30. Under the covers

• Compilers are free to implement virtual functions as they see fit.

• Generally, implementation is done with:

  • static tables of function pointers in each class with virtual functions,

  • and a vtbl pointer in each object.

• Thus, an object of a class with virtual functions may have an unusual size.

• Calling virtual functions requires a bit more time
  (but is still faster than faking it!)