f1301.cpp

it is a usefull thing

//=====================================
// f1301.cpp
// Abstract Classes
//=====================================
#include<iostream>
class Display{
public:
  virtual void init() = 0;
  virtual void write(char* pStr) = 0;
};//-----------------------------------
class Monochrome : public Display{
  virtual void init();                  // overlapped
  virtual void write(char* pStr);     // overlapped
};//-----------------------------------
class ColorAdapter : public Display{
public:
  virtual void write(char* pStr);     // overlapped
};//-----------------------------------
class SVGA : public ColorAdapter{
public:
  virtual void init();                  // overlapped
};//-----------------------------------
void Monochrome::init(){}
//-------------------------------------
void Monochrome::write(char* pStr){
  std::cout<<"Monochrome: "<<pStr;
}//------------------------------------
void ColorAdapter::write(char* pStr){
  std::cout<<"ColorAdapter: "<<pStr;
}//------------------------------------
void SVGA::init(){}
//-------------------------------------
void g(Display* d){
  d->init();
  d->write("hello.\n");
}//------------------------------------
int main(){
  Monochrome mc;
  SVGA svga;
  g(&mc);
  g(&svga);
}//====================================