CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

The bug is in your code.

You return the polygon by copy.
When you write:
Polygon::Vertex_const_iterator vertices = 
polygon.getCGALPolygon().vertices_begin();

you are taking an iterator to a std::vector that get destroyed at the
end of the line.
Then when you are using the iterator the object having been
destroyed you get only crappy things.

Sebastien.


On 01/20/2015 11:24 AM, Thomas Kluth wrote:
> Dear CGAL-Team,
>
> I think I found a bug in the Polygon_2::Vertex_const_iterator.
> I've attached a minimal working example that you should be able to compile
> and run with
>
>          cmake .
>          make
>          ./polytest
>
> You should see this output:
>
>         cgal version: 4.5.1
>         Polygon: Polygon_2(
>                 PointC2(10, 20)
>                 PointC2(10, 40)
>                 PointC2(50, 20)
>         )
>
>         first vertex: PointC2(10, 20)
>
>         vertices of the polygon from Printer.hhp:
>         CGAl Point: PointC2(0, 20)
>         raw coordinates: 0, 20
>         CGAl Point: PointC2(10, 40)
>         raw coordinates: 10, 40
>         CGAl Point: PointC2(50, 20)
>         raw coordinates: 50, 20
>         first vertex again:
>         CGAl Point: PointC2(10, 20)
>         raw coordinates: 10, 20
>
> The bug here is that Polygon_2::Vertex_const_iterator gives a wrong value of
> the x-value of the first vertex of the polygon in Printer.hpp, but not in
> MyPolygon.hpp (0 instead of 10).
> Furthermore, the same call of polygon.vertices_begin() gives a different
> output in the Printer.hpp. Please look to the attached code to understand
> the failure.
>
> The output was generated with CGAL 4.5.1 on Fedora 21, the version that is
> in the repository. I had similar prolems with CGAL 4.4.x on Fedora 20.
> Interestingly, the bug does _not_ happen with the same code and CGAL 4.5 on
> Mac OS X 10.7.5, installed via homebrew.
>
> It might be that I just have to little knowledge about objects, classes and
> CGAL and this is not a bug but actually I did a mistake.
> If this is the case I would be happy to know, how to pass CGAL-Objects from
> one object to another object correctly.
> Otherwise I'm asking you to fix the bug.
>
> Thank you!
> Thomas Kluth
>
> P.S.: It might be that my example is not minimal, but it reflects the way I
> use CGAL in my bigger project. cgalbug.zip
> <http://cgal-discuss.949826.n4.nabble.com/file/n4660327/cgalbug.zip>
>
>
>
> --
> View this message in context: 
> http://cgal-discuss.949826.n4.nabble.com/Polygon-2-Vertex-const-iterator-reports-wrong-first-vertex-tp4660327.html
> Sent from the cgal-discuss mailing list archive at Nabble.com.