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<!--$Id: db_set_bt_compare.so,v 10.24 2000/10/26 15:20:40 bostic Exp $-->
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<h1>Db::set_bt_compare</h1>
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<h3><pre>
#include <db_cxx.h>
<p>
extern "C" {
typedef int (*bt_compare_fcn_type)(DB *, const DBT *, const DBT *);
};
int
Db::set_bt_compare(bt_compare_fcn_type bt_compare_fcn);
</pre></h3>
<h1>Description</h1>
<p>Set the Btree key comparison function. The comparison function is
called when it is necessary to compare a key specified by the
application with a key currently stored in the tree. The first argument
to the comparison function is the <a href="../api_cxx/dbt_class.html">Dbt</a> representing the
application supplied key, the second is the current tree's key.
<p>The comparison function must return an integer value less than, equal
to, or greater than zero if the first key argument is considered to be
respectively less than, equal to, or greater than the second key
argument. In addition, the comparison function must cause the keys in
the database to be <i>well-ordered</i>. The comparison function
must correctly handle any key values used by the application (possibly
including zero-length keys). In addition, when Btree key prefix
comparison is being performed (see <a href="../api_cxx/db_set_bt_prefix.html">Db::set_bt_prefix</a> for more
information), the comparison routine may be passed a prefix of any
database key. The <b>data</b> and <b>size</b> fields of the
<a href="../api_cxx/dbt_class.html">Dbt</a> are the only fields that may be used for the purposes of
this comparison.
<p>If no comparison function is specified, the keys are compared lexically,
with shorter keys collating before longer keys. The same comparison
method must be used each time a particular Btree is opened.
<p>The Db::set_bt_compare interface may only be used to configure Berkeley DB before
the <a href="../api_cxx/db_open.html">Db::open</a> interface is called.
<p>The Db::set_bt_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.
<h1>Errors</h1>
<p><dl compact>
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
<p>Called after <a href="../api_cxx/db_open.html">Db::open</a> was called.
</dl>
<h3>Class</h3>
<a href="../api_cxx/db_class.html">Db</a>
<h1>See Also</h1>
<a href="../api_cxx/db_close.html">Db::close</a>,
<a href="../api_cxx/db_cursor.html">Db::cursor</a>,
<a href="../api_cxx/db_del.html">Db::del</a>,
<a href="../api_cxx/db_err.html">Db::err</a>,
<a href="../api_cxx/db_fd.html">Db::fd</a>,
<a href="../api_cxx/db_get.html">Db::get</a>,
<a href="../api_cxx/db_get_byteswapped.html">Db::get_byteswapped</a>,
<a href="../api_cxx/db_get_type.html">Db::get_type</a>,
<a href="../api_cxx/db_join.html">Db::join</a>,
<a href="../api_cxx/db_key_range.html">Db::key_range</a>,
<a href="../api_cxx/db_open.html">Db::open</a>,
<a href="../api_cxx/db_put.html">Db::put</a>,
<a href="../api_cxx/db_remove.html">Db::remove</a>,
<a href="../api_cxx/db_set_bt_compare.html">Db::set_bt_compare</a>,
<a href="../api_cxx/db_set_bt_minkey.html">Db::set_bt_minkey</a>,
<a href="../api_cxx/db_set_bt_prefix.html">Db::set_bt_prefix</a>,
<a href="../api_cxx/db_set_cachesize.html">Db::set_cachesize</a>,
<a href="../api_cxx/db_set_dup_compare.html">Db::set_dup_compare</a>,
<a href="../api_cxx/db_set_errcall.html">Db::set_errcall</a>,
<a href="../api_cxx/db_set_errfile.html">Db::set_errfile</a>,
<a href="../api_cxx/db_set_errpfx.html">Db::set_errpfx</a>,
<a href="../api_cxx/db_set_flags.html">Db::set_flags</a>,
<a href="../api_cxx/db_set_h_ffactor.html">Db::set_h_ffactor</a>,
<a href="../api_cxx/db_set_h_hash.html">Db::set_h_hash</a>,
<a href="../api_cxx/db_set_h_nelem.html">Db::set_h_nelem</a>,
<a href="../api_cxx/db_set_lorder.html">Db::set_lorder</a>,
<a href="../api_cxx/db_set_malloc.html">Db::set_malloc</a>,
<a href="../api_cxx/db_set_pagesize.html">Db::set_pagesize</a>,
<a href="../api_cxx/db_set_paniccall.html">Db::set_paniccall</a>,
<a href="../api_cxx/db_set_q_extentsize.html">Db::set_q_extentsize</a>,
<a href="../api_cxx/db_set_realloc.html">Db::set_realloc</a>,
<a href="../api_cxx/db_set_re_delim.html">Db::set_re_delim</a>,
<a href="../api_cxx/db_set_re_len.html">Db::set_re_len</a>,
<a href="../api_cxx/db_set_re_pad.html">Db::set_re_pad</a>,
<a href="../api_cxx/db_set_re_source.html">Db::set_re_source</a>,
<a href="../api_cxx/db_stat.html">Db::stat</a>,
<a href="../api_cxx/db_sync.html">Db::sync</a>,
<a href="../api_cxx/db_upgrade.html">Db::upgrade</a>
and
<a href="../api_cxx/db_verify.html">Db::verify</a>.
</tt>
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