Re: [Boost-users] Graph: create_subgraph not defined

Subject: Re: [Boost-users] Graph: create_subgraph not defined
From: Trevor Harmon (Trevor.W.Harmon_at_[hidden])
Date: 2010-06-28 15:23:18

On Jun 24, 2010, at 10:12 AM, Jeremiah Willcock wrote:

> Note that G0 is of type subgraph<...>, not adjacency_list<...> like  
> you
> were using.  Could that be the issue?

Yes, that's definitely something I was doing wrong. After rereading  
the docs, I see now that subgraphs must be of a special subgraph class  
type, but I don't understand why. Conceptually speaking, I see no  
reason for this class to exist. For example, when implementing a  
generic tree structure, there's no need to have separate "Node" and  
"Subnode" classes; all nodes can be of type "Node". The top-level node  
is distinguished simply by the fact that it has no parents. For the  
same reason, the top-level graph in a hierarchy of graphs can have the  
same type as any of its children (and vice versa). The way Boost  
implements this concept seems overly complicated.

Design issues aside, I'm now trying to modify my graph code to use  
subgraphs. To start off, I thought I would try changing my  
adjacency_list to subgraph<adjacency_list>. Theoretically, my code  
should still work the same way, right? But I'm getting compiler errors  
when calling get(). Pasted below is an example of the problem. The  
error is:

subgraph.cpp: In function ‘int main(int, char**)’:
subgraph.cpp:19: error: conversion from  
‘boost 
::subgraph_global_property_map 
<boost::subgraph<boost::adjacency_list<boost::vecS, boost::vecS,  
boost::bidirectionalS, boost::shared_ptr<MyVertex>,  
boost::property<boost::edge_index_t, size_t, boost::no_property>,  
boost::no_property, boost::listS> >*,  
boost::adj_list_edge_property_map<boost::bidirectional_tag, size_t,  
size_t&, size_t, boost::property<boost::edge_index_t, size_t,  
boost::no_property>, boost::edge_index_t>, boost::edge_index_t>’ to  
non-scalar type ‘boost::subgraph_global_property_map<MyGraph*,  
boost::adj_list_edge_property_map<boost::bidirectional_tag, size_t,  
size_t&, size_t, boost::property<boost::edge_index_t, size_t,  
boost::no_property>, boost::edge_index_t>, boost::edge_index_t>’  
requested

Any suggestions how to fix this?

Thanks,

Trevor

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/subgraph.hpp>

using namespace boost;

class MyVertex {
public:
     virtual ~MyVertex() {}
};

class MyGraph :
     public subgraph<adjacency_list<vecS, vecS, bidirectionalS,  
shared_ptr<MyVertex>, property<edge_index_t, std::size_t> > > {
};

typedef property_map<MyGraph, edge_index_t>::type EdgeIndexMap;

int main(int,char*[]) {
     MyGraph g;
     EdgeIndexMap edgeMap = get(edge_index, g);
     return 0;
}