mirror of
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Yasuhiro KIMURA
82 lines
4.3 KiB
HTML
82 lines
4.3 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Retrieved key/data permanence for C/C++</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="am_misc.html" title="Chapter 4. Access Method Wrapup" />
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<link rel="prev" href="am_misc_struct.html" title="Storing C/C++ structures/objects" />
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<div class="libver">
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<p>Library Version 18.1.40</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Retrieved key/data permanence for C/C++</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="am_misc_struct.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 4. Access Method Wrapup </th>
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<td width="20%" align="right"> <a accesskey="n" href="am_misc_error.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="am_misc_perm"></a>Retrieved key/data permanence for C/C++</h2>
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</div>
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</div>
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</div>
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<p>
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When using the non-cursor Berkeley DB calls to retrieve
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key/data items under the C/C++ APIs (for example, <a href="../api_reference/C/dbget.html" class="olink">DB->get()</a>),
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the memory to which the pointer stored into the <a href="../api_reference/C/dbt.html" class="olink">DBT</a> refers
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is only valid until the next call to Berkeley DB using the
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<a href="../api_reference/C/db.html" class="olink">DB</a> handle. (This includes <span class="bold"><strong>any</strong></span> use of the returned <a href="../api_reference/C/db.html" class="olink">DB</a> handle, including
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by another thread of control within the process. For this
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reason, when multiple threads are using the returned <a href="../api_reference/C/db.html" class="olink">DB</a>
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handle concurrently, one of the <a href="../api_reference/C/dbt.html#dbt_DB_DBT_MALLOC" class="olink">DB_DBT_MALLOC</a>,
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<a href="../api_reference/C/dbt.html#dbt_DB_DBT_REALLOC" class="olink">DB_DBT_REALLOC</a> or <a href="../api_reference/C/dbt.html#dbt_DB_DBT_USERMEM" class="olink">DB_DBT_USERMEM</a> flags must be specified
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with any non-cursor <a href="../api_reference/C/dbt.html" class="olink">DBT</a> used for key or data
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retrieval.)
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</p>
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<p>
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When using the cursor Berkeley DB calls to retrieve key/data
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items under the C/C++ APIs (for example, <a href="../api_reference/C/dbcget.html" class="olink">DBC->get()</a>), the memory
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to which the pointer stored into the <a href="../api_reference/C/dbt.html" class="olink">DBT</a> refers is only
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valid until the next call to Berkeley DB using the <a href="../api_reference/C/dbc.html" class="olink">DBC</a>
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returned by <a href="../api_reference/C/dbcursor.html" class="olink">DB->cursor()</a>.
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</p>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="am_misc_struct.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="am_misc.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="am_misc_error.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Storing C/C++
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structures/objects </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Error support</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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