man/sd_journal_enumerate_fields.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   Copyright 2016 Lennart Poettering
   9 -->
  10
  11 <refentry id="sd_journal_enumerate_fields" xmlns:xi="http://www.w3.org/2001/XInclude">
  12
  13   <refentryinfo>
  14     <title>sd_journal_enumerate_fields</title>
  15     <productname>systemd</productname>
  16
  17     <authorgroup>
  18       <author>
  19         <contrib>Developer</contrib>
  20         <firstname>Lennart</firstname>
  21         <surname>Poettering</surname>
  22         <email>lennart@poettering.net</email>
  23       </author>
  24     </authorgroup>
  25   </refentryinfo>
  26
  27   <refmeta>
  28     <refentrytitle>sd_journal_enumerate_fields</refentrytitle>
  29     <manvolnum>3</manvolnum>
  30   </refmeta>
  31
  32   <refnamediv>
  33     <refname>sd_journal_enumerate_fields</refname>
  34     <refname>sd_journal_restart_fields</refname>
  35     <refname>SD_JOURNAL_FOREACH_FIELD</refname>
  36     <refpurpose>Read used field names from the journal</refpurpose>
  37   </refnamediv>
  38
  39   <refsynopsisdiv>
  40     <funcsynopsis>
  41       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  42
  43       <funcprototype>
  44         <funcdef>int <function>sd_journal_enumerate_fields</function></funcdef>
  45         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  46         <paramdef>const char **<parameter>field</parameter></paramdef>
  47       </funcprototype>
  48
  49       <funcprototype>
  50         <funcdef>void <function>sd_journal_restart_fields</function></funcdef>
  51         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  52       </funcprototype>
  53
  54       <funcprototype>
  55         <funcdef><function>SD_JOURNAL_FOREACH_FIELD</function></funcdef>
  56         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  57         <paramdef>const char *<parameter>field</parameter></paramdef>
  58       </funcprototype>
  59
  60     </funcsynopsis>
  61   </refsynopsisdiv>
  62
  63   <refsect1>
  64     <title>Description</title>
  65
  66     <para><function>sd_journal_enumerate_fields()</function> may be used to iterate through all field names used in the
  67     opened journal files. On each invocation the next field name is returned. The order of the returned field names is
  68     not defined. It takes two arguments: the journal context object, plus a pointer to a constant string pointer where
  69     the field name is stored in. The returned data is in a read-only memory map and is only valid until the next
  70     invocation of <function>sd_journal_enumerate_fields()</function>. Note that this call is subject to the data field
  71     size threshold as controlled by <function>sd_journal_set_data_threshold()</function>.</para>
  72
  73     <para><function>sd_journal_restart_fields()</function> resets the field name enumeration index to the beginning of
  74     the list. The next invocation of <function>sd_journal_enumerate_fields()</function> will return the first field
  75     name again.</para>
  76
  77     <para>The <function>SD_JOURNAL_FOREACH_FIELD()</function> macro may be used as a handy wrapper around
  78     <function>sd_journal_restart_fields()</function> and <function>sd_journal_enumerate_fields()</function>.</para>
  79
  80     <para>These functions currently are not influenced by matches set with <function>sd_journal_add_match()</function>
  81     but this might change in a later version of this software.</para>
  82
  83     <para>To retrieve the possible values a specific field can take use
  84     <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  85   </refsect1>
  86
  87   <refsect1>
  88     <title>Return Value</title>
  89
  90     <para><function>sd_journal_enumerate_fields()</function> returns a
  91     positive integer if the next field name has been read, 0 when no
  92     more field names are known, or a negative errno-style error code.
  93     <function>sd_journal_restart_fields()</function> returns
  94     nothing.</para>
  95   </refsect1>
  96
  97   <refsect1>
  98     <title>Notes</title>
  99
 100     <para>All functions listed here are thread-agnostic and only a single thread may operate
 101     on a given <structname>sd_journal</structname> object.</para>
 102
 103     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 104   </refsect1>
 105
 106   <refsect1>
 107     <title>Examples</title>
 108
 109     <para>Use the <function>SD_JOURNAL_FOREACH_FIELD</function> macro to iterate through all field names in use in the
 110     current journal.</para>
 111
 112     <programlisting>#include &lt;stdio.h&gt;
 113 #include &lt;string.h&gt;
 114 #include &lt;systemd/sd-journal.h&gt;
 115
 116 int main(int argc, char *argv[]) {
 117         sd_journal *j;
 118         const char *field;
 119         int r;
 120
 121         r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);
 122         if (r &lt; 0) {
 123                 fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
 124                 return 1;
 125         }
 126         SD_JOURNAL_FOREACH_FIELD(j, field)
 127                 printf("%s\n", field);
 128         sd_journal_close(j);
 129         return 0;
 130 }</programlisting>
 131
 132   </refsect1>
 133
 134   <refsect1>
 135     <title>See Also</title>
 136
 137     <para>
 138       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 139       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 140       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 141       <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 142       <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 143       <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 144       <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 145     </para>
 146   </refsect1>
 147
 148 </refentry>