CGAL users discussion list

[Jason Park <>]

I really appreciate your help. I just start to use this library so it feels
so strange and confusing.
Thx again.

Best Regards,
Jason Park


Philipp Moeller-2 wrote
> Jason Park <

> kopfor@

> > writes:
> 
>> It's my mistake when I copy the code from VS. When it builds, it was
>> vertex(j+1). I think the problem lies other place.
> 
> Yes, I just checked: Polygon_2::vertex is documented as a random access
> method. From the error, it looks like you are using a Polygon_2 with a
> std::list as the container, so neither vertex(), operator[], or edge are
> going to work. You can use the corresponding begin iterators and
> std::advance to achieve the same effect. 
> 
> Technically, the member functions above can be written in a manor to
> work without degrading the performance. Attached is a patch to do that,
> if you want to patch CGAL.
> 
> 
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> 
> 
> diff --git a/Polygon/include/CGAL/Polygon_2.h
> b/Polygon/include/CGAL/Polygon_2.h
> index eaadb4b..fcc85a1 100644
> --- a/Polygon/include/CGAL/Polygon_2.h
> +++ b/Polygon/include/CGAL/Polygon_2.h
> @@ -418,8 +418,11 @@ class Polygon_2 {
>  
>      /// Returns a (const) reference to the `i`-th vertex.
>      const Point_2& vertex(std::size_t i) const
> -      { return *(d_container.begin() + i); }
> -
> +    { 
> +      Vertex_const_iterator it = d_container.begin();
> +      std::advance(it, i);
> +      return *it;
> +    }
>  
>      /// Returns a (const) reference to the `i`-th vertex.
>      const Point_2& operator[](std::size_t i) const
> @@ -427,7 +430,11 @@ class Polygon_2 {
>  
>      /// Returns the `i`-th edge.
>      Segment_2 edge(std::size_t i) const
> -      { return *(edges_begin() + i); }
> +    { 
> +      Edge_const_iterator it = edges_begin();
> +      std::advance(it, i);
> +      return *it;
> +    }
>  
>      /// @}





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