Adjacency list needs to handle self-edges correctly

[Aaron Windsor]

The following short program crashes as of boost 1.35:

#include <boost/graph/adjacency_list.hpp>

int main() {

using namespace boost; typedef adjacency_list<vecS, vecS, undirectedS > graph_t; graph_t g(5); add_edge(2, 2, g); remove_edge(2, 2, g);

}

The problem is that (2,2) is stored once in the list of edges in the graph and twice in the list of adjacent edges to the vertex 2. When remove_edge is called, the global graph edge (2,2) is deleted twice, causing a segfault. This problem is discussed in the following thread: ​http://lists.boost.org/Archives/boost/2007/02/116547.php.

[Andrew Sutton]

Removing the loop using remove_edge(e, g) does not seem to trigger the same segfault.

[Andrew Sutton]

(In [50206]) Fixed #1622. A viable solution relies on the fact that incident edges in a loop are stored adjacently in the out edge list of the vertex. A simple modification of the global edge erasing loop for undirected graphs will skip the next iterator if both the current and next contain the same iterator.