lo_creat SQL command

Hi,

I'd be so apprecited if somebody could help me to figure out the
meaning of required parameter for lo_creat() function. In libpq, you
just pass connection and mode params to lo_creat() function. But when
we look at the server-side lo_create() function:

Schema: pg_catalog
Name: lo_creat
Result data type: oid
Argument data types: integer

documentation/lo-funcs.html just uses -1 to create a new empty lo. I'm
cosidering parameter as the database connection to create the large
object. So -1 indicates the current connection. If this is right, how
can I pass another connection to lo_creat() SQL function?

Also it'd perfect if somebody can also point me the file in postgresql
source code which defines these lo functions.

Regards.