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;}