Hello, I Have 2 graphs: graph1 and graph2, and two sets of edge descriptors.

One set is associated to edges of graph1 and another set associated to edges of graph2.

I don't understand why is it possible to access information about edges of graph2 by using graph1 and the edge descriptors of graph2.

I realized of that because of an own mistake when using graphs.

What I would like to know is why is that possible to do and if it should be an exception that can handle this situation.

I send the code I was using to test this:

#include <iostream>

#include <boost/graph/adjacency_list.hpp>

#include <boost/graph/graphviz.hpp>

#include <fstream>

#include "GraphInfo.h"

using namespace std;

using namespace boost;

typedef adjacency_list<setS, vecS, bidirectionalS, VertexInfo, EdgeInfo> Graph;

void printGraph(Graph graph, string file)

{

ofstream ofs(file.c_str());

dynamic_properties dp;

dp.property("node_id", get(vertex_index, graph));

dp.property("label", get(&EdgeInfo::weight, graph));

write_graphviz_dp(ofs, graph, dp);

}

int main()

{

Graph graph1;

Graph::vertex_descriptor a1 = add_vertex(graph1);

Graph::vertex_descriptor b1 = add_vertex(graph1);

Graph::vertex_descriptor c1 = add_vertex(graph1);

Graph::edge_descriptor e1 = (add_edge(a1, b1, graph1)).first;

Graph::edge_descriptor e2 = (add_edge(b1, a1, graph1)).first;

graph1[a1].id = 10;

graph1[b1].id = 20;

graph1[c1].id = 30;

graph1[e1].weight = 1;

graph1[e2].weight = 2;

Graph graph2;

Graph::vertex_descriptor a2 = add_vertex(graph2);

Graph::vertex_descriptor b2 = add_vertex(graph2);

Graph::vertex_descriptor c2 = add_vertex(graph2);

Graph::vertex_descriptor d2 = add_vertex(graph2);

Graph::edge_descriptor e4 = (add_edge(c2, b2, graph2)).first;

Graph::edge_descriptor e5 = (add_edge(b2, c2, graph2)).first;

Graph::edge_descriptor e6 = (add_edge(d2, a2, graph2)).first;

Graph::edge_descriptor e7 = (add_edge(a2, d2, graph2)).first;

graph2[a2].id = 10;

graph2[b2].id = 20;

graph2[c2].id = 30;

graph2[e4].weight = 13;

graph2[e5].weight = 14;

graph2[e6].weight = 15;

graph2[e7].weight = 16;

// WHY IS THIS POSSIBLE TO DO

// IT IS ASKING FOR AN EDGE OF GRAPH2 BUT USING GRAPH1 ???

double weight = graph1[e7].weight;

cout<<"weight: "<<weight<<endl;

printGraph(graph1, "graph1.dot");

printGraph(graph2, "graph2.dot");

cout << "end" << endl;

return 0;

}

Thank you very much