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<title>Berkeley DB Reference Guide: Removing elements from a database</title>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Simple Tutorial</dl></h3></td>
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<p>
<h3 align=center>Removing elements from a database</h3>
<p>The simplest way to remove elements from a database is the
<a href="../../api_c/db_del.html">DB-&gt;del</a> method.</p>
<p>The <a href="../../api_c/db_del.html">DB-&gt;del</a> method takes four of the same five arguments the
<a href="../../api_c/db_get.html">DB-&gt;get</a> and <a href="../../api_c/db_put.html">DB-&gt;put</a> methods take.  The difference is there is
no need to specify a data item, as the delete operation is only
interested in the key that you want to remove.</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>txnid<dd>A transaction ID.
In our simple case, we aren't expecting to recover the database after
application or system crash, so we aren't using transactions, and will
leave this argument unspecified.
<p><dt>key<dd>The key item for the key/data pair that we want to delete from the
database.
<p><dt>flags<dd>Optional flags modifying the underlying behavior of the
<a href="../../api_c/db_del.html">DB-&gt;del</a> method.  There are currently no available flags for this
method, so the flags argument should always be set to 0.
</dl>
<p>Here's what the code to call <a href="../../api_c/db_del.html">DB-&gt;del</a> looks like:</p>
<blockquote><pre>#include &lt;sys/types.h&gt;
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;string.h&gt;
#include &lt;db.h&gt;
<p>
#define	DATABASE "access.db"
<p>
int
main()
{
	DB *dbp;
	DBT key, data;
	int ret;
<p>
	if ((ret = db_create(&dbp, NULL, 0)) != 0) {
		fprintf(stderr, "db_create: %s\n", db_strerror(ret));
		exit (1);
	}
	if ((ret = dbp-&gt;open(dbp,
	    NULL, DATABASE, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) {
		dbp-&gt;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-&gt;put(dbp, NULL, &key, &data, 0)) == 0)
		printf("db: %s: key stored.\n", (char *)key.data);
	else {
		dbp-&gt;err(dbp, ret, "DB-&gt;put");
		goto err;
	}
<p>
	if ((ret = dbp-&gt;get(dbp, NULL, &key, &data, 0)) == 0)
		printf("db: %s: key retrieved: data was %s.\n",
		    (char *)key.data, (char *)data.data);
	else {
		dbp-&gt;err(dbp, ret, "DB-&gt;get");
		goto err;
	}
<p><b>	if ((ret = dbp-&gt;del(dbp, NULL, &key, 0)) == 0)
		printf("db: %s: key was deleted.\n", (char *)key.data);
	else {
		dbp-&gt;err(dbp, ret, "DB-&gt;del");
		goto err;
	}
</b></pre></blockquote>
<p>After the <a href="../../api_c/db_del.html">DB-&gt;del</a> call returns, the entry to which the key
<b>fruit</b> refers has been removed from the database.</p>
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