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<!--$Id: del.so,v 10.20 2000/03/18 21:43:17 bostic Exp $-->
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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>
<h1 align=center>Removing elements from a database</h1>
<p>The simplest way to remove elements from a database is the <a href="../../api_c/db_del.html">DB->del</a>
interface.
<p>The <a href="../../api_c/db_del.html">DB->del</a> interface takes four of the same five arguments that
the <a href="../../api_c/db_get.html">DB->get</a> and <a href="../../api_c/db_put.html">DB->put</a> interfaces take. The difference
is that 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><dl compact>
<p><dt>db<dd>The database handle returned by <a href="../../api_c/db_create.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->del</a>
interface. There are currently no available flags for this interface,
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->del</a> looks like:
<p><blockquote><pre>#include <sys/types.h>
#include <stdio.h>
#include <db.h>
<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->open(
dbp, 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><b> 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;
}
</b></pre></blockquote>
<p>After the <a href="../../api_c/db_del.html">DB->del</a> call returns, the entry referenced by the key
fruit has been removed from the database.
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