Re: [Boost-users] Re: copy_if

From: Mr Zenaan Harkness (zen_at_[hidden])
Date: 2003-09-13 06:41:30

On Sat, 2003-09-13 at 20:52, 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<class II, class OI, class PRED>
> std::pair<II,OI> 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.
> 
> Witz

That's very useful. I've been wondering about that - backinserter is
fine if you really do want to append, but I'd never before seen mention
of a solution for limiting based on size of output.

I guess a final option would be "copy into, then append if full".
Although if you don't fill the container, then presumably there are some
elements still at the end - I can't imagine wanting this. What would
make more sense is "truncate container and then append" - which is
probably better done outside the algorithm, yes?

Thanks heaps - particularly that link is excellent,
Zenaan