Overriding a member variable in C++

Question

I have run into a bit of a tricky problem in some C++ code, which is most easily described using code. I have classes that are something like:

class MyVarBas         


        

Answer 1

Without knowing more of the context, it's hard to say for sure, but I'd reconsider whether you need this class hierarchy in the first place. Do you really need the MyVarBase and MyBase classes? Could you get away with composition instead of inheritance? Maybe you don't need the class heirarchy at all, if you template the functions and classes that work with the above classes. Maybe CRTP can help too. There are plenty of alternatives to using virtual functions (and to some extent, inheritance in general) in C++.

Anyway, your own suggested solution certainly shouldn't leak any memory (since it doesn't allocate any), and wouldn't break the default copy constructor either (since it just performs a member-wise copy. Now you just have an extra member in the derived class, but that gets copied too). Of course, you get the additional problem of keeping the two variables in sync, so I still don't like that solution much.

Alternatively, you may be able to remove the variable from the base class. Make the GetVar() function pure virtual, so it is only implemented in derived classes, which can define the member variable in any way they like.