单继承与多继承中的虚函数表和虚函数指针

单继承与多继承中的虚函数表和虚函数指针

 

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首先，我们了解一下何为单继承，何为多继承？？

单继承：一个子类只有一个直接父类。

多继承：一个子类有两个或多个直接父类。

单继承中的虚函数表分析：

示例程序：

[cpp] view plain copy print ?

1. #include <iostream> 
2. using namespace std; 
3.  
4. typedef void(*FUNC)(); 
5.  
6. class Base 
7. { 
8. public: 
9.     virtual void func1() 
10.     { 
11.         cout << "Base::func1()" << endl; 
12.     } 
13.     virtual void func2() 
14.     { 
15.         cout << "Base::func2()" << endl; 
16.     } 
17. private: 
18.     int _b; 
19. }; 
20.  
21. class Derive :public Base 
22. { 
23. public: 
24.     virtual void func1() 
25.     { 
26.         cout << "Derive::func1()" << endl; 
27.     } 
28.     virtual void func3() 
29.     { 
30.         cout << "Derive::func3()" << endl; 
31.     } 
32.     virtual void func4() 
33.     { 
34.         cout << "Derive::func4()" << endl; 
35.     } 
36. private: 
37.     int _d; 
38. }; 
39. void PrintVfptr(int* vptr) 
40.     //打印虚函数表 
41. { 
42.     cout << "虚函数表: " << vptr << endl; 
43.     for (int i = 0; vptr[i] != 0; ++i) 
44.     { 
45.         printf("第%d个虚函数：%p  >> ", i, vptr[i]); 
46. FUNC f = (FUNC)(vptr[i]);
47.         f(); 
48.     } 
49. } 
50.  
51. void Test() 
52. { 
53.     Base b; 
54.     Derive d; 
55.  
56.     int* vptrBase = (int*)(*(int*)(&b)); 
57.     int* vptrDeri = (int*)(*(int*)(&d)); 
58.  
59.     PrintVfptr(vptrBase); 
60.     cout << endl; 
61.     PrintVfptr(vptrDeri); 
62.  
63. } 
64.  
65. int main() 
66. { 
67.     Test(); 
68.     system("pause"); 
69.     return 0; 
70. } 

#include <iostream>
using namespace std;

typedef void(*FUNC)();

class Base
{
public:
	virtual void func1()
	{
		cout << "Base::func1()" << endl;
	}
	virtual void func2()
	{
		cout << "Base::func2()" << endl;
	}
private:
	int _b;
};

class Derive :public Base
{
public:
	virtual void func1()
	{
		cout << "Derive::func1()" << endl;
	}
	virtual void func3()
	{
		cout << "Derive::func3()" << endl;
	}
	virtual void func4()
	{
		cout << "Derive::func4()" << endl;
	}
private:
	int _d;
};
void PrintVfptr(int* vptr)
	//打印虚函数表
{
	cout << "虚函数表: " << vptr << endl;
	for (int i = 0; vptr[i] != 0; ++i)
	{
		printf("第%d个虚函数：%p  >> ", i, vptr[i]);
		FUNC f = (FUNC)(vptr[i]);
		f();
	}
}

void Test()
{
	Base b;
	Derive d;

	int* vptrBase = (int*)(*(int*)(&b));
	int* vptrDeri = (int*)(*(int*)(&d));

	PrintVfptr(vptrBase);
	cout << endl;
	PrintVfptr(vptrDeri);

}

int main()
{
	Test();
	system("pause");
	return 0;
}

程序运行结果：

Base类(基类)的虚函数表：

Derive类(派生类)的虚函数表：

结论：

如果有虚函数表，那么只有一个虚函数表，并且按照虚函数声明的顺序顺序排列，派生类的虚函数紧接着基类的虚函数排列。

多继承中的虚函数表分析：

示例代码：

[cpp] view plain copy print ?

1. #include <iostream> 
2. using namespace std; 
3.  
4. typedef void(*FUNC)(); 
5. class Base 
6. { 
7. public: 
8.     virtual void func1() = 0; 
9.     virtual void func2() = 0; 
10. }; 
11.  
12. class Base1:public Base 
13. { 
14. public: 
15.     virtual void func1() 
16.     { 
17.         cout << "Base1::func1()" << endl; 
18.     } 
19.     virtual void func2() 
20.     { 
21.         cout << "Base1::func2()" << endl; 
22.     } 
23. private: 
24.     int _b1; 
25. }; 
26.  
27. class Base2: public Base 
28. { 
29. public: 
30.     virtual void func1() 
31.     { 
32.         cout << "Base2::func1()" << endl; 
33.     } 
34.     virtual void func2() 
35.     { 
36.         cout << "Base2::func2()" << endl; 
37.     } 
38. private: 
39.     int _b2; 
40. }; 
41.  
42.  
43. class Derive : public Base1, public Base2 
44. { 
45. public: 
46.     virtual void func1() 
47.     { 
48.         cout << "Derive::func1()" << endl; 
49.     } 
50.     virtual void func3() 
51.     { 
52.         cout << "Derive::func3()" << endl; 
53.     } 
54.     virtual void func4() 
55.     { 
56.         cout << "Derive::func4()" << endl; 
57.     } 
58. private: 
59.     int _d; 
60. }; 
61.  
62. void PrintVfptr(Base* b) 
63. { 
64.     int* vTable1 = (int*)(*(int*)b); 
65.     cout << "虚函数表指针:" << vTable1 << endl; 
66.     for (int i = 0; vTable1[i] != 0; ++i) 
67.     { 
68.         printf("第%d个虚函数指针: %p   >>", i, vTable1[i]); 
69.         FUNC f = (FUNC)vTable1[i]; 
70.         f(); 
71.     } 
72.     //int* vTable2 = (int*)(*((int*)b + sizeof(Base1) / 4)); 
73.     int* vTable2 = (int*)(*((int*)((char*)b + sizeof(Base1)))); 
74.     cout << "虚函数表指针:" << vTable2 << endl; 
75.     for (int i = 0; vTable2[i] != 0; ++i) 
76.     { 
77.         printf("第%d个虚函数指针: %p   >>", i, vTable2[i]); 
78.         FUNC f = (FUNC)vTable2[i]; 
79.         f(); 
80.     } 
81. } 
82.  
83. void Test() 
84. { 
85.     Base1 b1; 
86.     Base2 b2; 
87.     Derive d; 
88.     PrintVfptr(&b1); 
89.     cout << endl; 
90.     PrintVfptr(&b2); 
91.     cout << endl; 
92.     PrintVfptr((Base1*)&d); 
93. } 
94.  
95. int main() 
96. { 
97.     Test(); 
98.     system("pause"); 
99.     return 0; 
100. } 

#include <iostream>
using namespace std;

typedef void(*FUNC)();
class Base
{
public:
	virtual void func1() = 0;
	virtual void func2() = 0;
};

class Base1:public Base
{
public:
	virtual void func1()
	{
		cout << "Base1::func1()" << endl;
	}
	virtual void func2()
	{
		cout << "Base1::func2()" << endl;
	}
private:
	int _b1;
};

class Base2: public Base
{
public:
	virtual void func1()
	{
		cout << "Base2::func1()" << endl;
	}
	virtual void func2()
	{
		cout << "Base2::func2()" << endl;
	}
private:
	int _b2;
};


class Derive : public Base1, public Base2
{
public:
	virtual void func1()
	{
		cout << "Derive::func1()" << endl;
	}
	virtual void func3()
	{
		cout << "Derive::func3()" << endl;
	}
	virtual void func4()
	{
		cout << "Derive::func4()" << endl;
	}
private:
	int _d;
};

void PrintVfptr(Base* b)
{
	int* vTable1 = (int*)(*(int*)b);
	cout << "虚函数表指针:" << vTable1 << endl;
	for (int i = 0; vTable1[i] != 0; ++i)
	{
		printf("第%d个虚函数指针: %p   >>", i, vTable1[i]);
		FUNC f = (FUNC)vTable1[i];
		f();
	}
	//int* vTable2 = (int*)(*((int*)b + sizeof(Base1) / 4));
	int* vTable2 = (int*)(*((int*)((char*)b + sizeof(Base1))));
	cout << "虚函数表指针:" << vTable2 << endl;
	for (int i = 0; vTable2[i] != 0; ++i)
	{
		printf("第%d个虚函数指针: %p   >>", i, vTable2[i]);
		FUNC f = (FUNC)vTable2[i];
		f();
	}
}

void Test()
{
	Base1 b1;
	Base2 b2;
	Derive d;
	PrintVfptr(&b1);
	cout << endl;
	PrintVfptr(&b2);
	cout << endl;
	PrintVfptr((Base1*)&d);
}

int main()
{
	Test();
	system("pause");
	return 0;
}

程序运行结果：

Base1的虚函数表：

Base2的虚函数表：

Derive的虚函数表：(有两个虚函数表)

多继承中的菱形继承：

示例代码：

[cpp] view plain copy print ?

1. #include <iostream> 
2. using namespace std; 
3.  
4. typedef void(*FUNC)(); 
5. class Base 
6. { 
7. public: 
8.     virtual void func1() 
9.     { 
10.         cout << "Base::func1()" << endl; 
11.     } 
12.     virtual void func2() 
13.     { 
14.         cout << "Base::func2()" << endl; 
15.     } 
16. private: 
17.     int _b; 
18. }; 
19.  
20. class Parent1 :public Base 
21. { 
22. public: 
23.     virtual void func1() 
24.     { 
25.         cout << "Parent1::func1()" << endl; 
26.     } 
27.     virtual void func3() 
28.     { 
29.         cout << "Parent1::func3()" << endl; 
30.     } 
31.     virtual void func4() 
32.     { 
33.         cout << "Parent1::func4()" << endl; 
34.     } 
35.     virtual void func5() 
36.     { 
37.         cout << "Parent1::func5()" << endl; 
38.     } 
39. private: 
40.     int _p1; 
41. }; 
42.  
43. class Parent2 :public Base 
44. { 
45. public: 
46.     virtual void func1() 
47.     { 
48.         cout << "Parent2::func1()" << endl; 
49.     } 
50.     virtual void func3() 
51.     { 
52.         cout << "Parent2::func3()" << endl; 
53.     } 
54.     virtual void func6() 
55.     { 
56.         cout << "Parent2::func6()" << endl; 
57.     }    
58.     virtual void func7() 
59.     { 
60.         cout << "Parent2::func7()" << endl; 
61.     } 
62. private: 
63.     int _p2; 
64. }; 
65.  
66. class Child :public Parent1, public Parent2 
67. { 
68. public: 
69.     virtual void func1() 
70.     { 
71.         cout << "Child::func1()" << endl; 
72.     } 
73.     virtual void func3() 
74.     { 
75.         cout << "Child::func3()" << endl; 
76.     } 
77.     virtual void func4() 
78.     { 
79.         cout << "Child::func4()" << endl; 
80.     } 
81.     virtual void func6() 
82.     { 
83.         cout << "Child::func6()" << endl; 
84.     }    
85.     virtual void func8() 
86.     { 
87.         cout << "Child::func8()" << endl; 
88.     } 
89. private: 
90.     int _c; 
91. }; 
92.  
93. void PrintVfptr(int* vptr) 
94.     //打印虚函数表 
95. { 
96.     cout << "虚函数表: " << vptr << endl; 
97.     for (int i = 0; vptr[i] != 0; ++i) 
98.     { 
99.         printf("第%d个虚函数：%p  >> ", i, vptr[i]); 
100.         FUNC f = (FUNC)(vptr[i]); 
101.         f(); 
102.     } 
103. } 
104. void Test() 
105. { 
106.     Base b; 
107.  
108.     Parent1 p1;  
109.     Parent2 p2; 
110.  
111.     Child c; 
112.  
113.     int* vptr_B = (int*)(*(((int*)(&b)))); 
114.  
115.     int* vptr_P1 = (int*)(*(((int*)(&p1)))); 
116.  
117.     int* vptr_P2= (int*)(*(((int*)(&p2)))); 
118.  
119.     PrintVfptr(vptr_B); 
120.     cout << endl; 
121.  
122.     PrintVfptr(vptr_P1); 
123.     cout << endl; 
124.  
125.     PrintVfptr(vptr_P2); 
126.     cout << endl; 
127.  
128.     int* vptr_C_1 = (int*)(*(((int*)(&c)))); 
129.     int* vptr_C_2 = (int*)(*(int*)((char*)(&c) + sizeof(Parent1))); 
130.  
131.     PrintVfptr(vptr_C_1); 
132.     cout << endl; 
133.     PrintVfptr(vptr_C_2); 
134.     cout << endl; 
135. } 
136. int main() 
137. { 
138.     Test(); 
139.     system("pause"); 
140.     return 0; 
141. } 

#include <iostream>
using namespace std;

typedef void(*FUNC)();
class Base
{
public:
	virtual void func1()
	{
		cout << "Base::func1()" << endl;
	}
	virtual void func2()
	{
		cout << "Base::func2()" << endl;
	}
private:
	int _b;
};

class Parent1 :public Base
{
public:
	virtual void func1()
	{
		cout << "Parent1::func1()" << endl;
	}
	virtual void func3()
	{
		cout << "Parent1::func3()" << endl;
	}
	virtual void func4()
	{
		cout << "Parent1::func4()" << endl;
	}
	virtual void func5()
	{
		cout << "Parent1::func5()" << endl;
	}
private:
	int _p1;
};

class Parent2 :public Base
{
public:
	virtual void func1()
	{
		cout << "Parent2::func1()" << endl;
	}
	virtual void func3()
	{
		cout << "Parent2::func3()" << endl;
	}
	virtual void func6()
	{
		cout << "Parent2::func6()" << endl;
	}	
	virtual void func7()
	{
		cout << "Parent2::func7()" << endl;
	}
private:
	int _p2;
};

class Child :public Parent1, public Parent2
{
public:
	virtual void func1()
	{
		cout << "Child::func1()" << endl;
	}
	virtual void func3()
	{
		cout << "Child::func3()" << endl;
	}
	virtual void func4()
	{
		cout << "Child::func4()" << endl;
	}
	virtual void func6()
	{
		cout << "Child::func6()" << endl;
	}	
	virtual void func8()
	{
		cout << "Child::func8()" << endl;
	}
private:
	int _c;
};

void PrintVfptr(int* vptr)
	//打印虚函数表
{
	cout << "虚函数表: " << vptr << endl;
	for (int i = 0; vptr[i] != 0; ++i)
	{
		printf("第%d个虚函数：%p  >> ", i, vptr[i]);
		FUNC f = (FUNC)(vptr[i]);
		f();
	}
}
void Test()
{
	Base b;

	Parent1 p1; 
	Parent2 p2;

	Child c;

	int* vptr_B = (int*)(*(((int*)(&b))));

	int* vptr_P1 = (int*)(*(((int*)(&p1))));

	int* vptr_P2= (int*)(*(((int*)(&p2))));

	PrintVfptr(vptr_B);
	cout << endl;

	PrintVfptr(vptr_P1);
	cout << endl;

	PrintVfptr(vptr_P2);
	cout << endl;

	int* vptr_C_1 = (int*)(*(((int*)(&c))));
	int* vptr_C_2 = (int*)(*(int*)((char*)(&c) + sizeof(Parent1)));

	PrintVfptr(vptr_C_1);
	cout << endl;
	PrintVfptr(vptr_C_2);
	cout << endl;
}
int main()
{
	Test();
	system("pause");
	return 0;
}

运行结果：

其中，Child有两个虚函数表，因为它有两个直接父类。

总结：多继承中会有多个虚函数表，几重继承就会有几个虚函数表。这些虚函数表会按照派生的顺序依次排列。如果子类改写了父类的虚函数，那么就会用子类自己的虚函数覆盖相应的父类虚函数；如果子类有新的虚函数，那么就添加到第一个虚函数表的末尾。