copysign, copysignf, copysignl

 

C

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headers

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Dynamic memory management

Error handling

Program utilities

Variadic function support

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

Technical Specifications

 

Numerics

Common mathematical functions

Floating-point environment

Complex number arithmetics

Random number generation

Type-generic math

 

Common mathematical functions

Functions
Basic operations
abslabsllabsimaxabs (C99) fabs divldivlldivimaxdiv (C99) fmod	remainder (C99) remquo (C99) fma (C99) fmax (C99) fmin (C99) fdim (C99) nannanfnanl (C99)(C99)(C99)
Exponential functions
exp exp2 (C99) expm1 (C99)	log log10 log1p (C99) log2 (C99)
Power functions
sqrt cbrt (C99)	hypot (C99) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C99) acosh (C99) atanh (C99)
Error and gamma functions
erf (C99) erfc (C99)	lgamma (C99) tgamma (C99)
Nearest integer floating point operations
ceil floor roundlroundllround (C99)(C99)(C99)	trunc (C99) nearbyint (C99) rintlrintllrint (C99)(C99)(C99)
Floating point manipulation functions
ldexp scalbnscalbln (C99)(C99) ilogb (C99) logb (C99)	frexp modf nextafternexttoward (C99)(C99) copysign (C99)
Classification
fpclassify (C99) isfinite (C99) isinf (C99) isnan (C99) isnormal (C99) signbit (C99)	isgreater (C99) isgreaterequal (C99) isless (C99) islessequal (C99) islessgreater (C99) isunordered (C99)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C99)(C99)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C99)(C99)(C99)(C99)(C99)

 

Defined in header <math.h>
float       copysignf( float x, float y );	(1)	(since C99)
double      copysign( double x, double y );	(2)	(since C99)
long double copysignl( long double x, long double y );	(3)	(since C99)
Defined in header <tgmath.h>
#define copysign(from, to)	(7)	(since C99)

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

4) Type-generic macro: If any argument has type long double, copysignl is called. Otherwise, if any argument has integer type or has type double, copysign is called. Otherwise, copysignf is called.

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

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 <stdio.h>
#include <math.h>
 
int main(void)
{
    printf("copysign(1.0,+2.0)      = %+.1f\n", copysign(1.0,+2.0));
    printf("copysign(1.0,-2.0)      = %+.1f\n", copysign(1.0,-2.0));
    printf("copysign(INFINITY,-2.0) = %f\n",    copysign(INFINITY,-2.0));
    printf("copysign(NAN,-2.0)      = %f\n",    copysign(NAN,-2.0));
}

Possible output:

copysign(1.0,+2.0)      = +1.0
copysign(1.0,-2.0)      = -1.0
copysign(INFINITY,-2.0) = -inf
copysign(NAN,-2.0)      = -nan

References

• C11 standard (ISO/IEC 9899:2011):

• 7.12.11.1 The copysign functions (p: 255)

• 7.25 Type-generic math <tgmath.h> (p: 373-375)

• F.10.8.1 The copysign functions (p: 529)

• C99 standard (ISO/IEC 9899:1999):

• 7.12.11.1 The copysign functions (p: 236)

• 7.22 Type-generic math <tgmath.h> (p: 335-337)

• F.9.8.1 The copysign functions (p: 465)

See also

fabsfabsffabsl (C99)(C99)	computes absolute value of a floating-point value (|x|) (function)
signbit (C99)	checks if the given number is negative (function)
C++ documentation for copysign