Why do we need virtual functions in C++?

Question

I\'m learning C++ and I\'m just getting into virtual functions.

From what I\'ve read (in the book and online), virtual functions are functions in the base class that

Answer 1

About efficiency, the virtual functions are slightly less efficient as the early-binding functions.

"This virtual call mechanism can be made almost as efficient as the "normal function call" mechanism (within 25%). Its space overhead is one pointer in each object of a class with virtual functions plus one vtbl for each such class" [A tour of C++ by Bjarne Stroustrup]