CGAL users discussion list

[Laurent Rineau <>]

On Monday 10 December 2007 13:50:57 

 wrote:
> > Can you send us a *complete* little program, with the headers inclusions
> > and
> > your typedefs?
>
> Sorry...

I know have the explanation... The parameter P of your function app2, is a 
copy: the edges/facets/vertices of the original polyhedron are copied. When 
app2 returns, the returned handle is a handle to a facet of a temporary 
object.  After the return of app2, the copy is destroyed, and your variable 
fd is a handle to an already destroyed object.

Make that change:

> Facet_handle app2( Polyhedron P){
>       return P.facets_begin();}

into:

Facet_handle app2( Polyhedron& P) { // pass P by reference
  return P.facets_begin();
}

If you do not need to modify your polyhedron, I suggest you to add "const" 
qualifiers almost every where, and use const version of the polyhedron types. 
That way, the compiler can make more optimizations, or triggers warning or 
errors when you make some programming error like the one described above. 
That is more difficult to write, because you need to think a bit, to know 
where you can use const or not, but it is a good practice, as it make the 
compiler verify more things.

I have attached your example, that I have constify to the most, maybe to 
much. :-)

-- 
Laurent Rineau
INRIA - Sophia Antipolis
BP 93, 2004 Route des Lucioles
06902 Sophia Antipolis Cedex FRANCE
Tel: +33 4 92 38 78 62 (Fax: +33.4.97.15.53.95)
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Polyhedron_3.h>

typedef CGAL::Exact_predicates_inexact_constructions_kernel  Kernel;
typedef Kernel::Point_3                       Point_3;
typedef CGAL::Polyhedron_3<Kernel>            Polyhedron;
typedef Polyhedron::Facet_const_iterator      Facet_const_iterator;
typedef Polyhedron::Vertex_const_handle       Vertex_const_handle;
typedef Polyhedron::Halfedge_const_handle     Halfedge_const_handle;

const Facet_const_iterator app2(const Polyhedron& P) {
  return P.facets_begin();
}

int main() {
  Polyhedron P;
  const Point_3 p1(0,0,0), p2(0,0,1), p3(0,1,0), p4(1,0,0);
  P.make_tetrahedron(p1,p2,p3,p4);
  const Vertex_const_handle& vh1 = P.facets_begin()->halfedge()->vertex();
  const Facet_const_iterator& fd = app2(P);
  const Halfedge_const_handle& hh = fd->halfedge();
  std::cerr << "All is ok." << std::endl;
  const Vertex_const_handle& vh2 = fd->halfedge()->vertex(); //segmentation fault
  return 0;
}