lemon get source node from arc code example

Example 1: lemon iterate over all arcs in graph

std::cout << "Edges:";
  for (EdgeIt i(g); i!=INVALID; ++i)
    std::cout << " (" << g.id(g.u(i)) << "," << g.id(g.v(i)) << ")";

Example 2: lemon get node from id

g.addArc(g.nodeFromId(n), g.nodeFromId(m));