Getting relation/attribute names from inside UDT input/output function

Hello,

I wrote the UDT input/output functions for my complex type
and everything is working well.
But now, in the input function, I need to get the relation/attribute
names where a new object is being inserted.

PG_FUNCTION_INFO_V1(complex_in);
Datum complex_in(PG_FUNCTION_ARGS) {
   char *arg1 = PG_GETARG_CSTRING(0);
   char *relname = ???
   char *attribname = ???
   ...
   PG_RETURN_POINTER(result);
}

Does anybody have an idea of how I get that?

Thanks in advance

Humberto Razente
hlr@icmc.usp.br