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

From: Sebastian Weber (sebastian.weber_at_[hidden])
Date: 2004-11-29 09:33:32

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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> 
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