求高手解答类中各种sizeof问题

下面是各种类中的sizeof问题，纯属好奇，求解答，涉及虚函数、虚继承、数据对齐问题；

其实还有好多不解的问题，先列以下这几种吧，求高手解答~~~

#include<iostream>
using namespace std;
class a{virtual void f(){}    double av;int ab;
//virtual void f1(){}
};
class b{//int  aa;int aad;
    //virtual void f1(){}
};
class c{//int aad
    ;};
class d{int aad;
};
class e:public virtual a//,public virtual bublic virtual c,public virtual d
{};
void main()
{cout<<sizeof(e)<<endl;} 

输出是32；

 

#include<iostream>
using namespace std;
class a{virtual void f(){}    double av;int ab;
//virtual void f1(){}
};
class b{//int  aa;int aad;
    //virtual void f1(){}
};
class c{//int aad
    ;};
class d{int aad;
};
class e:public virtual a,public virtual b,public virtual c//,public virtual d
{};
void main()
{cout<<sizeof(e)<<endl;} 

输出是 36；

 

#include<iostream>
using namespace std;
class a{virtual void f(){}    double av;int ab;
//virtual void f1(){}
};
class b{//int  aa;int aad;
    virtual void f1(){}
};
class c{//int aad
    ;};
class d{int aad;
};
class e:public virtual a,public virtual b,public virtual c//,public virtual d
{};
void main()
{cout<<sizeof(e)<<endl;} 

输出是36；

 

#include<iostream>
using namespace std;
class a{virtual void f(){}    double av;int ab;
//virtual void f1(){}
};
class b{int  aa;int aad;
    virtual void f1(){}
};
class c{//int aad
    ;};
class d{int aad;
};
class e:public virtual a,public virtual b,public virtual c//,public virtual d
{};
void main()
{cout<<sizeof(e)<<endl;} 

输出是44；

 

#include<iostream>
using namespace std;
class a{virtual void f(){}    double av;int ab;
//virtual void f1(){}
};
class b{int  aa;int aad;
    virtual void f1(){}
};
class c{//int aad;
    virtual void f2(){}
};
class d{//int aad;
};
class e:public virtual a,public virtual b,public virtual c,public virtual d
{};
void main()
{cout<<sizeof(e)<<endl;} 

输出是48；