I didn't find out yet what it is (it takes some time to get STLPort running...), but it works for c strings and crashes for std::string (see the first two calls of the library in the split testcase). These and other lines were changed a few days ago to fix a bug that we found on default constructed iterators for c strings. Now it seems there are also troubles with std::strings...
Let me try and be clearer: A singular iterator (that is to say one that is default constructed) has only one behaviour defined for it - you can assign to it a new value - and that's all you can do with it. You cannot compare a singular iterator with another iterator (not even another singular one), *unless* the particular iterator type has some implementation-defined behaviour specified for that particular type. For example the following is not legal code: template <class Iterator> foo(Iterator t) { Iterator a, b; a == b; // illegal operation. a == t; // also illegal. } Sorry! John.