Re: [Boost-users] Problems with property_maps

Subject: Re: [Boost-users] Problems with property_maps
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2010-02-28 12:14:04

On Sat, 27 Feb 2010, Trevin Murakami wrote:

> Hello all.
>
> I'm having issues getting property maps to work properly with my
> custom adjacency_list.  Here's a snippet of the code:
>
> // Definitions
> // define some of the properties the graphs will have
> // http://www.boost.org/doc/libs/1_42_0/libs/graph/doc/using_adjacency_list.html
> struct posx_t { typedef vertex_property_tag kind; };
> struct posy_t { typedef vertex_property_tag kind; };
>
> typedef property<posx_t, int> VertexPosX;
> // chain to add in posy
> typedef property<posy_t, int, VertexPosX> VertexPos;
> // chain to add in vertex_index
> typedef property<vertex_index_t, int, VertexPos> VertexProperty;
>
> // define our special graph
> typedef adjacency_list<listS, listS, undirectedS,
> VertexProperty,
> property<edge_weight_t, int> > AGraph;
>
> ...
>
> template<class T>
> void boostToVAGraph(const AGraph & g,
> 					const int num_nodes, const int num_edges,
> 					T ** idata,
> 					T ** odata,
> 					unsigned int ** segment_descriptor,
> 					unsigned int ** cross_pointers,
> 					unsigned int ** head_flags,
> 					T ** reference,
> 					const testrigOptions & testOptions)
> {
> 	typedef AGraph Graph;
>
>
> 	// define the manipulator for our special properties
> 	// http://www.boost.org/doc/libs/1_42_0/libs/graph/doc/using_adjacency_list.html
> 	// requires property_map.hpp
> 	// BROKEN!!!!!
> 	property_map<AGraph, posx_t>::type
> 		getposx = get(posx_t(), g);
> 	property_map<AGraph, posy_t>::type
> 		getposy = get(posy_t(), g);
>
> ...
>
> I used another function to generate the AGraph and apply values.  And
> using property map there seems to work.  However, I then pass it to
> this function using:
>
> boostToVAGraph(g, num_nodes, num_edges, idata, odata, segment_descriptor,
> 		cross_pointers, head_flags, reference,
> 		testOptions);
>
> On compile, I get this error:
> 1>agraph.cpp
> 1>c:/Documents and Settings/All Users/Application Data/NVIDIA
> Corporation/NVIDIA GPU Computing SDK/C/src/test/agraph.cpp(94) : error
> C2440: 'initializing' : cannot convert from
> 'boost::adj_list_vertex_property_map<Graph,ValueType,Reference,Tag>'
> to 'boost::adj_list_vertex_property_map<Graph,ValueType,Reference,Tag>'
> 1>        with
> 1>        [
> 1>            Graph=AGraph,
> 1>            ValueType=int,
> 1>            Reference=const int &,
> 1>            Tag=posx_t
> 1>        ]
> 1>        and
> 1>        [
> 1>            Graph=AGraph,
> 1>            ValueType=int,
> 1>            Reference=int &,
> 1>            Tag=posx_t
> 1>        ]
> 1>        No constructor could take the source type, or constructor
> overload resolution was ambiguous

The error seems to be that you are trying to convert from the const 
property map type (because the graph in boostToVAGraph is const) to the 
non-const one (property_map<AGraph, posx_t>::type).  I believe you would 
want property_map<AGraph, posx_t>::const_type as the property map type in 
your function instead.

-- Jeremiah Willcock