man/sd_journal_enumerate_fields.xml

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  25
  26 <refentry id="sd_journal_enumerate_fields">
  27
  28   <refentryinfo>
  29     <title>sd_journal_enumerate_fields</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Lennart</firstname>
  36         <surname>Poettering</surname>
  37         <email>lennart@poettering.net</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>sd_journal_enumerate_fields</refentrytitle>
  44     <manvolnum>3</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>sd_journal_enumerate_fields</refname>
  49     <refname>sd_journal_restart_fields</refname>
  50     <refname>SD_JOURNAL_FOREACH_FIELD</refname>
  51     <refpurpose>Read used field names from the journal</refpurpose>
  52   </refnamediv>
  53
  54   <refsynopsisdiv>
  55     <funcsynopsis>
  56       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  57
  58       <funcprototype>
  59         <funcdef>int <function>sd_journal_enumerate_fields</function></funcdef>
  60         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  61         <paramdef>const char **<parameter>field</parameter></paramdef>
  62       </funcprototype>
  63
  64       <funcprototype>
  65         <funcdef>void <function>sd_journal_restart_fields</function></funcdef>
  66         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  67       </funcprototype>
  68
  69       <funcprototype>
  70         <funcdef><function>SD_JOURNAL_FOREACH_FIELD</function></funcdef>
  71         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  72         <paramdef>const char *<parameter>field</parameter></paramdef>
  73       </funcprototype>
  74
  75     </funcsynopsis>
  76   </refsynopsisdiv>
  77
  78   <refsect1>
  79     <title>Description</title>
  80
  81     <para><function>sd_journal_enumerate_fields()</function> may be used to iterate through all field names used in the
  82     opened journal files. On each invocation the next field name is returned. The order of the returned field names is
  83     not defined. It takes two arguments: the journal context object, plus a pointer to a constant string pointer where
  84     the field name is stored in. The returned data is in a read-only memory map and is only valid until the next
  85     invocation of <function>sd_journal_enumerate_fields()</function>. Note that this call is subject to the data field
  86     size threshold as controlled by <function>sd_journal_set_data_threshold()</function>.</para>
  87
  88     <para><function>sd_journal_restart_fields()</function> resets the field name enumeration index to the beginning of
  89     the list. The next invocation of <function>sd_journal_enumerate_fields()</function> will return the first field
  90     name again.</para>
  91
  92     <para>The <function>SD_JOURNAL_FOREACH_FIELD()</function> macro may be used as a handy wrapper around
  93     <function>sd_journal_restart_fields()</function> and <function>sd_journal_enumerate_fields()</function>.</para>
  94
  95     <para>These functions currently are not influenced by matches set with <function>sd_journal_add_match()</function>
  96     but this might change in a later version of this software.</para>
  97
  98     <para>To retrieve the possible values a specific field can take use
  99     <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 100   </refsect1>
 101
 102   <refsect1>
 103     <title>Return Value</title>
 104
 105     <para><function>sd_journal_enumerate_fields()</function> returns a
 106     positive integer if the next field name has been read, 0 when no
 107     more field names are known, or a negative errno-style error code.
 108     <function>sd_journal_restart_fields()</function> returns
 109     nothing.</para>
 110   </refsect1>
 111
 112   <refsect1>
 113     <title>Notes</title>
 114
 115     <para>All functions listed here are thread-agnostic and only a single thread may operate
 116     on a given <structname>sd_journal</structname> object.</para>
 117
 118     <para>The <function>sd_journal_enumerate_fields()</function> and <function>sd_journal_restart_fields()</function>
 119     interfaces are available as a shared library, which can be compiled and linked to with the
 120     <constant>libsystemd</constant> <citerefentry
 121     project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
 122   </refsect1>
 123
 124   <refsect1>
 125     <title>Examples</title>
 126
 127     <para>Use the <function>SD_JOURNAL_FOREACH_FIELD</function> macro to iterate through all field names in use in the
 128     current journal.</para>
 129
 130     <programlisting>#include &lt;stdio.h&gt;
 131 #include &lt;string.h&gt;
 132 #include &lt;systemd/sd-journal.h&gt;
 133
 134 int main(int argc, char *argv[]) {
 135         sd_journal *j;
 136         const char *field;
 137         int r;
 138
 139         r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);
 140         if (r &lt; 0) {
 141                 fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
 142                 return 1;
 143         }
 144         SD_JOURNAL_FOREACH_FIELD(j, field)
 145                 printf("%s\n", field);
 146         sd_journal_close(j);
 147         return 0;
 148 }</programlisting>
 149
 150   </refsect1>
 151
 152   <refsect1>
 153     <title>See Also</title>
 154
 155     <para>
 156       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 157       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 158       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 159       <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 160       <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 161       <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 162       <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 163     </para>
 164   </refsect1>
 165
 166 </refentry>