CGAL users discussion list

[Andreas Fabri <>]

Hi Josip,

You shouldn't expect that ++vit works correctly after that you called
T.remove(vit).

You better write this

for(Finite_vertices_iterator vit = T.finite_vertices_begin();
                 vit != T.finite_vertices_end();) {
                 if(seen.find(vit->point()) != seen.end()) {
                     seen.erase(vit->point());
                     Vertex_handle vh = vit;
                     ++vit;
                     T.remove(vh);
                     break;
                 }
           }


Note that the same would be true for a std::list.

andreas

Josip Dzolonga wrote:
> Hi Nico,
>
> I thought of that, but at no point I am reusing old cell handles/vertex 
> handles. I thought that while removing them, I might be causing the 
> problem - but even if I change to code to the following, the problems 
> remains
>
> while(!seen.empty()) {
>           for(Finite_vertices_iterator vit = T.finite_vertices_begin();
>                 vit != T.finite_vertices_end(); ++vit) {
>                 if(seen.find(vit->point()) != seen.end()) {
>                     seen.erase(vit->point());
>                     T.remove(vit);
>                     break;
>                 }
>           }
> }
>
> That is, I am iterating again over all vertices.
>
> Thanks,
> Josip
>
> On Sun, Nov 15, 2009 at 8:42 PM, Nico Kruithof < 
> <mailto:>> wrote:
>
>     Hi Josip,
>
>     The assertion says that the vertex is not contained in the Cell.
>     When you remove vertices, cells get removed and added when
>     re-triangulating. Internally, CGAL will reuse the memory of deleted
>     cells for the new cells. This might be the reason you are getting
>     the assertion. 
>
>     -- Nico
>
>
>     On Sun, Nov 15, 2009 at 6:26 PM, Josip Dzolonga 
> <
>     
> <mailto:>>
>  wrote:
>
>         Hello everyone,
>
>         I am trying to remove some certain points from the Delaunay
>         triangulation. I had some problems even before, and got some
>         advice from here, but the problem still pertains. The
>         problematic code follows
>
>         for(Finite_vertices_iterator vit = T.finite_vertices_begin();
>                     vit != T.finite_vertices_end(); ++vit) {
>                     if(seen.find(vit->point()) != seen.end()) {
>                         seen.erase(vit->point());
>                         T.remove(vit);
>                    }
>         }
>
>         Where seen is of type std::set<Point> and has been already
>         filled. Later on when I try to use the triangulation, I get the
>         following error
>
>         CGAL error: assertion violation!
>         Expr: v == V[3]
>         File: /usr/include/CGAL/Triangulation_ds_cell_base_3.h
>         Line: 98
>         terminate called after throwing an instance of 'std::logic_error'
>           what():  basic_string::_S_construct NULL not valid
>         Aborted
>
>         Which comes from the function  int index(const Vertex_handle&
>         v). I can not remove the same vertex twice, since I am iterating
>         over the finite vertices and this is the only place where vertex
>         removal is taking place. Any ideas would be highly appreciated!
>
>         Best,
>         Josip