C++代理模式

主要根据代理模式整理，感谢作者分享！

 [DP]上的定义：为其他对象提供一种代理以控制对这个对象的访问。有四种常用的情况：（1）远程代理，（2）虚代理，（3）保护代理，（4）智能引用。本文主要介绍虚代理和智能引用两种情况。

       考虑一个可以在文档中嵌入图形对象的文档编辑器。有些图形对象的创建开销很大。但是打开文档必须很迅速，因此我们在打开文档时应避免一次性创建所有开销很大的对象。这里就可以运用代理模式，在打开文档时，并不打开图形对象，而是打开图形对象的代理以替代真实的图形。待到真正需要打开图形时，仍由代理负责打开。这是[DP]一书上的给的例子。下面给出代理模式的UML图。

#include <bits/stdc++.h>
//#include "solution.h"
using namespace std;

#define debug(x) cout << #x << " at line " << __LINE__ << " is: " << x << endl

class CImage
{
public:
    virtual ~CImage(){cout << "~CImage()
";}
    virtual void Show(){}
protected:
    CImage(string imgName): m_imgName(imgName){cout << "CImage()
";}
    string m_imgName;
};

//concrete implement
class CBigImage : public CImage
{
public:
    CBigImage(string imgName): CImage(imgName), m_bigImgName(imgName){
        cout << "CBigImage()
";
    }
    ~CBigImage(){
        cout << "~CBigImage()
";
    }
    void Show(){cout << "show big image" <<endl;}
protected:
    string m_bigImgName;
};

// proxy
class CBigImageProxy : public CImage
{
public:
    CBigImageProxy(string imgName): CImage(imgName), m_img(NULL), m_bigImgName(imgName){
        cout << "CBigImageProxy()
";
    }
    ~CBigImageProxy(){
        if(NULL != m_img){
            delete m_img;
            m_img = NULL;
        }
        cout << "~CBigImageProxy()
";
    }
    void Show(){
        if(NULL == m_img){
            m_img = new CBigImage(m_bigImgName);
        }
        m_img->Show();
    }
private:
    CImage *m_img;
    string m_bigImgName;
};


class Subject
{
public:
    virtual ~Subject(){cout << "~Subject()
";}
    virtual void Request()=0;
protected:
    Subject(){cout << "Subject()
";}
};


class ConcreteSubject : public Subject
{
public:
    ConcreteSubject(){
        cout << "ConcreteSubject()
";
    }
    ~ConcreteSubject(){
        cout << "~ConcreteSubject()
";
    }
    virtual void Request(){cout << "ConcreteSubject Request()
";}
};

class Proxy : public Subject
{
public:
    Proxy(){
        cout << "Proxy()
";
        this->m_sub = new ConcreteSubject();
    }
    //    Proxy(Subject* _sub):m_sub(_sub){
    //        cout << "Proxy(Subject)
";
    //    }

    virtual void Request()//实现对委托者的委托任务执行与补偿
    {
        this->m_sub->Request();
    }
    ~Proxy(){
        if(NULL != this->m_sub){
            delete this->m_sub;
            this->m_sub = NULL;
        }
        cout << "~Proxy()" << endl;
    }

private:
    Subject *m_sub;
};


int main(int argc, char *argv[])
{
    CBigImageProxy *bip = new CBigImageProxy("proxy.jpg");
    bip->Show();
    delete bip;
    bip = NULL;

    Proxy *py = new Proxy();
    py->Request();
    delete py;
    py = NULL;
    return 0;
}
// g++ -g -Wall main.cpp -o xmain

至于智能指针，建议可以参考C++11标准的智能指针。