实验四 继承
task2:
Code:
#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); }
使用虚函数前运行结果:
使用虚函数后运行结果:
总结:
当派生类中存在与基类同名的函数是,使用时默认调用派生类函数,基类函数会被隐藏,可以通过作用域符进行访问。
对于虚函数,虚函数通过虚函数表来实现。虚函数有利于函数的重写,当父类中定义了一个虚函数,子类中同名的函数也会是虚函数,这时我们可以通过虚函数很好的指向我们要访问的函数。
task3:
battery.hpp:
#include <iostream> #include <string> #include <iomanip> 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() = default; Car(string _maker, string _model, int _year, int _odo = 0) :maker(_maker), model(_model), year(_year), odometers(_odo){} void info() { cout.setf(ios::left); cout << setw(15) << "maker:" << maker << endl; cout << setw(15) << "model:" << model << endl; cout << setw(15) << "year:" << year << endl; cout << setw(15) << "odometers:" << odometers << endl; } void update_odometers(int _meters) { if ( _meters < odometers ) { cout << "Incorrect Value!!!" << endl; return; } else { odometers = _meters; } } private: string maker; string model; int year; int odometers; };
electricCar.hpp:
#include "battery.hpp" #include "car.hpp" #include <iostream> using namespace std; class ElectricCar :public Car { public: ElectricCar(string _maker, string _model, int _year, int _odo = 0, Battery _bat = Battery()) :Car(_maker, _model, _year, _odo),battery(_bat){} void info() { Car::info(); cout << setw(15) << "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("Audi", "a4", 2016); cout << "--------oldcar's info--------" << endl; oldcar.update_odometers(2430); oldcar.info(); cout << endl; // test class of ElectricCar ElectricCar newcar("Tesla", "model s", 2018); newcar.update_odometers(25020); cout << "\n--------newcar's info--------\n"; newcar.info(); }
运行结果:
task4:
pets.hpp:
#include <iostream> #include <string> using namespace std; class MachinePets { public: MachinePets(const string s) :nickname(s){} virtual string talk() { return "xixi"; } string get_nickname()const { return nickname; } 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); }
运行结果: