Maps in LEMON Graph C++

Question

I need a really simple thing in LEMON but I cannot solve it.

I have a weighted graph. Weights on arcs. I need to use the graph as part of a class object. Therefore I have the graph and the ArcMap (needed for the weights) as object attributes. Now, I have a function that computes both the graph and the Map, and later I will need in other function to use both graph and Map.

But I cannot create the map in the first function and then assign it to an attribute of the class. I get the following:

'operator=' is a private member of 'lemon::DigraphExtender<lemon::ListDigraphBase>::ArcMap<int>'

In the documentation I did not find anything, but it really seems a normal stuff computing something on a function to then use it into another.

I have my declaration like:

ListDigraph::ArcMap<int>& length;

And the assignment I try to do after the computation is:

ListDigraph::ArcMap<double> ll(g);
this->length = ll;

where g is:

ListDigraph g;

declared as a public attribute of the class.

EDIT:

#include <algorithm>
#include <random>
#include <thread>

#include <lemon/list_graph.h>
#include <lemon/maps.h>

#include "VLR_Config.h"
#include "VLR_Feed.h"
#include "VLR_Tools.h"

using namespace lemon;
class GraphSolver {
    public:
void compute_graph() {
            for (auto const &t: seq_trips) {
                auto tid = t[0].trip_id;
                for (int i = 0; i < t.size() - 1; ++i) {
                    auto from_sid = t[i].stop_id;
                    auto to_sid = t[i + 1].stop_id;

                    auto from_time = t[i].arrival_time;
                    auto to_time = t[i + 1].arrival_time;
                    auto delta = to_time - from_time;

                    ListDigraph::NodeMap<int> node2stop(g);

                    ListDigraph::Node from_node;
                    ListDigraph::Node to_node;
                    if (stop2node.find(from_sid) != stop2node.end())
                        from_node = stop2node.at(from_sid);
                    else {
                        from_node = g.addNode();
                        stop2node[from_sid] = from_node;
                        node2stop[from_node] = from_sid;
                    }
                    if (stop2node.find(to_sid) != stop2node.end())
                        to_node = stop2node.at(to_sid);
                    else {
                        to_node = g.addNode();
                        stop2node[to_sid] = to_node;
                        node2stop[to_node] = to_sid;
                    }

                    ListDigraph::Arc old_arc = findArc(g, from_node, to_node);

                    if(old_arc == INVALID) {
                        ListDigraph::Arc new_arc = g.addArc(from_node, to_node);
                        length[new_arc] = delta;
                    }
                    else
                        if(length[old_arc] < delta)
                            length[old_arc] = delta;
                }
            }


        }

 // Collect StopTimes by trips
        SeqTrips seq_trips;

        MapStop2Idx stop2idx;

        VecStops stops;
        VecTrips trips;
        VecRoutes routes;
        ListDigraph g;
        unordered_map<size_t, ListDigraph::Node> stop2node;
        ListDigraph::ArcMap<int> length(g);

};

with an error on the last line, since I cannot passing g in that context. But, if I do not pass g I get an error in the main when declaring the object of class GraphSolver :

GraphSolver graph_solver;

gives the error Call to implicitly-deleted default constructor of 'VLR::GraphSolver' default constructor of 'GraphSolver' is implicitly deleted because field 'length' has no default constructor

score 0 · Answer 1 · answered Jun 20 '23 at 13:05

The class GraphSolver needs a constructor.

Two possibilities:

The constructor has a parameter which specifies the size of the graph - in particular the number of arcs , so that the GraphSolver constructor can construct the graph AND the set the size of the ArcMap.
The graph is constructed somewhere else and the number of arcs is passed to the GraphSolver constructor so it can set the size of the ArcMap.

Maps in LEMON Graph C++

1 Answers1