<!--$Id: close.html,v 1.2 2004/03/30 01:22:58 jtownsen Exp $--> <!--Copyright 1997-2003 by Sleepycat Software, Inc.--> <!--All rights reserved.--> <!--See the file LICENSE for redistribution information.--> <html> <head> <title>Berkeley DB Reference Guide: Closing a database</title> <meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> <meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> </head> <body bgcolor=white> <table width="100%"><tr valign=top> <td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Simple Tutorial</dl></h3></td> <td align=right><a href="../simple_tut/del.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../am_conf/intro.html"><img src="../../images/next.gif" alt="Next"></a> </td></tr></table> <p> <h3 align=center>Closing a database</h3> <p>The only other operation that we need for our simple example is closing the database, and cleaning up the DB handle.</p> <p>It is necessary that the database be closed. The most important reason for this is that Berkeley DB runs on top of an underlying buffer cache. If the modified database pages are never explicitly flushed to disk and the database is never closed, changes made to the database may never make it out to disk, because they are held in the Berkeley DB cache. As the default behavior of the close function is to flush the Berkeley DB cache, closing the database will update the on-disk information.</p> <p>The <a href="../../api_c/db_close.html">DB->close</a> method takes two arguments:</p> <p><dl compact> <p><dt>db<dd>The database handle returned by <a href="../../api_c/db_class.html">db_create</a>. <p><dt>flags<dd>Optional flags modifying the underlying behavior of the <a href="../../api_c/db_close.html">DB->close</a> method. </dl> <p>Here's what the code to call <a href="../../api_c/db_close.html">DB->close</a> looks like:</p> <blockquote><pre>#include <sys/types.h> #include <stdio.h> #include <string.h> #include <stdlib.h> #include <db.h> <p> #define DATABASE "access.db" <p> int main() { DB *dbp; DBT key, data; <b>int ret, t_ret;</b> <p> if ((ret = db_create(&dbp, NULL, 0)) != 0) { fprintf(stderr, "db_create: %s\n", db_strerror(ret)); exit (1); } if ((ret = dbp->open(dbp, NULL, DATABASE, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) { dbp->err(dbp, ret, "%s", DATABASE); goto err; } <p> memset(&key, 0, sizeof(key)); memset(&data, 0, sizeof(data)); key.data = "fruit"; key.size = sizeof("fruit"); data.data = "apple"; data.size = sizeof("apple"); <p> if ((ret = dbp->put(dbp, NULL, &key, &data, 0)) == 0) printf("db: %s: key stored.\n", (char *)key.data); else { dbp->err(dbp, ret, "DB->put"); goto err; } <p> if ((ret = dbp->get(dbp, NULL, &key, &data, 0)) == 0) printf("db: %s: key retrieved: data was %s.\n", (char *)key.data, (char *)data.data); else { dbp->err(dbp, ret, "DB->get"); goto err; } <p> if ((ret = dbp->del(dbp, NULL, &key, 0)) == 0) printf("db: %s: key was deleted.\n", (char *)key.data); else { dbp->err(dbp, ret, "DB->del"); goto err; } <p> if ((ret = dbp->get(dbp, NULL, &key, &data, 0)) == 0) printf("db: %s: key retrieved: data was %s.\n", (char *)key.data, (char *)data.data); else dbp->err(dbp, ret, "DB->get"); <p><b>err: if ((t_ret = dbp->close(dbp, 0)) != 0 && ret == 0) ret = t_ret; </b> <p> exit(ret); }</pre></blockquote> <p>Note that we do not necessarily overwrite the <b>ret</b> variable, as it may contain error return information from a previous Berkeley DB call.</p> <table width="100%"><tr><td><br></td><td align=right><a href="../simple_tut/del.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../am_conf/intro.html"><img src="../../images/next.gif" alt="Next"></a> </td></tr></table> <p><font size=1><a href="../../sleepycat/legal.html">Copyright (c) 1996-2003</a> <a href="http://www.sleepycat.com">Sleepycat Software, Inc.</a> - All rights reserved.</font> </body> </html>