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Difference between revisions of "cpp/numeric/math/copysign"

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< cpp‎ | numeric‎ | math
 
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{{cpp/title|copysign}}
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{{cpp/title|copysign|copysignf|copysignl}}
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{{cpp/numeric/math/sidebar}}
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{{cpp/numeric/math/navbar}}
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{{ddcl list begin}}
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{{cpp/numeric/math/declarations
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{{ddcl list header | cmath}}
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|family=copysign
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{{ddcl list item | notes={{mark c++0x feature}} |
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|param1=mag
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float      copysign( float x, float y );
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|param2=sgn
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|constexpr_since=23
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|desc=Composes a floating point value with the magnitude of {{c|mag}} and the sign of {{c|sgn}}.
 
}}
 
}}
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{{ddcl list item | notes={{mark c++0x feature}} |
 
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double      copysign( double x, double y );
 
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}}
 
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{{ddcl list item | notes={{mark c++0x feature}} |
 
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long double copysign( long double x, long double y );
 
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}}
 
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{{ddcl list end}}
 
  
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Composes a floating point value with the magnitude of {{tt|x}} and the sign of {{tt|y}}.
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===Parameters===
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{{par begin}}
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{{par|mag, sgn|floating-point or integer values}}
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{{par end}}
  
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<!-- ======== -->
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===Return value===
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{{params}}
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If no errors occur, the floating point value with the magnitude of {{c|mag}} and the sign of {{c|sgn}} is returned.
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{{param list begin}}
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{{param list item | x, y | floating point values}}
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{{param list end}}
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<!-- ======== -->
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If {{c|mag}} is NaN, then NaN with the sign of {{c|sgn}} is returned.
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{{returns}}
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floating point value with the magnitude of {{tt|x}} and the sign of {{tt|y}}
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If {{c|sgn}} is -0, the result is only negative if the implementation supports the signed zero consistently in arithmetic operations.
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===Error handling===
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This function is not subject to any errors specified in {{lc|math_errhandling}}.
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If the implementation supports IEEE floating-point arithmetic (IEC 60559),
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* The returned value is exact ({{lc|FE_INEXACT}} is never raised) and independent of the current [[cpp/numeric/fenv/FE_round|rounding mode]].
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===Notes===
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{{tt|std::copysign}} is the only portable way to manipulate the sign of a NaN value (to examine the sign of a NaN, {{lc|std::signbit}} may also be used).
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{{cpp/numeric/math/additional overload note|copysign}}
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===Example===
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{{example
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|code=
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#include <cmath>
 +
#include <iostream>
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int main()
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{
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    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'
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              << "copysign(NaN,-2.0) = " << std::copysign(NAN, -2.0) << '\n';
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}
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|output=
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copysign(1.0,+2.0) = +1
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copysign(1.0,-2.0) = -1
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copysign(inf,-2.0) = -inf
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copysign(NaN,-2.0) = -nan
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}}
  
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<!-- ======== -->
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===See also===
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{{see also}}
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{{dsc begin}}
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{{dsc inc|cpp/numeric/math/dsc fabs}}
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{{dsc inc|cpp/numeric/math/dsc signbit}}
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{{dsc see c|c/numeric/math/copysign}}
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{{dsc end}}
  
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
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{{dcl list template | cpp/numeric/math/dcl list fabs}}
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{{dcl list template | cpp/numeric/math/dcl list signbit}}
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Latest revision as of 09:58, 28 June 2023

 
C++
 
Numerics library
Common mathematical functions
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Mathematical constants (C++20)
Basic linear algebra algorithms (C++26)
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copysign
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Classification and comparison
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Macro constants
 
Defined in header <cmath>
(1)
float       copysign ( float mag, float sgn );

double      copysign ( double mag, double sgn );

long double copysign ( long double mag, long double sgn );
 (until C++23)
constexpr /* floating-point-type */

            copysign ( /* floating-point-type */ mag,

                       /* floating-point-type */ sgn );
 (since C++23)
float       copysignf( float mag, float sgn );
 (2) (since C++11)
(constexpr since C++23)
long double copysignl( long double mag, long double sgn );
 (3) (since C++11)
(constexpr since C++23)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer >
double      copysign ( Integer mag, Integer sgn );
 (A) (constexpr since C++23)
1-3) Composes a floating point value with the magnitude of mag and the sign of sgn. The library provides overloads of std::copysign for all cv-unqualified floating-point types as the type of the parameters.(since C++23)
A) Additional overloads are provided for all integer types, which are treated as double.
 (since C++11)

Contents

[edit] Parameters

mag, sgn - floating-point or integer values

[edit] 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.

[edit] Error handling

This function is not subject to any errors specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

[edit] Notes

std::copysign is the only portable way to manipulate the sign of a NaN value (to examine the sign of a NaN, std::signbit may also be used).

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their first argument num1 and second argument num2:

  • If num1 or num2 has type long double, then std::copysign(num1, num2) has the same effect as std::copysign(static_cast<long double>(num1),
                  static_cast<long double>(num2))    .
  • Otherwise, if num1 and/or num2 has type double or an integer type, then std::copysign(num1, num2) has the same effect as std::copysign(static_cast<double>(num1),
                  static_cast<double>(num2))    .
  • Otherwise, if num1 or num2 has type float, then std::copysign(num1, num2) has the same effect as std::copysign(static_cast<float>(num1),
                  static_cast<float>(num2))    .
(until C++23)

If num1 and num2 have arithmetic types, then std::copysign(num1, num2) has the same effect as std::copysign(static_cast</* common-floating-point-type */>(num1),
              static_cast</* common-floating-point-type */>(num2)), where /* common-floating-point-type */ is the floating-point type with the greatest floating-point conversion rank and greatest floating-point conversion subrank between the types of num1 and num2, arguments of integer type are considered to have the same floating-point conversion rank as double.

If no such floating-point type with the greatest rank and subrank exists, then overload resolution does not result in a usable candidate from the overloads provided.

(since C++23)

[edit] Example

Run this code
#include <cmath>
#include <iostream>
 
int main()
{
    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

[edit] See also

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