class layout basic 2

#include<iostream>
using namespace std;

//虚函数和析构函数需要定义，否则
//a missing vtable usually means the first 
//non-inline virtual member function has no definition.

class a{
    virtual void func(){};
public:
    virtual ~a()=default;//析构函数需要为public
}aObj;

class b :public virtual a{
    virtual void foo(){};
public:
    virtual ~b()=default;
}bObj;

class ax{
    virtual void func(){};
    char x;
public:
    virtual ~ax()=default;
}axObj;

class bx:public virtual ax{
    virtual void foo(){};
public:
    virtual ~bx()=default;
}bxObj;

class c{
    virtual void func(){};
public:
    virtual ~c()=default;
}cObj;

class d :public c{
    virtual void foo(){};
public:
    virtual ~d()=default;
}dObj;

class cx{
    virtual void func(){};
public:
    virtual ~cx()=default;
    char x;
}cxObj;

class dx:public cx{
    virtual void foo(){};
public:
    virtual ~dx()=default;
}dxObj;

int main(){
    cout<<"aObj "<<sizeof(aObj)<<endl;
    cout<<"bObj "<<sizeof(bObj)<<endl;
    cout<<"axObj "<<sizeof(axObj)<<endl;
    cout<<"bxObj "<<sizeof(axObj)<<endl;
    cout<<"cObj "<<sizeof(cObj)<<endl;
    cout<<"dObj "<<sizeof(dObj)<<endl;
    cout<<"cxObj "<<sizeof(cxObj)<<endl;
    cout<<"dxObj "<<sizeof(dxObj)<<endl;
    return 0;
}

//clang3.8 gcc7.1
//aObj    8
//bObj    8
//axObj   16
//bxObj   16
//cObj    8
//dObj    8
//cxObj   16
//dxObj   16