舉例：

在一個聊天室裡，有一群人，每個人都會說自己的話

使用一個結構把一群人表達出來

#include <stdlib.h>

#include <iostream>
#include <string>
using namespace std;

class CPerson {
   public:
    CPerson() { m_nType = 0; }
    void speak() { cout << "speak" << endl; }
    int m_nType;
};

class CChinese : public
 
 CPerson {
   public:
    CChinese() { m_nType = 1; }
    void speak() { cout << "speak Chinese" << endl; }
};

class CEnglish : public CPerson {
   public:
    CEnglish() { m_nType = 2; }
    void speak() { cout << "speak English" << endl; }
};
int main(int argc, char const* argv[]) {
    CChinese chs;
    CChinese chs1;
    CEnglish eng;

    
 
// some person
    CPerson* ary[3];

    ary[0] = &chs;   //子類轉換為父類
    ary[1] = &chs1;
    ary[2] = &eng;

    ary[0]->speak();  //使用父類的指標呼叫，用的仍是父類的記憶體
    ary[1]->speak();
    ary[2]->speak();

    for (int i = 0; i < 3; i++) {
        cout << i + 1;
        if (ary[i]->m_nType == 1
 
) {   
            CChinese* pChs = (CChinese*)ary[i];
            pChs->speak();
        } else if (ary[i]->m_nType == 2) {
            CEnglish* pEng = (CEnglish*)ary[i];
            pEng->speak();
        }
    }

    return 0;
}

使用以上方法，每當增加一個人時，就會很麻煩

C++引用虛擬函式實現通過基類訪問派生類的函式

 1 #include <stdlib.h>
 2 
 3 #include <iostream>
 4 #include <string>
 5 using namespace std;
 6 
 7 class CPerson {
 8    public:
 9     CPerson() { m_nType = 0; }
10     virtual void speak() { cout << "speak" << endl; }   //虛擬函式
11     int m_nType;
12 };
13 
14 class CChinese : public CPerson {
15    public:
16     CChinese() { m_nType = 1; }
17     void speak() { cout << "speak Chinese" << endl; }
18 };
19 
20 class CEnglish : public CPerson {
21    public:
22     CEnglish() { m_nType = 2; }
23     void speak() { cout << "speak English" << endl; }
24 };
25 int main(int argc, char const* argv[]) {
26     CChinese chs;
27     CChinese chs1;
28     CEnglish eng;
29 
30     // some person
31     CPerson* ary[3];
32 
33     ary[0] = &chs;
34     ary[1] = &chs1;
35     ary[2] = &eng;
36 
37     ary[0]->speak();
38     ary[1]->speak();
39     ary[2]->speak();
40     return 0;
41 }

out: