Re: how to return rows of data via function written by language C strict

On Tue, Jul 9, 2019 at 1:00 PM Christoph Bilz <christoph(dot)bilz(at)icloud(dot)com>
wrote:

> Hello,
>
> i want write functions like this:
>
> CREATE FUNCTION foo(text) returns real as '<path>/foo.dll', 'foo' LANGUAGE C STRICT;"
> CREATE FUNCTION foo2(text) returns table(c1 text, c2 int) as '<path>/foo2.dll', 'foo' LANGUAGE C STRICT;
>
> So far, so clear. I don't want to return one scalar value or SETOF smth, I want to start the function like this:
>
> select * from foo; … and the rows will be returned.
>
> Maybe SQL or pl/pgSQL would be a better choice then?

Also, if you plan to return more than one row you are, by definition,
creating a SETOF (TABLE is just shorthand) function.

Also, for what its worth I have no idea with "smth" means here - but I also
don't program C.

> if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_RECORD)
> ereport(ERROR,
> (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
> errmsg("function returning record called in context "
> "that cannot accept type record")));
>
> The inequality check above seems wrong - you want to error if you are
presented with a record, not when you aren't.

But it doesn’t work. Either the get_call_result_type fails because the
> function definition doesn’t match or the the client process crashes because
> smth. happens and I don’t know how this stuff should work.
> So, due to the lack of examples in general and the sparse documentation
> about it, any help will be appreciate.
>

As Ian noted, contrib is usually the recommended source for up-to-date
coding examples.

David J.