[Boost-users] Re: howto store vertex-iterators as internal graph property?

From: Jeffrey Holle (jeff.holle_at_[hidden])
Date: 2004-11-29 13:14:59

Be aware that the vertex which a vertex descriptor references to can 
change as vertices are removed from the graph.  Its just a vector index 
after all...

Sebastian Weber wrote:
> Hi Jeremy!
> 
>> Why do you want to store vertex iterators instead of just vertex
>> descriptors?
> 
> 
> Maybe this is what I want to store :-)
> 
> I want to store something which points to a vertex which allows me the 
> fastest possible access to the vertex with all it's internal properties 
> connected to it. If a reference to a vertex descriptor does that, this 
> is what I want. I guess I gotta read a little more the docs
> 
>>
>> You can use adjacency_list_traits to get the vertex_descriptor type
>> prior to creating the graph type.
> 
> 
> Doug already pointed that out. Once again I gotta read a little more 
> documentation ...
> 
> Thanks although!
> 
> Greetings,
> 
> Sebastian
> 
>>
>> Cheers,
>> Jeremy
>>
>>
>> On Nov 29, 2004, at 7:14 AM, Vladimir Prus wrote:
>>
>>> Hi Sebastian,
>>>
>>>> Hi folks!
>>>>
>>>> I got a cyclic type-dependency problem. I am trying to let every vertex
>>>> store a iterator to a list which stores vertex-iterators. This sounds
>>>> weired, but I need to keep track of very few vertices within my graph
>>>> which have a particle located at it. Thus I created a list of
>>>> vertex-iterators who carry my particle positions in the graph. In order
>>>> to be able to tell quickly if a vertice is taken by a particle I want
>>>> each vertice to include a pointer to a null element representing the
>>>> absence of a particle or a pointer into that list. My non-working code
>>>> looks like:
>>>>
>>>> Definition of my graph:
>>>>
>>>> struct Spot {
>>>>    // acutally I need the vertex_iterator to be defined already
>>>>    // in order to define particle, but this is not yet defined
>>>>    // so I am using the knowledge that it is going to be represented
>>>>    // by a vector<std::size_t>::iterator (at least I hope so)
>>>>    // this assumption is WRONG!!
>>>>    typedef std::list< std::vector<std::size_t>::iterator >::iterator \\
>>>
>>>
>>>
>>> There are two approaches.
>>>
>>> 1. Use pimpl or incomplete type to postpone defining the property 
>>> type until
>>> you know the iterator type.
>>>
>>>   struct Spot;
>>>   typedef boost::adjacency_list<boost::vecS, boost::vecS, \\
>>>   boost::undirectedS, Spot* > graph_t;
>>>
>>>   struct Spot { ............. } ;
>>>
>>> 2. Don't bother with iterators, store vector<unsigned> inside the Spot
>>> class. For VecS/VecS graph, using unsigned to identify vertices 
>>> should be
>>> OK.
>>>
>>> BTW, I'm not sure why your code does not work. It should work, maybe 
>>> after
>>> changing size_t to int -- don't remember if vertex_descrption is 
>>> signed or
>>> not.
>>>
>>> - Volodya
>>>
>>>
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>> _______________________________________________
>> Jeremy Siek <jsiek_at_[hidden]>
>> http://www.osl.iu.edu/~jsiek
>> Ph.D. Student, Indiana University Bloomington
>> C++ Booster (http://www.boost.org)
>> _______________________________________________
>>
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