C++ 虚函数表与多态 —— 继承的虚函数表 & 内存布局

 1 #include <iostream>
 2 using namespace std;
 3 
 4 class Father
 5 {
 6 public:
 7     virtual void func_1() { cout << "Father::func_1"; }
 8     virtual void func_2() { cout << "Father::func_2"; }
 9     virtual void func_3() { cout << "Father::func_3"; }
10 public:
11     int x = 666;
12     int y = 999;
13 };
14 
15 class Son : public Father
16 {
17 public:
18     void func_1() { cout << "Son::func_1   "; }                //重写了虚函数
19     virtual void func_4() { cout << "Son::func_4   "; }        //子类对象新写的虚函数 func_4
20 };
21 
22 typedef void(*func_t)(void);
23 
24 int main(void)
25 {
26     Father father;
27     cout << "father 对象地址：" << (int*)&father << endl;
28     int* vptr_f = (int*)*(int*)&father;                                //虚表指针
29 
30     for (int i = 0; i < 3; i++)                //这里如果想循环4次往下访问，不会访问到子类的 func_4 ，会访问到非法内存
31     {
32         cout << "调用第" << i + 1 << "个虚函数：";
33         ((func_t) * (vptr_f + i))();
34         cout << "地址为:" << *(int*)(vptr_f + i) << endl;
35     }
36 
37     cout << "==============================================" << endl;
38 
39     Son son;
40     cout << "son 对象地址：" << (int*)&son << endl;
41     int* vptr_s = (int*)*(int*)&son;                                //虚表指针
42 
43     for (int i = 0; i < 4; i++)
44     {
45         cout << "调用第" << i + 1 << "个虚函数：";
46         ((func_t) * (vptr_s + i))();
47         cout << "地址为:" << *(int*)(vptr_s + i) << endl;            //打印每个虚函数的地址
48     }
49 
50     for (int i = 0; i < 2; i++)
51     {
52         cout << *(int*)((int)&son + 4 + i * 4) << endl;
53     }
54     cout << "sizof(son)==" << sizeof(son) << endl;
55 }