How many v_tables exist for a class that inherits twice

struct A 
{
    virtual void f1() {}
};

struct B: public A {};

struct C: public A {};

struct D: public B,public C {};

int main()
{
    cout<<sizeof(A)<<" "<<sizeof(B)<<" "<<sizeof(C)<<" "<<sizeof(D)<<endl;
    cout<<"_______"<<endl;
    return 0;
}

      

        
        
        
      

    

• Result on my system (c9.o): 8 8 8 16
  
  Does this mean D has 2 virtual pointers to 2 virtual tables? If so, where are the pointers?

• If we remove the fucntion f1
  
  of struct A
  
  , the output will be as follows: 1 8 8 16
  
  . The same question is being asked here.

• If we do not remove f1
  
  , and now B
  
  and C
  
  inherit the virtual machine from A
  
  the result: 8 8 8 16
  
  . The same question is being asked here.