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(3) in big‐endian.
SORTING OBJECTIDS¶
The typical way to sort in C is using qsort(3) qsort(3) compatible
callback function named bson_oid_compare(3) 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(3)
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 contianing a bson_oid_t 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(3)
time_t t;
t = bson_oid_get_time_t (oid);
printf ("The OID was generated at %u\n", (unsigned)t);
