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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="sd_journal_enumerate_fields" xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>sd_journal_enumerate_fields</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_journal_enumerate_fields</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_journal_enumerate_fields</refname>
+ <refname>sd_journal_restart_fields</refname>
+ <refname>SD_JOURNAL_FOREACH_FIELD</refname>
+ <refpurpose>Read used field names from the journal</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_enumerate_fields</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>const char **<parameter>field</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>void <function>sd_journal_restart_fields</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef><function>SD_JOURNAL_FOREACH_FIELD</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>const char *<parameter>field</parameter></paramdef>
+ </funcprototype>
+
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><function>sd_journal_enumerate_fields()</function> may be used to iterate through all field names used in the
+ opened journal files. On each invocation the next field name is returned. The order of the returned field names is
+ not defined. It takes two arguments: the journal context object, plus a pointer to a constant string pointer where
+ the field name is stored in. The returned data is in a read-only memory map and is only valid until the next
+ invocation of <function>sd_journal_enumerate_fields()</function>. Note that this call is subject to the data field
+ size threshold as controlled by <function>sd_journal_set_data_threshold()</function>.</para>
+
+ <para><function>sd_journal_restart_fields()</function> resets the field name enumeration index to the beginning of
+ the list. The next invocation of <function>sd_journal_enumerate_fields()</function> will return the first field
+ name again.</para>
+
+ <para>The <function>SD_JOURNAL_FOREACH_FIELD()</function> macro may be used as a handy wrapper around
+ <function>sd_journal_restart_fields()</function> and <function>sd_journal_enumerate_fields()</function>.</para>
+
+ <para>These functions currently are not influenced by matches set with <function>sd_journal_add_match()</function>
+ but this might change in a later version of this software.</para>
+
+ <para>To retrieve the possible values a specific field can take use
+ <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para><function>sd_journal_enumerate_fields()</function> returns a
+ positive integer if the next field name has been read, 0 when no
+ more field names are known, or a negative errno-style error code.
+ <function>sd_journal_restart_fields()</function> returns
+ nothing.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <xi:include href="threads-aware.xml" xpointer="strict" />
+
+ <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
+ </refsect1>
+
+ <refsect1>
+ <title>Examples</title>
+
+ <para>Use the <function>SD_JOURNAL_FOREACH_FIELD()</function> macro to iterate through all field names in use in the
+ current journal.</para>
+
+ <programlisting><xi:include href="journal-enumerate-fields.c" parse="text" /></programlisting>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</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_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>