多继承sizeof的求解

一：

#include "stdafx.h"
#include <iostream>
using namespace std;

class A {
int a;
virtual ~A(){}
};
class B:public A{
virtual void myfunB(){}
};
class C:public A{
virtual void myfunC(){}
};
class D:public B,public C{
virtual void myfunD(){}
};

int main( )
{
	cout<<sizeof(A)<<endl;   //结果8
	cout<<sizeof(B)<<endl;   //结果8
	cout<<sizeof(C)<<endl;   //结果8
	cout<<sizeof(D)<<endl;   //结果16
  return 0;
}

内存分析图：

二：

#include "stdafx.h"
#include <iostream>
using namespace std;

class A {
int a;
virtual ~A(){}
};
class B:public virtual A{
virtual void myfunB(){}
};
class C:public virtual A{
virtual void myfunC(){}
};
class D:public B,public C{
virtual void myfunD(){}
};

int main( )
{
	cout<<sizeof(A)<<endl;   //结果8
	cout<<sizeof(B)<<endl;   //结果16
	cout<<sizeof(C)<<endl;   //结果16
	cout<<sizeof(D)<<endl;   //结果24
  return 0;
}

内存分布图：

三：

#include "stdafx.h"
#include <iostream>
using namespace std;
class A
{
    char i[3];
public:
    virtual void aa() {}
};
class B : virtual public A
{
    char j[3];
public:
    virtual void bb() {}
};
class C : public virtual A
{
    char k[3];
public:
    virtual void cc() {}
};
class D : public B, public C
{
    char l[3];
public:
    virtual void dd() {}
};
void main()
{
    cout << sizeof(A) << endl;    //8
    cout << sizeof(B) << endl;    //20
    cout << sizeof(C) << endl;    //20
    cout << sizeof(D) << endl;    //36
}

四：

#include "stdafx.h"
#include <iostream>
using namespace std;
class A
{
    char i[3];
public:
    virtual void aa() {}
};
class B :  public A
{
    char j[3];
public:
    virtual void bb() {}
};
class C : public  A
{
    char k[3];
public:
    virtual void cc() {}
};
class D : public B, public C
{
    char l[3];
public:
    virtual void dd() {}
};
void main()
{
    cout << sizeof(A) << endl;    //8
    cout << sizeof(B) << endl;    //12
    cout << sizeof(C) << endl;    //12
    cout << sizeof(D) << endl;    //28
}