<parameter>len</parameter>).  The <parameter>fd</parameter>
     argument must have been returned by a previous
     <function>lo_open</function>.  The number of bytes actually read is
     returned; this will be less than <parameter>len</parameter> if the end of
     the large object is reached first.  In the event of an error, the return
     value is -1.
</para>

<para>
     Although the <parameter>len</parameter> parameter is declared as
     <type>size_t</type>, this function will reject length values larger than
     <literal>INT_MAX</literal>.  In practice, it's best to transfer data in chunks
     of at most a few megabytes anyway.
</para>
</sect2>

<sect2 id="lo-seek">
<title>Seeking in a Large Object</title>

<para>
     <indexterm><primary>lo_lseek</primary></indexterm>
     To change the current read or write location associated with a
     large object descriptor, call
<synopsis>
int lo_lseek(PGconn *conn, int fd, int offset, int whence);
</synopsis>
     This function moves the
     current location pointer for the large object descriptor identified by
     <parameter>fd</parameter> to the new location specified by
     <parameter>offset</parameter>.  The valid values for <parameter>whence</parameter>
     are <symbol>SEEK_SET</symbol> (seek from object start),
     <symbol>SEEK_CUR</symbol> (seek from current position), and
     <symbol>SEEK_END</symbol> (seek from object end).  The return value is
     the new location pointer, or -1 on error.
</para>

<para>
     <indexterm><primary>lo_lseek64</primary></indexterm>
     When dealing with large objects that might exceed 2GB in size,
     instead use
<synopsis>
int64_t lo_lseek64(PGconn *conn, int fd, int64_t offset, int whence);
</synopsis>
     This function has the same behavior
     as <function>lo_lseek</function>, but it can accept an
     <parameter>offset</parameter> larger than 2GB and/or deliver a result larger
     than 2GB.
     Note that <function>lo_lseek</function> will fail if the new location
     pointer would be greater than 2GB.
</para>

<para>
     <function>lo_lseek64</function> is new as of <productname>PostgreSQL</productname>
     9.3.  If this function is run against an older server version, it will
     fail and return -1.
</para>

</sect2>

<sect2 id="lo-tell">
<title>Obtaining the Seek Position of a Large Object</title>

<para>
     <indexterm><primary>lo_tell</primary></indexterm>
     To obtain the current read or write location of a large object descriptor,
     call
<synopsis>
int lo_tell(PGconn *conn, int fd);
</synopsis>
     If there is an error, the return value is -1.
</para>

<para>
     <indexterm><primary>lo_tell64</primary></indexterm>
     When dealing with large objects that might exceed 2GB in size,
     instead use
<synopsis>
int64_t lo_tell64(PGconn *conn, int fd);
</synopsis>
     This function has the same behavior
     as <function>lo_tell</function>, but it can deliver a result larger
     than 2GB.
     Note that <function>lo_tell</function> will fail if the current
     read/write location is greater than 2GB.
</para>

<para>
     <function>lo_tell64</function> is new as of <productname>PostgreSQL</productname>
     9.3.  If this function is run against an older server version, it will
     fail and return -1.
</para>
</sect2>

<sect2 id="lo-truncate">
<title>Truncating a Large Object</title>

<para>
     <indexterm><primary>lo_truncate</primary></indexterm>
     To truncate a large object to a given length, call
<synopsis>
int lo_truncate(PGconn *conn, int fd, size_t len);
</synopsis>
     This function truncates the large object
     descriptor <parameter>fd</parameter> to length <parameter>len</parameter>.  The
     <parameter>fd</parameter> argument must have been returned by a
     previous <function>lo_open</function>.  If <parameter>len</parameter> is
     greater than the large object's current length, the large object
     is extended to the specified length with null bytes ('\0').
     On success, <function>lo_truncate</function>