1<?xml version='1.0'?> <!--*-nxml-*-->
2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
5
6<refentry id="sd_journal_enumerate_fields" xmlns:xi="http://www.w3.org/2001/XInclude">
7
8  <refentryinfo>
9    <title>sd_journal_enumerate_fields</title>
10    <productname>systemd</productname>
11  </refentryinfo>
12
13  <refmeta>
14    <refentrytitle>sd_journal_enumerate_fields</refentrytitle>
15    <manvolnum>3</manvolnum>
16  </refmeta>
17
18  <refnamediv>
19    <refname>sd_journal_enumerate_fields</refname>
20    <refname>sd_journal_restart_fields</refname>
21    <refname>SD_JOURNAL_FOREACH_FIELD</refname>
22    <refpurpose>Read used field names from the journal</refpurpose>
23  </refnamediv>
24
25  <refsynopsisdiv>
26    <funcsynopsis>
27      <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
28
29      <funcprototype>
30        <funcdef>int <function>sd_journal_enumerate_fields</function></funcdef>
31        <paramdef>sd_journal *<parameter>j</parameter></paramdef>
32        <paramdef>const char **<parameter>field</parameter></paramdef>
33      </funcprototype>
34
35      <funcprototype>
36        <funcdef>void <function>sd_journal_restart_fields</function></funcdef>
37        <paramdef>sd_journal *<parameter>j</parameter></paramdef>
38      </funcprototype>
39
40      <funcprototype>
41        <funcdef><function>SD_JOURNAL_FOREACH_FIELD</function></funcdef>
42        <paramdef>sd_journal *<parameter>j</parameter></paramdef>
43        <paramdef>const char *<parameter>field</parameter></paramdef>
44      </funcprototype>
45
46    </funcsynopsis>
47  </refsynopsisdiv>
48
49  <refsect1>
50    <title>Description</title>
51
52    <para><function>sd_journal_enumerate_fields()</function> may be used to iterate through all field names used in the
53    opened journal files. On each invocation the next field name is returned. The order of the returned field names is
54    not defined. It takes two arguments: the journal context object, plus a pointer to a constant string pointer where
55    the field name is stored in. The returned data is in a read-only memory map and is only valid until the next
56    invocation of <function>sd_journal_enumerate_fields()</function>. Note that this call is subject to the data field
57    size threshold as controlled by <function>sd_journal_set_data_threshold()</function>.</para>
58
59    <para><function>sd_journal_restart_fields()</function> resets the field name enumeration index to the beginning of
60    the list. The next invocation of <function>sd_journal_enumerate_fields()</function> will return the first field
61    name again.</para>
62
63    <para>The <function>SD_JOURNAL_FOREACH_FIELD()</function> macro may be used as a handy wrapper around
64    <function>sd_journal_restart_fields()</function> and <function>sd_journal_enumerate_fields()</function>.</para>
65
66    <para>These functions currently are not influenced by matches set with <function>sd_journal_add_match()</function>
67    but this might change in a later version of this software.</para>
68
69    <para>To retrieve the possible values a specific field can take use
70    <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
71  </refsect1>
72
73  <refsect1>
74    <title>Return Value</title>
75
76    <para><function>sd_journal_enumerate_fields()</function> returns a
77    positive integer if the next field name has been read, 0 when no
78    more field names are known, or a negative errno-style error code.
79    <function>sd_journal_restart_fields()</function> returns
80    nothing.</para>
81  </refsect1>
82
83  <refsect1>
84    <title>Notes</title>
85
86    <xi:include href="threads-aware.xml" xpointer="strict" />
87
88    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
89  </refsect1>
90
91  <refsect1>
92    <title>Examples</title>
93
94    <para>Use the <function>SD_JOURNAL_FOREACH_FIELD()</function> macro to iterate through all field names in use in the
95    current journal.</para>
96
97    <programlisting>#include &lt;stdio.h&gt;
98#include &lt;string.h&gt;
99#include &lt;systemd/sd-journal.h&gt;
100
101int main(int argc, char *argv[]) {
102        sd_journal *j;
103        const char *field;
104        int r;
105
106        r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);
107        if (r &lt; 0) {
108                fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
109                return 1;
110        }
111        SD_JOURNAL_FOREACH_FIELD(j, field)
112                printf("%s\n", field);
113        sd_journal_close(j);
114        return 0;
115}</programlisting>
116
117  </refsect1>
118
119  <refsect1>
120    <title>See Also</title>
121
122    <para>
123      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
124      <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
125      <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
126      <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
127      <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
128      <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
129      <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
130    </para>
131  </refsect1>
132
133</refentry>
134