1 //=======================================================================
2 // Copyright 2009 Trustees of Indiana University
3 // Author: Jeremiah Willcock
4 //
5 // Distributed under the Boost Software License, Version 1.0. (See
6 // accompanying file LICENSE_1_0.txt or copy at
7 // http://www.boost.org/LICENSE_1_0.txt)
8 //=======================================================================
9 
10 #ifndef BOOST_GRAPH_LOOKUP_EDGE_HPP
11 #define BOOST_GRAPH_LOOKUP_EDGE_HPP
12 
13 #include <utility>
14 #include <boost/config.hpp>
15 #include <boost/utility/enable_if.hpp>
16 #include <boost/graph/graph_traits.hpp>
17 
18 // lookup_edge: a function that acts like edge() but falls back to out_edges()
19 // and a search when edge() is not provided.
20 
21 namespace boost {
22 
23   template <typename Graph>
24   std::pair<typename boost::graph_traits<Graph>::edge_descriptor, bool>
lookup_edge(typename boost::graph_traits<Graph>::vertex_descriptor src,typename boost::graph_traits<Graph>::vertex_descriptor tgt,const Graph & g,typename boost::enable_if<is_adjacency_matrix<Graph>,int>::type=0)25   lookup_edge(typename boost::graph_traits<Graph>::vertex_descriptor src,
26               typename boost::graph_traits<Graph>::vertex_descriptor tgt,
27               const Graph& g,
28               typename boost::enable_if<is_adjacency_matrix<Graph>, int>::type = 0) {
29     return edge(src, tgt, g);
30   }
31 
32   template <typename Graph>
33   std::pair<typename boost::graph_traits<Graph>::edge_descriptor, bool>
lookup_edge(typename boost::graph_traits<Graph>::vertex_descriptor src,typename boost::graph_traits<Graph>::vertex_descriptor tgt,const Graph & g,typename boost::disable_if<is_adjacency_matrix<Graph>,int>::type=0)34   lookup_edge(typename boost::graph_traits<Graph>::vertex_descriptor src,
35               typename boost::graph_traits<Graph>::vertex_descriptor tgt,
36               const Graph& g,
37               typename boost::disable_if<is_adjacency_matrix<Graph>, int>::type = 0) {
38     typedef typename boost::graph_traits<Graph>::out_edge_iterator it;
39     typedef typename boost::graph_traits<Graph>::edge_descriptor edesc;
40     std::pair<it, it> oe = out_edges(src, g);
41     for (; oe.first != oe.second; ++oe.first) {
42       edesc e = *oe.first;
43       if (target(e, g) == tgt) return std::make_pair(e, true);
44     }
45     return std::make_pair(edesc(), false);
46   }
47 
48 }
49 
50 #endif // BOOST_GRAPH_LOOKUP_EDGE_HPP
51