Re: [Boost-users] [graph] in-depth parsing and modifications of the graph

Subject: Re: [Boost-users] [graph] in-depth parsing and modifications of the graph
From: Orianne Siret (orianne.siret_at_[hidden])
Date: 2013-07-12 04:42:50

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.

Best regards.

Orianne Siret