How can I return a bigint value from a C extension function?
I have a table with a bytea column:
CREATE TABLE mydata(data bytea);
I would like to select and index based on a subset of the data:
CREATE FUNCTION get_key(bytea) returns BIGINT AS '/lib/data.so'
LANGUAGE C IMMUTABLE;
CREATE INDEX mydata_key_idx on mydata(get_key(data));
# SELECT get_key(data) FROM mydata;
My code :
PG_FUNCTION_INFO_V1(get_key);
Datum get_key(PG_FUNCTION_ARGS)
{
bytea *val;
unsigned int len;
long long res;
val = PG_GETARG_BYTEA_P(0);
len = VARSIZE(val) - VARHDRSZ;
res = _extract_key(VARDATA(val), len);
PG_FREE_IF_COPY(val, 0);
PG_RETURN_INT32(res);
}
The PG_RETURN_INT32() macro causes the server to terminate.
It works if I convert to a cstring:
char *result = palloc(32);
snprintf(result, 32, "%lld", res);
PG_RETURN_CSTRING(result);
But then I can't index it, or sort on it either.
(And, as a side note, is the above code the correct way to use bytea
data from C?)
Regards,
--
Jason Armstrong