Re: [Boost-users] [BGL] null_vertex()

Subject: Re: [Boost-users] [BGL] null_vertex()
From: Andreas Fabri (andreas.fabri_at_[hidden])
Date: 2013-06-18 05:26:56

On 18/06/2013 10:28, Szymon Gatner wrote:
> 2013/6/18 Andreas Fabri <andreas.fabri_at_[hidden]
> <mailto:andreas.fabri_at_[hidden]>>
>
>     Hello,
>
>     I am wondering what the function
>     boost::graph_traits<G>::null___vertex()
>     http://www.boost.org/doc/libs/__1_53_0/libs/graph/doc/Graph.__html
>     <http://www.boost.org/doc/libs/1_53_0/libs/graph/doc/Graph.html>
>     is for, and why there is no equivalent
>     function null_edge()
>
>
> Because often you will want to assign some data to point back to a
> vertex. I mean, a graph holds a vertex -> custom data mapping, but that
> custom data will want to keep vertex id back. Thing is it has to store
> some "invalid" value before mapping happens and that is when
> null_vertex() helps. I hope that is clear enough.

and why is it not the same for edges?

andreas

>
> Cheers
>
>
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-- 
Andreas Fabri, PhD
Chief Officer, GeometryFactory
Editor, The CGAL Project
phone: +33.492.954.912    skype: andreas.fabri