超简单!c++虚函数例子解析

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#include <iostream>
using namespace std;
class Shape
{
public:
//普通函数前加virtual,普通函数变成了虚函数
  // =0表示抽象虚函数,子类必须实现该函数 virtual void printarea()=0; void hello(){cout<<"Shape hello function"<<endl;}; }; class Circle:public Shape { public: Circle(int a):r(a){} void hello(){cout<<"Circle hello function"<<endl;}; void printarea(){cout<<"圆形面积为:"<<r*r*3.14<<endl;} private: int r; }; class Rectangle:public Shape { public: Rectangle(int a,int b):x(a),y(b){} void hello(){cout<<"Rectangle hello function"<<endl;}; void printarea(){cout<<"矩形面积为:"<<x*y<<endl;} private: int x; int y; }; class Square:public Shape { public: Square(int a):l(a){} void hello(){cout<<"Square hello function"<<endl;}; void printarea(){cout<<"正方形面积为:"<<l*l<<endl;} private: int l; }; void prints(Shape *s) {
  //基类指针s指向子类对象
//s调用的函数printarea是虚函数,所以会调用子类实例的printarea s->printarea();
//s调用的函数hello不是虚函数,所以只会调用基类的hello s->hello(); } int main() { Circle a(1); prints(&a); Square b(2); prints(&b); Rectangle c(1,2); prints(&c); return 0; }

输出:

圆形面积为:3.14
Shape hello function
正方形面积为:4
Shape hello function
矩形面积为:2
Shape hello function

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