Perhaps nit picky, and I know you were joking, but I think this is the wrong way to think about it. It's not that the other behavior is undefined, it's you esse

Perhaps nit picky, and I know you were joking, but I think this is the wrong way to think about it. It's not that the other behavior is undefined, it's you essentially have all of these functions that use "C" in their definitions, and then you have "#define C ..." in a header file somewhere.