Boost.Graph and Graphviz nested subgraphs

Question

I expected the code

#include 
#include 
#include 
#include          


        

Answer 1

The trouble was caused by supplying make_iterator_vertex_map(names), which returns chars from names ('A', 'B'). This is incompatible with the expected (and default) vertex_index properties (0, 1). After the fix, I get:

digraph G0 {
subgraph clusterG1 {
subgraph clusterG2 {
1;
}
0;
}
0 -> 1;
}

vertex_marker, which is std::vector of 2 elements in my case, not 67 and more was expected to be indexed by vertex indices. I was experiencing undefined behavior,
and if ( vertex_marker[pos] ) was never fulfilled.

The responsible portion of boost::detail::write_graphviz_subgraph:

// Print out vertices and edges not in the subgraphs.

typename graph_traits::vertex_iterator i, end;
typename graph_traits::edge_iterator ei, edge_end;

for(boost::tie(i,end) = vertices(g); i != end; ++i) {
  Vertex v = g.local_to_global(*i);
  int pos = get(vertex_id, v); // 66, 65, should be 1, 0
  if ( vertex_marker[pos] ) {  // out-of-bounds access
    vertex_marker[pos] = false;
    out << escape_dot_string(pos);
    make_vertex_attributes_writer(g.root())(out, v);
    out << ";" << std::endl;
  }
}

A static_assert/SFINAE of the vertex_id parameter type against Graph's vertex_id type (which can be done immediately in boost::write_graphviz) would be greatly welcome. On a side note, the hardcoded int pos = ... does not look too professional...

And if we want to keep the custom names, we have to provide them via label attributes instead.