Hi all,<br><br> Although I was attracted to BGL since I have to use a lot of graph algorithms for my work, and I have managed to read through as much online documentation as possible, <br> generic programming is still very mysterious to me. <br>
 <br> All I need to do is compute reachability from vertex B to vertex A before I add the edge A-&gt;B to a graph (directed and acyclic) so that I can maintain its acyclic property.<br> I do not want to add the edge, discover a cycle and then remove it.<br>
<br> I saw a very closely related example here. (thanks to Steven Watanabe)<br> <a href="http://lists.boost.org/boost-users/2009/03/46396.php">http://lists.boost.org/boost-users/2009/03/46396.php</a><br><br> That was helpful, but I&#39;m still not able to adapt this to my need mainly because I find the syntax and concepts of generic programming extremely confusing.<br>
<br> I am not sure how I can pass an extra parameter into a BFSVisitor which the member function discover_vertex can use. Does discover_vertex have to have only a vertex_descriptor and a Graph?<br> I want to pass another constant vertex to it so I can return on equality.<br>
<br> I need to initiate a BFS from vertex B, (and not continue with new trees once the tree with B as root is finished) .<br> On discovering vertex A in this search I need to return true, false for all other cases.<br><br>
 Pretty simple, and I am hoping someone would write a code snippet for me that will solve the problem and also provide me with the baby step I need to  wrap my head around this Visitor concept.<br> <br><br> Thanks in advance. <br>
<br> - Roshan Rammohan <br> PhD Candidate, A.I. lab, Dept of C.S., <br> Univ. of New Mexico, USA<br>