C++学习笔记－－抽象基类

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There is another solution: You can abstract from the Ellipse and Circle classes what they have in common and place those feature in an Abstract Base Class.

椭圆和圆有很多相似的地方，但是圆又不能直接从椭圆中继承，比较好的解决方法是把它们共有的部分放到抽象基类中。

When a class declaration contains a pure virtual function, you can't create an object of that class.

当一个类含有纯虚函数时，你不能创建那个类的对象。

#include <iostream>using namespace std;// Base classclass Shape{public:    // Pure virtual function providing interface framework.    virtual int getArea() = 0;    void setWidth(int w)    {        width = w;    }    void setHeight(int h)    {        height = h;    }protected:    int width;    int height;};// Derived classesclass Rectangle : public Shape{public:    int getArea()    {        return (width * height);    }};class Triangle : public Shape{public:    int getArea()    {        return (width * height) / 2;    }};int main(void){    Rectangle Rect;    Triangle Tri;    Rect.setWidth(5);    Rect.setHeight(7);    // Print the area of the object.    cout << "Total Rectangle area: " << Rect.getArea() << endl;    Tri.setWidth(5);    Tri.setHeight(7);    // Print the area of the object.    cout << "Total Triangle area: " << Tri.getArea() << endl;    return 0;}

输出：

wang@wang:~/c++$ ./a.out
Total Rectangle area: 35
Total Triangle area: 17

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