Boost C++ Libraries: Ticket #3506: Graph's Tour / Dijkstra's parent nodes

Jeremiah Willcock — Sun, 04 Oct 2009 01:48:19 GMT

(In [56563]) Changed from Vertex() to null_vertex() in examples; refs #3506

status changed; resolution set

Jeremiah Willcock — Sun, 04 Oct 2009 01:50:49 GMT

status new → closed
resolution → fixed

This does appear to be a bug in the example -- there is a special null_vertex() value that is used to mark invalid vertices. I changed the code to use that, but it is probably not a good idea to look at the predecessor of the start vertex anyway. I do not believe the visitor ever sets the predecessor since it never has an edge coming in that is discovering the start vertex.

severity changed

JDKunkMailing@… — Sun, 04 Oct 2009 12:46:37 GMT

severity Problem → Not Applicable

Replying to jewillco:

This does appear to be a bug in the example -- there is a special null_vertex() value that is used to mark invalid vertices. I changed the code to use that, but it is probably not a good idea to look at the predecessor of the start vertex anyway. I do not believe the visitor ever sets the predecessor since it never has an edge coming in that is discovering the start vertex.

I discovered that if a parent does not exist, it does not set anything to the property map. Therefore, algorithms (maybe just dijkstra) will not change an element if there is nothing to set it to. I recommend that all users should place default values into the analysis from algorithms, but this is just good application programming practice.