[Boost-users] re: copy_if

...

template std::pair copy_if(II ibegin, II iend, OI obegin, OI oend, PRED p) { for(; ibegin != iend; ++ibegin) { if(p(*ibegin)) { *obegin = *ibegin; if(++obegin == oend) break; } } return std::make_pair(ibegin, obegin); }

This should check whether obegin == end before copying, in case obegin == oend initially. I don't know whether it should stop as soon as it finds obegin == oend or wait until it knows there's another item to be copied. The former behaviour saves a little time in the case that no more items are wanted once the output buffer is full. The latter behaviour avoids the occasional need for another pass that copies nothing, if copy_if is called repeatedly to fill an output buffer which is then flushed.

Ben.

I've tended to rely on the common sense of the user (after all i cannot detect other possible errors such as 'oend < obegin') but i suppose the following addition at the start would seem sensible: ASSERT(obegin != oend); As for your second point - the amount of time saved by 'the former behaviour' depends on how expensive the predicate is and how many times it will be called if no more satisfactory items are available. As the entries in the output buffer are overwritten as and when required there is no need in any general sense to clear it between calls and this surely obviates any advantage your proposed approach may have. Witz