C++中用成员函数指针模拟多态

 1 #include <iostream>
 2 using namespace std;
 3 class base
 4 {
 5 public:
 6    int test(int lhs,int rhs)
 7     {
 8         cout<<"base test"<<endl;
 9         return 1;
10     }
11 };
12 class derived:public base
13 {
14 public:
15     int test(int lhs,int rhs)
16     {
17         cout<<"derived test"<<endl;
18         return 2;
19     }
20 };
21 int main()
22 {
23     base *p;
24     derived d;
25     int (base::*baseFunction)(int,int);
26     int (derived::*derivedFunction)(int,int);
27     //基类指针指向子类对象＋基类成员函数指针调用基类成员函数
28     p=&d;
29     baseFunction=&base::test;
30     (p->*baseFunction)(1,2);//相当于d.base::test(int,int);
31     //基类指针指向子类对象＋基类成员函数指针调用子类成员函数
32     p=&d;
33     baseFunction=(int (base::*)(int,int))&derived::test;
34     (p->*baseFunction)(1,2);//相当于d.test(int,int);
35     return 0;
36 }

 1 #include <iostream>
 2 using namespace std;
 3 class base
 4 {
 5 public:
 6     base()
 7     {
 8         virtualFunctionPointer=&base::test;
 9     }
10     ~base()
11     {
12         
13     }
14     int (base::*virtualFunctionPointer)();
15 
16     int test()
17     {
18         //判断是否为基类实例，防止无限递归
19         if(virtualFunctionPointer==&base::test)
20         {
21             cout<<"base"<<endl;
22             return 1;
23         }
24         //子类对象通过基类指针调用test，多态
25         else
26            return (this->*virtualFunctionPointer)();
27       
28     }
29 
30 };
31 class derived:public base
32 {
33 public:
34   
35     derived()
36     {
37         virtualFunctionPointer=(int (base::*)())&derived::test;
38     }
39     ~derived()
40     {
41         
42     }
43     int test()
44     {
45         cout<<"derived"<<endl;
46         return 2;
47     }
48 
49 };
50 int main()
51 {
52     derived d;
53     base *p=&d;
54     cout<<p->test()<<endl;
55     base b;
56     p=&b;
57     cout<<p->test()<<endl;
58 
59     return 0;
60 }