Get node label from boost::labeled_graph

Question

I would like to retrieve the label of a labeled node in BGL's labeled_graph but cannot find a method to do this.

The following MWE demonstrates what I am looking for:

//g++ -O3 question.cpp -o question.exe -I. --std=c++11 -lprotobuf-lite -lpthread -lz -losmpbf
#include <iostream>

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/labeled_graph.hpp>
#include <boost/graph/iteration_macros.hpp>

typedef long long node_id_t;

typedef boost::adjacency_list<
  boost::listS,           // Store out-edges of each vertex in a std::list
  boost::listS,           // Store vertex set in a std::list
  boost::bidirectionalS,  // The file dependency graph is directed
  boost::no_property,     // vertex properties
  boost::no_property      // edge properties
> AdjGraph;

typedef boost::labeled_graph<
  AdjGraph,
  node_id_t          // Node ID
> LabeledGraph;

int main(){
  LabeledGraph g;

  add_vertex( 10, g );
  add_vertex( 20, g );
  add_vertex( 30, g );
  add_vertex( 40, g );
  add_vertex( 50, g );

  boost::add_edge_by_label(10,30,g);
  boost::add_edge_by_label(10,50,g);
  boost::add_edge_by_label(30,40,g);
  boost::add_edge_by_label(50,20,g);

  BGL_FORALL_EDGES(e, g, LabeledGraph){
    auto source_n = boost::source(e,g);
    //How do I do the following?
    //std::cerr<<boost::get_label_of_vertex(source_n)<<std::endl;
  }
}

The command boost::get_label_of_vertex(source_n) does not seem to exist in my diggings.

Do you know if it does, or if there is another way to get this information?

Answer 1

Ah. I found your questions in the wrong order :)

I don't think labeled_graph<> adaptor has this feature. Instead, like in my other answer I suggest storing the label as a vertex property (bundled or vertex_index_t).

Bundled

Live On Coliru

// g++ -O3 question.cpp -o question.exe -I. --std=c++11 -lprotobuf-lite -lpthread -lz -losmpbf
#include <iostream>

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/labeled_graph.hpp>
#include <boost/graph/iteration_macros.hpp>

struct MyVertex {
    long long label;

    MyVertex(long long label = 0) : label(label) {}
};


typedef boost::adjacency_list<boost::listS,          // Store out-edges of each vertex in a std::list
                              boost::listS,          // Store vertex set in a std::list
                              boost::bidirectionalS, // The file dependency graph is directed
                              MyVertex,              // vertex properties
                              boost::no_property     // edge properties
                              > AdjGraph;

int main() {
    AdjGraph g;

    std::map<size_t, AdjGraph::vertex_descriptor> vertex_map;

    for (int i = 1; i<6; ++i)
        vertex_map.emplace(10*i, add_vertex(10*i, g));

    boost::add_edge(vertex_map[10], vertex_map[30], g);
    boost::add_edge(vertex_map[10], vertex_map[50], g);
    boost::add_edge(vertex_map[30], vertex_map[40], g);
    boost::add_edge(vertex_map[50], vertex_map[20], g);

    BGL_FORALL_EDGES(e, g, AdjGraph) {
        auto source_n = boost::source(e, g);
        std::cerr << g[source_n].label << "\n";
    }
}

vertex_index_t interior property

Live On Coliru

// g++ -O3 question.cpp -o question.exe -I. --std=c++11 -lprotobuf-lite -lpthread -lz -losmpbf
#include <iostream>

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/labeled_graph.hpp>
#include <boost/graph/iteration_macros.hpp>

typedef boost::adjacency_list<boost::listS,          // Store out-edges of each vertex in a std::list
                              boost::listS,          // Store vertex set in a std::list
                              boost::bidirectionalS, // The file dependency graph is directed
                              boost::property<boost::vertex_index_t, size_t>,    // vertex properties
                              boost::no_property     // edge properties
                              > AdjGraph;

int main() {
    AdjGraph g;

    std::map<size_t, AdjGraph::vertex_descriptor> vertex_map;

    for (int i = 1; i<6; ++i)
        vertex_map.emplace(10*i, add_vertex(10*i, g));

    boost::add_edge(vertex_map[10], vertex_map[30], g);
    boost::add_edge(vertex_map[10], vertex_map[50], g);
    boost::add_edge(vertex_map[30], vertex_map[40], g);
    boost::add_edge(vertex_map[50], vertex_map[20], g);

    auto index = boost::get(boost::vertex_index, g);

    BGL_FORALL_EDGES(e, g, AdjGraph) {
        auto source_n = boost::source(e, g);
        std::cerr << boost::get(index, source_n) << "\n";
    }
}