CGAL users discussion list

["Olivier Tournaire" <>]

Hi,

The code in the push_back method is the following :

  void push_back (const Point_2 & p)
  {
    Point_2 pt = p;
    Point_2 ps = segments.back().target();
    segments.push_back (Segment_2 (ps, pt));
  }

As I use the empty constructor, the std::vector<Segment_2> segments; is empty. Then, if I want to insert a point in the polyline, segments.back() returns a null iterator, and, .target() on a null iterator certainly crashes. So, how can we use this method ? Maybe I did not understand the underlying concept of CGAL polylines ...

Regards,

Olivier

2008/3/4, Olivier Tournaire <>:

Hi all,

I have a problem with a push_back on a polyline. Here are some samples of my code :

typedef CGAL::Arr_polyline_traits_2< CGAL::Arr_segment_traits_2< CGAL::Cartesian<int> > >::Curve_2 polyline_int;

// ...

polyline_int polyline;
chains.push_back( polyline ); // chains is a std::vector< polyline_int >
MakeAChain( *copy , NLD[iNode].position , iDirection , chains[chains.size()-1] , FinalNode , FinalDirection );

// MakeAChain
void MakeAChain( itk::Image<unsigned char,2> &image , CGAL_Point2i BeginPoint , unsigned char BeginDirection , polyline_int &CurrentPolyline , CGAL_Point2i EndPoint , unsigned char EndDirection )
{
    // ...
    CurrentPolyline.push_back( BeginPoint ); // crashes because CurrentPolyline.segments is NULL (from the debugger)
    // ...
}

I do not understand why CurrentPolyline.segments is NULL. Could you please help ?

Regards.

Olivier