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173 lines
8.3 KiB
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<?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>Chapter 25. DbstlDbt</title>
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<link rel="stylesheet" href="apiReference.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 C++ Standard Template Library API Reference" />
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<link rel="up" href="index.html" title="Berkeley DB C++ Standard Template Library API Reference" />
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<link rel="prev" href="stlElementRef_DB_STL_value.html" title="_DB_STL_value" />
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<link rel="next" href="stlDbstlDbtdstr_DbstlDbt.html" title="~DbstlDbt" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 11.2.5.2</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">Chapter 25.
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DbstlDbt </th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="stlElementRef_DB_STL_value.html">Prev</a> </td>
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<th width="60%" align="center"> </th>
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<td width="20%" align="right"> <a accesskey="n" href="stlDbstlDbtdstr_DbstlDbt.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="chapter" 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"><a id="DbstlDbt"></a>Chapter 25.
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DbstlDbt </h2>
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</div>
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</div>
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</div>
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<p>You can persist all bytes in a chunk of contiguous memory by constructing an <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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object A(use malloc to allocate the required number of bytes for A.data and copy the bytes to be stored into A.data, set other fields as necessary) and store A into a container, e.g. </p>
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<p>db_vector<DbstlDbt>, this stores the bytes rather than the object A into the underlying database. The <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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class can help you avoid memory leaks, so it is strongly recommended that you use <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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rather than Dbt class.</p>
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<p><a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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derives from Dbt class, and it does an deep copy on copy construction and assignment --by calling malloc to allocate its own memory and then copying the bytes to it; Conversely the destructor will free the memory on destruction if the data pointer is non-NULL. The destructor assumes the memory is allocated via malloc, hence why you are required to call malloc to allocate memory in order to use <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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.</p>
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<p><a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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simply inherits all methods from Dbt with no extra new methods except the constructors/destructor and assignment operator, so it is easy to use.</p>
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<p>In practice you rarely need to use <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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or Dbt because dbstl enables you to store any complex objects or primitive data. Only when you need to store raw bytes, e.g. a bitmap, do you need to use <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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.</p>
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<p>Hence, <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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is the right class to use to store any object into Berkeley DB via dbstl without memory leaks.</p>
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<p>Don't free the memory referenced by <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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objects, it will be freed when the <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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object is destructed.</p>
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<p>Please refer to the two examples using <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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in TestAssoc::test_arbitrary_object_storage and TestAssoc::test_char_star_string_storage member functions, which illustrate how to correctly use <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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in order to store raw bytes.</p>
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<p>This class handles the task of allocating and de-allocating memory internally. Although it can be used to store data which cannot be handled by the <a class="link" href="DbstlElemTraits.html" title="Chapter 26. DbstlElemTraits">DbstlElemTraits</a>
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class, in practice, it is usually more convenient to register callbacks in the <a class="link" href="DbstlElemTraits.html" title="Chapter 26. DbstlElemTraits">DbstlElemTraits</a>
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class for the type you are storing/retrieving using dbstl. </p>
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<h4><a id="id3540830"></a> Public Members </h4>
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<div class="informaltable">
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<table border="1" width="80%">
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<colgroup>
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<col />
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<col />
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</colgroup>
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<thead>
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<tr>
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<th>Member</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>
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<a class="xref" href="DbstlDbt.html#stlDbstlDbtDbstlDbt" title="DbstlDbt">DbstlDbt</a>
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</td>
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<td>
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<p>Construct an object with an existing chunk of memory of size1 bytes, refered by data1,. </p> </td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="stlDbstlDbtdstr_DbstlDbt.html" title="~DbstlDbt">~DbstlDbt</a>
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</td>
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<td>
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<p>The memory will be free'ed by the destructor. </p> </td>
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</tr>
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<tr>
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<td>
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<a class="xref" href="stlDbstlDbtoperator_assign.html" title="operator=">operator=</a>
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</td>
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<td>
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<p>The memory will be reallocated if neccessary. </p> </td>
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</tr>
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</tbody>
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</table>
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</div>
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<h4><a id="id3540922"></a>
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Group</h4>
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<p>
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<a class="xref" href="dbstl_helper_classes.html" title="Chapter 21. Dbstl Helper Classes">
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Dbstl Helper Classes </a>
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</p>
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<p>
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</p>
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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="stlDbstlDbtDbstlDbt"></a>DbstlDbt</h2>
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</div>
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</div>
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</div>
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<div class="sect2" 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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<h3 class="title"><a id="stlDbstlDbtDbstlDbt_details"></a>Function Details</h3>
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</div>
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</div>
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</div>
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<pre class="programlisting">
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DbstlDbt(void *data1,
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u_int32_t size1)
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</pre>
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<p>Construct an object with an existing chunk of memory of size1 bytes, refered by data1,. </p>
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<pre class="programlisting">
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DbstlDbt()
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</pre>
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<pre class="programlisting">
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DbstlDbt(const DbstlDbt &d)
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</pre>
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<p>This copy constructor does a deep copy. </p>
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</div>
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<div class="sect2" 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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<h3 class="title"><a id="id3540725"></a>Class</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a>
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</p>
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</div>
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</div>
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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="stlElementRef_DB_STL_value.html">Prev</a> </td>
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<td width="20%" align="center"> </td>
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<td width="40%" align="right"> <a accesskey="n" href="stlDbstlDbtdstr_DbstlDbt.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">_DB_STL_value </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"> ~DbstlDbt</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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