copysign(), copysignf(), copysignl()

Updated: October 26, 2022

Copy the sign bit from one number to another

Synopsis:

#include <math.h>

double copysign ( double x,
                  double y);

float copysignf ( float x,
                  float y );

long double copysignl ( long double x,
                        long double y);

Arguments:

x
The number to use the magnitude of.
y
The number to use the sign of.

Library:

libm
The general-purpose math library.
libm-sve
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

Description:

The copysign(), copysignf(), and copysignl() functions return the magnitude of x with the sign bit of y.

To check for error situations, use feclearexcept() and fetestexcept(). For example:

Returns:

The magnitude of x with the sign bit of y.

If x is: These functions return: Errors:
NaN NaN, with the same sign as y

Examples:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(int argc, char** argv) 
{
   double a, b, c;

   a = 27.0;
   b = -5;
   c = copysign(a, b);
   printf("The magnitude of %f and sign of %f gives %f\n",
          a, b, c);

   return(EXIT_SUCCESS);
}

produces the output:

The magnitude of 27.000000 and sign of -5.000000 gives -27.000000

Classification:

C11, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes