Re: [Boost-users] BGL: Copying graphs and edge_descriptors confusion

Subject: Re: [Boost-users] BGL: Copying graphs and edge_descriptors confusion
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2011-06-28 13:29:51

On Mon, 27 Jun 2011, David Doria wrote:

>> Iterators are not preserved among copies of an object; they aren't in STL
>> either.  You need to use iterators from the same graph that you are trying
>> to access with them.  Note that this is also true for vertex and edge
>> descriptors for some graph types (listS is the most common).
>
> Ah I see. Phew, that has been driving me nuts all morning. I was
> looking at the output (operator<<) of the edge_descriptors and they
> looked correct, but I guess they were pointing to the correct
> vertices, only in the wrong graph?

Yes, probably.  Some graph types do have descriptors that work across 
separate graph objects, but you should not rely on that.

> Does the copy constructor do anything different than the copy_graph
> function that Cedric pointed out?

The copy constructor for adjacency_list just copies the raw data without 
actually traversing the graph.  I know the compressed_sparse_row version 
takes arbitrary graphs and does a special-purpose algorithm that is 
similar to copy_graph in behavior; I do not know what other graph types 
do, but it should be equivalent to copy_graph.

-- Jeremiah Willcock