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Is it possible to change the condition for completing the first search condition in BGL?

I am new to BGL (Advanced Graph Library). I am learning the breadth_first_search interface and it looks comfortable. However, in my application, I need to cut out breadth_first_search when some other termination condition is met, such as the number of spaces of the node corresponds to the maximum.

Can I add a new termination condition using BFSVisitors or is there another trick?

Thank!

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( ) @yuyoyuppe, --, , . , , discover_vertex examine_edge. false:

namespace details {

struct no_halting {
    template <typename GraphElement, typename Graph>
    bool operator()(GraphElement const&, Graph const&) {
        return false;
    }
};
} // namespace details

.

template <typename VertexPredicate = details::no_halting,
          typename EdgePredicate = details::no_halting,
          typename BFSVisitor = boost::default_bfs_visitor>
struct bfs_halting_visitor : public BFSVisitor {
    // ... Actual implementation ...
private:
    VertexPredicate vpred;
    EdgePredicate epred;
};

3 :

  • , discover_vertex ( )
  • , examine_edge ( )
  • ,

, :

template <typename VPred, typename EPred, typename ... VisArgs>
bfs_halting_visitor(VPred&& vpred, EPred&& epred, VisArgs&&... args) :
                    BFSVisitor(std::forward<VisArgs>(args)...),
                    vpred(vpred), epred(epred) {}

() - :

template <typename Pred, typename R, typename ... FArgs, typename ... Args>
void throw_on_predicate(R (BFSVisitor::*base_fct)(FArgs...), Pred&& pred, Args&&... args) {
    bool result = pred(args...);
    (this->*base_fct)(std::forward<Args>(args)...);
    if (result) {
        throw std::runtime_error("A predicate returned true");
    }
}

, std::runtime_error, , std::exception .

:

template <typename Edge, typename Graph>
void examine_edge(Edge&& e, Graph&& g) {
    throw_on_predicate(&BFSVisitor::template examine_edge<Edge, Graph>, epred,
                       std::forward<Edge>(e), std::forward<Graph>(g));
}

template <typename Vertex, typename Graph>
void discover_vertex(Vertex&& v, Graph&& g) {
    throw_on_predicate(&BFSVisitor::template discover_vertex<Vertex, Graph>, vpred,
                       std::forward<Vertex>(v), std::forward<Graph>(g));
}

, true N- .

struct VertexCounter {
    VertexCounter(std::size_t limit) : count(0), limit(limit) {}
    VertexCounter() : VertexCounter(0) {}

    template <typename V, typename G>
    bool operator()(V&&, G&&) {
        return ((++count) > limit);
    }
private:
    std::size_t count;
    std::size_t const limit;
};

bfs :

Graph graph = get_graph();
Vertex start_vertex;
bfs_halting_visitor<VertexCounter> vis(VertexCounter(2), details::no_halting());
try {
    boost::breadth_first_search(graph, start_vertex, boost::visitor(vis));
} catch (std::runtime_error& e) {
    std::cout << e.what() << std::endl;
}

A Coliru , .

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