samiksc

 Profile Answers by samiksc 

• Jan 20th, 2006

 

Virtual base class is a term used in C++ multiple inheritance.

Assume the following -- base class P. Two classes A and B derive from P. A third class C derives from both A and B.

P has a protected variable pvar. A class C method accesses this variable. Now there are two copies of pvar available for C to use -- A::pvar and B::pvar. So the compiler gives error for ambiguity.

If, however, classes A and B declare P as virtual base class this problem would be avoided. When a base class is declared as virtual only one copy of its data members exist in memory. At runtime it will be checked whether an object of the base class P is created in memory, if not it will be created, if yes the same copy will be referred. So there will be no ambiguity.