lo_open() - truncate a large object?

RedHat 5.1
Kernel 2.0.35 (i686)
Postgresql 6.3.2

I'd like to be able to open a large object and have it truncated,
something like this:

    int fd = lo_open(conn, oid, INV_READ | INV_WRITE | O_TRUNC);

But of course that doesn't work.  Is there a way to do this
with postgresql?

Gregory W Burnham
Software Engineer
Excite Labs
Simon Fraser University
Vancouver, BC
V5A 1S6
604 291 3615 ph
604 291 5679 fx