binary_function Struct

 

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An empty base struct that defines types that may be inherited by derived classes that provides a binary function object.

struct binary_function { typedef Arg1 first_argument_type; typedef Arg2 second_argument_type; typedef Result result_type; };

The template struct serves as a base for classes that define a member function of the form:

result_type operator()( constfirst_argument_type&,

const second_argument_type& ) const

All such binary functions can refer to their first argument type as first_argument_type, their second argument type as second_argument_type, and their return type as result_type.

// functional_binary_function.cpp  
// compile with: /EHsc  
#include <vector>  
#include <functional>  
#include <algorithm>  
#include <iostream>  
  
using namespace std;  
  
template <class Type> class average:   
binary_function<Type, Type, Type>   
{  
public:  
   result_type operator( ) ( first_argument_type a,   
                 second_argument_type b )  
   {  
      return (result_type) ( ( a + b ) / 2 );  
   }  
};  
  
int main( )  
{  
   vector <double> v1, v2, v3 ( 6 );  
   vector <double>::iterator Iter1, Iter2, Iter3;  
  
   for ( int i = 1 ; i <= 6 ; i++ )  
      v1.push_back( 11.0 / i );  
  
   for ( int j = 0 ; j <= 5 ; j++ )  
      v2.push_back( -2.0 * j );  
  
   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 averages of the elements of v1 & v2  
   transform ( v1.begin( ),  v1.end( ), v2.begin( ), v3.begin ( ),   
      average<double>( ) );  
  
   cout << "The element-wise averages are: ( " ;  
   for ( Iter3 = v3.begin( ) ; Iter3 != v3.end( ) ; Iter3++ )  
      cout << *Iter3 << " ";  
   cout << ")" << endl;  
}  
\* Output:   
The vector v1 = ( 11 5.5 3.66667 2.75 2.2 1.83333 )  
The vector v2 = ( -0 -2 -4 -6 -8 -10 )  
The element-wise averages are: ( 5.5 1.75 -0.166667 -1.625 -2.9 -4.08333 )  
*\  
  

Header: <functional>

Namespace: std

binary_function Structure Sample
Thread Safety in the C++ Standard Library
Standard Template Library

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