抽象基类（abstract base class,ABC）
例子：圆与椭圆。建立一个基类BaseEllipse，建立它的恋歌继承了Ellipse和Circle。
ellipse.h
#ifndef ELLIPSE_H_
#define ELLIPSE_H_ class BaseEllipse
{
public:
virtual double Area() const =;
}; class Ellipse : public BaseEllipse
{
private:
double a, b;
public:
Ellipse(double a, double b) : a(a), b(b) {}
virtual double Area() const;
}; class Circle : public BaseEllipse
{
private:
double r;
public:
Circle(double r) : r(r) { }
virtual double Area() const;
}; #endif // ELLIPSE_H_
ellipse.cpp
#include "ellipse.h" double Ellipse::Area() const
{
return 3.14159 * a * b;
} double Circle::Area() const
{
return 3.14159 * r * r;
}
测试类
#include <iostream>
#include "ellipse.h" int main()
{
using std::cout;
using std::endl;
double a = 1.0, b = 2.0, r = 3.0;
Ellipse * ellipse = new Ellipse(a, b);
cout << ellipse->Area() << endl;
Circle * circle = new Circle(r);
cout << circle->Area() << endl;
return ;
}
输出效果：
6.28318
28.2743