+<?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">
+
+<!--
+ 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_next">
+
+ <refentryinfo>
+ <title>sd_journal_next</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_next</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_journal_next</refname>
+ <refname>sd_journal_previous</refname>
+ <refname>sd_journal_next_skip</refname>
+ <refname>sd_journal_previous_skip</refname>
+ <refpurpose>Advance or set back the read pointer in the journal</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_next</function></funcdef>
+ <paramdef>sd_journal* <parameter>j</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_previous</function></funcdef>
+ <paramdef>sd_journal* <parameter>j</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_next_skip</function></funcdef>
+ <paramdef>sd_journal* <parameter>j</parameter></paramdef>
+ <paramdef>uint64_t <parameter>skip</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_previous_skip</function></funcdef>
+ <paramdef>sd_journal* <parameter>j</parameter></paramdef>
+ <paramdef>uint64_t <parameter>skip</parameter></paramdef>
+ </funcprototype>
+
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><function>sd_journal_next()</function> advances
+ the read pointer into the journal by one entry. The
+ only argument taken is a journal context object as
+ allocated via
+ <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>. After
+ successful invocation the entry may be read with
+ functions such as
+ <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
+
+ <para>Similar, <function>sd_journal_previous()</function> sets
+ the read pointer back one entry.</para>
+
+ <para><function>sd_journal_next_skip()</function> and
+ <function>sd_journal_previous_skip()</function>
+ advance/set back the read pointer by multiple entries
+ at once, as specified in the <varname>skip</varname>
+ parameter.</para>
+
+ <para>The journal is strictly ordered by reception
+ time, and hence advancing to the next entry guarantees
+ that the entry then pointing to is later in time than
+ then previous one, or has the same timestamp.</para>
+
+ <para>Note that the
+ <function>SD_JOURNAL_FOREACH()</function> macro may be used
+ as a wrapper around
+ <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ and <function>sd_journal_next()</function> in order to
+ make iteratring through the journal easier. See below
+ for an example. Similar,
+ <function>SD_JOURNAL_FOREACH_BACKWARDS()</function>
+ may be used for iterating the journal in reverse
+ order.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para>The four calls return the number of entries
+ advanced/set back on success or a negative errno-style
+ error code. When the end (resp. beginning) of the journal
+ is reached a number smaller than requested is
+ returned. More specifically, if
+ <function>sd_journal_next()</function> or
+ <function>sd_journal_previous()</function> reach the
+ end/beginning of the journal they will return 0,
+ instead of 1 when they are successful. This should be
+ considered an EOF marker.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <para>The <function>sd_journal_next()</function>, <function>sd_journal_previous()</function>,
+ <function>sd_journal_next_skip()</function> and
+ <function>sd_journal_previous_skip()</function> interfaces are
+ available as shared library, which can be compiled and
+ linked to with the
+ <literal>libsystemd-journal</literal>
+ <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ file.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Examples</title>
+
+ <para>Iterating through the journal:</para>
+
+ <programlisting>#include <stdio.h>
+#include <string.h>
+#include <systemd/sd-journal.h>
+
+int main(int argc, char *argv[]) {
+ int r;
+ sd_journal *j;
+ r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
+ if (r < 0) {
+ fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
+ return 1;
+ }
+ SD_JOURNAL_FOREACH(j) {
+ const char *d;
+ size_t l;
+
+ r = sd_journal_get_data(j, "MESSAGE", &d, &l);
+ if (r < 0) {
+ fprintf(stderr, "Failed to read message field: %s\n", strerror(-r));
+ continue;
+ }
+
+ printf("%.*s\n", (int) l, d);
+ }
+ sd_journal_close(j);
+ return 0;
+}</programlisting>
+
+ </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_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>
~ianmdlvl / elogind.git / commitdiff