bson_oid man page

ObjectIDs — None


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)


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);


This page is part of libbson. Please report any bugs at


2017‐01‐11 libbson