| Current Path : /proc/self/root/proc/2/root/usr/local/ssl/share/doc/db4-devel-4.7.25/gsg/CXX/ |
| Current File : //proc/self/root/proc/2/root/usr/local/ssl/share/doc/db4-devel-4.7.25/gsg/CXX/DB.html |
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Chapter 2. Databases</title>
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
<meta name="generator" content="DocBook XSL Stylesheets V1.62.4" />
<link rel="home" href="index.html" title="Getting Started with Berkeley DB" />
<link rel="up" href="index.html" title="Getting Started with Berkeley DB" />
<link rel="previous" href="gettingit.html" title="Getting and Using DB " />
<link rel="next" href="coredbclose.html" title="Closing Databases" />
</head>
<body>
<div class="navheader">
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Chapter 2. Databases</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="gettingit.html">Prev</a> </td>
<th width="60%" align="center"> </th>
<td width="20%" align="right"> <a accesskey="n" href="coredbclose.html">Next</a></td>
</tr>
</table>
<hr />
</div>
<div class="chapter" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title"><a id="DB"></a>Chapter 2. Databases</h2>
</div>
</div>
<div></div>
</div>
<div class="toc">
<p>
<b>Table of Contents</b>
</p>
<dl>
<dt>
<span class="sect1">
<a href="DB.html#DBOpen">Opening Databases</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="coredbclose.html">Closing Databases</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="DBOpenFlags.html">Database Open Flags</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="CoreDBAdmin.html">Administrative Methods</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="dbErrorReporting.html">Error Reporting Functions</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="CoreEnvUsage.html">Managing Databases in Environments</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="CoreDbCXXUsage.html">Database Example</a>
</span>
</dt>
</dl>
</div>
<p>In Berkeley DB, a database is a collection of <span class="emphasis"><em>records</em></span>. Records,
in turn, consist of key/data pairings.
</p>
<p>
Conceptually, you can think of a
<span>database</span>
as containing a two-column table where column 1 contains a key and column 2
contains data. Both the key and the data are managed using
<tt class="classname">Dbt</tt>
<span>class instances</span>
(see <a href="DBEntry.html">Database Records</a> for details on this
<span>class</span>
).
So, fundamentally, using a DB
<span>database</span>
involves putting, getting, and deleting database records, which in turns involves efficiently
managing information
<span>encapsulated by </span>
<tt class="classname">Dbt</tt>
<span>objects.</span>
The next several chapters of this book are dedicated to those activities.
</p>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="DBOpen"></a>Opening Databases</h2>
</div>
</div>
<div></div>
</div>
<p>
You open a database by instantiating a <tt class="classname">Db</tt> object
and then calling its <tt class="methodname">open()</tt> method.
</p>
<p>
Note that by default, DB does not create databases if they do not already exist.
To override this behavior, specify the
<a href="DBOpenFlags.html" title="Database Open Flags"><tt class="literal">DB_CREATE</tt></a> flag on the
<tt class="methodname">open()</tt> method.
</p>
<p>
The following code fragment illustrates a database open:
</p>
<a id="cxx_db1"></a>
<pre class="programlisting">#include <db_cxx.h>
...
Db db(NULL, 0); // Instantiate the Db object
u_int32_t oFlags = DB_CREATE; // Open flags;
try {
// Open the database
db.open(NULL, // Transaction pointer
"my_db.db", // Database file name
NULL, // Optional logical database name
DB_BTREE, // Database access method
oFlags, // Open flags
0); // File mode (using defaults)
// DbException is not subclassed from std::exception, so
// need to catch both of these.
} catch(DbException &e) {
// Error handling code goes here
} catch(std::exception &e) {
// Error handling code goes here
} </pre>
</div>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="gettingit.html">Prev</a> </td>
<td width="20%" align="center">
<a accesskey="u" href="index.html">Up</a>
</td>
<td width="40%" align="right"> <a accesskey="n" href="coredbclose.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">Getting and Using DB </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> Closing Databases</td>
</tr>
</table>
</div>
</body>
</html>
Copyright 2K16 - 2K18 Indonesian Hacker Rulez
;?>)