CGAL users discussion list

[Peter Hachenberger <>]

On Sat, 2007-11-10 at 17:36 -0800, Peter Schröder wrote:
> Assuming that I am not changing a Polyhedron_3 data structure with any 
> topological operations, will I always get the same edge when calling 
> vertex_begin()? Given a vertex I need to consistently identify a "first" 
> edge incident on it. vertex_begin() would serve this as long as it 
> always returns the same edge. What are the guarantees? Can a similar 
> thing be asserted about vertex->halfedge()? I just need to consistently 
> get the same edge.
> 
> Peter

Hi Peter,

the procedure Halfedge::vertex_begin() returns a Circulator starting
with Vertex::halfedge(). That is an implementation detail that will not
change. If you want to make sure that this will always be the case for
your code, you can instead define a new circulator as follows:

Halfedge_around_vertex_circulator eavc(v->halfedge());

The halfedge returned by Vertex::halfedge stays the same as long as the
halfedges incident to that vertex stay the same. So, if you don't do any
topological operations, there should be no change.

Peter