Understanding virtual base classes and constructor calls

Question

I\'m a bit confused about how virtual base classes work. In particular, I was wondering how the constructor of the base class gets called. I wrote an example to understand

Answer 1

There is always just one constructor call, and always of the actual, concrete class that you instantiate. It is your responsibility to endow each derived class with a constructor which calls the base classes' constructors if and as necessary, as you did in B's constructor.

Update: Sorry for missing your main point! Thanks to ildjarn.

However, your B inherits virtually from A. According to the standard (10.1.4 in the FIDS), "for each distinct baseclass that is specified virtual, the most derived object shall contain a single base class subobject of that type". In your case this means that when constructing the base, your class F immediately calls A's default constructor, not B's.

Answer 2

Virtual base classes are always constructed by the most derived class.