Re: [Boost-users] BGL: Trying to get my property bundle-using adjacency list to use a vector for its WeightMap.

14 Aug 2008

      Hmm, maybe if I add some extra information someone will be better able 
to answer...

The basic premise is that I want the dijkstra algorithm to iterate 
through the Bar weights making its comparisons as it would were it only 
a POD (ie, as if it were using Foo instead). I've been reading the 
mailing list, online documentation and examples all day while trying 
different things, but I can't get it working. :|

I also tried this (weightMap is a local variable in main()):
dijkstra_shortest_paths(mygraph, *vi,
	weight_map(
		make_iterator_property_map(weightMap.begin(), get(edge_index, mygraph)
		)
	)
	.distance_map(
			make_iterator_property_map(distances.begin(), vertex_ind)
	)
	.predecessor_map(
		make_iterator_property_map(predecessors.begin(), vertex_ind))
	.visitor(vis)
	);

This compiles (with warnings).. and runs without issue... but what I 
want is to point it towards the Bar member in my EdgeProperty struct.
Is it just a syntax issue? What is it I should alter?

Thanks again,
Geoff

Geoff Hilton wrote:
...
Hi, I'm new to the boost and the BGL, and as the subject suggests, I'm
trying to get my property bundle-using adjacency list to use a vector 
for its WeightMap.
First off, the property bundles in question:
template
struct EdgeProperty
{
    EdgeProperty(long double foo = 0):Foo(foo),
Bar(NumberOfBar){}
    long double Foo;
    vector<long long> Bar;
};
template
struct VertexProperty
{
    VertexProperty():Baz(NumberOfBar){}
    vector > Baz;
};
The visitor:
struct MyVisitor
: public default_dijkstra_visitor
{
    template 
    void discover_vertex(Vertex u, const Graph& g)
    {
        cout << "discovered " << u << '\n';
    }
template 
    void tree_edge(Edge e, const Graph& g)
    {
        cout << "tree edge " << e << '\n';
    }
template 
    void examine_edge(Edge e, const Graph& g)
    {
        cout << "examining edge " << e << '\n';
    }
    template 
    void finish_vertex(Vertex u, const Graph& g)
    {
        cout << "finishing vertex " << u << endl;
    }
};
The graph typedef:
typedef adjacency_list< vecS, vecS, bidirectionalS, 
property >, 
property > > graph_t;
Adding edges and vertices to the graph works without issue, as does 
assigning values to the properties, and navigating it, I was also able 
to get my test visitor to work.. using this code:
int _tmain(int argc, _TCHAR* argv[])
{
    graph_t mygraph;
    //build graph
    //...
    //set up property accessors
    typedef EdgeProperty<1> EdgeProp;
    property_map::type edge_foo_t = 
get(&EdgeProp::foo, mygraph);
    property_map::type 
edge_bar_t = get(&EdgeProp::Bar, mygraph);
    property_map::type vertex_ind = 
get(vertex_index, mygraph);
    //dijkstra stuff
    size_t numberOfVertices = num_vertices(mygraph);
    std::vector<long double> distances(numberOfVertices, 
(numeric_limits<long double>::max)());
    vector predecessors(numberOfVertices);
MyVisitor vis;
    dijkstra_shortest_paths(mygraph, *vi,
        weight_map(edge_foo_t)
        .weight_map2(edge_bar_t)
        .distance_map(
            make_iterator_property_map(distances.begin(), vertex_ind)
        )
        .predecessor_map(
            make_iterator_property_map(predecessors.begin(), vertex_ind)
        )
        .visitor(vis)
    );
    return 0;
}
However when I switch edge_bar_t and edge_foo_t within the 
weight_map/weight_map2 parentheses, I get this error (Visual Studio 
2005) 'bool std::less<_Ty>::operator ()(const _Ty &,const _Ty &) const' 
: cannot convert parameter 1 from 'std::vector<_Ty>' to 'const D &'
Of course that's normal because it's a vector. I figure I'm supposed to 
use make_iterator_property_map and somehow point it to 
&EdgeProp::Bar::begin() (or &EdgeProp::Bar::rbegin()) with a 
property_map<...> as I did with the others...but what I've tried so far 
hasn't worked.
Any ideas?
Thanks very much and best wishes,
Geoff