//Example 9.2:虛函數實現多態性
#include <iostream.h> 
class Pet 						//基類
{
public:
	virtual void Speak() 
	{ cout<<"How does a pet speak ?"<<endl; } 
};       

class Cat : public Pet 				//派生類	
{
public:
	virtual void Speak()
	{ cout<<"miao!miao!"<<endl; }
}; 
class Dog : public Pet				//派生類
{
public:
	virtual void Speak()
	{ cout<<"wang!wang!"<<endl; }
};
void main()
{
	Pet	*p1, *p2, *p3,obj;			//基類對象指針p1, 基類對象obj
	Dog dog1;
	Cat cat1; 
	obj = dog1;					//用Dog類對象給Pet類對象賦值
	obj.Speak();	
	p1 = &cat1; 					//用Cat類對象地址給基類指針賦值
	p1->Speak(); 
	p1 = &dog1; 					//用Dog類對象地址給基類指針賦值
	p1->Speak(); 
	p2=new Cat;					//動態生成Cat類對象
	p2->Speak();
	p3=new Dog;					//動態生成Dog類對象
	p3->Speak();
	Pet	&p4 = cat1;				//以Cat類對象初始化Pet類引用 
	p4.Speak();
	delete p2;
	delete p3;
}