Re: [Boost-users] A question about boost::graph iterators

From: Douglas Gregor (doug.gregor_at_[hidden])
Date: 2005-11-03 16:52:41

On Nov 3, 2005, at 12:23 PM, Jeffrey Holle wrote:

> I'm using gcc 4.0.2 with boost 1.33.0.
> I'm getting a compiler warning about taking the address of a  
> temporary with the
> following code:
> Edge*
> TransshipmentPivotingRule::enteringEdge(const FeasibleSpanningTree*  
> pFST)
> {
>    graph_traits<AntiTree>::edge_iterator ei,ei_out;
>    tie(ei,ei_out)=edges(*m_pAntiTree);
>    return (find_if(ei,ei_out,
>        ProfitableEdge(*m_pAntiTree,m_c,m_y,*pFST))!=ei_out) ?  
> &*ei : NULL;
> }
>
> Note the "&*ei".
> I know that the iterator is tempory, but what the iterator is  
> pointing to isn't.
> Is this a legit warning that I need to be concerned about?

It is probably a legitimate warning. Many of the iterators into  
graphs actually do return temporaries, because they build vertex or  
edge descriptors on-the-fly from a (typically smaller) internal  
representation.

I'd suggest replacing the Edge* with boost::optional<Edge>. You'll  
get about the same behavior but without the potential problems with  
taking the address of a temporary.

     Doug