更新时间:2022-10-04 23:16:05
返回:贺老师课程教学链接
#include<iostream> using namespace std; class A { int a; public: A():a(5){} virtual void print()const { cout<<a;} }; class B: public A { char b; public: B() { b='E'; } void print() const { cout<<b; } }; void show(A &x) { x.print(); } int main() { A d1,*p; B d2; p=&d2; d1.print(); d2.print(); p->print(); show(d1); show(d2); return 0; }
#include <iostream> using namespace std; class BASE { private: char c; public: BASE(char n):c(n) {} virtual ~BASE() { cout<<c; } }; class DERIVED:public BASE { private: char c; public: DERIVED(char n):BASE(n+1),c(n) {} ~DERIVED(){ cout<<c; } }; int main(){ DERIVED d('X'); return 0; }
#include <iostream> using namespace std; class Base { public: virtual void Who() =0; }; class FirstDerived:public Base { public: void Who() { cout<<"F"; } }; class SecondDerived:public Base { public: void Who() { cout<<"S"; } }; int main() { FirstDerived first_obj; SecondDerived second_obj; Base &bref=first_obj; bref.Who(); bref=second_obj; bref.Who(); Base *bp; bp=&first_obj; bp->Who(); bp=&second_obj; bp->Who(); return 0; }
#include <iostream> using namespace std; class Vehicle //交通工具 { public: void run() const { cout << "run a vehicle. "<<endl; } }; class Car: public Vehicle //汽车 { public: void run() const { cout << "run a car. "<<endl; } }; class Airplane: public Vehicle //飞机 { public: void run() const { cout << "run a airplane. "<<endl; } }; int main() { cout<<"(a) 直接用对象访问成员函数: "<<endl; Vehicle v; v.run(); Car car; Airplane airplane; car.run(); airplane.run(); cout<<"(b)用指向基类的指针访问成员函数: "<<endl; Vehicle *vp; vp=&car; vp->run(); vp=&airplane; vp->run(); return 0; }请回答:当基类的指针指向派生类时,用指针调用同名成员函数,执行的是基类的成员函数,还是派生类的成员函数?为什么会这样?
class Vehicle { public: virtual void run() const { cout << "run a vehicle. "<<endl; } //(2) run()为虚函数 };请回答:当基类的指针指向派生类时,用指针调用同名虚成员函数,执行的是基类的成员函数,还是派生类的成员函数?为什么会这样?什么是多态性?请结合本例的运行结果说明。
class Vehicle{ public: virtual void run() const = 0; //(3) run()为纯虚函数,const意指其为常成员函数,并非纯虚函数之必要 };请回答:当基类同名成员函数定义为纯虚函数后,发生了什么现象?为什么会这样?