On Wed, Oct 13, 2010 at 3:16 PM, Steinar Bang <s...@dod.no> wrote: >>>>>> "Hyrum K. Wright" <hyrum_wri...@mail.utexas.edu>: > >> At this point, it's my turn to get confused. I'm speaking >> specifically of cases where we return STL classes. Brane's earlier >> suggestion to create an implicit bool conversion works fine for our >> custom classes. The problem I'm trying to solve is "how does one >> return the equivalent of '(const char *) NULL' in an std::string?" >> It's a this point that pointers start coming into play, because a NULL >> std::string * is quite feasible, whereas a NULL std::string isn't. > > Ah, ok. That was at a different part of the thread... which I avoided > responding to because I have any good answers at hand. :-) > > Do you need the distrinction between an empty string and a NULL? > > If not then I would return an empty string for a NULL on the C side.
Yes, so that's a no-go. > There's also the consideration that some std::string implementations are > deep copying (the gcc version uses refcounting (or at least used to do > so), but the VC++ one used to use deep copying. I'm not sure if that > still is the case). > > Then maybe what you want to return is const std::string& (which leaves > you with the headache of managing the life cycle of the std::string, so > maybe not... though... you have the context of the wrapper class and > could cache them lazily there. That would increase the footprint of the > wrapper, though). I don't want the caller to have to depend upon the lifetime of the source object, hence the desire to return something by value or a newly allocated pointer. Additionally, it still wouldn't work, since references have to point to some object, hence there is no such thing as a "null reference". (This entire conversation is reminding my why I *hate* C++. To bad there isn't too much of an alternative here... :/) -Hyrum
