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<h1>Db::key_range</h1>
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<h3><pre>
#include <db_cxx.h>
<p>
int
Db::key_range(DbTxn *txnid
Dbt *key, DB_KEY_RANGE *key_range, u_int32_t flags);
</pre></h3>
<h1>Description</h1>
<p>The Db::key_range method returns an estimate of the proportion of keys
that are less than, equal to, and greater than the specified key. The
underlying database must be of type Btree.
<p>The information is returned in the <b>key_range</b> argument, which
contains three elements of type double: <b>less</b>, <b>equal</b>,
and <b>greater</b>. Values are in the range of 0 to 1; for example,
if the field <b>less</b> is 0.05, 5% of the keys in the database are
less than the key argument. The value for <b>equal</b> will be zero
if there is no matching key, and will be non-zero otherwise.
<p>If the operation is to be transaction-protected, the <b>txnid</b>
parameter is a transaction handle returned from <a href="../api_cxx/txn_begin.html">DbEnv::txn_begin</a>;
otherwise, NULL.
The Db::key_range method does not retain the locks it acquires for the
life of the transaction, so estimates may not be repeatable.
<p>The <b>flags</b> parameter is currently unused, and must be set to 0.
<p>The Db::key_range 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>The Db::key_range method may fail and throw an exception or return a non-zero error for the following conditions:
<p><dl compact>
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
<p>The underlying database was not of type Btree.
</dl>
<p>If the operation was selected to resolve a deadlock, the
Db::key_range method will fail and
and either return <a href="../ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> or
throw a <a href="../api_cxx/deadlock_class.html">DbDeadlockException</a> exception.
<p>The Db::key_range method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods.
If a catastrophic error has occurred, the Db::key_range method may fail and
either return <a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a> or throw a
<a href="../api_cxx/runrec_class.html">DbRunRecoveryException</a>,
in which case all subsequent Berkeley DB calls will fail in the same way.
<h1>Class</h1>
<a href="../api_cxx/db_class.html">Db</a>
<h1>See Also</h1>
<a href="../api_cxx/db_list.html">Databases and Related Methods</a>
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