sd_journal_get_data

Index

## Name

sd_journal_get_data, sd_journal_enumerate_data, sd_journal_restart_data, SD_JOURNAL_FOREACH_DATA — Read data fields from the current journal entry

## Synopsis

    #include <systemd/sd-journal.h>

`int sd_journal_get_data(` | sd_journal* j,
| const char* field,
| const void** data,
| size_t* length`)`;

`int sd_journal_enumerate_data(` | sd_journal* j,
| const void** data,
| size_t* length`)`;

`int sd_journal_restart_data(` | sd_journal* j`)`;

`SD_JOURNAL_FOREACH_DATA(` | sd_journal* j,
| const void* data,
| size_t length`)`;

## Description

`sd_journal_get_data()` gets the data object associated with a specific field from the current journal entry. It takes four arguments: the journal context object, a string with the field name to request, plus a pair of pointers to pointer/size variables where the data object and its size shall be stored in. The field name should be an entry field name. Well-known field names are listed in systemd.journal-fields(7). The returned data is in a read-only memory map and is only valid until the next invocation of `sd_journal_get_data()` or `sd_journal_enumerate_data()`, or the read pointer is altered. Note that the data returned will be prefixed with the field name and '='.

`sd_journal_enumerate_data()` may be used to iterate through all fields of the current entry. On each invocation the data for the next field is returned. The order of these fields is not defined. The data returned is in the same format as with `sd_journal_get_data()` and also follows the same life-time semantics.

`sd_journal_restart_data()` resets the data enumeration index to the beginning of the entry. The next invocation of `sd_journal_enumerate_data()` will return the first field of the entry again.

Note that the `SD_JOURNAL_FOREACH_DATA()` macro may be used as a wrapper around `sd_journal_restart_data()` and `sd_journal_enumerate_data()`.

Note that these functions will not work before sd_journal_next(3) (or related call) has been called at least once, in order to position the read pointer at a valid entry.

## Return Value

`sd_journal_get_data()` returns 0 on success or a negative errno-style error code. If the current entry does not include the specified field -ENOENT is returned. If sd_journal_next(3) has not been called at least once -EADDRNOTAVAIL is returned. `sd_journal_enumerate_data()` returns a positive integer if the next field has been read, 0 when no more fields are known, or a negative errno-style error code. `sd_journal_restart_data()` returns nothing.

## Notes

The `sd_journal_get_data()`, `sd_journal_enumerate_data()` and `sd_journal_restart_data()` interfaces are available as shared library, which can be compiled and linked to with the `libsystemd-journal` pkg-config(1) file.

## Examples

See sd_journal_next(3) for a complete example how to use `sd_journal_get_data()`.

Use the `SD_JOURNAL_FOREACH_DATA` macro to iterate through all fields of the current journal entry:

    ...
    int print_fields(sd_journal *j) {
            const void *data;
            size_t l;
            SD_JOURNAL_FOREACH_DATA(j, data, length)
                    printf("%.*s\n", (int) length, data);
    }
    ...

## See Also

systemd(1), systemd.journal-fields(7), sd-journal(3), sd_journal_open(3), sd_journal_next(3), sd_journal_get_realtime_usec(3)