Writing Advanced Functions in C - PostgreSQL Server Programming - page 235

(c,b,a,x=c*b+a) , and then expand it to return set of permutations such as the
sample pl/pythonu function.
Returning a single tuple of a complex type
The first step in constructing a version of the reverse permutations function in C is to
start with simply being able to return a single record of type abc .
Datum
c_reverse_tuple(PG_FUNCTION_ARGS)
{
HeapTupleHeader th;
int32 a,b,c;
bool aisnull, bisnull, cisnull;
TupleDesc resultTupleDesc;
Oid resultTypeId;
Datum retvals[4];
bool retnulls[4];
HeapTuple rettuple;
// get the tuple header of 1st argument
th = PG_GETARG_HEAPTUPLEHEADER(0);
// get argument Datum's and convert them to
int32
a = DatumGetInt32(GetAttributeByName (th,
"a", &aisnull));
b = DatumGetInt32(GetAttributeByName(th,
"b", &bisnull));
c = DatumGetInt32(GetAttributeByName(th,
"c", &cisnull));
// debug: report the extracted field values
ereport(INFO,
(errmsg("arg: (a: %d,b: %d, c:
%d)", a, b, c)) );