函数对象

函数对象\

函数对象有三种类型：关系、逻辑、运算。为使用函数对象，应包含<functional>头文件。

想了解C++中定义的函数对象，看这个链接：http://msdn.microsoft.com/zh-cn/library/vstudio/86ke4swd.aspx

1.关系类型的函数对象：

equal_to<T>               测试是否相等

not_equal_to<T>        测试是否不相等

greater<T>                 测试是否大于

greater_equal<T>

less<T>                       测试是否小于

less_equal<T>

2.逻辑类型的函数对象：

logical_end<T>           

logical_not<T>            

logical_or<T>

3.算术类型的函数对象：

divides<T>

modulus<T>

negate<T>

函数对象就是一个重载了操作符()的对象，例如C++中greater的定义：

template<class Type>
   struct greater : public binary_function <Type, Type, bool> 
   {
      bool operator()(
         const Type& _Left, 
         const Type& _Right
      ) const;
   };

equal_to对象：

template<class Type>
   struct equal_to : public binary_function<Type, Type, bool> 
   {
      bool operator()(
         const Type& _Left, 
         const Type& _Right
      ) const;
   };

logical_and对象：

template<class Type>
   struct logical_and : public binary_function<Type, Type, bool> 
   {
      bool operator()(
         const Type& _Left, 
         const Type& _Right
      ) const;
   };

 

一个使用equal_to的例子：

// functional_equal_to.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+=2 )
   {
      v1.push_back( 2.0 *i );
      v1.push_back( 2.0 * i + 1.0 );
   }

   int j;
   for ( j = 0 ; j <= 5 ; j+=2 )
   {
      v2.push_back( - 2.0 * j );
      v2.push_back( 2.0 * j + 1.0 );
   }

   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;

   // Testing for the element-wise equality between v1 & v2
   transform ( v1.begin( ),  v1.end( ), v2.begin( ), v3.begin ( ), 
      equal_to<double>( ) );

   cout << "The result of the element-wise equal_to comparison\n"
      << "between v1 & v2 is: ( " ;
   for ( Iter3 = v3.begin( ) ; Iter3 != v3.end( ) ; Iter3++ )
      cout << *Iter3 << " ";
   cout << ")" << endl;
}