man/sd_journal_enumerate_fields.xml

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  23
  24 <refentry id="sd_journal_enumerate_fields">
  25
  26   <refentryinfo>
  27     <title>sd_journal_enumerate_fields</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Lennart</firstname>
  34         <surname>Poettering</surname>
  35         <email>lennart@poettering.net</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sd_journal_enumerate_fields</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_journal_enumerate_fields</refname>
  47     <refname>sd_journal_restart_fields</refname>
  48     <refname>SD_JOURNAL_FOREACH_FIELD</refname>
  49     <refpurpose>Read used field names from the journal</refpurpose>
  50   </refnamediv>
  51
  52   <refsynopsisdiv>
  53     <funcsynopsis>
  54       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  55
  56       <funcprototype>
  57         <funcdef>int <function>sd_journal_enumerate_fields</function></funcdef>
  58         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  59         <paramdef>const char **<parameter>field</parameter></paramdef>
  60       </funcprototype>
  61
  62       <funcprototype>
  63         <funcdef>void <function>sd_journal_restart_fields</function></funcdef>
  64         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  65       </funcprototype>
  66
  67       <funcprototype>
  68         <funcdef><function>SD_JOURNAL_FOREACH_FIELD</function></funcdef>
  69         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  70         <paramdef>const char *<parameter>field</parameter></paramdef>
  71       </funcprototype>
  72
  73     </funcsynopsis>
  74   </refsynopsisdiv>
  75
  76   <refsect1>
  77     <title>Description</title>
  78
  79     <para><function>sd_journal_enumerate_fields()</function> may be used to iterate through all field names used in the
  80     opened journal files. On each invocation the next field name is returned. The order of the returned field names is
  81     not defined. It takes two arguments: the journal context object, plus a pointer to a constant string pointer where
  82     the field name is stored in. The returned data is in a read-only memory map and is only valid until the next
  83     invocation of <function>sd_journal_enumerate_fields()</function>. Note that this call is subject to the data field
  84     size threshold as controlled by <function>sd_journal_set_data_threshold()</function>.</para>
  85
  86     <para><function>sd_journal_restart_fields()</function> resets the field name enumeration index to the beginning of
  87     the list. The next invocation of <function>sd_journal_enumerate_fields()</function> will return the first field
  88     name again.</para>
  89
  90     <para>The <function>SD_JOURNAL_FOREACH_FIELD()</function> macro may be used as a handy wrapper around
  91     <function>sd_journal_restart_fields()</function> and <function>sd_journal_enumerate_fields()</function>.</para>
  92
  93     <para>These functions currently are not influenced by matches set with <function>sd_journal_add_match()</function>
  94     but this might change in a later version of this software.</para>
  95
  96     <para>To retrieve the possible values a specific field can take use
  97     <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  98   </refsect1>
  99
 100   <refsect1>
 101     <title>Return Value</title>
 102
 103     <para><function>sd_journal_enumerate_fields()</function> returns a
 104     positive integer if the next field name has been read, 0 when no
 105     more field names are known, or a negative errno-style error code.
 106     <function>sd_journal_restart_fields()</function> returns
 107     nothing.</para>
 108   </refsect1>
 109
 110   <refsect1>
 111     <title>Notes</title>
 112
 113     <para>The <function>sd_journal_enumerate_fields()</function> and <function>sd_journal_restart_fields()</function>
 114     interfaces are available as a shared library, which can be compiled and linked to with the
 115     <constant>libsystemd</constant> <citerefentry
 116     project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
 117   </refsect1>
 118
 119   <refsect1>
 120     <title>Examples</title>
 121
 122     <para>Use the <function>SD_JOURNAL_FOREACH_FIELD</function> macro to iterate through all field names in use in the
 123     current journal.</para>
 124
 125     <programlisting>#include &lt;stdio.h&gt;
 126 #include &lt;string.h&gt;
 127 #include &lt;systemd/sd-journal.h&gt;
 128
 129 int main(int argc, char *argv[]) {
 130         sd_journal *j;
 131         const char *field;
 132         int r;
 133
 134         r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);
 135         if (r &lt; 0) {
 136                 fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
 137                 return 1;
 138         }
 139         SD_JOURNAL_FOREACH_FIELD(j, field)
 140                 printf("%s\n", field);
 141         sd_journal_close(j);
 142         return 0;
 143 }</programlisting>
 144
 145   </refsect1>
 146
 147   <refsect1>
 148     <title>See Also</title>
 149
 150     <para>
 151       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 152       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 153       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 154       <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 155       <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 156       <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 157       <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 158     </para>
 159   </refsect1>
 160
 161 </refentry>