Two questions related to virtual functions

Question

I was reading this articles , was at this heading Inheritance of Base-class vPtrs , but couldn\'t understand what did he mean in this para :

"However, due to mul

Answer 1

If Derived inherits from Base, its vtable will extend Base's. Now, if it also inherits Base2, its vtable will not include Base2's - Base2's part will retain its vtable (updated with Derived virtual functions, if they override Base2's).

  Base members      Base2 members    Derived members
+--+------------+----+------------+------------------+
 |                |
 V                V
Derived + Base   Base2 vtable  
vtable

To make the second question easier to understand, and since I enjoy drawing with fixed width font... here's the memory layout of a. For a full explanation about that expression, see James Kanze's answer.

        +---+----------+
a:      | | |    A     |
        +-+-+----------+
          |
          V
vtable: +---+
        | --+--> f2()
        +---+
        | --+--> f3()
        +---+

HTH...