实验三虚函数与多态纯虚函数

1、-. z实验三虚函数与多态、纯虚函数一.实验目的1. 在掌握继承与派生关系的根底上，进一步理解虚函数与多态性的关系，实现运行时的多态。2. 学会定义和使用纯虚函数二、实验容1例：了解单接口，多方法的概念。现有称为figure的基类，存放了各二维对象三角形、矩形和圆形三个类的各维数据，set_dim()设置数据，是标准成员函数。show_area()为虚函数，因为计算各对象的面积的方法是不同的。【程序】#include using namespace std;class figureprotected:double *,y;public:void set_dim(double i,double

2、j=0) *=i; y=j; virtual void show_area() coutNo area putation defined for this class.n;class triangle:public figurepublic:void show_area() coutTriangle with height * and base y has an area of *0.5*y endl; ;class square:public figurepublic:void show_area() coutSquare with dimensions * and y has an are

3、a of *y endl; ;class circle:public figurepublic: void show_area() coutCircle with radius * has an area of 3.14159*set_dim(10.0,5.0);p-show_area();p=&s;p-set_dim(10.0,5.0);p-show_area();p=&c; p-set_dim(10.0);p-show_area(); return 0; 【要求】建立工程，录入上述程序，调试运行并记录运行结果。修改上述程序，将virtual void show_area()中的virtua

4、l去掉，重新调试运行观察结果有何变化？为什么？在不使用关键字virtual后，基类指针p对show-area的p-show_area()没有针对所指对象的类型调用不同的函数，而是直接根据p的类型调用了基类的成员函数show-area。修改上述程序入口函数，使其动态建立三角形、矩形和圆形3个对象，通过基类指针这3个对象，然后释放这3个对象。#include using namespace std;class figureprotected:double *,y;public:void set_dim(double i,double j=0) *=i; y=j; virtual void show

5、_area() coutNo area putation defined for this class.n;class triangle:public figurepublic:void show_area() coutTriangle with height * and base y has an area of *0.5*y endl; ;class square:public figurepublic:void show_area() coutSquare with dimensions * and y has an area of *y endl; ;class circle:publ

6、ic figurepublic: void show_area() coutCircle with radius * has an area of 3.14159*set_dim(10.0,5.0);p-show_area();p=p2;p-set_dim(10.0,5.0);p-show_area();p=p3;p-set_dim(10.0);p-show_area();delete p1;delete p2;delete p3;4修改类定义中的析构函数，使之适应用户动态定义对 2、使用纯虚函数和抽象类对实验二中的题1进展改良。#include using namespace std;cla

7、ss figureprotected:double *,y;public:void set_dim(double i,double j=0) *=i; y=j; virtual void show_area() coutNo area putation defined for this class.n;/在此处将基类的析构函数声明为虚析构就OK了virtual figure()/;class triangle:public figurepublic:void show_area() coutTriangle with height * and base y has an area of *0.

8、5*y endl; ;class square:public figurepublic:void show_area() coutSquare with dimensions * and y has an area of *y endl; ;class circle:public figurepublic: void show_area() coutCircle with radius * has an area of 3.14159*set_dim(10.0,5.0);p-show_area();p=&s;p-set_dim(10.0,5.0);p-show_area();p=&c; p-s

9、et_dim(10.0);p-show_area(); return 0; 2、编程：自定义一个抽象类Element,提供显示、求面积等公共接口虚函数，派生出Point、Line、Circle等图形元素类，并重新定义override这些虚函数，完成各自的任务。在这里，Element是抽象基类，它不能提供具体的显示操作，应将其成员函数定义为纯虚函数。只有采用指向基类的指针或对基类的引用进展调用，实现的才是动态绑定，完成运行时的多态性。#include using namespace std;const double PI=3.14159;class Elementpublic:virtual c

10、onst char* Name() const =0;virtual double Area() const =0;class Point:public Elementprotected:double *,y;public:Point(double *v=0,double yv=0):*(*v),y(yv)virtual const char* Name() constreturn Point;virtual double Area() constreturn 0;class Line:public Elementprotected:double length;public:Line(double l=0):length(l)virtual const char* Name() constreturn Line;virtual double Area() constreturn 0;class Circle:public Elementprotected:double radius;public:Circle(double r):radius(r)virtual const char* Name() constreturn Circle;virtual doub