实验4 继承

实验任务2

<task2.cpp>

#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：

同名覆盖原则：派生类和基类具有相同成员时，通过派生类对象访问，默认访问的是派生类的同名成员

二元作用域分辨符（::）：用于显式指定使用的是哪个类的重名成员

类型兼容原则：派生类对象也可以当作基类对象来使用，但只能使用从基类继承的那部分功能

在Graph类的成员函数draw()前加上virtual，重新编译运行。结果为：

调用虚函数时，根据指针实际指向的对象，选择相应的函数实现。

实验任务3

使用类的组合和继承模拟简单的车辆信息管理。

<battery.hpp>

#ifndef BATTERY_HPP
#define BATTERY_HPP

class Battery
{
public:
    Battery(int cap=70):capacity{cap}{}
    //Battery(Battery& b):capacity(b.capacity){}
    int get_capacity(){return capacity;}
private:
    int capacity;
};
#endif

<car.hpp>

#ifndef CAR_HPP
#define CAR_HPP

#include <iostream>
#include <iomanip>
using namespace std;
class Car
{
public:
    Car() = default;
    Car(string ma, string mo, int y, int meters = 0);
    void info();
    void update_odometers(int meters);

    string maker;  //制造商
    string model;  //型号
    int year;      //生产年份
    int odometers; //行车里程数
};

Car::Car(string ma, string mo, int y, int meters)
{
    maker = ma;
    model = mo;
    year = y;
    odometers = meters;
}

void Car::info()
{
    cout.setf(ios::left);
    cout << setw(20) << "maker:" << maker << endl;
    cout << setw(20) << "model:" << model << endl;
    cout << setw(20) << "year:" << year << endl;
    cout << setw(20) << "odometers:" << odometers << endl;
}

void Car::update_odometers(int meters)
{
    if (meters < odometers)
        cout << "new odometers is wrong!!!" << endl;
    else
    {
        odometers = meters;
    }
}
#endif

<electricCar.hpp>

#ifndef ELECTRICCAR_HPP
#define ELECTRICCAR_HPP

#include"battery.hpp"
#include"car.hpp"
using namespace std;

class ElectricCar : public Car
{
public:
    ElectricCar(string ma,string mo,int y,int cap=70,int meters=0):Car(ma,mo,y,meters),battery(cap){}
    void info();
private:
    Battery battery;
};

void ElectricCar::info()
{
    cout.setf(ios::left);
    cout << setw(20) << "maker:" << maker << endl;
    cout << setw(20) << "model:" << model << endl;
    cout << setw(20) << "year:" << year << endl;
    cout << setw(20) << "odometers:" << odometers << endl;
    cout << setw(20) << "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("BWM", "a4", 2016);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(25000);
    oldcar.info();

    cout << endl;

    // test class of ElectricCar
    ElectricCar newcar("Tesla", "model A", 2016);
    newcar.update_odometers(5000);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
}

测试结果：

 实验任务4

使用类的继承，模拟简单的机器宠物。

<pets.hpp>

#ifndef PETS_HPP
#define PETS_HPP

using namespace std;
class MachinePets
{
public:
    MachinePets(const string s) : nickname{s} {}
    string get_nickname() const { return nickname; }
    virtual string talk() { return "ze~ze~"; }

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~";
    }
};
#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);
}

测试结果：

总结与体会

1、加了{}就是定义了，而不是声明

2、派生类构造函数初始化，通过参数化列表，先调用基类构造函数初始化基类，再初始化派生类成员

3、有默认值的形参才可以没有实参