关于虚函数表的讨论

Virtual function is realized by virtual table usually. 

At there is a virtual table pointer in a class object. 

This pointer points to the virtual table. 

The virtual table is unique for a class. 

Different instances of this class shares the unique table.

Every class has a virtual table if it contains one 

or more virtual functions. 

In 32bit system, if get “sizeof”this class, your will 

find an additional 4 byte larger 

which is for the virtual table.

In virtual table, there are virtual function address records. 

Every record is a pointer to a virtual function 

which belongs to the class.

In memory, the virtual table is located at the global sections. 

In a class, the virtual table pointer is at the head of 

the class’s memory scope.

Notes:

In a subclass, the functions sequence in the v-table is:

1. subclass derived virtual functions

2. baseclass not derived functions

3. other subclass functions

In this case f is a virtual function which is derived. 

Other functions are normal.

The v-table is like this:

A good artical is as below:

http://www.qqread.com/cpp/h387617_2.html