The code works...
I'm not convinced that it does. First, the predecessor map is not actually a property map - you are using it to accumulate relaxed edges. Second, the order of edges may be arbitrary and certainly not contiguous. I'm not sure I see how to efficiently recover the path using this approach.
I don't know how to use edge_predecessor_recorder, it seems unable to slove
this problem, because it just has a operator().
I think it maps onto a visitor that has a tree_edge function, so its only useful for BSF, DSF, and MST visitors.
And I has some additional questions:
1. Why BGL introduce descriptor? This new thing bring what advantage? In
STL, the communication between Algo & Container is iterator. But in BGL, a
new "iterator-like" thing: descriptor has been introduced. What is the
difference? The document says descriptor is a "handle", isn't iterator also
a "handle"??
Descriptors can't "move" (++/--) and can't be dereferenced. The biggest reason for using descriptors is that they can provide a higher degree of stability than iterators. For example, a vector will invalidate all iterators on insert and remove. This makes it virtually impossible to build a relational data structure (like a graph) on top of vectors, if you use iterators (or pointers) from vertex to edge, edge to vertex, and both their properties.
2. Can descriptor convertable with iterator?
The BGL does not provide a translation between iterators and descriptors.