I don't know what the odds are that anyone actually having this problem will run across this on google. But maybe someone will read it and remember before-hand.

I have an inheritance hierarchy something like

Interface -> ABC -> C -> D.

Each constructor explicitly calls its parent class' constructor, with the appropriate parameter.

Originally, ABC had a default parameter to its constructor. Things just weren't working right, and I noticed that the constructors were getting called out of order. ABC was getting called first, with the default parameter, then Interface, C, and D. When I got rid of the default parameter, D (and all its siblings) quit compiling because ABC didn't have a default constructor.

After a great deal of frustration and trying to isolate the problem, I realized that C was inheriting virtually from ABC. I think I was planning on it being a mixin with other classes that also inherit from ABC. (This project has no architecture or up-front planning. It's cowboy-coding at its finest. And C++ is the wrong language for that).

I don't know whether this is a C++ bug or just part of the standard that I missed, and I've already wasted *way* too much time on it. Hopefully this will help someone else avoid making the same mistake.