编写一个哺乳动物类Mammal，再由此派生出狗类Dog，二者都声明speak（）成员函数，该函数在基类中被声明为虚函数，声明一个Dog类的对象，通过此对象调用speak函数，观察运行结果

#include<iostream>
using namespace std;

class Mammal{
	public:
		Mammal(){
			cout<<"Mammal coustructor...\n";
		}
		virtual ~Mammal(){
			cout<<"Mammal destructor...\n";
		} 
		virtual void speak() const{
			cout<<"Mammal speak!\n";
		}
};

class Dog: public Mammal{
	public:
		Dog(){
			cout<<"Dog Constructor...\n";
		}
		~Dog(){
			cout<<"Dog destructor...\n";
		}
		void speak() const{
			cout<<"Woof!\n";
		}
};

int main(){
	Mammal*pDog=new Dog;
	pDog->speak();
	delete pDog;
	return 0;
}

运行结果：