floating point manipulation functions
ldexp scalbnscalbln (C++11)(C++11) ilogb (C++11) logb (C++11)	frexp modf nextafternexttoward (C++11)(C++11) copysign (C++11)
Classification/Comparison
fpclassify (C++11) isfinite (C++11) isinf (C++11) isnan (C++11) isnormal (C++11) signbit (C++11)	isgreater (C++11) isgreaterequal (C++11) isless (C++11) islessequal (C++11) islessgreater (C++11) isunordered (C++11)
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HUGE_VALFHUGE_VALHUGE_VALL (C++11)(C++11) INFINITY (C++11) NAN (C++11) math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C++11)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C++11)(C++11)(C++11)(C++11)(C++11)

 

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

1-3) Composes a floating point value with the magnitude of mag and the sign of sgn.

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.

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

See also

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