C++中的抽象基类示例

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