Embedded C function returning a set of rows

I have read http://www.postgresql.org/docs/9.0/static/xfunc-c.html, but
it is not clear to me how to implement a function which retrieve a set
of rows.
In the example given it seems that I have to recall my function for
every row, but this is not what I want.
With libpq I can perform a query which returns a set of rows in a single
operation.

What types and methos have I to use in order to output my result,
embedding my function in postgresql?

Can anyone give me a simple example?

I want to do something like this:
psql -p 5433 -d mydb -U myuser -C "SELECT myfunc(SELECT * FROM mytable);"

I know that this seems stupid, but please answer me only if you know how
to do this...

Thanks in advance.

--
Alessandro Candini

MEEO S.r.l.
Via Saragat 9
I-44122 Ferrara, Italy
Tel: +39 0532 1861501
Fax: +39 0532 1861637
http://www.meeo.it

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