plus Struct

[アーティクル]
01/02/2018

The latest version of this topic can be found at plus Struct.

A predefined function object that performs the addition operation (binary operator+) on its arguments.

Syntax

template <class Type = void>
struct plus : public binary_function <Type, Type, Type>  
{
    Type operator()(
    const Type& Left,
    const Type& Right) const;

 };

// specialized transparent functor for operator+
template <>  
struct plus<void>  
{
template <class T, class U>
auto operator()(T&& Left, U&& Right) const
 ->  
decltype(std::forward<T>(Left)
 + std::forward<U>(Right));

 };

Parameters

Type, T, U
A type that supports a binary operator+ that takes operands of the specified or inferred types.

Left
The left operand of the addition operation. The unspecialized template takes an lvalue reference argument of type Type. The specialized template does perfect forwarding of lvalue and rvalue reference arguments of inferred type T.

Right
The right operand of the addition operation. The unspecialized template takes an lvalue reference argument of type Type. The specialized template does perfect forwarding of lvalue and rvalue reference arguments of inferred type U.

Return Value

The result of Left``+``Right. The specialized template does perfect forwarding of the result, which has the type that's returned by binary operator+.

Example

// functional_plus.cpp  
// compile with: /EHsc  
#include <vector>  
#include <functional>  
#include <algorithm>  
#include <iostream>  
  
using namespace std;  
  
int main( )  
{  
   vector <double> v1, v2, v3 ( 6 );  
   vector <double>::iterator Iter1, Iter2, Iter3;  
  
   int i;  
   for ( i = 0 ; i <= 5 ; i++ )  
      v1.push_back( 4 * i );  
  
   int j;  
   for ( j = 0 ; j <= 5 ; j++ )  
      v2.push_back( -2.0 * j - 4 );  
  
   cout << "The vector v1 = ( " ;  
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )  
      cout << *Iter1 << " ";  
   cout << ")" << endl;  
  
   cout << "The vector v2 = ( " ;  
   for ( Iter2 = v2.begin( ) ; Iter2 != v2.end( ) ; Iter2++ )  
      cout << *Iter2 << " ";  
   cout << ")" << endl;  
  
   // Finding the element-wise sums of the elements of v1 & v2  
   transform (v1.begin( ), v1.end( ), v2.begin( ), v3.begin ( ), plus<double>( ) );  
  
   cout << "The element-wise sums are: ( " ;  
   for ( Iter3 = v3.begin( ) ; Iter3 != v3.end( ) ; Iter3++ )  
      cout << *Iter3 << " ";  
   cout << ")" << endl;  
}  
\* Output:   
The vector v1 = ( 0 4 8 12 16 20 )  
The vector v2 = ( -4 -6 -8 -10 -12 -14 )  
The element-wise sums are: ( -4 -2 0 2 4 6 )  
*\

Requirements

Header: <functional>

Namespace: std

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