# Db::set_dup_compare

`

###

    #include <db_cxx.h>

    extern "C" {
    	typedef int (*dup_compare_fcn_type)(const DBT *, const DBT *);
    };
    int
    Db::set_dup_compare(dup_compare_fcn_type dup_compare_fcn);

# 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 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. The comparison function must correctly handle any data item values used by the application (possibly including zero-length data items). The data, size and app_private fields of the Dbt are the only fields that may be used for the purposes of this comparison.

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 only be used to configure Berkeley DB before the Db::open interface is called.

The Db::set_dup_compare method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success.

# Errors

EINVAL
  An invalid flag value or parameter was specified.

### Class

Db

# See Also

Db::close, Db::cursor, Db::del, Db::err, Db::fd, Db::get, Db::get_byteswapped, Db::get_type, Db::join, Db::key_range, Db::open, Db::put, Db::remove, 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_flags, Db::set_h_ffactor, Db::set_h_hash, Db::set_h_nelem, Db::set_lorder, Db::set_malloc, Db::set_pagesize, Db::set_paniccall, Db::set_realloc, Db::set_re_delim, Db::set_re_len, Db::set_re_pad, Db::set_re_source, Db::stat, Db::sync, Db::upgrade and Db::verify.`

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