虚函数

class Father
{
public:
	virtual ~Father()
	{
		cout<<"destruct father"<<endl;
	}
	void nationality()
	{
		cout<<"nationality is China"<<endl;
	}
	void born()
	{
		cout<<"was born in China"<<endl;
	}
	virtual void appearance(std::string str = "handsome")
	{
		cout<<"He is "<<str<<endl;
	}
};

class Daughter:public Father
{
public:
	Daughter(std::string name)
	{
		cout<<name<<endl;
	}
	~Daughter()
	{
		cout<<"destruct daughter"<<endl;
	}
	void born() //隐藏了父类的born，即使参数不同
	{
		cout<<"was born in HongKong"<<endl;
	}
	virtual void appearance(std::string str = "pretty") override  //覆盖父类的版本,可以不加virtual，实际上也是虚函数,
	{
		cout<<"She is "<<str<<endl;                          
	}
};

void main()
{
	// f的静态类型是Father*，动态类型是Daughter*
	Father *f = new Daughter("Li Liang");  

	//父类的born不是虚函数，（编译时已绑定）静态绑定，所以派生类最好不要重用基类中的名字，除非是覆盖继承而来的虚函数
	f->born();

	//父类的appearance为虚函数，动态绑定，多态性，默认参数由静态类型决定
	f->appearance();

	//不存在从基类向派生类的隐式类型转换,f转换为d是安全的，使用static_cast来强制覆盖编译器的检查
	Daughter *d = static_cast<Daughter *>(f);
	d->born();
	delete f;
}