task 2

未修改前：

#include <iostream>
#include <typeinfo>

// definitation of Graph
class Graph
{
public:
    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);
}

 

 修改后：

#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);
}

 

 

归纳总结

①同名覆盖原则：当派生类和基类中有相同成员时，若未强行指明，则通过派生类对象使用的是派生类的中的同名成员。

②二元作用域分辨符：若果要通过派生类对象访问基类中被覆盖的同名成员，应使用基类名加二元作用域分辨符来限定。

③类型兼容原则：基类对像可以使用公有派生类的对象来替代。

 

 task 3

battery.hpp

#ifndef BATTERY_HPP
#define BATTERY_HPP
#include<iostream>
using namespace std;

class Battery
{
    private:
        int capacity;//车载动力电池容量
    public:
        Battery(int x=70):capacity(x){}
        int get_capacity(){return capacity;}
        ~Battery(){}
};
#endif

car.hpp

#ifndef CAR_HPP
#define CAR_HPP
#include<iostream>
#include <iomanip> 
using namespace std;

class Car
{
    public:
        Car(string a,string b,int c,int d=0):maker(a),model(b),year(c),odometers(d){}
        void info();
        ~Car(){}
        void update_odometers(int newodo); 
    private:
        string maker,model;//制造商，型号
        int year,odometers;//生产年份，行车里程数 
};
void Car::info() 
{
    cout<<left<<setw(16)<<"maker:"<<maker<<endl;
    cout<<left<<setw(16)<<"model:"<<model<<endl;
    cout<<left<<setw(16)<<"year:"<<year<<endl;
    cout<<left<<setw(16)<<"odometers:"<<odometers<<endl;
}

void Car::update_odometers(int newodo)
{
    if(newodo<odometers)
        cout<<"error！更新数值有误！"<<endl;
    else odometers=newodo;
}
#endif

electricCar.hpp

#ifndef ELECTRICAR_HPP
#define ELECTRICAR_HPP
#include<iostream>
#include <iomanip>
#include "car.hpp"
#include "battery.hpp"
using namespace std;
class ElectricCar : public Car
{
    private:
        Battery battery;
    public:
        ElectricCar(string a,string b,int c,int x=70):Car(a,b,c),battery(x){}
        void info();
        ~ElectricCar(){}
};
void ElectricCar::info() 
{
    Car::info() ;
    cout<<left<<setw(16)<<"capacity:"<<battery.get_capacity()<<"-KWh"<<endl; 
}
#endif

task3.cpp

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

int main()
{
    using namespace std;

    // test class of Car
    Car oldcar("Audi", "a4", 2016);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(25000);
    oldcar.info();

    cout << endl;

    // test class of ElectricCar
    ElectricCar newcar("Porsche", "911", 2018,150);
    newcar.update_odometers(3500);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
    return 0;
}

 

 

task 4

pets.hpp

#ifndef PETS_HPP
#define PETS_HPP
#include<iostream>
using namespace std;
class MachinePets
{
    private:
        string nickname;
    public:
        MachinePets(const string s):nickname(s){}
        string get_nickname()const {return nickname;}
        virtual string talk(){}
        ~MachinePets(){}
};

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

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

#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);
}