1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
|
<?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>Dbstl container specific notes</title>
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
<link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
<link rel="up" href="stl.html" title="Chapter 7. Standard Template Library API" />
<link rel="prev" href="stl_persistence.html" title="Dbstl persistence" />
<link rel="next" href="stl_efficienct_use.html" title="Using dbstl efficiently" />
</head>
<body>
<div xmlns="" class="navheader">
<div class="libver">
<p>Library Version 12.1.6.1</p>
</div>
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Dbstl container specific
notes</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="stl_persistence.html">Prev</a> </td>
<th width="60%" align="center">Chapter 7. Standard Template Library API</th>
<td width="20%" align="right"> <a accesskey="n" href="stl_efficienct_use.html">Next</a></td>
</tr>
</table>
<hr />
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="stl_container_specific"></a>Dbstl container specific
notes</h2>
</div>
</div>
</div>
<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="stl_container_specific.html#idp873704">db_vector specific notes</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="stl_container_specific.html#idp948648">Associative container specific notes</a>
</span>
</dt>
</dl>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp873704"></a>db_vector specific notes</h3>
</div>
</div>
</div>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
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
<code class="classname">db_vector<></code> to
work like <code class="classname">std::vector</code> or
<code class="classname">std::deque</code>. Do not set
<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 <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,
<code class="classname">db_vector<></code> can
work faster.
</p>
<p>
For example, to construct a fast
std::queue/std::stack object, you only need a
<code class="classname">db_vector<></code>
object whose database handle does not have
<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 still works for
this kind of scenario, just not as fast.
</p>
<p>
<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 you do not set
it, <code class="classname">db_vector<></code> will
not work like
std::vector<>/std::deque<> with regard
to operator[], because the indices are not
maintained in that case.
</p>
<p>
You can find example code showing how to use
this feature in the
<code class="methodname">StlAdvancedFeaturesExample::queue_stack()</code>
method.
</p>
</li>
<li>
<p>
Just as is the case with
<code class="classname">std::vector</code>,
inserting/deleting in the middle of a
<code class="classname">db_vector</code> is slower
than doing the same action at the end of the
sequence. This is because the underlying DB_RECNO
DB (with 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 or the
head — it has to update the index numbers of
all the records following the one that was
inserted/deleted. If you do not need to keep the
index ordered on insert/delete, you can use
<code class="classname">db_map</code> instead.
</p>
<p>
<code class="classname">db_vector</code> also contains
methods inherited from
<code class="classname">std::list</code> and
<code class="classname">std::deque</code>, including
<code class="classname">std::list<>'s</code>
unique methods <code class="methodname">remove()</code>,
<code class="methodname">remove_if()</code>,
<code class="methodname">unique()</code>,
<code class="methodname">merge()</code>,
<code class="methodname">sort()</code>,
<code class="methodname">reverse()</code>, and
<code class="methodname">splice()</code>. These use
the identical semantics/behaviors of the
<code class="classname">std::list<></code>
methods, although pushing/deleting at the head is
slower than the
<code class="methodname">std::deque</code> and
<code class="methodname">std::list</code> equivalent
when there are quite a lot of elements in the
database.
</p>
</li>
<li>
<p>
You can use <code class="classname">std::queue</code>,
<code class="classname">std::priority_queue</code> and
<code class="classname">std::stack</code> container
adapters with <code class="classname">db_vector</code>;
they work with db_vector even without
<a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_RENUMBER" class="olink">DB_RENUMBER</a> set.
</p>
</li>
</ul>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp948648"></a>Associative container specific notes</h3>
</div>
</div>
</div>
<p>
<code class="classname">db_map</code> contains the union of method
set from <code class="classname">std::map</code> and
<code class="classname">hash_map</code>, but there are some
methods that can only be called on containers backed by
<code class="literal">DB_BTREE</code> or
<code class="literal">DB_HASH</code> databases. You can call
<code class="function">db_map<>::is_hash()</code> to
figure out the type of the backing database. If you call
unsupported methods then an InvalidFunctionCall exception
is thrown.
</p>
<p>
These are the <code class="literal">DB_BTREE</code> specific
methods: <code class="methodname">upper_bound()</code>,
<code class="methodname">lower_bound()</code>,
<code class="methodname">key_comp()</code>, and
<code class="methodname">value_comp()</code>. The
<code class="literal">DB_HASH</code> specific methods are
<code class="methodname">key_eq()</code>,
<code class="methodname">hash_funct()</code>.
</p>
</div>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="stl_persistence.html">Prev</a> </td>
<td width="20%" align="center">
<a accesskey="u" href="stl.html">Up</a>
</td>
<td width="40%" align="right"> <a accesskey="n" href="stl_efficienct_use.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">Dbstl persistence </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> Using dbstl
efficiently</td>
</tr>
</table>
</div>
</body>
</html>
|
