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168 lines
9 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>Dbstl container specific notes</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="stl.html" title="Chapter 7. Standard Template Library API" />
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<link rel="prev" href="stl_persistence.html" title="Dbstl persistence" />
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<link rel="next" href="stl_efficienct_use.html" title="Using dbstl efficiently" />
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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">Dbstl container specific notes</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="stl_persistence.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 7. Standard Template Library API</th>
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<td width="20%" align="right"> <a accesskey="n" href="stl_efficienct_use.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="stl_container_specific"></a>Dbstl container specific notes</h2>
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</div>
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</div>
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</div>
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<div class="toc">
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<dl>
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<dt>
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<span class="sect2">
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<a href="stl_container_specific.html#id3944988">db_vector specific notes</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="stl_container_specific.html#id3946124">Associative container specific notes</a>
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</span>
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</dt>
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</dl>
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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="id3944988"></a>db_vector specific notes</h3>
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</div>
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</div>
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</div>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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Set the <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> flag in the database handle if you want
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<code class="classname">db_vector<></code> to work like
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<code class="classname">std::vector</code> or <code class="classname">std::deque</code>. Do not set
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<a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> if you want <code class="classname">db_vector<></code> to work like
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<code class="classname">std::list</code>. Note that without <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> set,
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<code class="classname">db_vector<></code> can work faster.
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</p>
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<p>
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For example, to construct a fast std::queue/std::stack object, you only need a
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<code class="classname">db_vector<></code> object whose database handle does not have
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<a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> set. Of course, if the database handle has <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> set, it
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still works for this kind of scenario, just not as fast.
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</p>
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<p>
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<code class="classname">db_vector</code> does not check whether <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> is set. If
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you do not set it, <code class="classname">db_vector<></code> will not work like
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std::vector<>/std::deque<> with regard to operator[], because the
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indices are not maintained in that case.
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</p>
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<p>
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You can find example code showing how to use this feature in the
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<code class="methodname">StlAdvancedFeaturesExample::queue_stack()</code> method.
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</p>
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</li>
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<li>
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<p>
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Just as is the case with <code class="classname">std::vector</code>, inserting/deleting in
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the middle of a <code class="classname">db_vector</code> is slower than doing the same
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action at the end of the sequence. This is because the underlying DB_RECNO DB (with
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the <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> flag set) is relatively slow when inserting/deleting in the middle
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or the head — it has to update the index numbers of all the records following
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the one that was inserted/deleted. If you do not need to keep the index ordered on
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insert/delete, you can use <code class="classname">db_map</code> instead.
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</p>
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<p>
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<code class="classname">db_vector</code> also contains methods inherited from
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<code class="classname">std::list</code> and <code class="classname">std::deque</code>,
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including <code class="classname">std::list<>'s</code> unique methods
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<code class="methodname">remove()</code>, <code class="methodname">remove_if()</code>,
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<code class="methodname">unique()</code>, <code class="methodname">merge()</code>,
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<code class="methodname">sort()</code>, <code class="methodname">reverse()</code>, and
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<code class="methodname">splice()</code>. These use the identical semantics/behaviors
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of the <code class="classname">std::list<></code> methods, although
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pushing/deleting at the head is slower than the
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<code class="methodname">std::deque</code> and <code class="methodname">std::list</code>
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equivalent when there are quite a lot of elements in the database.
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</p>
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</li>
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<li>
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<p>
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You can use <code class="classname">std::queue</code>,
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<code class="classname">std::priority_queue</code> and <code class="classname">std::stack</code>
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container adapters with <code class="classname">db_vector</code>; they work with db_vector
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even without <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> set.
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</p>
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</li>
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</ul>
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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="id3946124"></a>Associative container specific notes</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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<code class="classname">db_map</code> contains the union of method set from
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<code class="classname">std::map</code> and <code class="classname">hash_map</code>, but there are some
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methods that can only be called on containers backed by <code class="literal">DB_BTREE</code> or
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<code class="literal">DB_HASH</code> databases. You can call
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<code class="function">db_map<>::is_hash()</code> to figure out the type of the backing
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database. If you call unsupported methods then an InvalidFunctionCall exception is thrown.
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</p>
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<p>
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These are the <code class="literal">DB_BTREE</code> specific methods: <code class="methodname">upper_bound()</code>,
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<code class="methodname">lower_bound()</code>, <code class="methodname">key_comp()</code>,
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and <code class="methodname">value_comp()</code>. The <code class="literal">DB_HASH</code> specific methods are
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<code class="methodname">key_eq()</code>, <code class="methodname">hash_funct()</code>.
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</p>
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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="stl_persistence.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="stl.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="stl_efficienct_use.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">Dbstl persistence </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"> Using dbstl efficiently</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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