class boost::graph_traits< DGtal::DigitalSurface< TDigitalSurfaceContainer > >::out_edge_iterator
Iterator for visiting out edges. We use an iterator facade to create a STL-compliant iterator with as little effort as possible.
- The difficulty is that DGtal graphs do not provide iterators for visiting edges or adjacent vertices, but merely provide a method that outputs them. Therefore, this iterator shares the container of out edges (a std::vector) with other (potentially) iterators, through a DGtal::CountedPtr. When the last iterator pointing in this structure is desallocated, the container is automatically desallocated. This is for instance used by function out_edges, which returns a pair of out_edge_iterator, both points on the same container. Another problem is that the user may have called twice out_edges on the same vertex, and may wish to compare iterators obtained by two different calls..
typedef typename DigitalSurface<...> G;
std::pair<out_edge_iterator,out_edge_iterator> vp1 = boost::out_edges
( vertex, g );
std::pair<out_edge_iterator,out_edge_iterator> vp2 = boost::out_edges
( vertex, g );
In this case, vp1 and vp2 are not pointing on the same structure, hence the address pointed by vp1 is different from the address pointed by vp2. They are then not comparable a priori. The out_edge_iterator is written so that vp1 (.first or .second) and vp2 (.first or .second) are comparable, using value comparison and out-of-range check.
Definition at line 251 of file DigitalSurfaceBoostGraphInterface.h.