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<! "@(#)del.so 10.5 (Sleepycat) 10/20/98">
<!Copyright 1997, 1998 by Sleepycat Software, Inc. All rights reserved.>
<html>
<body bgcolor=white>
<head>
<title>Berkeley DB Reference Guide: Simple Tutorial</title>
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
<meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btr
ee,hash,hashing,transaction,transactions,locking,logging,access method,access me
thods,java,C,C++">
</head>
<h3>Berkeley DB Reference Guide: Simple Tutorial</h3>
<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. This interface is accessed through a function pointer that is
an element of the database handle returned by <a href="../../api_c/Db/open.html">db_open</a>.
<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.
<dl compact>
<p><dt>db<dd>The database handle returned by <a href="../../api_c/Db/open.html">db_open</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 retrieve 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><ul><pre>
#include <sys/types.h>
#include <stdio.h>
#include <db.h>
<p>
#define DATABASE "access.db"
<p>
int
main()
{
extern int errno;
DB *dbp;
DBT key, data;
<p>
if ((errno = db_open(DATABASE,
DB_BTREE, DB_CREATE, 0664, NULL, NULL, &dbp)) != 0) {
fprintf(stderr, "db: %s: %s\n", DATABASE, strerror(errno));
exit (1);
}
<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>
switch (errno = dbp->put(dbp, NULL, &key, &data, 0)) {
case 0:
printf("db: %s: key stored.\n", (char *)key.data);
break;
default:
fprintf(stderr, "db: put: %s\n", strerror(errno));
exit (1);
}
<p>
switch (errno = dbp->get(dbp, NULL, &key, &data, 0)) {
case 0:
printf("db: %s: key retrieved: data was %s.\n",
(char *)key.data, (char *)data.data);
break;
case DB_NOTFOUND:
printf("db: %s: key not found.\n", (char *)key.data);
break;
default:
fprintf(stderr, "db: get: %s\n", strerror(errno));
exit (1);
}
<p><a name="startcode"><b>
switch (errno = dbp->del(dbp, NULL, &key, 0)) {
case 0:
printf("db: %s: key was deleted.\n", (char *)key.data);
break;
default:
fprintf(stderr, "db: del: %s\n", strerror(errno));
exit (1);
}
<p>
switch (errno = dbp->get(dbp, NULL, &key, &data, 0)) {
case 0:
printf("db: %s: key retrieved: data was %s.\n",
(char *)key.data, (char *)data.data);
break;
case DB_NOTFOUND:
printf("db: %s: key not found.\n", (char *)key.data);
break;
default:
fprintf(stderr, "db: get: %s\n", strerror(errno));
exit (1);
}
</b>
</pre></ul><p>
<p>
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<a href="../../ref/toc.html"><img src="../../images/toc.gif"></a>
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