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<title>Berkeley DB Reference Guide: Opening databases within the environment</title>
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<td><b><dl><dt>Berkeley DB Reference Guide:<dd>Environment</dl></b></td>
<td align=right><a href="../env/create.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../env/error.html"><img src="../../images/next.gif" alt="Next"></a>
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<p align=center><b>Opening databases within the environment</b></p>
<p>Once the environment has been created, database handles may be created
and then opened within the environment.  This is done by calling the
<a href="../../api_c/db_class.html">db_create</a> function and specifying the appropriate environment
as an argument.</p>
<p>File naming, database operations, and error handling will all be done as
specified for the environment.  For example, if the <a href="../../api_c/env_open.html#DB_INIT_LOCK">DB_INIT_LOCK</a>
or <a href="../../api_c/env_open.html#DB_INIT_CDB">DB_INIT_CDB</a> flags were specified when the environment was
created or joined, database operations will automatically perform all
necessary locking operations for the application.</p>
<p>The following is a simple example of opening two databases within a
database environment:</p>
<blockquote><pre>	DB_ENV *dbenv;
	DB *dbp1, *dbp2;
	int ret;
<p>
	dbenv = NULL;
	dbp1 = dbp2 = NULL;
<p>
	/*
	 * Create an environment and initialize it for additional error
	 * reporting.
	 */
	if ((ret = db_env_create(&dbenv, 0)) != 0) {
		fprintf(errfp, "%s: %s\n", progname, db_strerror(ret));
		return (ret);
	}
<p>
	dbenv-&gt;set_errfile(dbenv, errfp);
	dbenv-&gt;set_errpfx(dbenv, progname);
<p>
	/* Open an environment with just a memory pool. */
	if ((ret =
	    dbenv-&gt;open(dbenv, home, DB_CREATE | DB_INIT_MPOOL, 0)) != 0) {
		dbenv-&gt;err(dbenv, ret, "environment open: %s", home);
		goto err;
	}
<p>
	/* Open database #1. */
	if ((ret = db_create(&dbp1, dbenv, 0)) != 0) {
		dbenv-&gt;err(dbenv, ret, "database create");
		goto err;
	}
	if ((ret = dbp1-&gt;open(dbp1,
	    NULL, DATABASE1, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) {
		dbenv-&gt;err(dbenv, ret, "DB-&gt;open: %s", DATABASE1);
		goto err;
	}
<p>
	/* Open database #2. */
	if ((ret = db_create(&dbp2, dbenv, 0)) != 0) {
		dbenv-&gt;err(dbenv, ret, "database create");
		goto err;
	}
	if ((ret = dbp2-&gt;open(dbp2,
	    NULL, DATABASE2, NULL, DB_HASH, DB_CREATE, 0664)) != 0) {
		dbenv-&gt;err(dbenv, ret, "DB-&gt;open: %s", DATABASE2);
		goto err;
	}
<p>
	return (0);
<p>
err:	if (dbp2 != NULL)
		(void)dbp2-&gt;close(dbp2, 0);
	if (dbp1 != NULL)
		(void)dbp2-&gt;close(dbp1, 0);
	(void)dbenv-&gt;close(dbenv, 0);
	return (1);
}</pre></blockquote>
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<p><font size=1>Copyright (c) 1996,2008 Oracle.  All rights reserved.</font>
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