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

Subject: Re: [Boost-users] [BGL] null_vertex()
From: Szymon Gatner (szymon.gatner_at_[hidden])
Date: 2013-06-18 04:28:00

2013/6/18 Andreas Fabri <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
>

> 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.

Cheers