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.TH "BSON_OID" "3" "Feb 22, 2024" "1.26.0" "libbson"
.sp
Libbson provides a simple way to generate ObjectIDs. It can be used in a single\-threaded or multi\-threaded manner depending on your requirements.
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The \fI\%bson_oid_t\fP structure represents an \fBObjectID\fP in MongoDB. It is a 96\-bit identifier.
.SH COMPOSITION
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.IP \(bu 2
4 bytes : The UNIX timestamp in big\-endian format.
.IP \(bu 2
5 bytes : A random number.
.IP \(bu 2
3 bytes : A 24\-bit monotonic counter incrementing from \fBrand()\fP in big\-endian.
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.SH SORTING OBJECTIDS
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The typical way to sort in C is using \fBqsort()\fP\&. Therefore, Libbson provides a \fBqsort()\fP compatible callback function named \fI\%bson_oid_compare()\fP\&. It returns \fBless than 1\fP, \fBgreater than 1\fP, or \fB0\fP depending on the equality of two \fI\%bson_oid_t\fP structures.
.SH COMPARING OBJECT IDS
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If you simply want to compare two \fI\%bson_oid_t\fP structures for equality, use \fI\%bson_oid_equal()\fP\&.
.SH GENERATING
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To generate a \fI\%bson_oid_t\fP, you may use the following.
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.INDENT 3.5
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.EX
bson_oid_t oid;

bson_oid_init (&oid, NULL);
.EE
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.SH PARSING OBJECTID STRINGS
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You can also parse a string containing a \fI\%bson_oid_t\fP\&. The input string \fIMUST\fP be 24 characters or more in length.
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.EX
bson_oid_t oid;

bson_oid_init_from_string (&oid, \(dq123456789012345678901234\(dq);
.EE
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.EX
bson_oid_t oid;

bson_oid_init_from_string_unsafe (&oid, \(dq123456789012345678901234\(dq);
.EE
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.SH HASHING OBJECTIDS
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If you need to store items in a hashtable, you may want to use the \fI\%bson_oid_t\fP as the key. Libbson provides a hash function for just this purpose. It is based on DJB hash.
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.INDENT 3.5
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.EX
unsigned hash;

hash = bson_oid_hash (oid);
.EE
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.SH FETCHING OBJECTID CREATION TIME
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You can easily fetch the time that a \fI\%bson_oid_t\fP was generated using \fI\%bson_oid_get_time_t()\fP\&.
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.EX
time_t t;

t = bson_oid_get_time_t (oid);
printf (\(dqThe OID was generated at %u\en\(dq, (unsigned) t);
.EE
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.SH AUTHOR
MongoDB, Inc
.SH COPYRIGHT
2017-present, MongoDB, Inc
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