for_each用法

Posted 2020-06-17

for_each()是个function template

#include <algorithm>头文件说明
template<class _InIt,
    class _Fn1> inline
    void _For_each(_InIt _First, _InIt _Last, _Fn1& _Func)
    {    // perform function for each element
    for (; _First != _Last; ++_First)
        _Func(*_First);
    }

由以上source可知，for_each()只能配合global function和function object。

#include <iostream>
#include <stdlib.h>
#include "vector"
#include "map"
#include <algorithm>
#include <atlstr.h>
#include <xfunctional>
using namespace std;

//单一类对象
class CClassObj
{
public:
    CClassObj(void){}
    ~CClassObj(void){}
    void PrintElem(){
        std::cout << "mem_fun_ref" << std::endl;
    }
};
class ClassController
{
protected:
    vector<CClassObj> _ObjVec;
public:
    ClassController(void){}
    ~ClassController(void){}
    void AddClass(CClassObj cObj){
        _ObjVec.push_back(cObj);
    }
    void PrintElem(){
        for_each(_ObjVec.begin(), _ObjVec.end(), mem_fun_ref(&CClassObj::PrintElem));
    }
};

//多态
class AbstactClass
{
public:
    virtual void PrintElem(){
        std::cout << "Abstact mem_fun 1" << std::endl;
    }
};

class MyClass1 : public AbstactClass{};
class MyClass2 : public AbstactClass
{
public:
    void PrintElem(){
        std::cout << "Abstact mem_fun 2" << std::endl;
    }
};

class ClassCont
{
protected:
    vector<AbstactClass*> _ObjVec;

public:
    void AddClass(AbstactClass& obj){
        _ObjVec.push_back(&obj);
    }
    void PrintElem(){
        for_each(_ObjVec.begin(), _ObjVec.end(), mem_fun(&AbstactClass::PrintElem));
    }
};


struct  Mystruct
{
    int cnt;
    string str;
    Mystruct()
    {
        cnt = 0;
        str = "str";
    }
};

//函数调用对象 for_each()只能配合global function和function object。
/*void Print(const Mystruct stru){ cout << stru.cnt << ", " << stru.str.c_str() << endl; }*/
void Print(const Mystruct stru, const char* str){ cout << str << stru.cnt << ", " << stru.str.c_str() << endl; }

struct PrintStru
{
    string _str = "";
    PrintStru(string str) : _str(str){
    }
    void operator()(string &str){
        cout << _str.c_str() << str.c_str() << endl;
    }
};
int main()
{
/*    Add a(1, 2), b(3, 4);*/
/*    std::cout << a << " + " << b << " = " << (a + b) << std::endl;*/
    vector<Mystruct> vecStru;
    Mystruct stru;
    vecStru.push_back(stru);
    vecStru.push_back(stru);
    /*for_each(vecStru.begin(), vecStru.end(), [](const Mystruct stru){cout << stru.cnt << ", " << stru.str.c_str() << endl; });//lambda可调用对象*/

    //Procedure Based與for_each()搭配
    /*for_each(vecStru.begin(), vecStru.end(), Print);//print： 不传入参数*/
    for_each(vecStru.begin(), vecStru.end(), bind2nd(ptr_fun(Print), "elem: "));//print：  传入参数

    //Object Oriented與for_each()搭配
    string Arr[] = { "123", "123456", "12345", "12", "1" };
    vector<string> vecStr(Arr, Arr + sizeof(Arr) / sizeof(string));
    for_each(vecStr.begin(), vecStr.end(), PrintStru(""));//print： 不传入参数
    //若使用function object，也可以將參數傳給PrintStru()，透過constructor的技巧接收參數。
    for_each(vecStr.begin(), vecStr.end(), PrintStru("Elem: "));//print： 不传入参数

    ClassController cConT;
    cConT.AddClass(CClassObj());
    cConT.AddClass(CClassObj());
    cConT.PrintElem();

    //多态
    ClassCont cT;
    cT.AddClass(MyClass1());
    cT.AddClass(MyClass2());
    cT.PrintElem();

}

 

借鉴：http://www.cnblogs.com/Purple_Xiapei/archive/2012/05/27/2520477.html