C / C++ / MFC

template class__declspec(dllexport) Element<int>;

extern template class __declspec(dllimport) Element<int>;

__declspec(dllimport) ostream& __cdecl operator<< (ostream&, ListeChaineSimple&);

__declspec(dllexport) ostream& __cdecl operator<< (ostream&, ListeChaineSimple&)
{
  ...
}

1. The header demo.h must read __declspec(dllexport) when building the DLL and __declspec(dllimport) when using it in the program test.cpp. I guess you already knew that and didn't bother to specify in your post. The standard technique to have this done is with some macro hackery.
   
2. Provided the first point is not the issue, then maybe you're having problems explicitly instantiating the functions. Try forcing an implicit instantiation:

   void __declspec(dllexport) dummy()
   {
     // a dummy function intended to instantiate the functions.
     // declared as __declspec(dllexport) to make sure the linker will not
     // strip it off as it's not actually used.
    
     typedef ListeChaineSimple<int> LCS_int;
     LCS_int liste:
     int n;
     ofstream ofs("quelque chose");
     ofs<<liste;
     liste<<n;
     liste>>n;
   }