实验四 继承

实验任务二

#include <iostream>
#include <typeinfo>

// definitation of Graph
class Graph
{
public:
  virtual  void draw() { std::cout << "Graph::draw() : just as an interface\n"; }
};


// definition of Rectangle, derived from Graph
class Rectangle : public Graph
{
public:
    void draw() { std::cout << "Rectangle::draw(): programs of draw a rectangle\n"; }
};


// definition of Circle, derived from Graph
class Circle : public Graph
{
public:
    void draw() { std::cout << "Circle::draw(): programs of draw a circle\n"; }
};


// definitaion of fun(): as a call interface
////通过在Graph类接口draw（），不加/加关键字virtual，可以观察到运行时ptr实际指向的对象不同
void fun(Graph* ptr)
{
    std::cout << "pointer type: " << typeid(ptr).name() << "\n";
    std::cout << "RTTI type: " << typeid(*ptr).name() << "\n";
    ptr->draw();
}

// test 
int main()
{
    Graph g1;
    Rectangle r1;
    Circle c1;

    // call by object name
    g1.draw();
    r1.draw();
    c1.draw();

    std::cout << "\n";

    // call by object name, and using the scope resolution operator::
    r1.Graph::draw();
    c1.Graph::draw();

    std::cout << "\n";

    // call by pointer to Base class
    fun(&g1);
    fun(&r1);
    fun(&c1);
}

　　无关键词virtual

 有关键词virtual

 归纳总结：

（1）在多继承时，基类与派生类之间，或基类之间出现同名成员时，

　　将出现访问时的二义性（不确定性），需要采用同名覆盖原则来解决

（2）Graph::draw()中的::在这作一元作用域分辨符 它的作用是：当局部

　　变量和全局变量同名时 ，在局部变量所在作用域中访问全局变量

（3）在需要基类对象的任何地方，都可以使用共有派生类的对象来替

　　代，派生类对象的地址可以赋值给基类的指针

 

实验任务三 

battery.hpp

#pragma once

#include<iostream>
using namespace std;

class Battery {
public:
    Battery(int capacity0 = 70) :capacity(capacity0) {};
    int get_capacity()
    {
        return capacity;
    }

private:
    int capacity;
};

car.hpp

#include<iostream>
#include<string>
using namespace std;

class Car {
public:
    Car(string maker0, string model0, int year0, int odometers0 = 0) :maker(maker0), model(model0), year(year0), odometers(odometers0) {};

    void info() {
        cout << "maker:\t\t" << maker << endl;
        cout << "model:\t\t" << model << endl;
        cout << "year:\t\t" << year << endl;
        cout << "odometers:\t" << odometers << endl;
    }
    
    void update_odometers(int odometers0)
    {
        if (odometers0 < odometers)
        {
            cout << "The update_odometers is wrong" << endl;
        }
        else
        {
            odometers = odometers0;
        }

    }
    
private:
    string maker;
    string model;
    int year;
    int odometers;
};

electricCar.hpp

#include"battery.hpp"
#include"car.hpp"
#include<iostream>

using namespace std;


class ElectricCar :public Car {
public:
    ElectricCar(string maker0, string model0, int year0, int odometers0 = 0, int battrey0 = 70) :Car(maker0, model0, year0, odometers0), battery(battrey0) {};
    

    void info()
    {
        Car::info();
        cout << "capacity:\t" << battery.get_capacity() << "-KWh" << endl;
    }
private:
    Battery battery;
    
};

task3.cpp

#include <iostream>
#include "electricCar.hpp"


int main()
{
    using namespace std;

    // test class of Car
    Car oldcar("Audi", "a4", 2021);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(17000);
    oldcar.info();

    cout << endl;

    // test class of ElectricCar
    ElectricCar newcar("Tesla", "model s", 2020);
    newcar.update_odometers(1100);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
}

 

任务四

pets.hpp

#ifndef _PETS_HPP
#define _PETS_HPP

#include<iostream>
#include<string>
using namespace std;

class MachinePets {
public:
    MachinePets(const string s) : nickname(s) {};
    
    virtual string talk() {};
    string get_nickname()
    {
        return nickname;
    }
private:
    string nickname;
};

class PetCats :public MachinePets {
public:
    PetCats(const string s) :MachinePets(s) {};
    string talk()
    {
        return "miao wu~";
    }

};

class PetDogs :public MachinePets {
public:
    PetDogs(const string s) :MachinePets(s) {};
    string talk()
    {
        return "wang wang~";
    }
};
#endif // !_PETS_HPP

task4.cpp

#include <iostream>
#include "pets.hpp"

void play(MachinePets* ptr)
{
    std::cout << ptr->get_nickname() << " says " << ptr->talk() << std::endl;
}

int main()
{
    PetCats cat("miku");
    PetDogs dog("da huang");

    play(&cat);
    play(&dog);
}