virtual inheritance / dreaded diamond again

[Alexander Stippler]

Hello,

I want to build up an inheritance structure looking like two coupled dreaded
diamonds. It's similar to an old posting of me. Now my question is, where
to use the keyword virtual.

CV
/ \
/ \
V CDV
\ / \
\ / \
DV CMI
\ /
\ /
MI

I placed virtual like this:

V : public virtual CV
CDV : public virtual CV
DV : public virtual CDV, public V
CMI : public virtual CDV
MI : public DV, public CMI

My porblem is, that the construction process of an MI does not do the
conctructor calls, I would expect. There is a constructor

MI(const CDV &rhs) : DV(rhs) {} // CMI has a default constructor.

which calls

DV(const CDV &rhs) : V(rhs) {} // CDV has a default constructor.

and now I would expect

V(const CV &rhs) {} // CV has a default constructor.

to be called, but actually

V() {}

is called. And here I wonder. Where am I wrong. I hope I provided enough
information. Else ask please. All classes are template classes by the way,
if relevant.

regards,
alex

 

[Ron Natalie]

V() {}

is called. And here I wonder. Where am I wrong. I hope I provided enough
information. Else ask please. All classes are template classes by the way,
if relevant.

All virtual base classes are initialized by the most derived object before any
non-virtual bases. It is the constructor of your most derived class (MI) that
needs to pass any arguments to the virtual bases.

MI(const CDV& rhs) : DV(rhs), CV(rhs) { }

or the like.

The order of construction of your heirarchy is:
CV, CDV, V, DV, CMI, MI