<?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 25. DbstlDbt</title> <link rel="stylesheet" href="apiReference.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> <link rel="start" href="index.html" title="Berkeley DB C++ Standard Template Library API Reference" /> <link rel="up" href="index.html" title="Berkeley DB C++ Standard Template Library API Reference" /> <link rel="prev" href="stlElementRef_DB_STL_value.html" title="_DB_STL_value" /> <link rel="next" href="stlDbstlDbtdstr_DbstlDbt.html" title="~DbstlDbt" /> </head> <body> <div xmlns="" class="navheader"> <div class="libver"> <p>Library Version 11.2.5.3</p> </div> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Chapter 25. DbstlDbt </th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="stlElementRef_DB_STL_value.html">Prev</a> </td> <th width="60%" align="center"> </th> <td width="20%" align="right"> <a accesskey="n" href="stlDbstlDbtdstr_DbstlDbt.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="DbstlDbt"></a>Chapter 25. DbstlDbt </h2> </div> </div> </div> <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> 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> <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> 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> rather than Dbt class.</p> <p><a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a> 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> .</p> <p><a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a> 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> <p>In practice you rarely need to use <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a> 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> .</p> <p>Hence, <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a> is the right class to use to store any object into Berkeley DB via dbstl without memory leaks.</p> <p>Don't free the memory referenced by <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a> objects, it will be freed when the <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a> object is destructed.</p> <p>Please refer to the two examples using <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a> 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> in order to store raw bytes.</p> <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> 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> class for the type you are storing/retrieving using dbstl. </p> <h4><a id="idp51587824"></a> Public Members </h4> <div class="informaltable"> <table border="1" width="80%"> <colgroup> <col /> <col /> </colgroup> <thead> <tr> <th>Member</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td> <a class="xref" href="DbstlDbt.html#stlDbstlDbtDbstlDbt" title="DbstlDbt">DbstlDbt</a> </td> <td> <p>Construct an object with an existing chunk of memory of size1 bytes, refered by data1,. </p> </td> </tr> <tr> <td> <a class="xref" href="stlDbstlDbtdstr_DbstlDbt.html" title="~DbstlDbt">~DbstlDbt</a> </td> <td> <p>The memory will be free'ed by the destructor. </p> </td> </tr> <tr> <td> <a class="xref" href="stlDbstlDbtoperator_assign.html" title="operator=">operator=</a> </td> <td> <p>The memory will be reallocated if neccessary. </p> </td> </tr> </tbody> </table> </div> <h4><a id="idp51593232"></a> Group</h4> <p> <a class="xref" href="dbstl_helper_classes.html" title="Chapter 21. Dbstl Helper Classes"> Dbstl Helper Classes </a> </p> <p> </p> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="stlDbstlDbtDbstlDbt"></a>DbstlDbt</h2> </div> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="stlDbstlDbtDbstlDbt_details"></a>Function Details</h3> </div> </div> </div> <pre class="programlisting"> DbstlDbt(void *data1, u_int32_t size1) </pre> <p>Construct an object with an existing chunk of memory of size1 bytes, refered by data1,. </p> <pre class="programlisting"> DbstlDbt() </pre> <pre class="programlisting"> DbstlDbt(const DbstlDbt &d) </pre> <p>This copy constructor does a deep copy. </p> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp51589656"></a>Class</h3> </div> </div> </div> <p> <a class="link" href="DbstlDbt.html" title="Chapter 25. DbstlDbt">DbstlDbt</a> </p> </div> </div> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="stlElementRef_DB_STL_value.html">Prev</a> </td> <td width="20%" align="center"> </td> <td width="40%" align="right"> <a accesskey="n" href="stlDbstlDbtdstr_DbstlDbt.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">_DB_STL_value </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> ~DbstlDbt</td> </tr> </table> </div> </body> </html>