RE: [Boost-users] Re: copy_if

Witz wrote:

You can find an implementation of copy_if in Boost Wiki here:

http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl ?STLAlgorithmExtensions

An extension that i find useful is the following:

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); }

Here we have a finite sized sink. Items are copied from the source if they satisfy the condition and if there is room left in the sink. The positions reached are returned on termination of the algorithm.

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.