1.什么是多态

　　

　　

2.

　　

 

　　示例代码：　　

 1 #include <iostream>
 2 
 3 using namespace std;
 4 
 5 //形状:位置、绘制
 6 //+--圆形:半径、（绘制）
 7 //+--矩形:长宽、（绘制）
 8 //形状
 9 class Shape{
10 public:
11         Shape(int x, int y): m_x(x), m_y(y){}
12         virtual void draw(void) const
13         {
14             cout << "形状(" << m_x << ',' << m_y << ')' << endl;
15         }
16     
17 protected:
18     int m_x;
19     int m_y;
20 };
21 
22 //圆形
23 class Circle: public Shape{
24 public:
25     Circle(int x, int y, int r): Shape(x, y), m_r(r){}
26     void draw(void) const
27     {
28         cout << "圆形（" << m_x << ',' << m_y << ',' << m_r << ')' << endl;
29     }
30 private:
31     int m_r;
32 };
33 
34 //矩形
35 class Rectangle: public Shape{
36 public:
37     Rectangle(int x, int y, int w, int h): Shape(x, y), m_w(w), m_h(h){}
38     void draw(void) const
39     {
40         cout << "矩形(" << m_x << ',' << m_y << ',' << m_w << ',' << m_h << ')' << endl;
41     }
42 private:
43     int m_w;
44     int m_h;
45 };
46 
47 void render(Shape* shapes[])
48 {
49     for(size_t i = 0; shapes[i]; ++i)
50         shapes[i]->draw();
51 }
52 
53 void drawAny(Shape const& shape)
54 {
55     shape.draw();
56 }
57 
58 int main(void)
59 {
60     Shape* shapes[10] = {0};
61     shapes[0] = new Circle (1,2,3);
62     shapes[1] = new Circle(4,5,6);
63     shapes[2] = new Rectangle(7,8,9,10);
64     shapes[3] = new Rectangle(11,12,13,14);
65     shapes[4] = new Circle(15,16,17);
66     render(shapes);
67     /*
68     Circle c(18,19,20);
69     Shape& r = c;
70     r.draw();
71     */
72     Circle cr(18,19,20);
73     drawAny(cr);
74     Rectangle rc(21,22,23,24);
75     drawAny(rc);
76     
77     return 0;
78 }

 协变类型只能是指针或者引用，不能是对象。