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Berkeley DB: DB->set_dup_compare
DB->set_dup_compare
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#include <db.h>
int
DB->set_dup_compare(DB *db,
int (*dup_compare_fcn)(DB *, const DBT *, const DBT *));
Description
Set the duplicate data item comparison function. The comparison function
is called when it is necessary to compare a data item specified by the
application with a data item currently stored in the tree. The first
argument to the comparison function is the DBT representing the
application's data item; the second is the current tree's data item.
The comparison function must return an integer value less than, equal
to, or greater than zero if the first data item argument is considered
to be respectively less than, equal to, or greater than the second data
item argument. In addition, the comparison function must cause the data
items in the set to be well-ordered. The comparison function
must correctly handle any data item values used by the application
(possibly including zero-length data items). The data and
size fields of the DBT are the only fields that may be
used for the purposes of this comparison, and no particular alignment
of the memory to which the data field refers may be assumed.
If no comparison function is specified, the data items are compared
lexically, with shorter data items collating before longer data items.
The same duplicate data item comparison method must be used each time
a particular Btree is opened.
The DB->set_dup_compare interface may be used only to configure Berkeley DB before
the DB->open interface is called.
The DB->set_dup_compare function returns a non-zero error value on failure and 0 on success.
Errors
The DB->set_dup_compare function may fail and return a non-zero error for the following conditions:
- EINVAL
- An invalid flag value or parameter was specified.
The DB->set_dup_compare function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
If a catastrophic error has occurred, the DB->set_dup_compare function may fail and return
DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail
in the same way.
See Also
db_create,
DB->associate,
DB->close,
DB->cursor,
DB->del,
DB->err, DB->errx
DB->fd,
DB->get,
DB->pget,
DB->get_byteswapped,
DB->get_type,
DB->join,
DB->key_range,
DB->open,
DB->put,
DB->remove,
DB->rename,
DB->set_alloc,
DB->set_append_recno,
DB->set_bt_compare,
DB->set_bt_minkey,
DB->set_bt_prefix,
DB->set_cachesize,
DB->set_dup_compare,
DB->set_errcall,
DB->set_errfile,
DB->set_errpfx,
DB->set_feedback,
DB->set_flags,
DB->set_h_ffactor,
DB->set_h_hash,
DB->set_h_nelem,
DB->set_lorder,
DB->set_pagesize,
DB->set_paniccall,
DB->set_q_extentsize,
DB->set_re_delim,
DB->set_re_len,
DB->set_re_pad,
DB->set_re_source,
DB->stat,
DB->sync,
DB->truncate,
DB->upgrade,
and
DB->verify.
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