c++ boost::graph get parent vertices from directed graph

Question

I have a directed graph (implemented via an adjacency_graph from the boost::graph library) and I'm trying to find the parent vertices of a certain vertex.

In the past (via pygraph) I have simply reversed the digraph, then done a neighbours search, but it appears that reversing the graph with boost::reverse_graph turns my digraph into a bidirectional graph, and therefore I can't use the adjacent_vertices method anymore.

Is there a better way to get the parent vertices?

Thanks.

Here's my current example code:

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/reverse_graph.hpp>
#include <iostream>

typedef boost::adjacency_list< boost::setS, boost::vecS, boost::directedS > Graph;
typedef boost::reverse_graph<Graph> Rgraph;
typedef Graph::vertex_descriptor Vertex;

int main()
{
    Graph graph;
    Vertex v0 = boost::add_vertex(graph);
    Vertex v1 = boost::add_vertex(graph);
    Vertex v2 = boost::add_vertex(graph);
    Vertex v3 = boost::add_vertex(graph);
    Vertex v4 = boost::add_vertex(graph);
    Vertex v5 = boost::add_vertex(graph);
    Vertex v6 = boost::add_vertex(graph);

    boost::add_edge(v0,v1,graph);
    boost::add_edge(v1,v2,graph);
    boost::add_edge(v2,v3,graph);
    boost::add_edge(v2,v4,graph);
    boost::add_edge(v3,v5,graph);
    boost::add_edge(v4,v5,graph);
    boost::add_edge(v5,v6,graph);

    Graph::adjacency_iterator ibegin, iend;
    for (boost::tie(ibegin, iend) = boost::adjacent_vertices(v2, graph); ibegin != iend; ++ibegin)
    {
        std::cout << *ibegin << std::endl;
    }

    std::cout << std::endl << "############# RGRAPH #############" << std::endl << std::endl;

    Rgraph rgraph(graph);
    Rgraph::adjacency_iterator rbegin, rend;
    for (boost::tie(rbegin, rend) = boost::adjacent_vertices(v2, rgraph); rbegin != rend; ++rbegin)
    {
        std::cout << *rbegin << std::endl;
    }
    std::cout << std::endl;

    return 0;
}

Answer 1

reverse_graph requires that the adapted graph be a model of BidirectionalGraph. If you change your graph to typedef boost::adjacency_list< boost::setS, boost::vecS, boost::bidirectionalS > Graph; your program compiles and gives the result:

3
4

############# RGRAPH #############

1

that I believe is what you should expect.

Another way that does not require the reverse_graph (but still requires bidirectionalS) is to use:

Graph::out_edge_iterator out_begin, out_end;
for (boost::tie(out_begin, out_end) = out_edges(v2,graph); out_begin != out_end; ++out_begin)
{   
    std::cout << target(*out_begin,graph) << std::endl;
}
std::cout << std::endl;

Graph::in_edge_iterator in_begin, in_end;
for (boost::tie(in_begin, in_end) = in_edges(v2,graph); in_begin != in_end; ++in_begin)
{   
    std::cout << source(*in_begin,graph) << std::endl;
}
std::cout << std::endl;