Re: [Boost-users] newbie's questions about multi_index

From: Guillaume Lazzara (glazzara_at_[hidden])
Date: 2007-04-02 12:25:21

Hi,

On 4/2/07, "JOAQUIN LOPEZ MU?Z" <joaquin_at_[hidden]> wrote:
> Hi Guillaume
>
> ----- Mensaje original -----
> De: Guillaume Lazzara <glazzara_at_[hidden]>
> Fecha: Lunes, Abril 2, 2007 5:13 am
> Asunto: [Boost-users] newbie's questions about multi_index
> Para: boost-users_at_[hidden]
>
> Well, I'd say that the potential problem is not that es.second
> is modified when inside the loop, but rather that elements are
> repositioned between es.second-1 and es.second, so that the
> loop revisits them again, right?
>
> A solution is to modify the loop so as to not use es.second
> but the immediately preceding position, just as this (beware,
> uncompiled code follows):
>
>   std::pair<EquivSet::iterator, EquivSet::iterator> es =
>     contains.equal_range(*it);
>   if(es.first!=es.second){
>     EquivSet::iterator last=es.second;
>     --last;
>     EquivSet::iterator next=es.first;
>     EquivSet::iterator it_equiv;
>     do{
>       it_equiv=next;
>       ++next;
>       contains.modify_key(it_equiv, update_equiv(nbEns));
>     }while(it_equiv!=last);
>   }
>
> Does this work?
>

Yes, it's perfect!
Maybe I didn't see it, but IMHO I think you should include such an
example in the multi_index documentation, it would be helpful. :)

> > - If I can choose between a std::set and a multi_index used as
> > a set, which one should I use?
>
> If you don't use any of the added functionality provided
> by Boost.MultiIndex (suboject searching, modify(), etc.) using
> std::set will yield faster compile times. Other than that,
> a multi_index_container with a single ordered_unique index is
> entirely equivalent to std::set.
>
Ok.

Thanks again!
-- 
Guillaume Lazzara
Epita CSI 2008