CGAL users discussion list

[Marc Glisse <>]

On Thu, 28 May 2020, Marc Alexa  wrote:

> Thanks! I’d say it’s still a little confusing that one casts to the element 
> handles and the other doesn’t. Plus for 3D triangulations it works the same 
> for both iterators.
>
> I needed it because rather than extending the base classes for attaching 
> information I like to create a hash map to int and than use the indices, like 
> so:
>
>    int nv = 0;
>    CGAL::Unique_hash_map<T::Vertex_handle, int> VH;
>    T::Finite_vertex_iterator vit=t.finite_vertices_begin();
>    for (; vit != t.finite_vertices_end(); ++vit)
>        VH[vit] = nv++; // error here: no known conversion

You could use unordered_map<T::Vertex*, int> and VH[&*vit] (or operator->) 
which then works both for finite and regular iterators but that's not 
super convenient either.

> This works for the non-finite iterators. Which, frankly, took me some time to 
> figure out. I believe this construction can also be found in the CGAL source 
> code, at least for 3D triangulations.

You could file an issue on github asking to document how to get a handle 
from a finite iterator and/or provide a conversion operator. It isn't 
hard, but I cannot promise than anyone will get to it anytime soon.

--
Marc Glisse