The iterator adapter has no way of knowing it has reached the end.
Consider this in u16_to_u32_iterator:
void increment() { // skip high surrogate first if there is one: if(detail::is_high_surrogate(*m_position)) ++m_position; ++m_position; m_value = pending_read; }
If the last character is a high surrogate, you increment the iterator twice, while it is only allowed to do it once.
Fixing the bug means making the iterator adapter have knowledge of the beginning, the end, and the current position.
Ah, guilty as charged :-( The fix is horrible though :-(
Of course a more complete solution would always be welcome....
My library deals with this.
Good! As I keep saying this was only supposed to be an interim solution until someone did it properly... I'll look forward to seeing yours being reviewed! Cheers, John.