C++ A multiple inheritance pproblem with pure virtual functions

Question

I have produced a minimal example to replicate the problem I am seeing with a more complex class hierarchy structure:

#include 
#include 

        

Answer 1

Currently your F is derived from C in two different ways. This means that an F object has two separate C bases, and so there are two instances of C::Print().

You only override the one coming via E currently.

To solve this you must take one of the following options:

• Also override the one coming via D, either by implementing D::Print() or F::Print()
• Make Print non-pure
• Use virtual inheritance so that there is only a single C base.

For the latter option, the syntax adjustments would be:

class E : virtual public C

and

class D : public B, public BB, virtual public C

This means that D and E will both have the same C instance as their parent, and so the override E::Print() overrides the function for all classes 'downstream' of that C.

For more information , look up "diamond inheritance problem". See also Multiple inheritance FAQ