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
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
|
<?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>DB->set_bt_compare()</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 API Reference" />
<link rel="up" href="db.html" title="Chapter 2. The DB Handle" />
<link rel="prev" href="dbset_append_recno.html" title="DB->set_append_recno()" />
<link rel="next" href="dbset_bt_compress.html" title="DB->set_bt_compress()" />
</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">DB->set_bt_compare()</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="dbset_append_recno.html">Prev</a> </td>
<th width="60%" align="center">Chapter 2.
The DB Handle
</th>
<td width="20%" align="right"> <a accesskey="n" href="dbset_bt_compress.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="dbset_bt_compare"></a>DB->set_bt_compare()</h2>
</div>
</div>
</div>
<pre class="programlisting">#include <db.h>
int
DB->set_bt_compare(DB *db, int (*bt_compare_fcn)(DB *db,
const DBT *dbt1, const DBT *dbt2, size_t *locp)); </pre>
<p>
Set the Btree key comparison function. The comparison function is
called whenever it is necessary to compare a key specified by the
application with a key currently stored in the tree.
</p>
<p>
If no comparison function is specified, the keys are compared
lexically, with shorter keys collating before longer keys.
</p>
<p>
The <code class="methodname">DB->set_bt_compare()</code> method configures operations performed using
the specified <a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a> handle,
not all operations performed on the underlying database.
</p>
<p>
The <code class="methodname">DB->set_bt_compare()</code> method may not be called after the
<a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> method is called. If
the database already exists when <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a>
is called, the information specified to <code class="methodname">DB->set_bt_compare()</code> must be the same as
that historically used to create the database or corruption can occur.
</p>
<p>
The <code class="methodname">DB->set_bt_compare()</code> <span>
<span>
method returns a non-zero error value on failure and 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm7888584"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idm4000632"></a>bt_compare_fcn</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>bt_compare_fcn</strong></span> function is the
application-specified Btree comparison function. The comparison
function takes four parameters:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="literal">db</code>
</p>
<p>
The <span class="bold"><strong>db</strong></span> parameter is the enclosing
database handle.
</p>
</li>
<li>
<p>
<code class="literal">dbt1</code>
</p>
<p>
The <span class="bold"><strong>dbt1</strong></span> parameter is the
<a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> representing the application
supplied key.
</p>
</li>
<li>
<p>
<code class="literal">dbt2</code>
</p>
<p>
The <span class="bold"><strong>dbt2</strong></span> parameter is the
<a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> representing the current
tree's key.
</p>
</li>
<li>
<p>
<code class="literal">locp</code>
</p>
<p>
The <span class="bold"><strong>locp</strong></span> parameter is currently
unused, and must be set to NULL or corruption can occur.
</p>
</li>
</ul>
</div>
<p>
The <span class="bold"><strong>bt_compare_fcn</strong></span> function must return an
integer value less than, equal to, or greater than zero if the first key
parameter is considered to be respectively less than, equal to, or greater than
the second key parameter. In addition, the comparison function must cause the
keys in the database to be <span class="emphasis"><em>well-ordered</em></span>. The comparison
function must correctly handle any key values used by the application (possibly
including zero-length keys). In addition, when Btree key prefix comparison is
being performed (see
<a class="xref" href="dbset_bt_prefix.html" title="DB->set_bt_prefix()">DB->set_bt_prefix()</a>
for more information), the comparison routine may be passed a prefix of any database
key. The <span class="bold"><strong>data</strong></span> and <span class="bold"><strong>size</strong></span>
fields of the <a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> are the only fields
that may be used for the purposes of this comparison, and no particular
alignment of the memory to which by the <span class="bold"><strong>data</strong></span>
field refers may be assumed.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm2282848"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DB->set_bt_compare()</code> <span>
<span>
method may fail and return one of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idm1666048"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
If the method was called after <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a>
was called; or if an invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm2168672"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm4439112"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a>
</p>
</div>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="dbset_append_recno.html">Prev</a> </td>
<td width="20%" align="center">
<a accesskey="u" href="db.html">Up</a>
</td>
<td width="40%" align="right"> <a accesskey="n" href="dbset_bt_compress.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">DB->set_append_recno() </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> DB->set_bt_compress()</td>
</tr>
</table>
</div>
</body>
</html>
|
