systemd/man/sd_journal_next.xml
Jan Engelhardt 3b3d7d069d doc: balance C indirections in function prototypes
Shift the asterisks in the documentation's prototypes such that they
are consistent among each other. Use the right side to match what is
used in source code.

Addendum to commit v209~82.
2014-05-07 20:13:27 -04:00

214 lines
9.5 KiB
XML
Raw Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

<?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>
<refname>SD_JOURNAL_FOREACH</refname>
<refname>SD_JOURNAL_FOREACH_BACKWARDS</refname>
<refpurpose>Advance or set back the read pointer in the journal</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</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>
<funcprototype>
<funcdef><function>SD_JOURNAL_FOREACH</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef><function>SD_JOURNAL_FOREACH_BACKWARDS</function></funcdef>
<paramdef>sd_journal *<parameter>j</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>Similarly, <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
<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
and related calls will fail unless
<function>sd_journal_next()</function> has been
invoked at least once in order to position the read
pointer on a journal entry.</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 iterating through the journal easier. See below
for an example. Similarly,
<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 or 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 a shared library, which can be compiled and
linked to with the
<constant>libsystemd</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>Iterating through the journal:</para>
<programlisting>#include &lt;stdio.h&gt;
#include &lt;string.h&gt;
#include &lt;systemd/sd-journal.h&gt;
int main(int argc, char *argv[]) {
int r;
sd_journal *j;
r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);
if (r &lt; 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", &amp;d, &amp;l);
if (r &lt; 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>,
<citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>