第一章C++的初步知识第二章类和对象第三章再论类和对象第四章运算符重载第五章继承与派生第六章多态性与虚函数第七章输入输出流第八章C++工具6.1多态性的概念6.2一个典型的例子6.3虚函数6.4纯虚函数与抽象类6.1多态性的概念6.1多态性的概念6.2一个典型的例子①先声明基类point②再声明派生类circle类③最后声明cylinder类最后写出主函数6.2一个典型的例子6.3虚函数6.3虚函数6.3虚函数6.3虚函数6.3虚函数6.3虚函数6.3虚函数6.3虚函数6.3虚函数6.3虚函数6.3虚函数6.4纯虚函数与抽象类6.4纯虚函数与抽象类6.4纯虚函数与抽象类6.4纯虚函数与抽象类6.4纯虚函数与抽象类#include<iostream.h>classshape{public:virtualfloatarea()const{return0.0;}//虚函数virtualfloatvolume()const{return0.0;}//虚函数virtualvoidshapeName()const=0;//纯虚函数};//抽象类不能也不必定义对象classpoint:publicshape{public:point(float=0,float=0);voidsetPoint(float,float);floatgetX(){returnx;}floatgetY(){returny;}virtualvoidshapeName()const{cout<<“point:”;}//对虚函数再定义friendostream&operator<<(ostream&,constpoint&);protected:floatx,y;};classcircle:publicpoint{public:circle(floatx=0,floaty=0,floatr=0);floatgetRadius()const;virtualfloatarea()const;//因为基类此函数定义为虚函数，所以在这里，不管有没有virtual,只要函数名、参数表相同，都是虚函数virtualvoidshapeName()const{cout<<“circle:”;}//对虚函数再定义friendostream&operator<<(ostream&,constcircle&);protected:floatradius;};//定义circle类成员函数circle::circle(floatx,floaty,floatr):point(x,y),radius(r){}classcylinder:publiccircle{public:cylinder(floatx=0,floaty=0,floatr=0,floath=0);voidsetHeight(float);virtualfloatarea()const;virtualfloatvolume()const;virtualvoidshapeName()const{cout<<“cylinder:”;}//对虚函数再定义friendostream&operator<<(ostream&,constcylinder&);protected:floatheight;};//定义cylinder类成员函数cylinder::cylinder(floata,floatb,floatr,floath):circle(a,b,r),height(h){}voidcylinder::setHeight(floath){height=h;}voidmain(){pointp1(3.2,4.5);circlec1(2.4,1.2,5.6);cylindercy1(3.5,6.4,5.2,10.5);p1.shapeName();//静态关联cout<<p1<<endl;c1.shapeName();//静态关联cout<<c1<<endl;cy1.shapeName();//静态关联cout<<cy1<<endl;shape*pt;//定义基类指针pt=&p1;//指针指向point对象p1pt->shapeName();//动态关联cout<<“x=“<<p1.getX()<<“,y=“<<p1.getY()<<“\narea=“<<pt->area()<<“\nvolume=“<<pt->volume()<<“\n\n”;6.4纯虚函数与抽象类习题：本章习题请上网查阅教学网页：http://staff.ustc.edu.cn/~lee