Add CDT::write_missing_segments_file

Triangulation_3/include/CGAL/Conforming_Delaunay_triangulation_3.h

@@ -236,6 +236,19 @@ public:
                        });
   }
 
+  void write_missing_segments_file(std::ostream &out) {
+    return std::for_each(
+        constraint_hierarchy.sc_begin(), constraint_hierarchy.sc_end(),
+        [this, &out](const auto &sc) {
+          if (!tr.tds().is_edge(sc.first.first, sc.first.second)) {
+            const auto v0 = sc.first.first;
+            const auto v1 = sc.first.second;
+            out << "2 " << this->tr.point(v0) << " " << this->tr.point(v1)
+                << '\n';
+          }
+        });
+  }
+
   /// @{
   /// remove functions cannot be called
   void remove(Vertex_handle) = delete;

Triangulation_3/test/Triangulation_3/cdt_3_from_off.cpp

@@ -59,6 +59,10 @@ int main(int argc, char* argv[])
     std::ofstream missing_faces("missing_faces.polylines.txt");
     cdt.write_missing_subfaces_file(missing_faces);
   }
+  {
+    std::ofstream missing_edges("missing_segments.polylines.txt");
+    cdt.write_missing_segments_file(missing_edges);
+  }
   // auto edge_is_feature_map = get(CGAL::edge_is_feature, mesh);
   // auto face_patch_id_map = get(CGAL::face_patch_id_t<int>(), mesh);