预定义函数对象

#include <iostream>    
#include<string>    
#include <vector>    
#include <list>    
#include <set>    
#include <map>    
#include <algorithm>    
#include <functional>  
using namespace std; 
 
//plus 预定义函数对象 能实现不能类型数据的+运算
// 实现了算法和数据类型的分离 ===》通过函数对象技术实现的
/*
template<class _Ty>
struct plus
: public binary_function<_Ty, _Ty, _Ty>
{	// functor for operator+
_Ty operator()(const _Ty& _Left, const _Ty& _Right) const
{	// apply operator+ to operands
return (_Left + _Right);
}
};
*/
void display()
{
	
	plus<int> intadd;
	int x = 10l;
	int y = 200;
	int z = intadd(x,y);
	cout<<z<<endl;
 
	plus<string> stringadd;
	string s1 = "aaaa";
	string s2 = "bbbb";
	string s3 = stringadd(s1,s2);
	cout<<s3<<endl;
	cout<<"---------------"<<endl;
 
	/*
	template<class _RanIt,
	class _Pr> inline
	void sort(_RanIt _First, _RanIt _Last, _Pr _Pred)
	{	// order [_First, _Last), using _Pred
	_DEBUG_RANGE(_First, _Last);
	_DEBUG_POINTER(_Pred);
	_Sort(_Unchecked(_First), _Unchecked(_Last), _Last - _First, _Pred);
	}
	*/
	vector<string> v;
	v.push_back("dddd");
	v.push_back("aaaa");
	v.push_back("cccc");
	v.push_back("cccc");
	v.push_back("bbbb");
 
	sort(v.begin(),v.end(),greater<string>());
 
	for (vector<string>::iterator it  = v.begin();it!=v.end();it++)
	{
		cout<<*it<<endl;
	}
	
	
	//统计和字符串相等的个数
	//equal_to<string> 有两个参数 left参数来自容器，right参数来自sc；
	//bind2nd函数适配器 把预定义函数对象和第二个参数进行绑定
	string sc = "cccc";
 
	int num = count_if(v.begin(),v.end(),bind2nd(equal_to<string>(),sc));
 
	cout<<num<<endl;
}
int main()
{
	display();
	system("pause");
	return 0;
}