Re: reverse_iterator problem

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.stl

Date:

Fri, 12 May 2006 10:36:05 -0400

Message-ID:

<#3XBsIddGHA.4892@TK2MSFTNGP02.phx.gbl>

Massif <Massif@discussions.microsoft.com> wrote:

I've got a reverse_iterator going through a vector. It has to start
at a point somewhere in the middle of the vector, run backwards
through it in a circle until it reaches the point it started at.

The cut down version of the code is as follows:

vector<CMLSection*>::reverse_iterator
itBack; vector<CMLSection*>::reverse_iterator itMarkerBack;

itBack= find_if(m_Vect.rbegin(), m_Vect.rend(), IsMatch);

itMarkerBack= itBack;

do
     {
        if( itBack== m_Vect.rend() )
        {
           itBack= m_Vect.rbegin();
        }

        DoSomething(itBack);

     }while( ++itBack!= itMarkerBack);

It's a bit more complicated than that - but you get the idea.

The problem is - when I'm in that if clause - i.e. the iterator is
equal to rend() then the iterator is still pointing to a valid
address, and when it gets set to rbegin() it no longer points to a
valid address.

How do you determine that? Do you inspect the iterator in the debugger?
Be aware that reverse iterators are usually implemented to hold a
regular iterator pointing to one past the element that a reverse
iterator would return from operator*. Thus, rend() usually holds begin()
internally, and rbegin() holds end() internally.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925