适配器初识

#include <iostream>  
#include <algorithm>  
#include <functional>  
#include <vector>

using namespace std;

//缺省版本
bool count_f(const int a)
{
    return a > 8;
}

//ptr_fun版本
bool greater_f(const int a, const int b)
{
    return a > b;
}

//构造的类模板版本
struct greater_if : public binary_function<int, int, bool>
{
    bool operator()(const int& _Left, const int& _Right) const
    {
        return (_Left > _Right);
    }
};

template <typename PF>
void f(std::vector<int>& v, PF pf)
{
    int count = std::count_if(v.begin(), v.end(), pf);
    std::cout << count << std::endl;
}

int main()
{  
    std::vector<int> v;
    for (int i=0; i<10; i++)
        v.push_back(i); 

    //普通函数 
    f(v, count_f);                            //大于8的元素
    f(v, bind1st(ptr_fun(&greater_f), 8));    //greater_f(8,v) 小于8的元素
    f(v, bind2nd(ptr_fun(&greater_f), 8));    //greater_f(v,8) 大于8的元素

    //STL仿函数
    f(v, bind1st(greater<int>(), 8));         //greater<int>(8,v) 小于8的元素
    f(v, bind2nd(greater<int>(), 8));         //greater<int>(v,8) 大于8的元素
    f(v, bind1st(greater_if(), 8));           //greater_(8,v) 小于8的元素
    f(v, bind2nd(greater_if(), 8));           //greater_(v,8) 大于8的元素

    system("pause");
    return 0;
}