虚继承

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 
 4 class Ap {
 5     public:
 6         Ap(int a) {
 7             this->a = a;
 8             cout << "constructor Ap " << a << endl;
 9         }
10         virtual ~Ap() {}
11 
12         int a;
13 } ;
14 
15 class A : public Ap {
16     public:
17         A(int a) : Ap(a) {
18             cout << "constructor A " << a << endl;
19         }
20         virtual ~A() {}
21 
22         virtual void F1() {
23             cout << "A F1" << endl;
24         }
25 
26         virtual void F2() {
27             cout << "A F2" << endl;
28         }
29 } ;
30 
31 class B1 : virtual public A {
32     public:
33         B1(int a) : A(a) {
34             cout << "constructor B1 " << a << endl;
35         }
36         virtual ~B1() {}
37 
38         virtual void F1() {
39             cout << "B1" << endl;
40         }
41 } ;
42 
43 class B2 : virtual public A {
44     public:
45         B2(int a) : A(a) {
46             cout << "constructor B2 " << a << endl;
47         }
48         virtual ~B2() {}
49 
50         //virtual void F2() {
51             //cout << "B2" << endl;
52         //}
53 } ;
54 
55 class C : public B1, public B2 {
56     public:
57         C(int a) : A(a), B1(a), B2(a) {
58             cout << "constructor C " << a << endl;
59         }
60         virtual ~C() {}
61 
62         virtual void F2() {
63             a = 1;
64             cout << "C" << endl;
65         }
66 } ;
67 
68 void F2(A *p) {
69     p->F2();
70 }
71 
72 void F1(A *p) {
73     p->F1();
74 }
75 
76 int main() {
77     A a(1);
78     B1 b1(2);
79     B2 b2(3);
80     C c(4);
81 
82     cout << a.a << ' ' << b1.a << ' ' << b2.a << ' ' << c.a << endl;
83     F1(&c);
84     F2(&a);
85     F2(&b2);
86     F2(&c);
87     cout << a.a << ' ' << b1.a << ' ' << b2.a << ' ' << c.a << endl;
88 
89     return 0;
90 }

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　　记录一下代码，没有默认构造器的情况下，初始化需要把所有相关的虚函数加进去。

　　因为类A只有一个副本，所以最终只是初始化了一次。

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 
 4 class A {
 5     public:
 6         A(int a) {
 7             cout << "A construct" << endl;
 8         } 
 9         ~A() {
10             cout << "A destruct" << endl;
11         }
12 } ;
13 
14 class B : public A {
15     public:
16         B(int a) : A(a) {
17             cout << "B construct" << endl;
18         }
19         ~B() {
20             cout << "B destruct" << endl;
21         }
22 } ;
23 
24 class C1 : virtual public B {
25     public:
26         C1(int a) : B(a) {
27             cout << "C1 construct" << endl;
28         }
29         ~C1() {
30             cout << "C1 destruct" << endl;
31         }
32 } ;
33 
34 class C2 : virtual public B {
35     public:
36         C2(int a) : B(a) {
37             cout << "C2 construct" << endl;
38         }
39         ~C2() {
40             cout << "C2 destruct" << endl;
41         }
42 } ;
43 
44 class D1 : virtual public C1, virtual public C2 {
45     public:
46         D1(int a) : B(a), C1(a), C2(a) {
47             cout << "D1 construct" << endl;
48         }
49         ~D1() {
50             cout << "D1 destruct" << endl;
51         }
52 } ;
53 
54 class D2 : virtual public C1, virtual public C2 {
55     public:
56         D2(int a) : B(a), C1(a), C2(a) {
57             cout << "D2 construct" << endl;
58         }
59         ~D2() {
60             cout << "D2 destruct" << endl;
61         }
62 } ;
63 
64 class E1 : virtual public D1, virtual public D2 {
65     public:
66         E1(int a) : B(a), C1(a), C2(a), D1(a), D2(a) {
67             cout << "E1 construct" << endl;
68         }
69         ~E1() {
70             cout << "E1 destruct" << endl;
71         }
72 } ;
73 
74 class E2 : virtual public D1, virtual public D2 {
75     public:
76         E2(int a) : B(a), C1(a), C2(a), D1(a), D2(a) {
77             cout << "E2 construct" << endl;
78         }
79         ~E2() {
80             cout << "E2 destruct" << endl;
81         }
82 } ;
83 
84 class F : virtual public E1, virtual public E2 {
85     public:
86         F(int a) : B(a), C1(a), C2(a), D1(a), D2(a), E1(a), E2(a) {
87             cout << "F construct" << endl;
88         }
89         ~F() {
90             cout << "F destruct" << endl;
91         }
92 } ;
93 
94 int main() {
95     F obj(1);
96 
97     return 0;
98 }

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——written by LyonLys