实验四 继承

实验任务二

task2.cpp

#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
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);
}

　　运行结果

 

 总结

1.对于同名的函数，继承类会将基类的函数覆盖掉。

2.对于继承的类的对象，可以通过 对象.基类::(同名)函数 的方式来访问被覆盖掉的同名函数。

3.如果一个类有直接或间接的虚基类，则先执行虚基类的构造函数。

​4. 如果该类有其他基类，则按照它们在继承声明列表中的出现的次序，分别执行它们的构造函数，但构造过程中，不再执行它们的虚基类的构造函数。

 5.添加了virtual后，fun函数输出不同。通过使函数变为虚拟函数，可以使派生类对象指针模拟为基类对象来使调用函数发生改变。 

 

实验任务三

Battery.hpp

#ifndef BATTERY_HPP
#define BATTERY_HPP

#include <bits/stdc++.h>
using namespace std;
class Battery
{
    public:
        Battery(int _capacity = 70 ):capacity(_capacity){}
        void get_capacity() const;
    private:
        int capacity;
};

void Battery::get_capacity() const
{
    cout << "capacity:      " << capacity << "-kWh" << endl;
}

#endif

Car.cpp

#ifndef CAR_HPP
#define CAR_HPP


#include <bits/stdc++.h>
using namespace std;
class Car
{
    public:
        Car(string a="",string b = "", int c = -1, int d = 0):maker(a),model(b),year(c),odometers(d){}
        void info();
        void update_odometers(int a);
    protected:
        string maker;
        string model;
        int year;
        int odometers;
};

void Car::info()
{
    cout << "maker:         " << maker << endl;
    cout << "mode:          " << model << endl;
    cout << "year:          " << year << endl;
    cout << "odometers:     " << model << endl;
}

void Car::update_odometers(int a)
{
    if(a < odometers) cout << "ERROR!"<<endl;
    else odometers = a;
}
#endif

ElectricCar.hpp

#ifndef ELECTRICCAR_HPP
#define ELECTRICCAR_HPP

#include "car.hpp"
#include "Battery.hpp"
#include <iostream>
using namespace std;

class ElectricCar:public Car
{
    public:
        ElectricCar(string a="",string b="", int c=-1, int d=0,int e = 70):Car(a,b,c,d),battery(e){}
        void info();
    private:
        Battery battery;
};
void ElectricCar::info()
{
    Car::info();
    battery.get_capacity();
}

#endif

task3.cpp

#include <iostream>
#include "electricCar.hpp"
using namespace std;


int main()
{
    using namespace std;

    // test class of Car
    Car oldcar("audi", "A4", 2077);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(25000);
    oldcar.info();

    cout << endl;

    // test class of ElectricCar
    ElectricCar newcar("Tesla", "model S+", 2078);
    newcar.update_odometers(2500);
    cout << "\n--------newcar's info--------\n";
    newcar.info();

运行结果

 

实验任务四

pets.hpp

#include<iostream>
#include<string>

using namespace std;

class MachinePets {
private:
    string nickname;
public:
    MachinePets(const string s) :nickname(s) {}
    string get_nickname()const { return nickname; }
    virtual string talk() { return "0"; }
};

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

class PetDogs :public MachinePets {
public:
    PetDogs(const string s) :MachinePets(s) {}
    string talk() { return "woof"; }
};

task.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);
}

运行结果