实验4 继承

四、实验结论

1.实验任务1

验证性内容。

2.实验任务2

• 程序源码，及，运行结果截图

  #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);
  }
  

  

• 归纳总结：

  同名覆盖原则：若未明确指出，则通过派生类对象使用的是派生类中的同名成员。

  二元作用域分辨符：类名::成员 //数据成员 类目::成员名(参数表) //函数成员

  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。在替代之后，派生类对象就可以作为基类的对象使用，但只能使用从基类继承的成员。

• 对代码微调后，运行结果截图

  // 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"; }
  };
  

  

3.实验任务3

• 完整源代码：

  Battery.hpp

  #ifndef BATTERY_H
  #define BATTERY_H
  
  #include <iostream>
  using namespace std;
  
  class Battery
  {
  public:
      Battery(int capacity0);
      int get_capacity();
      ~Battery() = default;
  
  private:
      int capacity;
  };
  
  Battery::Battery(int capacity0 = 70) : capacity(capacity0) {}
  
  int Battery::get_capacity()
  {
      return capacity;
  }
  #endif
  

  Car.hpp

  #ifndef CAR_H
  #define CAR_H
  
  #include <iostream>
  #include <iomanip>
  using namespace std;
  
  class Car
  {
  public:
      Car(string maker0, string model0, int year0);
      void info() const;
      void update_odometers(int newOdometers);
      ~Car() = default;
  
  private:
      string maker;
      string model;
      int year;
      int odometers;
  };
  
  Car::Car(string maker0, string model0, int year0) : maker(maker0), model(model0), year(year0)
  {
      odometers = 0;
  }
  
  void Car::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 Car::update_odometers(int newOdometers)
  {
      if (newOdometers < odometers)
          cout << "update error" << endl;
      else
          odometers = newOdometers;
  }
  #endif
  

  ElectricCar.hpp

  #ifndef ELECTRIC_CAR_H
  #define ELECTRIC_CAR_H
  
  #include <iostream>
  #include "car.hpp"
  #include "battery.hpp"
  using namespace std;
  
  class ElectricCar : public Car
  {
  public:
      ElectricCar(string maker, string model, int year);
      void info();
      ~ElectricCar() = default;
  
  private:
      Battery battery;
  };
  
  ElectricCar::ElectricCar(string maker, string model, int year) : Car(maker, model, year), battery(70) {}
  
  void ElectricCar::info()
  {
      Car::info();
      cout << left << 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("Audi", "a7", 2021);
    cout << "--------oldcar's info--------" << endl;
    oldcar.update_odometers(30000);
    oldcar.info();
  
    cout << endl;
  
    // test class of ElectricCar
    ElectricCar newcar("Tesla", "model s", 2022);
    newcar.update_odometers(3000);
    cout << "\n--------newcar's info--------\n";
    newcar.info();
  }
  

• 运行测试截图

  

4.实验任务4

• 完整源代码：

  pets.hpp

  #ifndef PETS_H
  #define PETS_H
  
  #include <iostream>
  using namespace std;
  
  class MachinePets
  {
  
  public:
      MachinePets(const string nickname);
      virtual string talk();
      const string get_nickname();
      ~MachinePets() = default;
  
  private:
      string nickname;
  };
  
  MachinePets::MachinePets(const string nickname0) : nickname(nickname0) {}
  
  string MachinePets::talk() { return ""; }
  
  const string MachinePets::get_nickname()
  {
      return nickname;
  }
  
  class PetCats : public MachinePets
  {
  public:
      PetCats(const string s);
      string talk();
      ~PetCats() = default;
  };
  
  PetCats::PetCats(const string s) : MachinePets(s) {}
  
  string PetCats::talk()
  {
      return "miao wu~";
  }
  
  class PetDogs : public MachinePets
  {
  public:
      PetDogs(const string s);
      string talk();
      ~PetDogs() = default;
  };
  
  PetDogs::PetDogs(const string s) : MachinePets(s) {}
  
  string PetDogs::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);
  }
  

• 运行测试截图

  

五、实验总结（选）