Re: inheriting from ostream to customize standard output

Hi everybody,

I was wondering if there is an easy way that one could create a custom
class that inherits from std::ostream to override the functionality of
operator<<.

Since I work with several processes, I want to avoid some of them to
print information to standard output (or enable that to print
information concurrently). I tried the following but it didn't work:

         class Output_strem : public std::ostream {
             typedef std::ostream base_type;
         public:
             Output_strem() : base_type() {}
             template<typename T>
             std::ostream& operator<<(T t) {
#ifdef MPI
                 std::ostream& os = *this;
                 os<<"["<<Parallel_base::rank_<<"] ";
#endif
                 return *this;
             }
         };

As you see, nothing is telling the ostream object to print to standard
output. I saw the definition of the cout in the standard library and
it looks like this:

   ios_base::Init::Init()
   {
     if (__gnu_cxx::__exchange_and_add_dispatch(&_S_refcount, 1) == 0)
       {
         // Standard streams default to synced with "C" operations.
         _S_synced_with_stdio = true;
         new (&buf_cout_sync) stdio_sync_filebuf<char>(stdout);
         // other created objects
         // The standard streams are constructed once only and never
         // destroyed.
         new (&cout) ostream(&buf_cout_sync);
         // other created objects
         // NB: Have to set refcount above one, so that standard
         // streams are not re-initialized with uses of ios_base::Init
         // besides<iostream> static object, ie just using<ios> with
         // ios_base::Init objects.
         __gnu_cxx::__atomic_add_dispatch(&_S_refcount, 1);
       }
   }

Can someone point me in the right direction?