std::copysign

 

C++

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Technical Specifications

 

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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)
Exponential functions
exp exp2 (C++11) expm1 (C++11)	log log10 log1p (C++11) log2 (C++11)
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sqrt cbrt (C++11)	hypot (C++11) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C++11) acosh (C++11) atanh (C++11)

Error and gamma functions
erf (C++11) erfc (C++11)	lgamma (C++11) tgamma (C++11)
Nearest integer floating point operations
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)
Macro constants
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 x, float y );	(1)	(since C++11)
double      copysign( double x, double y );	(2)	(since C++11)
long double copysign( long double x, long double y );	(3)	(since C++11)
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.

Parameters

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.

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 << "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	absolute value of a floating point value (|x|) (function)
signbit (C++11)	checks if the given number is negative (function)
C documentation for copysign