实验四

任务2

task2.cpp

#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);
}

微调后

#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，应使用基类名及作用域分辨符限定。当多个基类存在同名成员时，如果通过派生类对象访问存在二义性，也应使用基类名及作用域分辨符限定。

（3）类型兼容原则：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。

任务3

battery.hpp

#ifndef BATTERY_HPP
#define BATTERY_HPP
#include<iostream>
using namespace std;
class Battery{
    public:
        Battery(int c=70):capacity(c){}
        int get_capacity(){
            return capacity;
        }
    private:
        int capacity;
};
#endif

car.hpp

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

class Car {
private:
    string maker, model;
    int year, odometers;
public:
    Car(string a, string b, int c) :maker(a), model(b), year(c) {
        odometers = 0;
    }
    void info();
    void update_odometers(int a) {
        if (a < odometers)
            cout << "error" << endl;
        else
            odometers = a;
    }
};
void Car::info() {
    cout<< "maker:" << maker << endl;
    cout<< "model:" << model << endl;
    cout<< "year:" << year << endl;
    cout<< "odometers:" << odometers << endl;
};
#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,int d=70):Car(a,b,c),battery(d){}
        void info();    
    private:
        Battery battery;
};
void ElectricCar::info(){
   Car::info();
   cout<<"capacity:"<<battery.get_capacity()<<"-kWh"<<endl; 
}
#endif

task3.cpp

#include"ElectricCar.hpp"
#include <iostream>
int main()
{
    using namespace std;

    // test class of Car
    Car oldcar("Lamborghini", "Aventador", 2019);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(25000);
    oldcar.info();

    cout << endl;

    // test class of ElectricCar
    ElectricCar newcar("Tesla", "model h", 2030);
    newcar.update_odometers(2888);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
}

任务4

pets.hpp

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