On Fri, 12 Jul 2013, Orianne Siret wrote:

I mean traverse when i said parse. So the problem is i can't traverse in depth-first order my graph and modify  node (or edge) properties. I wrote a basic case which doesn't work.

----------------------------------------- // Begin main.cpp

#include <boost/graph/adjacency_list.hpp> #include <boost/graph/depth_first_search.hpp> #include <vector>

// Node properties struct MyNode { int node_id; MyNode() : node_id() {} MyNode(int id) : node_id(id) {} };

//Edge Properties struct MyEdge { int edge_id; MyEdge() : edge_id() {} MyEdge(int id) : edge_id(id) {} };

// Graph definition typedef boost::adjacency_list< boost::vecS, boost::vecS, boost::directedS, MyNode, MyEdge

...

MyGraph;

typedef boost::graph_traits<MyGraph>::vertex_descriptor MyGraphVD;

//My idiot visitor class my_dfs_visitor : public boost::default_dfs_visitor { public: template < typename Vertex, typename Graph > void discover_vertex(Vertex u, Graph & g) {                 // here i cant assign 0 to m node_id. however g is not cont.. I didn't find a code with a depth-first traversal and assign ment. g[u].node_id = 0; } };

int main() { MyGraph g; MyGraphVD vd0 = boost::add_vertex(MyNode(0), g); MyGraphVD vd1 = boost::add_vertex(MyNode(1), g);

boost::add_edge(vd0, vd1, MyEdge(), g); boost::add_edge(vd1, vd0, MyEdge(), g);

my_dfs_visitor visitor; boost::depth_first_search(g, boost::visitor(visitor)); return 0; }

// end

------------------------------------------

This code doesn't work. I have the following error : ../main.cpp:35:3: erreur: assignment of member ‘MyNode::node_id’ in read-only object.  (I do: "g++ -O3 -Wall -c -o main.o main.cpp " for compilation, i run on linux ubuntu 12.04 with gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3) I didn't find any example on the web.. 

Thanks for spending time on my problem. It is very nice of you.

I think the easiest solution for you is to put a non-const reference to your graph into the visitor as a data member, then have your visitor's member functions refer to that reference rather than using the graph passed in by the algorithm. -- Jeremiah Willcock