text: <!--$Id: db_exists.so,v 1.1 2007/07/12 18:27:42 bostic Exp $-->
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  <title>Berkeley DB: DB-&gt;exists</title>
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  <b>DB-&gt;exists</b>
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  <b><pre>
  #include &lt;db.h&gt;
  <p>
  int
  DB-&gt;exists(DB *db, DB_TXN *txnid, DBT *key, u_int32_t flags);
  </pre></b>
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  <b>Description: DB-&gt;exists</b>
  <p>The DB-&gt;exists method returns if the specified key appears in the
  database.</p>
  <p>The DB-&gt;exists method will return <a href="../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="../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.
  </p>
  <b>Parameters</b> <br>
   <b>flags</b><ul compact><li>The <b>flags</b> parameter must be set to 0 or
  one of the following values:
  In addition, the following flags may be set by
  bitwise inclusively <b>OR</b>'ing them into the <b>flags</b> parameter:
  <br>
  <b><a name="DB_READ_COMMITTED">DB_READ_COMMITTED</a></b><ul compact><li>Configure a transactional read operation to have degree 2 isolation (the
  read is not repeatable).</ul>
  <b><a name="DB_READ_UNCOMMITTED">DB_READ_UNCOMMITTED</a></b><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="../api_c/db_open.html#DB_READ_UNCOMMITTED">DB_READ_UNCOMMITTED</a> flag was not specified when the underlying
  database was opened.</ul>
  <b><a name="DB_RMW">DB_RMW</a></b><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.
  <p>Because the DB-&gt;exists method will not hold locks across
  Berkeley DB calls in non-transactional operations, the <a href="../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.</p></ul>
  <br></ul>
   <b>key</b><ul compact><li>The key <a href="../api_c/dbt_class.html">DBT</a> operated on.</ul>
   <b>txnid</b><ul compact><li>If the operation is part of an application-specified transaction, the
  <b>txnid</b> parameter is a transaction handle returned from
  <a href="../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
  <b>txnid</b> parameter is a handle returned from
  <a href="../api_c/env_cdsgroup_begin.html">DB_ENV-&gt;cdsgroup_begin</a>; otherwise NULL.
  </ul>
  <br>
  <hr size=1 noshade>
  <br><b>Class</b>
  <a href="../api_c/db_class.html">DB</a>
  <br><b>See Also</b>
  <a href="../api_c/db_list.html">Databases and Related Methods</a>
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