c++之多态

#include<iostream>
using namespace std;

class Animal{
public:
    virtual void speak() {
        cout << "动物在说话" << endl;
    }

};
class Cat :public Animal {
public:
    void speak() {
        cout << "喵喵喵" << endl;
    }
};
class Dog :public Animal {
public:
    void speak() {
        cout << "汪汪汪" << endl;
    }
};

//这里必须传入地址
//父类的引用指向子类的对象，实现动态多态
void doSpeak(Animal &animal) {
    animal.speak();
}
void test() {
    Cat cat;
    doSpeak(cat);
    Dog dog;
    doSpeak(dog);
}

int main() {
    test();
    system("pause");
    return 0;
}

#include<iostream>
using namespace std;

class Animal{
public:
    virtual void speak() {
        cout << "动物在说话" << endl;
    }

};
class Cat :public Animal {
public:
    void speak() {
        cout << "喵喵喵" << endl;
    }
};
class Dog :public Animal {
public:
    void speak() {
        cout << "汪汪汪" << endl;
    }
};

//这里必须传入地址
//父类的引用指向子类的对象，实现动态多态
void doSpeak(Animal &animal) {
    animal.speak();
}
void test() {
    Cat cat;
    doSpeak(cat);
    Dog dog;
    doSpeak(dog);
}

int main() {
    //test();
    Animal animal;
    cout << "不加virtual的：" << sizeof(animal) << endl;//结果为1，成员函数和成员变量是分开存储的，空对象占1个字节
    cout << "加了virtual之后的：" << sizeof(animal) << endl;
    //结果为4，animal里面存储有虚函数指针，虚函数指针指向虚函数表，表内记录虚函数的地址
    //最开始时是Animal &animal speak，子类继承了父类，则子类也有一个虚函数指针，该虚函数指针指向的
    //虚函数表存储着Animal &animal speak，子类重写了虚函数，那么子类会将虚函数表里面的数据
    //替换成子类虚函数的地址，变为Animal &Cat speak
    system("pause");
    return 0;
}