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c++boostboost-graph

Boost graph unable to union_set


This question is connected with: Using boost connected components with cartesian points

I've made some changes in example to use cartesian points. Here is my current code:

using namespace boost;
typedef adjacency_list <vecS, vecS, undirectedS, cv::Point> Graph;
typedef graph_traits<Graph>::vertex_descriptor Vertex;
typedef graph_traits<Graph>::vertices_size_type VertexIndex;

int main()
{
    const int VERTEX_COUNT = 10;
    Graph graph(VERTEX_COUNT);

    std::vector<VertexIndex> rank(num_vertices(graph));
    std::vector<Vertex> parent(num_vertices(graph));

    typedef VertexIndex* Rank;
    typedef Vertex* Parent;

    disjoint_sets<Rank,Parent> ds(&rank[0], &parent[0]);

    initialize_incremental_components(graph,ds);
    incremental_components(graph,ds);

    graph_traits<Graph>::edge_descriptor edge;
    bool flag;

    std::vector<Vertex> verticesVector;
    //vector of points which creates graph
    std::vector<cv::Point> points;

    points.push_back(cv::Point(0,0));
    points.push_back(cv::Point(1,1));
    points.push_back(cv::Point(2,2));
    points.push_back(cv::Point(3,1));
    points.push_back(cv::Point(4,2));
    points.push_back(cv::Point(0,2));
    points.push_back(cv::Point(2,3));
    points.push_back(cv::Point(3,3));

    int i = 0;
    for(std::vector<cv::Point>::iterator it = points.begin(); 
            it !=points.end();it++, i++)  
    {
        verticesVector.push_back(add_vertex(graph));
        graph[i].x = (*it).x;
        graph[i].y = (*it).y;
    }

    typedef component_index<VertexIndex> Components;
    Components components(parent.begin(), parent.end());

    BOOST_FOREACH(VertexIndex current_index, components)
    {
        std::cout<<"component "<<current_index<<" contains: ";
        BOOST_FOREACH(VertexIndex child_index, components[current_index])
        {
            std::cout<<child_index<<" "<<" x = "<<graph[current_index].x<<";"<<graph[current_index].y<<"||";
        }
        std::cout<<std::endl;
    }

    boost::tie(edge,flag) = add_edge(verticesVector[0],verticesVector[1],graph);
    ds.union_set(verticesVector[0],verticesVector[1]);
    boost::tie(edge,flag) = add_edge(verticesVector[1],verticesVector[2],graph);
    ds.union_set(verticesVector[1],verticesVector[2]);
    boost::tie(edge,flag) = add_edge(verticesVector[2],verticesVector[3],graph);
    ds.union_set(verticesVector[2],verticesVector[3]);
    boost::tie(edge,flag) = add_edge(verticesVector[3],verticesVector[4],graph);
    ds.union_set(verticesVector[3],verticesVector[4]);
    boost::tie(edge,flag) = add_edge(verticesVector[1],verticesVector[5],graph);
    ds.union_set(verticesVector[1],verticesVector[5]);
    boost::tie(edge,flag) = add_edge(verticesVector[5],verticesVector[6],graph);
    ds.union_set(verticesVector[5],verticesVector[6]);
    boost::tie(edge,flag) = add_edge(verticesVector[6],verticesVector[7],graph);
    ds.union_set(verticesVector[6],verticesVector[7]);

    Components components2(parent.begin(), parent.end());


    /*BOOST_FOREACH(Vertex current_vertex, vertices(graph)) 
    {
        std::cout<< "representative["<<current_vertex<<"] = "
        << ds.find_set(current_vertex)<<std::endl;
    }

    std::cout<<std::endl;*/

    for(std::vector<Vertex>::iterator it = verticesVector.begin(); it !=  verticesVector.end(); it++)
    {
        std::cout<<"representative = "<<ds.find_set((*it))<<std::endl;
    }

    BOOST_FOREACH(VertexIndex current_index, components2)
    {
        std::cout<<"component "<<current_index<<" contains: ";
        BOOST_FOREACH(VertexIndex child_index, components[current_index])
        {
            std::cout<<child_index<<" "<<" x,y = "<<graph[current_index].x<<";"<<graph[current_index].y<<"||";
        }
        std::cout<<std::endl;
    }

    //write_graphviz(std::cout, graph);

    getchar();
    return 0;
}

I'm getting exception when trying to union_set(): Access violation reading location... I can not figure out the reason. I've read all topics on boost lib, tried to search in docs.


Solution

  • I've figured it out thanks to this tutorial: Algorithm for selecting all edges and vertices connected to one vertex

    The problems was:

    • I initialized vector with some vertices first (copy paste from example and modifying wasn't best idea)
    • As tutorial says "Notice that graph[ a VertexID ] gives a Vertex, but graph[ an EdgeID ] gives an Edge "
    • Disjoint set should be initialized after adding some vertices

    Working code:

    using namespace boost;
    
    typedef adjacency_list <vecS, vecS, undirectedS, cv::Point> Graph;
    typedef graph_traits<Graph>::vertex_descriptor Vertex;
    typedef graph_traits<Graph>::vertices_size_type VertexIndex;
    
    int main()
    {
        Graph graph;
    
        graph_traits<Graph>::edge_descriptor edge;
        bool flag;
    
        std::vector<Vertex> verticesVector;
        Vertex verticesTable[8];
        std::vector<cv::Point> points;
    
        points.push_back(cv::Point(0,0));
        points.push_back(cv::Point(1,1));
        points.push_back(cv::Point(2,2));
        points.push_back(cv::Point(3,1));
        points.push_back(cv::Point(4,2));
        points.push_back(cv::Point(0,2));
        points.push_back(cv::Point(2,3));
        points.push_back(cv::Point(3,3));
    
        int i = 0;
        for(std::vector<cv::Point>::iterator it = points.begin(); it != points.end(); it++, i++)
        {
            verticesTable[i] = add_vertex(graph);
            graph[verticesTable[i]].x = (*it).x;
            graph[verticesTable[i]].y = (*it).y;
        }
    
        std::vector<VertexIndex> rank(num_vertices(graph));
        std::vector<Vertex> parent(num_vertices(graph));
    
        typedef VertexIndex* Rank;
        typedef Vertex* Parent;
    
        disjoint_sets<Rank,Parent> ds(&rank[0], &parent[0]);
    
        initialize_incremental_components(graph,ds);
        incremental_components(graph,ds);
    
        typedef component_index<VertexIndex> Components;
        Components components(parent.begin(), parent.end());
    
        Graph::vertex_iterator vertexIt, vertexEnd;
        boost::tie(vertexIt,vertexEnd) = vertices(graph);
        for(;vertexIt != vertexEnd; ++vertexIt)
        {
            Vertex a = *vertexIt;
            cv::Point &b = graph[a];
            std::cout<<"Point: "<<b.x<<";"<<b.y<<std::endl;
        }
    
        boost::tie(edge,flag) = add_edge(verticesTable[0],verticesTable[1],graph);
        ds.union_set(verticesTable[0],verticesTable[1]);
        boost::tie(edge,flag) = add_edge(verticesTable[1],verticesTable[2],graph);
        ds.union_set(verticesTable[1],verticesTable[2]);
        //boost::tie(edge,flag) = add_edge(verticesTable[2],verticesTable[3],graph);
        //ds.union_set(verticesTable[2],verticesTable[3]);
        boost::tie(edge,flag) = add_edge(verticesTable[3],verticesTable[4],graph);
        ds.union_set(verticesTable[3],verticesTable[4]);
        boost::tie(edge,flag) = add_edge(verticesTable[1],verticesTable[5],graph);
        ds.union_set(verticesTable[1],verticesTable[5]);
        boost::tie(edge,flag) = add_edge(verticesTable[5],verticesTable[6],graph);
        ds.union_set(verticesTable[5],verticesTable[6]);
        boost::tie(edge,flag) = add_edge(verticesTable[6],verticesTable[7],graph);
        ds.union_set(verticesTable[6],verticesTable[7]);
    
        BOOST_FOREACH(Vertex current_vertex, vertices(graph)) 
        {
            std::cout<< "representative["<<current_vertex<<"] = "
            << ds.find_set(current_vertex)<<std::endl;
        }
    
        std::cout<<std::endl;
    
        Components components2(parent.begin(), parent.end());
    
        BOOST_FOREACH(VertexIndex current_index, components2)
        {
            std::cout<<"component "<<current_index<<" contains: ";
            BOOST_FOREACH(VertexIndex child_index, components2[current_index])
            {
                  std::cout<<child_index<<" "<<" x,y = "<<graph[verticesTable[child_index]].x<<";"<<graph[verticesTable[child_index]].y<<"||";
            }
            std::cout<<std::endl;
        }
    
        //write_graphviz(std::cout, graph);
    
        getchar();
    
        return 0;
    }
    

    I'm still learning boost Graph so please correct my mistakes, make more elegant solutions. My conclusions also can be not exactly correct.