C++中的菱形繼承深入分析

2020-01-26 14:02:24

字體：大中小

供稿：網(wǎng)友

菱形繼承

class Person {   int _AA; }; class Student:public Person {   int _BB; }; class Teacher :public Person {   int _CC; }; class Assistant :public Student, public Teacher {   int _DD; };

PS:

Assistant的對(duì)象中存在兩份Person成員

菱形繼承存在二義性和數(shù)據(jù)冗余

解決：

使用虛繼承

首先不使用虛繼承時(shí)：

#include<iostream> using namespace std;  class AA { public:   string _aa; }; class BB :public AA { public:   int _bb; }; class CC :public AA { public:   int _cc; }; class DD :public BB, public CC { public:   int _dd; };  int main() {   DD d;   d.BB::_aa = 1;   d.CC::_aa = 2;   d._bb = 3;   d._cc = 4;   d._dd = 5;   cout << sizeof(d) << endl;   return 0; }

菱形繼承對(duì)象模型：

使用虛繼承時(shí)：

#include<iostream> using namespace std;  class AA { public:   string _aa; }; class BB :<span style="color:#FF0000;">virtual</span> public AA { public:   int _bb; }; class CC :<span style="color:#FF0000;">virtual</span> public AA { public:   int _cc; }; class DD :public BB, public CC { public:   int _dd; };  int main() {   DD d;   d.BB::_aa = 1;   d.CC::_aa = 2;   d._bb = 3;   d._cc = 4;   d._dd = 5;   cout << sizeof(d) << endl;   return 0; }