Re: [Boost-users] [BGL] segFault

Subject: Re: [Boost-users] [BGL] segFault
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2010-08-21 14:27:01

On Fri, 20 Aug 2010, John Robertson wrote:

> I'm trying to obtain an iterator of edges with a different ordering than that given in egdes(g).
> 
> The following compiles but segfaults at
> std::sort( VE.begin(), VE.end(), ordering< Graph, edd >() );
> (runs ok if the above line is commented out)
> 
> ////////////////////////////////////////////////////////////////////////////////////////////////////////////////
> 
>   typedef Traits::edge_descriptor edd;
> 
>   // Create ordering
>   template < typename Graph, typename edd >
>     struct ordering {
>         Graph & g;
>                 bool operator ()(const edd & a, const edd & b) {
>                         return g[a].eName < g[b].eName;
>                 }
>     };
> 
> 
>   template < typename Graph >
>     int initialize_container( Graph & g )
>   {
> 
>     typename graph_traits<Graph>::edge_iterator edge_iter, edges_end;
> 
>     // create vector of edge descriptors.
>     std::vector< Traits::edge_descriptor > VE(num_edges(g)+1);
> 
>     int i = 1;  // (Sometimes I like to start at 1.)
> 
>         //insert edge descriptors into vector of edge descriptors.
>         for (tie(edge_iter, edges_end) = edges(g); edge_iter != edges_end; ++edge_iter) {
>                 cout << " *edge_iter = " << *edge_iter << endl;
>                 VE[i++] = *edge_iter;
>         }
> 
>          // segfaults here
>         //sort vector of edge descriptors.
>         std::sort( VE.begin(), VE.end(), ordering< Graph, edd >() );
> 
>         //print sorted edge descriptors.
>         for( int i = 1; i < num_edges(g)+1; ++i )
>                 cout << " -Edge " << i << " = " << VE[i] << endl;
> 
> 
> 
>   }

What is edd (i.e., what members does it have)?  Also, if you are indexing 
from 1, you should sort from VE.begin() + 1 to VE.end() to skip the 
uninitialized element 0.

-- Jeremiah Willcock