#include<stdio.h>
#include<iostream>
#include<queue>
using namespace std;

class A {
public:
    A(){printf("A create.\n");}
    int a;
    virtual void fun(){}
};

class B: public A{
public:
    B(){printf("B create.\n");}
    int b;
    virtual void fun1(){}
};

class C: public A
{
public :
    int c;
    C(){printf("C create.\n");}
    virtual void fun3(){printf("fun3 .\n");}
};

class D:public C,public B{
public:
    int d;
    D(){printf("D create.\n");}
    virtual void fun3(){printf("fun4 .\n");}
}; 
//二義性問題的開銷 
int main() {
    D *pd=new D;
    printf("%d\n",sizeof(D));
    getchar();
}
 

相當於baseClass A在類中有兩個，這可能不是我們想要的結果，增加呼叫的困難，同時也會浪費記憶體資源。

那怎麼解決這種問題呢？使用虛擬繼承！

#include<iostream>
using namespace std;
class A{
public:
    A(char *s)
    {
        cout<<s<<endl;
    }
    ~A(){}
};
class B:virtual public A
{
public:
    B(char *s1,char*s2):A(s1){
        cout<<s2<<endl;
    }
};
class C:virtual public A
{
public:
    C(char *s1,char*s2):A(s1){
        cout<<s2<<endl;
    }
};
class D:public B,public C
{
public:
    D(char *s1,char *s2,char *s3,char *s4):B(s1,s2),C(s1,s3),A(s1)
    {
        cout<<s4<<endl;
    }
};
int main() {
    D *p=new D("class A","class B","class C","class D");
    delete p;
    return 0;
}