虚函数

 1 #include <iostream>
 2 using namespace std;
 3 class base{         //基类
 4 public:
 5     void a(void)
 6     { 
 7         cout<<"base::a called\n";
 8     }
 9     virtual void b(void)   //虚函数
10     {
11         cout<<"base::b called\n";
12     }
13     virtual void c(void)   //虚函数
14     {
15         cout<<"base::c called\n";
16     }
17 };
18 
19 class derived:public base{     //派生类
20 public: 
21     void a(void) {cout<<"derived::a called\n";}   //派生类自定义的成员函数a 和 b，c继承于基类
22     void b(void) {cout<<"derived::b called\n";}
23 };
24 
25 void do_base(base &a_base)  //  基类作为变量，只在基类找成员函数
26 {
27 cout<<"call function in the base class\n";
28 a_base.a();  //base::a called\n
29 a_base.b();  //derived::b called\n  虚函数作用
30 a_base.c();  //base::c called\n
31 }
32 
33 int main()
34 {
35 derived a_derived;  //定义derived对象
36 cout<<"calling function in the derived class\n";
37 
38 a_derived.a();  //调用a时，查看派生类，derived：：a called
39 a_derived.b();  //derived::b called\n
40 a_derived.c();  //base::c called\n  派生类寻找失败，基类寻找 
41 
42 do_base(a_derived); 
43 system("pause");
44 return (0);
45 }