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diff --git a/db/docs/ref/simple_tut/get.html b/db/docs/ref/simple_tut/get.html new file mode 100644 index 000000000..697aa8f51 --- /dev/null +++ b/db/docs/ref/simple_tut/get.html @@ -0,0 +1,97 @@ +<!--$Id: get.so,v 10.23 2000/12/14 21:42:18 bostic Exp $--> +<!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.--> +<!--All rights reserved.--> +<html> +<head> +<title>Berkeley DB Reference Guide: Retrieving elements from 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><tr valign=top> +<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Simple Tutorial</dl></h3></td> +<td width="1%"><a href="../../ref/simple_tut/put.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../ref/toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/simple_tut/del.html"><img src="../../images/next.gif" alt="Next"></a> +</td></tr></table> +<p> +<h1 align=center>Retrieving elements from a database</h1> +<p>The simplest way to retrieve elements from a database is the +<a href="../../api_c/db_get.html">DB->get</a> interface. +<p>The <a href="../../api_c/db_get.html">DB->get</a> interface takes the same five arguments that the +<a href="../../api_c/db_put.html">DB->put</a> interface takes: +<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 NULL. +<p><dt>key<dd>The key item for the key/data pair that we want to retrieve from the +database. +<p><dt>data<dd>The data 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_get.html">DB->get</a> +interface. +</dl> +<p>Here's what the code to call <a href="../../api_c/db_get.html">DB->get</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><b> 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; + } +</b></pre></blockquote> +<p>It is not usually necessary to clear the <a href="../../api_c/dbt.html">DBT</a> structures passed +to the Berkeley DB functions between calls. This is not always true, when +some of the less commonly used flags for <a href="../../api_c/dbt.html">DBT</a> structures are +used. The <a href="../../api_c/dbt.html">DBT</a> manual page specified the details of those cases. +<p>It is possible, of course, to distinguish between system errors and the +key/data pair simply not existing in the database. There are three +standard returns from <a href="../../api_c/db_get.html">DB->get</a>: +<p><ol> +<p><li>The call might be successful and the key found, in which case the return +value will be 0. +<li>The call might be successful, but the key not found, in which case the +return value will be <a href="../../ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a>. +<li>The call might not be successful, in which case the return value will +be a system error. +</ol> +<table><tr><td><br></td><td width="1%"><a href="../../ref/simple_tut/put.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../ref/toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/simple_tut/del.html"><img src="../../images/next.gif" alt="Next"></a> +</td></tr></table> +<p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font> +</body> +</html> |