sd_journal_restart_fields(3)

1SD_JOURNAL_ENUMERATE_FIELDSs(d3_)journal_enumerate_fiSeDl_dJsOURNAL_ENUMERATE_FIELDS(3)
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NAME

6       sd_journal_enumerate_fields, sd_journal_restart_fields,
7       SD_JOURNAL_FOREACH_FIELD - Read used field names from the journal
8

SYNOPSIS

10       #include <systemd/sd-journal.h>
11
12       int sd_journal_enumerate_fields(sd_journal *j, const char **field);
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14       void sd_journal_restart_fields(sd_journal *j);
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16       SD_JOURNAL_FOREACH_FIELD(sd_journal *j, const char *field);
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DESCRIPTION

19       sd_journal_enumerate_fields() may be used to iterate through all field
20       names used in the opened journal files. On each invocation the next
21       field name is returned. The order of the returned field names is not
22       defined. It takes two arguments: the journal context object, plus a
23       pointer to a constant string pointer where the field name is stored in.
24       The returned data is in a read-only memory map and is only valid until
25       the next invocation of sd_journal_enumerate_fields(). Note that this
26       call is subject to the data field size threshold as controlled by
27       sd_journal_set_data_threshold().
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29       sd_journal_restart_fields() resets the field name enumeration index to
30       the beginning of the list. The next invocation of
31       sd_journal_enumerate_fields() will return the first field name again.
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33       The SD_JOURNAL_FOREACH_FIELD() macro may be used as a handy wrapper
34       around sd_journal_restart_fields() and sd_journal_enumerate_fields().
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36       These functions currently are not influenced by matches set with
37       sd_journal_add_match() but this might change in a later version of this
38       software.
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40       To retrieve the possible values a specific field can take use
41       sd_journal_query_unique(3).
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RETURN VALUE

44       sd_journal_enumerate_fields() returns a positive integer if the next
45       field name has been read, 0 when no more field names are known, or a
46       negative errno-style error code.  sd_journal_restart_fields() returns
47       nothing.
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NOTES

50       All functions listed here are thread-agnostic and only a single
51       specific thread may operate on a given object during its entire
52       lifetime. It's safe to allocate multiple independent objects and use
53       each from a specific thread in parallel. However, it's not safe to
54       allocate such an object in one thread, and operate or free it from any
55       other, even if locking is used to ensure these threads don't operate on
56       it at the very same time.
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58       These APIs are implemented as a shared library, which can be compiled
59       and linked to with the libsystemd pkg-config(1) file.
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EXAMPLES

62       Use the SD_JOURNAL_FOREACH_FIELD() macro to iterate through all field
63       names in use in the current journal.
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65           #include <stdio.h>
66           #include <string.h>
67           #include <systemd/sd-journal.h>
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69           int main(int argc, char *argv[]) {
70                   sd_journal *j;
71                   const char *field;
72                   int r;
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74                   r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
75                   if (r < 0) {
76                           fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
77                           return 1;
78                   }
79                   SD_JOURNAL_FOREACH_FIELD(j, field)
80                           printf("%s\n", field);
81                   sd_journal_close(j);
82                   return 0;
83           }
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NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

NOTES

EXAMPLES

SEE ALSO