实现:
    1) cImage:抽象类;
       cImageReal:派生类, 不可直接实例化;
       cImageProxy:派生代理类, 可直接实例化用来代理cImageReal;
    NOTICE:派生代理类用来简化对特定派生类的使用.

使用:
    实例化代理类, 然后使用.

1) 设计框架

        /*image.hpp*/
#pragma once
#ifndef __IMAGE__HPP
#define __IMAGE__HPP
#include <string>

namespace __proxy{

class cImage{
public:
  virtual ~cImage();
protected: 
  cImage();
public:
  virtual void display() = 0;
};

}
#include "image_real_proxy.hpp"

#endif

        /*image_real_proxy.hpp*/
#pragma once
#ifndef __IMAGE_REAL_PROXY_HPP
#define __IMAGE_REAL_PROXY_HPP
#include "image.hpp"
#include <string>

namespace __proxy{

class cImageReal:virtual public cImage{
public:
  cImageReal(std::string const &filename);
public:
  void display() override;
private:
  void loadFromDisk(std::string const &filename);
  std::string _M_filename;
};

}

namespace __proxy{

class cImageProxy:virtual public cImage{
public:
  cImageProxy(std::string const &filename);
public:
  void display() override;
private:
  cImageReal *_M_image = nullptr;
  std::string _M_filename;
};

}
#endif

2) 实现框架

        /*image.cpp*/
#include "image.hpp"
#include <stdio.h>

namespace __proxy{

cImage::~cImage()
{
  
}
cImage::cImage()
{
  
}

}

        /*image_real_proxy.cpp*/
#include "image_real_proxy.hpp"
#include <stdio.h>

namespace __proxy{

cImageReal::cImageReal(std::string const &filename)
{
  _M_filename = filename;
  loadFromDisk(_M_filename);
}
void cImageReal::display()
{
  printf("Displaying %s\n", _M_filename.c_str() );
}
void cImageReal::loadFromDisk(std::string const &filename)
{
  printf("Loading %s ... ok!\n", _M_filename.c_str() );
}

}

namespace __proxy{

cImageProxy::cImageProxy(std::string const &filename)
{
  _M_filename = filename;
}
void cImageProxy::display()
{
  if( nullptr == _M_image )
  {
    _M_image = new cImageReal(_M_filename);
  }

  if( _M_image != nullptr)
  {
    _M_image->display();
  }
}

}

3) 用户使用

#include "image.hpp"
#include <cstdlib>
#include <cstdio>

int main(int argc, char *argv[])
{
  if( argc != (1 + 1) ){
    fprintf(stderr, "Usage:%s <display-times>\n", argv[0]);
    return EXIT_FAILURE;
  }

  long long DISPLAY_TIMES = atoll(argv[1]);
  __proxy::cImage *image = new __proxy::cImageProxy("test_18mb.jpg");
  if( image != NULL)
  {
    printf("---------------------------------\n");
    image->display();

    printf("---------------------------------\n");
    for(long long idisp = 1; idisp < DISPLAY_TIMES; idisp++ )
    {
      image->display();
    }

    delete image, image = NULL;
  }

  return EXIT_SUCCESS;
}

4) 编译与运行