C++语言基础 例程 纯虚函数

#include "iostream"
using namespace std;
class Animal
{
public:
    virtual void cry() = 0;
};

class Mouse : public Animal
{
public:
    void cry()
    {
        cout<<"吱！"<<endl;
    }
};

class Cat : public Animal
{
public:
    virtual void cry()
    {
        cout<<"喵！"<<endl;
    }
};

class Dog : public Animal
{
public:
    virtual void cry()
    {
        cout<<"汪！"<<endl;
    }
};

int main( )
{
    Animal *p;
    //p = new Animal();
    //p->cry();
    Mouse m1;
    p=&m1;
    p->cry();
    Cat c1;
    p=&c1;
    p->cry();
    Dog d1;
    p=&d1;
    p->cry();
    return 0;
}