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(at)icmc(dot)usp(dot)br