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   sd_journal_enumerate_fields    ( 3 )

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Имя (Name)

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

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Синопсис (Synopsis)

#include <systemd/sd-journal.h>

       int sd_journal_enumerate_fields(sd_journal *j,
                                       const char **field);

       void sd_journal_restart_fields(sd_journal *j);

       SD_JOURNAL_FOREACH_FIELD(sd_journal *j, const char *field);

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Описание (Description)

sd_journal_enumerate_fields() 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
       sd_journal_enumerate_fields(). Note that this call is subject to
       the data field size threshold as controlled by
       sd_journal_set_data_threshold().

       sd_journal_restart_fields() resets the field name enumeration
       index to the beginning of the list. The next invocation of
       sd_journal_enumerate_fields() will return the first field name
       again.

       The SD_JOURNAL_FOREACH_FIELD() macro may be used as a handy
       wrapper around sd_journal_restart_fields() and
       sd_journal_enumerate_fields().

       These functions currently are not influenced by matches set with
       sd_journal_add_match() but this might change in a later version
       of this software.

       To retrieve the possible values a specific field can take use
       sd_journal_query_unique(3).

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Возвращаемое значение (Return value)

sd_journal_enumerate_fields() 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.
       sd_journal_restart_fields() returns nothing.

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Примечание (Note)

All functions listed here are thread-agnostic and only a single
       specific thread may operate on a given object during its entire
       lifetime. It's safe to allocate multiple independent objects and
       use each from a specific thread in parallel. However, it's not
       safe to allocate such an object in one thread, and operate or
       free it from any other, even if locking is used to ensure these
       threads don't operate on it at the very same time.

       These APIs are implemented as a shared library, which can be
       compiled and linked to with the libsystemd pkg-config(1) file.

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Примеры (Examples)

Use the SD_JOURNAL_FOREACH_FIELD() macro to iterate through all
       field names in use in the current journal.

           #include <stdio.h>
           #include <string.h>
           #include <systemd/sd-journal.h>

           int main(int argc, char *argv[]) {
                   sd_journal *j;
                   const char *field;
                   int r;

                   r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
                   if (r < 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;
           }

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Смотри также (See also)

systemd(1), systemd.journal-fields(7), sd-journal(3),
       sd_journal_open(3), sd_journal_query_unique(3),
       sd_journal_get_data(3), sd_journal_add_match(3)

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