ofstream out("exit.txt");
out << "Showing info of graph:nn";
out << "Number of vertices: " << V;
out << "nNumber of edges: " << map_edges.size() << "n";
out.close();

ofstream out("exit.txt", ios::app);
//out.open("exit.txt", std::ofstream::out | std::ofstream::app);
out << "hello";
map<pair<int, int>, int>::iterator it;
for (it = map_edges.begin(); it != map_edges.end(); ++it)

    out << it->first.first << " linked to vertex " << it->first.second << " with weight " << it->second << endl;
    out.close();