[Lemon-user] Template Class of LEMON Graphs

[Alpár Jüttner]

Hi,

> I want to write a class, which does e.g. some calculations on given
> graphs (ListDigraph, FullDigraph or own derived LEMON-graphes). Now I
> have to write implementations for each graph type, which could be
> avoided via templates.
> Unfortunatly I am not very experienced with templates. How does a
> template access functions of the graph or even the NodeMaps, if a
> template doesn't know the type beforehand?

This is in fact a kind of stupidity of C++ and is independent from
LEMON. When you want to use a type defined by a template parameter, you
must tell the compiler that what you using is a type (or is a template
type). Don't ask me why the compiler cannot figure it out, it is
required by the C++ standard. Actually, the older versions of gcc was
able to do it, but newer versions are stricter in following the C++
standard, thus now they do not allow this kind of laziness.

See the examples on how to use sub-type declaration properly below.

> template < typename DGR>    class   outputClass {
> public:
>     DGR                 &mGraph;
>     DGR::NodeMap<int>   mMap;
> 
typename DGR:: template NodeMap<int>   mMap;

or

typedef typename DGR:: template NodeMap<int> IntNodeMap;
IntNodeMap mMap;

>     
>     outputClass( const DGR &graph)
>     : mGraph(graph), mMap(graph){};
>     
>     void output(){
>         for (DGR::NodeIt n( mGraph ); n!=INVALID; ++n) {

for (typename DGR::NodeIt n( mGraph ); n!=INVALID; ++n) {

>             std::cout << "value: " << mMap[ n ] << endl;
>         }
>     }
> };

I hope this helps.

Regards,
Alpar