NAME

       bson_oid - ObjectIDs

       Libbson  provides  a simple way to generate ObjectIDs. It can be used in a single-threaded
       or multi-threaded manner depending on your requirements.

       The bson_oid_t structure represents an ObjectID in MongoDB. It is a 96-bit identifier that
       includes various information about the system generating the OID.

COMPOSITION

       • 4 bytes : The UNIX timestamp in big-endian format.

       • 3 bytes : The first 3 bytes of MD5(hostname).

       • 2 bytes : The pid_t of the current process. Alternatively the task-id if configured.

       • 3 bytes : A 24-bit monotonic counter incrementing from rand() in big-endian.

SORTING OBJECTIDS

       The  typical  way  to  sort  in  C is using qsort(). Therefore, Libbson provides a qsort()
       compatible callback function named bson_oid_compare(). It returns  less  than  1,  greater
       than 1, or 0 depending on the equality of two bson_oid_t structures.

COMPARING OBJECT IDS

       If   you   simply   want   to   compare   two  bson_oid_t  structures  for  equality,  use
       bson_oid_equal().

GENERATING

       To generate a bson_oid_t, you may use the following.

          bson_oid_t oid;

          bson_oid_init (&oid, NULL);

PARSING OBJECTID STRINGS

       You can also parse a  string  containing  a  bson_oid_t.  The  input  string  MUST  be  24
       characters or more in length.

          bson_oid_t oid;

          bson_oid_init_from_string (&oid, "123456789012345678901234");

       If  you  need  to parse may bson_oid_t in a tight loop and can guarantee the data is safe,
       you might consider using the inline variant. It will be inlined into your code and  reduce
       the need for a foreign function call.

          bson_oid_t oid;

          bson_oid_init_from_string_unsafe (&oid, "123456789012345678901234");

HASHING OBJECTIDS

       If  you need to store items in a hashtable, you may want to use the bson_oid_t as the key.
       Libbson provides a hash function for just this purpose. It is based on DJB hash.

          unsigned hash;

          hash = bson_oid_hash (oid);

FETCHING OBJECTID CREATION TIME

       You can easily fetch the time that a bson_oid_t was generated using bson_oid_get_time_t().

          time_t t;

          t = bson_oid_get_time_t (oid);
          printf ("The OID was generated at %u\n", (unsigned) t);

AUTHOR

       MongoDB, Inc

COPYRIGHT

       2018, MongoDB, Inc