mirror of
https://github.com/yasuhirokimura/db18
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Yasuhiro KIMURA
210 lines
10 KiB
HTML
210 lines
10 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 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">Dbstl container specific
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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
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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#idm140654539330192">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#idm140654539204112">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="idm140654539330192"></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
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handle if you want
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<code class="classname">db_vector<></code> to
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work like <code class="classname">std::vector</code> or
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<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
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<code class="classname">db_vector<></code> to
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work like <code class="classname">std::list</code>. Note
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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
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work faster.
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</p>
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<p>
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For example, to construct a fast
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std::queue/std::stack object, you only need a
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<code class="classname">db_vector<></code>
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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
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handle has <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> set, it still works for
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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
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whether <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> is set. If you do not set
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it, <code class="classname">db_vector<></code> will
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not work like
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std::vector<>/std::deque<> with regard
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to operator[], because the indices are not
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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
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this feature in the
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<code class="methodname">StlAdvancedFeaturesExample::queue_stack()</code>
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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
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<code class="classname">std::vector</code>,
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inserting/deleting in the middle of a
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<code class="classname">db_vector</code> is slower
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than doing the same action at the end of the
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sequence. This is because the underlying DB_RECNO
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DB (with the <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> flag set) is relatively
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slow when inserting/deleting in the middle or the
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head — it has to update the index numbers of
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all the records following the one that was
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inserted/deleted. If you do not need to keep the
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index ordered on insert/delete, you can use
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<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
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methods inherited from
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<code class="classname">std::list</code> and
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<code class="classname">std::deque</code>, including
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<code class="classname">std::list<>'s</code>
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unique methods <code class="methodname">remove()</code>,
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<code class="methodname">remove_if()</code>,
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<code class="methodname">unique()</code>,
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<code class="methodname">merge()</code>,
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<code class="methodname">sort()</code>,
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<code class="methodname">reverse()</code>, and
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<code class="methodname">splice()</code>. These use
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the identical semantics/behaviors of the
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<code class="classname">std::list<></code>
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methods, although pushing/deleting at the head is
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slower than the
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<code class="methodname">std::deque</code> and
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<code class="methodname">std::list</code> equivalent
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when there are quite a lot of elements in the
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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
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<code class="classname">std::stack</code> container
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adapters with <code class="classname">db_vector</code>;
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they work with db_vector even without
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<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="idm140654539204112"></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
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set from <code class="classname">std::map</code> and
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<code class="classname">hash_map</code>, but there are some
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methods that can only be called on containers backed by
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<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
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figure out the type of the backing database. If you call
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unsupported methods then an InvalidFunctionCall exception
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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
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methods: <code class="methodname">upper_bound()</code>,
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<code class="methodname">lower_bound()</code>,
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<code class="methodname">key_comp()</code>, and
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<code class="methodname">value_comp()</code>. The
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<code class="literal">DB_HASH</code> specific methods are
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<code class="methodname">key_eq()</code>,
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<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
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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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