Re: [Boost-users] [BGL] Unable to sort list of edge_descriptors

Subject: Re: [Boost-users] [BGL] Unable to sort list of edge_descriptors
From: Cedric Laczny (cedric.laczny_at_[hidden])
Date: 2010-11-07 05:27:44

Hi,

first of all, nice example you specified and also a good idea to include the 
command-line used to compile.

On Sunday, 7. November 2010 05:55:14 Mike Douglass wrote:
> I have attached a minimal working program to test the sort function on a
> list of edges.
> Compile with : g++ -O3 prog.cpp -o prog
> 
> The problem is line "myList.sort(SortByName< graph_t <edge_t> >);" near the
> bottom of the page.
> See comments.

Interstingly, the problem is not BGL related.
You simply have mixed up some things with using templates here.
When you define a struct-template with one parameter, as you do with Graph, 
then you must also only specify one. You specified a graph_t< edge_t >. 
However, your graph_t is just a typedef for an adjacency_list and this 
adjacency_list is not a template. And that's exactly what the compiler is 
complaining about.
So if you change: 
myList.sort(SortByName< graph_t <edge_t> >);
to:
myList.sort(SortByName< graph_t >());

your example compiles fine here on my Linux machine.
I didn't check if it behaves the way you want it to, but this should be easier 
to do by yourself when your program is now running.

Best,

Cedric

> 
> 
//=======================================================================
> // Sort Testing Program - prog.cpp
> 
//=======================================================================
> 
> #include <iostream>
> #include <string>
> #include <boost/graph/adjacency_list.hpp>
> #include <boost/graph/properties.hpp>
> 
> using namespace boost;
> using namespace std;
> 
>   struct vertex_properties
>   {
> 
>   };
> 
>   struct edge_properties
>   {
>         string eName;
>   };
> 
> 
>   typedef adjacency_list < vecS, vecS, bidirectionalS >::edge_descriptor
> edge_t; typedef adjacency_list < vecS, vecS, bidirectionalS
> >::vertex_descriptor vertex_t;
>   typedef adjacency_list < vecS, vecS, bidirectionalS, vertex_properties,
> edge_properties > graph_t;
> 
> 
> ///////////////////////////////////////////////////////////////////////////
> /////////////////////////////////////////
> 
> 
>   template < typename Graph >
>     void add_edges(Graph & g)
>   { // Add some edges with names.
> 
>     typename graph_traits<Graph>::edge_iterator edge_iter, edges_end;
> 
>     std::pair< typename graph_traits<Graph>::edge_descriptor, bool > a =
> add_edge(1,2,g); g[a.first].eName = "A";
>     std::pair< typename graph_traits<Graph>::edge_descriptor, bool > b =
> add_edge(1,3,g); g[b.first].eName = "B";
>     std::pair< typename graph_traits<Graph>::edge_descriptor, bool > c =
> add_edge(2,1,g); g[c.first].eName = "C";
>     std::pair< typename graph_traits<Graph>::edge_descriptor, bool > d =
> add_edge(2,3,g); g[d.first].eName = "D";
> 
>     cout << endl << " list of edges " << endl;
>     for (tie(edge_iter, edges_end) = edges(g); edge_iter != edges_end;
> ++edge_iter)
>           cout <<  " " << g[*edge_iter].eName << endl;
> 
> }
> 
> 
>   template < typename Graph >
>     struct SortByName
>  { // The Predicate
> 
>       template < typename edge_t >
>         bool operator()(const edge_t& a, const edge_t& b) const
>       {
>         return g[a].eName < g[b].eName;
>       }
> 
> 
>     Graph g;
> 
>  };
> 
> 
>   template < typename Graph >
>     void Sort_Test(Graph & g)
>   { // Test the sort function.
> 
>     typedef std::list<graph_traits<graph_t>::edge_descriptor> edge_list;
>     typename graph_traits<Graph>::edge_iterator edge_iter, edges_end;
> 
>     edge_list myList;
> 
>     // Load myList with the edges of g
>     for (tie(edge_iter, edges_end) = edges(g); edge_iter != edges_end;
> ++edge_iter)
>         myList.push_back(*edge_iter);
> 
>     // Write out myList
>     cout << endl << " myList " << endl;
>     for (edge_list::iterator i = myList.begin(); i != myList.end(); ++i)
>           cout <<  " " << g[*i].eName << endl;
> 
>     // Sort myList
>     // If the following line is commented out the program compiles and runs
> OK. myList.sort(SortByName< graph_t <edge_t> >);
>     //With the above line uncommented the compiler says:
>     // "prog.cpp:88: error: ‘graph_t’ is not a template" -- I'm stumped.
> 
>  }
> 
> 
>   int main()
>   {
> 
>       graph_t g;
> 
>     add_edges(g);
> 
>     Sort_Test(g);
> 
>   }
> 
> 
> 
> 
> ________________________________
> From: Cedric Laczny <cedric.laczny_at_[hidden]>
> To: boost-users_at_[hidden]
> Sent: Sat, November 6, 2010 3:54:49 AM
> Subject: Re: [Boost-users] [BGL] Unable to sort list of edge_descriptors
> 
>  if my suggestion does not fix the problem, please include a complete
> example.