assigned can be
     specified by <replaceable class="parameter">lobjId</replaceable>;
     if so, failure occurs if that OID is already in use for some large
     object.  If <replaceable class="parameter">lobjId</replaceable>
     is <symbol>InvalidOid</symbol> (zero) then <function>lo_import_with_oid</function> assigns an unused
     OID (this is the same behavior as <function>lo_import</function>).
     The return value is the OID that was assigned to the new large object,
     or <symbol>InvalidOid</symbol> (zero) on failure.
    </para>

    <para>
     <function>lo_import_with_oid</function> is new as of <productname>PostgreSQL</productname>
     8.4 and uses <function>lo_create</function> internally which is new in 8.1; if this function is run against 8.0 or before, it will
     fail and return <symbol>InvalidOid</symbol>.
    </para>
   </sect2>

   <sect2 id="lo-export">
    <title>Exporting a Large Object</title>

    <para>
     <indexterm><primary>lo_export</primary></indexterm>
     To export a large object
     into an operating system file, call
<synopsis>
int lo_export(PGconn *conn, Oid lobjId, const char *filename);
</synopsis>
     The <parameter>lobjId</parameter> argument specifies the OID of the large
     object to export and the <parameter>filename</parameter> argument
     specifies the operating system name of the file.  Note that the file is
     written by the client interface library, not by the server.  Returns 1
     on success, -1 on failure.
    </para>
   </sect2>

   <sect2 id="lo-open">
    <title>Opening an Existing Large Object</title>

    <para>
     <indexterm><primary>lo_open</primary></indexterm>
     To open an existing large object for reading or writing, call
<synopsis>
int lo_open(PGconn *conn, Oid lobjId, int mode);
</synopsis>
     The <parameter>lobjId</parameter> argument specifies the OID of the large
     object to open.   The <parameter>mode</parameter> bits control whether the
     object is opened for reading (<symbol>INV_READ</symbol>), writing
     (<symbol>INV_WRITE</symbol>), or both.
     (These symbolic constants are defined
     in the header file <filename>libpq/libpq-fs.h</filename>.)
     <function>lo_open</function> returns a (non-negative) large object
     descriptor for later use in <function>lo_read</function>,
     <function>lo_write</function>, <function>lo_lseek</function>,
     <function>lo_lseek64</function>, <function>lo_tell</function>,
     <function>lo_tell64</function>, <function>lo_truncate</function>,
     <function>lo_truncate64</function>, and <function>lo_close</function>.
     The descriptor is only valid for
     the duration of the current transaction.
     On failure, -1 is returned.
    </para>

    <para>
     The server currently does not distinguish between modes
     <symbol>INV_WRITE</symbol> and <symbol>INV_READ</symbol> <literal>|</literal>
     <symbol>INV_WRITE</symbol>: you are allowed to read from the descriptor
     in either case.  However there is a significant difference between
     these modes and <symbol>INV_READ</symbol> alone: with <symbol>INV_READ</symbol>
     you cannot write on the descriptor, and the data read from it will
     reflect the contents of the large object at the time of the transaction
     snapshot that was active when <function>lo_open</function> was executed,
     regardless of later writes by this or other transactions.  Reading
     from a descriptor opened with <symbol>INV_WRITE</symbol> returns
     data that reflects all writes of other committed transactions as well
     as writes of the current transaction.  This is similar to the behavior
     of <literal>REPEATABLE READ</literal> versus <literal>READ COMMITTED</literal> transaction
     modes for ordinary SQL <command>SELECT</command> commands.
    </para>

    <para>
     <function>lo_open</function> will fail if <literal>SELECT</literal>
     privilege is not available for the large object, or
     if <symbol>INV_WRITE</symbol> is specified