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