CGAL users discussion list

[Laurent Rineau <>]

On Friday 11 May 2007 03:04:00 

 wrote:
> Ok i have founded the Vertex_iterator to access the vertex of the Polygon
>
>
> Vertex_iterator vertit;
>
> vertit = polygon.vertices_begin ();
> double x1 = vertit->x();
> double x2 = vertit->y();
>
>
> but the manual say into Polygon_2
>
>  Point_2        pgn [ int i]           Returns a (const) reference to the 
> i-th
> vertex.

More precisely, the manual says:
----------------------------
Random access methods

These methods are only available for random access containers. 

Point_2     pgn.vertex ( int i)  
   Returns a (const) reference to the i-th vertex. 

Point_2     pgn [ int i]     
   Returns a (const) reference to the i-th vertex. 
----------------------------
http://www.cgal.org/Manual/3.2/doc_html/cgal_manual/Polygon_ref/Class_Polygon_2.html

The important part is "only available for random access containers".

I had a look at your error messages, and the Container template parameter of 
Polygon_2 was instantiated with a list. As the container do not have random 
access iterators, you cannot have them at the polygon level either.

If you instantiate you polygon type like that: "CGAL::Polygon_2<Traits>", 
that 
is without specifying the Container parameter, the container will be a 
std::vector, which has random access iterators.

-- 
Laurent Rineau
INRIA - Sophia Antipolis
BP 93, 2004 Route des Lucioles
06902 Sophia Antipolis Cedex FRANCE