实验4 继承

实验任务2

修改前：

#include <iostream>
#include <typeinfo>

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

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


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


void fun(Graph *ptr)
{
    std::cout << "pointer type: " << typeid(ptr).name() << "\n";
    std::cout << "RTTI type: " << typeid(*ptr).name() << "\n";
    ptr -> draw();
}

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

    g1.draw();
    r1.draw();
    c1.draw();

    std::cout << "\n";

    r1.Graph::draw();
    c1.Graph::draw();

    std::cout << "\n";

    fun(&g1);
    fun(&r1);
    fun(&c1);
}

运行结果：

 

 

修改后：

#include <iostream>
#include <typeinfo>

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

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


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


void fun(Graph *ptr)
{
    std::cout << "pointer type: " << typeid(ptr).name() << "\n";
    std::cout << "RTTI type: " << typeid(*ptr).name() << "\n";
    ptr -> draw();
}

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

    g1.draw();
    r1.draw();
    c1.draw();

    std::cout << "\n";

    r1.Graph::draw();
    c1.Graph::draw();

    std::cout << "\n";

    fun(&g1);
    fun(&r1);
    fun(&c1);
}

运行结果：

归纳总结：

1.同名覆盖原则：

若派生类中声明了与基类成员函数同名的新函数，即使函数的参数表不同，从基类继承的同名函数的所有重载形式也都会被隐藏。如果某派生类的多个基类拥有同名的成员，同时，派生类有新增这样的同名成员，这种情况下，派生类成员将隐藏所有基类的同名成员。

2.二元作用域分辨符：

当派生类新增成员隐藏了基类的同名成员，这时使用”对象名.成员名“的访问方式只能访问到派生类新增的成员。对基类同名成员的访问，只能通过基类名和作用域分辨符来实现。

3.类型兼容原则：

 类型兼容规则是指在需要基类对象的任何地方，都可以使用公有派生类的对象来替代。通过公有继承，派生类得到了基类中除构造函数、析构函数之外的所有成员。公有派生类实际就具备了基类的所有功能，凡是基类能解决的问题，公有派生类都可以解决。

 

实验任务3

Battery.hpp

#ifndef BATTERY
#define BATTERY
#include<iostream>
#include<string>

using namespace std;

class Battery{
    public:
        Battery(int b=70):capacity(b){};
        int get_capacity() const{return capacity;}
    private:
        int capacity;
};

#endif

Car.hpp

#ifndef CAR
#define CAR
#include<iostream>
#include<string>
#include<iomanip>

using namespace std;
class Car{
    public:
        Car(string s1,string s2,int a,int b=0):maker(s1),model(s2),year(a),odometers(b){};
        void info() const {
            cout<<left<<setw(20)<<"maker: "<<maker<<endl;
            cout<<left<<setw(20)<<"model: "<<model<<endl;
            cout<<left<<setw(20)<<"year: "<<year<<endl;
            cout<<left<<setw(20)<<"odometers: "<<odometers<<endl;
        }
        void update_odometers(int meters){
            if(meters<odometers)
            cout<<"The updated number of odometers is wrong."<<endl;
            else
            odometers=meters;
        }
    private:
            string maker;
            string model;
            int year;
            int odometers;
};

#endif

ElectricCar.hpp

#ifndef ELECTRICCAR
#define ELECTRICCAR
#include"battery.hpp"
#include"car.hpp"
#include<iostream>
#include<string>
#include<iomanip>

class ElectricCar:public Car{
    public:
        ElectricCar(string s1,string s2,int a,int b=0,int ca=70):Car(s1,s2,a,b),battery(ca){};
        void info() const {
            Car::info();
            cout<<left<<setw(20)<<"capacity: "<<battery.get_capacity()<<"-kWh"<<endl;
        }
    private:
            Battery battery;    
};

#endif

task3.cpp

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

int main(){
    using namespace std;

    Car oldcar("Maserati","Ghibli",2019);
    cout<<"--------oldcar's info--------"<<endl;
    oldcar.update_odometers(25000);
    oldcar.info();

    cout<<endl;

    ElectricCar newcar("BYD", "SUV", 2020);
    newcar.update_odometers(25000);
    cout<<"\n--------newcar's info--------\n";
    newcar.info();
}

运行结果：

 

  实验任务4

pets.hpp

#ifndef PETS
#define PETS
#include <iostream>
#include <string>

using namespace std;

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

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

class PetDogs: public MachinePets{
    public:
    PetDogs(const string s):MachinePets(s){}
    string talk() const {
        string voice="wang wang~";
        return voice;
         }
};

#endif

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);
}

运行结果：