纯虚基类与虚函数的使用

图形虚基类，定义计算面积跟周长的函数。派生出圆形，三角形，矩形子类，并重新定义基类计算面积与周长的函数。

注意：当基类的指针指向派生类的时候，只能操作派生类中从基类中继承过来的数据。

虚基类：

class graph  {public:virtual double perimeter() const= 0;virtual double area() const= 0; };

circle类：

#include"graph.h"class circle:public graph {public:circle(double r):radius(r){};//初始化成员列表virtual ~circle();double perimeter() const;double area() const;private:double radius;};

#include "circle.h"#define PI 3.14159double circle::area() const{return this->radius*this->radius*PI;}double circle::perimeter() const{return 2*this->radius*PI;}

rectangle类：

#include"graph.h"class rectangle:public graph{public:rectangle(double w,double h):width(w),height(h){};virtual ~rectangle();double perimeter() const;double area() const; private:double width;double height;};

#include "rectangle.h"double rectangle::area() const{return this->height*this->width;}double rectangle::perimeter() const{return 2*(this->height+this->width);}

triangle类：

#include"graph.h"class triangle:public graph{public:triangle(double a,double b,double c):boder1(a),boder2(b),boder3(c){};virtual ~triangle();double area() const;double perimeter() const;private:double boder1;double boder2;double boder3;};

#include "triangle.h"#include<cmath>double triangle::area() const{double ave = (this->boder1+this->boder2+this->boder3)/2;return sqrtf(ave*(ave-this->boder1)*(ave-this->boder2)*(ave-this->boder3)); //利用海伦公式}double triangle::perimeter() const{return this->boder1+this->boder2+this->boder3;}

主函数：

#include<iostream>#include<stdlib.h>#include<vector>#include<iterator>#include"circle.h"#include"graph.h"#include"triangle.h"#include"rectangle.h"using namespace std;int main(){graph* c = new circle(22.3);graph* r = new rectangle(4.5,6.7);graph* t = new triangle(2.3,4.4,5.5);cout<<c->area()<<endl;cout<<r->area()<<endl;cout<<t->area()<<endl;vector<graph*> all;all.push_back(c);all.push_back(r);all.push_back(t);vector<graph*>::iterator ptr = all.begin();for(ptr;ptr != all.end();ptr++){cout<<(*ptr)->area()<<endl;cout<<(*ptr)->perimeter()<<endl;}system("pause");return 0;}