<citerefentry><refentrytitle>sd_journal_query_enumerate</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_journal_query_enumerate</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<?xml version='1.0'?> <!--*-nxml-*-->

<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"

"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<refentry id="sd_journal_enumerate_fields">

<refentryinfo>

<title>sd_journal_enumerate_fields</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Lennart</firstname>

<surname>Poettering</surname>

<email>lennart@poettering.net</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>sd_journal_enumerate_fields</refentrytitle>

<manvolnum>3</manvolnum>

</refmeta>

<refnamediv>

<refname>sd_journal_enumerate_fields</refname>

<refname>sd_journal_restart_fields</refname>

<refname>SD_JOURNAL_FOREACH_FIELD</refname>

<refpurpose>Read used field names from the journal</refpurpose>

</refnamediv>

<refsynopsisdiv>

<funcsynopsis>

<funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>

<funcprototype>

<funcdef>int <function>sd_journal_enumerate_fields</function></funcdef>

<paramdef>sd_journal *<parameter>j</parameter></paramdef>

<paramdef>const char **<parameter>field</parameter></paramdef>

</funcprototype>

<funcprototype>

<funcdef>void <function>sd_journal_restart_fields</function></funcdef>

<paramdef>sd_journal *<parameter>j</parameter></paramdef>

</funcprototype>

<funcprototype>

<funcdef><function>SD_JOURNAL_FOREACH_FIELD</function></funcdef>

<paramdef>sd_journal *<parameter>j</parameter></paramdef>

<paramdef>const char *<parameter>field</parameter></paramdef>

</funcprototype>

</funcsynopsis>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para><function>sd_journal_enumerate_fields()</function> may be used to iterate through all field names used in the

opened journal files. On each invocation the next field name is returned. The order of the returned field names is

not defined. It takes two arguments: the journal context object, plus a pointer to a constant string pointer where

the field name is stored in. The returned data is in a read-only memory map and is only valid until the next

invocation of <function>sd_journal_enumerate_fields()</function>. Note that this call is subject to the data field

size threshold as controlled by <function>sd_journal_set_data_threshold()</function>.</para>

<para><function>sd_journal_restart_fields()</function> resets the field name enumeration index to the beginning of

the list. The next invocation of <function>sd_journal_enumerate_fields()</function> will return the first field

name again.</para>

<para>The <function>SD_JOURNAL_FOREACH_FIELD()</function> macro may be used as a handy wrapper around

<function>sd_journal_restart_fields()</function> and <function>sd_journal_enumerate_fields()</function>.</para>

<para>These functions currently are not influenced by matches set with <function>sd_journal_add_match()</function>

but this might change in a later version of this software.</para>

<para>To retrieve the possible values a specific field can take use

<citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

</refsect1>

<refsect1>

<title>Return Value</title>

<para><function>sd_journal_enumerate_fields()</function> returns a

positive integer if the next field name has been read, 0 when no

more field names are known, or a negative errno-style error code.

<function>sd_journal_restart_fields()</function> returns

nothing.</para>

</refsect1>

<refsect1>

<title>Notes</title>

<para>The <function>sd_journal_enumerate_fields()</function> and <function>sd_journal_restart_fields()</function>

interfaces are available as a shared library, which can be compiled and linked to with the

<constant>libsystemd</constant> <citerefentry

project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>

</refsect1>

<refsect1>

<title>Examples</title>

<para>Use the <function>SD_JOURNAL_FOREACH_FIELD</function> macro to iterate through all field names in use in the

current journal.</para>

<programlisting>#include &lt;stdio.h&gt;

#include &lt;string.h&gt;

#include &lt;systemd/sd-journal.h&gt;

int main(int argc, char *argv[]) {

sd_journal *j;

const char *field;

int r;

r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);

if (r &lt; 0) {

fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));

return 1;

}

SD_JOURNAL_FOREACH_FIELD(j, field)

printf("%s\n", field);

sd_journal_close(j);

return 0;

}</programlisting>

</refsect1>

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>

<para>To enumerate all field names currently in use (and thus all suitable field parameters for

<function>sd_journal_query_unique()</function>), use the

<citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>

call.</para>

sd_journal *j;

const void *d;

size_t l;

int r;

r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);

if (r &lt; 0) {

fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));

return 1;

}

r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");

if (r &lt; 0) {

fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));

return 1;

}

SD_JOURNAL_FOREACH_UNIQUE(j, d, l)

printf("%.*s\n", (int) l, (const char*) d);

sd_journal_close(j);

return 0;

<citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

/* Iterating through unique fields and their data values */

/* Iterating through known fields */

JournalFile *fields_file;

uint64_t fields_offset;

uint64_t fields_hash_table_index;

char *fields_buffer;

size_t fields_buffer_allocated;

bool on_network:1;

bool no_new_files:1;

bool unique_file_lost:1; /* File we were iterating over got

bool fields_file_lost:1;