C++多态

Polymorphism(多态)

Upcast:take an object of the derived class as an object of the base one.

　　-Ellipse can be treated as a Shape

Dynamic binding(动态绑定)

　　-Binding:which function to be called

　　　　-Static binding: call the function as the code(静态绑定，编译的时已经确定，)

　　　　-Dynamic binding: call the function of the object（动态绑定，运行时根据指针所指向的对象来确定call哪个函数k,跟virtual render()有关系）

class XYPos{};//xy,point

class Shape
{
public:
    Shape();
    virtual ~Shape();//虚函数，子类 和 父类的函数有关系
    virtual void render();
    void move(const XYPos &);
    virtual void resize();
protected:
    XYPos center;
};

class Ellipse : public Shape
{
public:
    Ellipse(float maj, float minr);
    virtual void render();//will define own
protected:
    float major_axis, minor_axis;
};

class Circle : public Ellipse
{
public:
    Circle(float radius) : Ellipse(radius, radius){};
    virtual void render();
};

void render(Shape* p)
{
    p->render();//根据给定的形状调用正确的render函数；
}
void func()
{
    Ellipse ell(10,20);
    ell.render();
    circle circ(40);
    circ.render();
    render(&ell);
    render(&circ);
}