CGAL users discussion list

[Philipp Moeller <>]

Jason Park 
<>
 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.

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;
+    }
 
     /// @}