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DB-&gt;exists
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#include &lt;db.h&gt;

int
DB-&gt;exists(DB *db, DB_TXN *txnid, DBT *key, u_int32_t flags);
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Description: DB-&gt;exists
The DB-&gt;exists method returns if the specified key appears in the
database.
The DB-&gt;exists method will return <a href="../../db4-devel-4.7.25/ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a> if the specified key is not in the database.
The DB-&gt;exists method will return <a href="../../db4-devel-4.7.25/ref/program/errorret.html#DB_KEYEMPTY">DB_KEYEMPTY</a> if the database is a Queue or Recno database and
the specified key exists, but was never explicitly created by the
application or was later deleted.
Unless otherwise specified, the DB-&gt;exists method
returns a non-zero error value on failure
and 0 on success.

Parameters 
 flags<ul compact><li>The flags parameter must be set to 0 or
one of the following values:
In addition, the following flags may be set by
bitwise inclusively OR'ing them into the flags parameter:
 
<a name="DB_READ_COMMITTED">DB_READ_COMMITTED</a><ul compact><li>Configure a transactional read operation to have degree 2 isolation (the
read is not repeatable).</ul>
<a name="DB_READ_UNCOMMITTED">DB_READ_UNCOMMITTED</a><ul compact><li>Configure a transactional read operation to have degree 1 isolation,
reading modified but not yet committed data. Silently ignored if the
<a href="../../db4-devel-4.7.25/api_c/db_open.html#DB_READ_UNCOMMITTED">DB_READ_UNCOMMITTED</a> flag was not specified when the underlying
database was opened.</ul>
<a name="DB_RMW">DB_RMW</a><ul compact><li>Acquire write locks instead of read locks when doing the read, if
locking is configured. Setting this flag can eliminate deadlock during
a read-modify-write cycle by acquiring the write lock during the read
part of the cycle so that another thread of control acquiring a read
lock for the same item, in its own read-modify-write cycle, will not
result in deadlock.
Because the DB-&gt;exists method will not hold locks across
Berkeley DB calls in non-transactional operations, the <a href="../../db4-devel-4.7.25/api_c/dbc_get.html#DB_RMW">DB_RMW</a> flag to
the DB-&gt;exists call is meaningful only in the presence of
transactions.</ul>
 </ul>
 key<ul compact><li>The key <a href="../../db4-devel-4.7.25/api_c/dbt_class.html">DBT</a> operated on.</ul>
 txnid<ul compact><li>If the operation is part of an application-specified transaction, the
txnid parameter is a transaction handle returned from
<a href="../../db4-devel-4.7.25/api_c/txn_begin.html">DB_ENV-&gt;txn_begin</a>; if the operation is part of a Berkeley DB Concurrent Data Store group, the
txnid parameter is a handle returned from
<a href="../../db4-devel-4.7.25/api_c/env_cdsgroup_begin.html">DB_ENV-&gt;cdsgroup_begin</a>; otherwise NULL.
</ul>
 
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 Class
<a href="../../db4-devel-4.7.25/api_c/db_class.html">DB</a>
 See Also
<a href="../../db4-devel-4.7.25/api_c/db_list.html">Databases and Related Methods</a>
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