int DB->set_dup_compare(DB *db, int (*dup_compare_fcn)(DB *, const DBT *, const DBT *));
Set the duplicate data item comparison function. The comparison function is called whenever it is necessary to compare a data item specified by the application with a data item currently stored in the database. Calling DB->set_dup_compare implies calling DB->set_flags with the DB_DUPSORT flag.
If no comparison function is specified, the data items are compared lexically, with shorter data items collating before longer data items.
The DB->set_dup_compare method may not be called after the DB->open method is called. If the database already exists when DB->open is called, the information specified to DB->set_dup_compare must be the same as that historically used to create the database or corruption can occur.
The DB->set_dup_compare method returns a non-zero error value on failure and 0 on success.
The dup_compare_fcn function must return an integer value less than, equal to, or greater than zero if the first data item parameter is considered to be respectively less than, equal to, or greater than the second data item parameter. 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.
The DB->set_dup_compare method may fail and return one of the following non-zero errors:
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