What C++(98/03) features are not-so-well supported by poor compilers?

Question

Often I read of some software cutting out some C++ features in order to be compliant with poor/old/exotic C++ compilers.

This one is just the last one I got into: Box2D isn't using namespaces because they need to support:

poor C++ compilers where namespace support can be spotty

A bigger example I can think of is Qt, which is relying upon MOC, is limiting template usage a lot and is avoiding templates (well, this is at least true for Qt3 and previous versions, Qt4 is mostly doing that to keep to their conventions).

---

I'm wondering what compilers are that poor?
There are lots of C++ compilers out there (I never heard of most of them), but I would hope that all of them are supporting most common(/simple?) C++ features like namespaces (unless they're dead); isn't this the case?

What are the most unsupported features?
I can easily expect the lack of external templates, maybe template partial specialization and similar features. At most even RTTI or exceptions, but I would have never suspected of namespaces.

Answer 1

In my experience, people are just scared of new things and especially things that broke on them once, 20 decades ago. There's no valid reason against using namespaces in anything written during this century.

If you're looking for things to toss out though, if you happened to be targeting windows not too long ago you had to do more than just toss features out of C++ and not use them, you had to use different syntax. Templates come to mind as one of the worse supported features in VC. They've gotten much better but still fail sometimes.

Another one that is not supported by that particular compiler (STILL!) is overloading virtual functions to return derived type pointers to the types the base version returned when using MI. VC just plain freaks out and you end up having to do virtual_xxx() and providing non-virtual "xxx()" functions to replicate the standard behavior.

Answer 2

What are the most unsupported features?

Let's abstract away export, which, sadly, was an experiment that failed. Then, by count of compiler users this is probably two-phase lookup, which Visual C++ still doesn't properly implement. And VC has a lot of users.