Re: [Boost-users] [BGL] Problems with remove_vertex

From: Adrian Boeing (junk_at_[hidden])
Date: 2007-01-30 10:36:05

Hello,

Yes, I've been finding strange problems but as Doug mentioned, it's hard 
to use properly, so instead of removing them I am just clearing the 
vertex. (ie: clear_vertex(u, g);) It makes it a bit more annoying to use 
the graph, but at least I get no more crashes; and programing around the 
empty vertices is easier than trying to remove them from the graph.

Cheers,
-Adrian

Leandro Melo wrote:
> Hi.
> 
> I had similar problems. Unfortunately, I can't remember right now what
> the particular situation was. I wrote the code in different ways
> (because of the invalidation process), but still my program crashed.
> Then I tried running the same code on GCC (in a debian machine). For
> my surprise, the problem no longer happened.
> 
> 
> Leandro Melo
> 
> 
> On 1/29/07, Doug Gregor <dgregor_at_[hidden]> wrote:
>> On Jan 29, 2007, at 2:38 PM, Adrian Boeing wrote:
>>
>>> Hi Jens,
>>>
>>> Unfortunately it's all part of a larger program so I can't easily
>>> provide a small example.
>>>
>>> Yes, I am using the vecS storage:
>>> typedef
>>> boost::adjacency_list<boost::vecS,boost::vecS,boost::bidirectionalS,bo
>>> ost::property<vertex_prop_t,
>>> T>,boost::property<edge_prop_t, U>,boost::no_property, boost::listS >
>>> graph_type;
>>>
>>> I'm not sure how to remove the property descriptor, there does not
>>> seem
>>> to be a boost::remove(vertex prop,graph) that I can find anywhere.
>> Hmmm. So, when one removes a vertex from an adjacency_list with
>> VertexListS=vecS, it actually invalidates all of the existing vertex
>> descriptors. So simple code like the following causes problems:
>>
>>         graph_type::vertex_descriptor u = *vertices(g).first;
>>         graph_type::vertex_descriptor v = *(++vertices(g).first);
>>         clear_vertex(u, g);
>>         remove_vertex(u, g);
>>         adjacent_vertices(v, g); // v has been invalidated
>>
>> vecS is a tricky beast. I usually recommend avoiding the removal of
>> vertices when VertexListS=vecS... it's inefficient and hard to use
>> properly.
>>
>>         Cheers,
>>         Doug
>>
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