cursor interface to libpq

I am trying to run a select statement, and I keep running out of
memory.  I have noticed that libpq has the nice feature that I don't have
to request each row one at a time.  After a little investigate, I found
that libpq appears to get the entire result set at once.  Well, at least
PQgetvalue() doesn't appear to do anything besides return a pointer to a
string.  There is no lazy evaluation.  It doesn't just fetch the row I
need, and flush old ones as memory permits.
Is there any interface that I can link to a C/C++ program that
will allow me row at a time access to the data?  Not being able to run
select statements is going to be a fairly sizeable problem for me.

This might also explain why when I attempt to dump my database, it also
fails, pg_dump seems to be based on libpq.  I have shutting down my
database and just backing up the filesystem to be safe.  I run in a shop
that hopes to go 24/7 sometime soon, so I need to find an answer RSN.
    Thanks,        Kirby