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()\n";}
     virtual void Show(){}
 protected:
     CImage(string imgName): m_imgName(imgName){cout << "CImage()\n";}
     string m_imgName;
 };

 //concrete implement
 class CBigImage : public CImage
 {
 public:
     CBigImage(string imgName): CImage(imgName), m_bigImgName(imgName){
         cout << "CBigImage()\n";
     }
     ~CBigImage(){
         cout << "~CBigImage()\n";
     }
     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()\n";
     }
     ~CBigImageProxy(){
         if(NULL != m_img){
             delete m_img;
             m_img = NULL;
         }
         cout << "~CBigImageProxy()\n";
     }
     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()\n";}
     virtual void Request()=;
 protected:
     Subject(){cout << "Subject()\n";}
 };

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

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

     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 ;
 }
 // g++ -g -Wall main.cpp -o xmain

两个代理模式的示例

至于智能指针，建议可以参考C++11标准的智能指针。