sd_journal_previous(3) [centos man page]

SD_JOURNAL_NEXT(3)						  sd_journal_next						SD_JOURNAL_NEXT(3)

NAME

       sd_journal_next, sd_journal_previous, sd_journal_next_skip, sd_journal_previous_skip, SD_JOURNAL_FOREACH, SD_JOURNAL_FOREACH_BACKWARDS -
       Advance or set back the read pointer in the journal

SYNOPSIS

       #include <systemd/sd-journal.h>

       int sd_journal_next(sd_journal* j);

       int sd_journal_previous(sd_journal* j);

       int sd_journal_next_skip(sd_journal* j, uint64_t skip);

       int sd_journal_previous_skip(sd_journal* j, uint64_t skip);

       SD_JOURNAL_FOREACH(sd_journal* j);

       SD_JOURNAL_FOREACH_BACKWARDS(sd_journal* j);

DESCRIPTION

       sd_journal_next() advances the read pointer into the journal by one entry. The only argument taken is a journal context object as allocated
       via sd_journal_open(3). After successful invocation the entry may be read with functions such as sd_journal_get_data(3).

       Similarly, sd_journal_previous() sets the read pointer back one entry.

       sd_journal_next_skip() and sd_journal_previous_skip() advance/set back the read pointer by multiple entries at once, as specified in the
       skip parameter.

       The journal is strictly ordered by reception time, and hence advancing to the next entry guarantees that the entry then pointing to is
       later in time than then previous one, or has the same timestamp.

       Note that sd_journal_get_data(3) and related calls will fail unless sd_journal_next() has been invoked at least once in order to position
       the read pointer on a journal entry.

       Note that the SD_JOURNAL_FOREACH() macro may be used as a wrapper around sd_journal_seek_head(3) and sd_journal_next() in order to make
       iterating through the journal easier. See below for an example. Similarly, SD_JOURNAL_FOREACH_BACKWARDS() may be used for iterating the
       journal in reverse order.

RETURN VALUE

       The four calls return the number of entries advanced/set back on success or a negative errno-style error code. When the end or beginning of
       the journal is reached, a number smaller than requested is returned. More specifically, if sd_journal_next() or sd_journal_previous() reach
       the end/beginning of the journal they will return 0, instead of 1 when they are successful. This should be considered an EOF marker.

NOTES

       The sd_journal_next(), sd_journal_previous(), sd_journal_next_skip() and sd_journal_previous_skip() interfaces are available as a shared
       library, which can be compiled and linked to with the libsystemd-journal pkg-config(1) file.

EXAMPLES

       Iterating through the journal:

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

	   int main(int argc, char *argv[]) {
		   int r;
		   sd_journal *j;
		   r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
		   if (r < 0) {
			   fprintf(stderr, "Failed to open journal: %s
", strerror(-r));
			   return 1;
		   }
		   SD_JOURNAL_FOREACH(j) {
			   const char *d;
			   size_t l;

			   r = sd_journal_get_data(j, "MESSAGE", &d, &l);
			   if (r < 0) {
				   fprintf(stderr, "Failed to read message field: %s
", strerror(-r));
				   continue;
			   }

			   printf("%.*s
", (int) l, d);
		   }
		   sd_journal_close(j);
		   return 0;
	   }

SEE ALSO

       systemd(1), sd-journal(3), sd_journal_open(3), sd_journal_get_data(3), sd_journal_get_realtime_usec(3), sd_journal_get_cursor(3)

systemd 208															SD_JOURNAL_NEXT(3)

SD_JOURNAL_NEXT(3)						  sd_journal_next						SD_JOURNAL_NEXT(3)

NAME

       sd_journal_next, sd_journal_previous, sd_journal_next_skip, sd_journal_previous_skip, SD_JOURNAL_FOREACH, SD_JOURNAL_FOREACH_BACKWARDS -
       Advance or set back the read pointer in the journal

SYNOPSIS

       #include <systemd/sd-journal.h>

       int sd_journal_next(sd_journal* j);

       int sd_journal_previous(sd_journal* j);

       int sd_journal_next_skip(sd_journal* j, uint64_t skip);

       int sd_journal_previous_skip(sd_journal* j, uint64_t skip);

       SD_JOURNAL_FOREACH(sd_journal* j);

       SD_JOURNAL_FOREACH_BACKWARDS(sd_journal* j);

DESCRIPTION

       sd_journal_next() advances the read pointer into the journal by one entry. The only argument taken is a journal context object as allocated
       via sd_journal_open(3). After successful invocation the entry may be read with functions such as sd_journal_get_data(3).

       Similarly, sd_journal_previous() sets the read pointer back one entry.

       sd_journal_next_skip() and sd_journal_previous_skip() advance/set back the read pointer by multiple entries at once, as specified in the
       skip parameter.

       The journal is strictly ordered by reception time, and hence advancing to the next entry guarantees that the entry then pointing to is
       later in time than then previous one, or has the same timestamp.

       Note that sd_journal_get_data(3) and related calls will fail unless sd_journal_next() has been invoked at least once in order to position
       the read pointer on a journal entry.

       Note that the SD_JOURNAL_FOREACH() macro may be used as a wrapper around sd_journal_seek_head(3) and sd_journal_next() in order to make
       iterating through the journal easier. See below for an example. Similarly, SD_JOURNAL_FOREACH_BACKWARDS() may be used for iterating the
       journal in reverse order.

RETURN VALUE

       The four calls return the number of entries advanced/set back on success or a negative errno-style error code. When the end or beginning of
       the journal is reached, a number smaller than requested is returned. More specifically, if sd_journal_next() or sd_journal_previous() reach
       the end/beginning of the journal they will return 0, instead of 1 when they are successful. This should be considered an EOF marker.

NOTES

       The sd_journal_next(), sd_journal_previous(), sd_journal_next_skip() and sd_journal_previous_skip() interfaces are available as a shared
       library, which can be compiled and linked to with the libsystemd-journal pkg-config(1) file.

EXAMPLES

       Iterating through the journal:

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

	   int main(int argc, char *argv[]) {
		   int r;
		   sd_journal *j;
		   r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
		   if (r < 0) {
			   fprintf(stderr, "Failed to open journal: %s
", strerror(-r));
			   return 1;
		   }
		   SD_JOURNAL_FOREACH(j) {
			   const char *d;
			   size_t l;

			   r = sd_journal_get_data(j, "MESSAGE", &d, &l);
			   if (r < 0) {
				   fprintf(stderr, "Failed to read message field: %s
", strerror(-r));
				   continue;
			   }

			   printf("%.*s
", (int) l, d);
		   }
		   sd_journal_close(j);
		   return 0;
	   }

SEE ALSO

       systemd(1), sd-journal(3), sd_journal_open(3), sd_journal_get_data(3), sd_journal_get_realtime_usec(3), sd_journal_get_cursor(3)

systemd 208															SD_JOURNAL_NEXT(3)