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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
This file is part of systemd.
Copyright 2012 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="sd_journal_get_cursor">
<refentryinfo>
<title>sd_journal_get_cursor</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>sd_journal_get_cursor</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_journal_get_cursor</refname>
<refname>sd_journal_test_cursor</refname>
<refpurpose>Get cursor string for or test cursor string against the current journal entry</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_journal_get_cursor</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>char **<parameter>cursor</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_test_cursor</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>const char *<parameter>cursor</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_journal_get_cursor()</function> returns a
cursor string for the current journal entry. A cursor is a
serialization of the current journal position formatted as text.
The string only contains printable characters and can be passed
around in text form. The cursor identifies a journal entry
globally and in a stable way and may be used to later seek to it
via
<citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
The cursor string should be considered opaque and not be parsed by
clients. Seeking to a cursor position without the specific entry
being available locally will seek to the next closest (in terms of
time) available entry. The call takes two arguments: a journal
context object and a pointer to a string pointer where the cursor
string will be placed. The string is allocated via libc
<citerefentry project='man-pages'><refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum></citerefentry>
and should be freed after use with
<citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para>Note that <function>sd_journal_get_cursor()</function> will
not work before
<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
(or related call) has been called at least once, in order to
position the read pointer at a valid entry.</para>
<para><function>sd_journal_test_cursor()</function>
may be used to check whether the current position in
the journal matches the specified cursor. This is
useful since cursor strings do not uniquely identify
an entry: the same entry might be referred to by
multiple different cursor strings, and hence string
comparing cursors is not possible. Use this call to
verify after an invocation of
<citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
whether the entry being sought to was actually found
in the journal or the next closest entry was used
instead.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para><function>sd_journal_get_cursor()</function> returns 0 on
success or a negative errno-style error code.
<function>sd_journal_test_cursor()</function> returns positive if
the current entry matches the specified cursor, 0 if it does not
match the specified cursor or a negative errno-style error code on
failure.</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>All functions listed here are thread-agnostic and only a single thread may operate
on a given <structname>sd_journal</structname> object.</para>
<para>The <function>sd_journal_get_cursor()</function> and
<function>sd_journal_test_cursor()</function> interfaces are
available as a shared library, which can be compiled and linked to
with the
<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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