Hi everybody,
I was just going through the "File Dependency" example for the graph
library and found this piece of code which is a very simple cycle
detector:
struct cycle_detector : public dfs_visitor<>
{
cycle_detector( bool& has_cycle)
: _has_cycle(has_cycle) { }
template
void back_edge(Edge, Graph&) {
_has_cycle = true;
}
protected:
bool& _has_cycle;
};
It takes a reference and manipulates the externally declared variable
hasCyle via that reference. I tried to change hasCylce to a "regular"
member variable, and I just want to read it afterwards, like
cycle_detector detector();
boost::depth_first_search(graph, boost::visitor(detector));
if (detector.foundCycles)
{
//do something
}
I also thought about giving the cycle detector other member variables,
like a list of back edges that gets filled. However, I found that none
of those variables gets set the right way, starting with the
very simple "bool hasCycle" member.
I guess there must be a reason why the person that made the example
chose to use a reference, and it only works that way... any ideas why?
Thanks a lot in advance.
