虚函数

#include <iostream>
using namespace std;
class Vehicle  //交通工具
{
public:
    void run() const
    {
        cout << "run a vehicle. " << endl;
    }
};
class Car : public Vehicle  //汽车
{
public:
    void run() const
    {
        cout << "run a car. " << endl;
    }
};
class Airplane : public Vehicle  //飞机
{
public:
    void run() const
    {
        cout << "run a airplane. " << endl;
    }
};
int main()
{
    cout << "(a) 直接用对象访问成员函数: " << endl;
    Vehicle v;
    Car car;
    Airplane airplane;

    v.run();
    car.run();
    airplane.run();

    cout << "(b)用指向基类的指针访问成员函数: " << endl;
    Vehicle* vp;
    vp = &car;
    vp->run();

    vp = &airplane;
    vp->run();
    return 0;
}

【运行结果】

纯虚函数

#include <bits/stdc++.h>
using namespace std;

class Animal { //抽象类，类似java中的接口
public:
    virtual void makeSound() = 0; //纯虚函数定义=0
};

class Cat : public Animal {
public:
    void makeSound() {
        cout << "Cat is meowing." << endl;
    }
};

class Dog : public Animal {
public:
    void makeSound() {
        cout << "Dog is barking." << endl;
    }
};

int main() {
    Animal* pAnimal1 = new Cat;
    Animal* pAnimal2 = new Dog;

    pAnimal1->makeSound(); // 输出 Cat is meowing.
    pAnimal2->makeSound(); // 输出 Dog is barking.

    delete pAnimal1;
    delete pAnimal2;
    return 0;
}

【运行结果】