C++程序设计实验四 继承

程序源码：

#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);
}

运行结果截图：

归纳总结：

　　1. 当派生类出现与基类同名成员时：同名覆盖原则（使用派生类所实现的接口），二元作用域分辨符（通过 :: 使用基类所实现的接口）

　　2. 类型兼容原则：派生类对象可以被当作基类对象使用，但是，当作基类对象使用时，只能使用作为基类的那一部分接口

改动后的代码：

// definitation of Graph
class Graph
{
public:
    // 声明时加了关键字virtual
    virtual void draw() { std::cout << "Graph::draw() : just as an interface\n"; }
};

运行结果截图：

battery.hpp

#include<iostream>

using namespace std;

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

private:
    int capacity;
};

car.hpp

#include<iostream>
#include<string>
#include<iomanip>

using namespace std;

class Car
{
public:
    Car(string _maker, string _model, int _year) : maker(_maker), model(_model), year(_year) { odometers = 0; }
    void info()
    {
        cout << left << setw(20) << "maker:" << maker << endl;
        cout << setw(20) << "model:" << model << endl;
        cout << setw(20) << "year:" << year << endl;
        cout << setw(20) << "odomerters:" << odometers << endl;
    }
    void update_odometers(int new_odometers)
    {
        if (new_odometers < odometers)
        {
            cout << "\nERROR!! updata odometers small than origin odometers" << endl;
            return;
        }
        odometers = new_odometers;
    }

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

electricCar.hpp

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

using namespace std;

class ElectricCar : public Car
{
public:
    ElectricCar(string _maker, string _model, int _year, Battery _battery=70) : Car(_maker, _model, _year), battery(_battery) { }
    void info()
    {
        cout << left << setw(20) << "maker:" << maker << endl;
        cout << setw(20) << "model:" << model << endl;
        cout << setw(20) << "year:" << year << endl;
        cout << setw(20) << "odomerters:" << odometers << endl;
        cout << setw(20) << "capacity:" << 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("DingDing", "maka", 2008);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(2500);
    oldcar.info();
    cout << endl;
    // test class of ElectricCar
    ElectricCar newcar("kapani", "soucat", 2015);
    newcar.update_odometers(5000);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
    newcar.update_odometers(2500);
}

运行测试截图：

pets.hpp

#include<string>

using namespace std;

class MachinePets
{
public:
    MachinePets(const string s) : nickname(s) { }
    string get_nickname() const { return nickname; }
    virtual string talk() { return "bing bo~"; }
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~"; }
};

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);
}

运行测试截图：