1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Db::set_dup_compare()</title> 7 <link rel="stylesheet" href="apiReference.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Berkeley DB C++ API Reference" /> 10 <link rel="up" href="db.html" title="Chapter 2. The Db Handle" /> 11 <link rel="prev" href="dbset_create_dir.html" title="Db::set_create_dir()" /> 12 <link rel="next" href="dbset_encrypt.html" title="Db::set_encrypt()" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Db::set_dup_compare()</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="dbset_create_dir.html">Prev</a> </td> 22 <th width="60%" align="center">Chapter 2. 23 The Db Handle 24 </th> 25 <td width="20%" align="right"> <a accesskey="n" href="dbset_encrypt.html">Next</a></td> 26 </tr> 27 </table> 28 <hr /> 29 </div> 30 <div class="sect1" lang="en" xml:lang="en"> 31 <div class="titlepage"> 32 <div> 33 <div> 34 <h2 class="title" style="clear: both"><a id="dbset_dup_compare"></a>Db::set_dup_compare()</h2> 35 </div> 36 </div> 37 </div> 38 <pre class="programlisting">#include <db_cxx.h> 39 40extern "C" { 41 typedef int (*dup_compare_fcn_type)(DB *db, const DBT *dbt1, 42 const DBT *dbt2); 43}; 44int 45Db::set_dup_compare(dup_compare_fcn_type dup_compare_fcn);</pre> 46 <p> 47 Set the duplicate data item comparison function. The comparison 48 function is called whenever it is necessary to compare a data item 49 specified by the application with a data item currently stored in the 50 database. Calling <code class="methodname">Db::set_dup_compare()</code> implies calling 51 <a class="xref" href="dbset_flags.html" title="Db::set_flags()">Db::set_flags()</a> with the 52 <a class="link" href="dbset_flags.html#dbset_flags_DB_DUPSORT">DB_DUPSORT</a> 53 flag. 54 </p> 55 <p> 56 If no comparison function is specified, the data items are compared 57 lexically, with shorter data items collating before longer data items. 58 </p> 59 <p> 60 The <code class="methodname">Db::set_dup_compare()</code> method may not be called after the 61 <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> method is called. If 62 the database already exists when <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> 63 is called, the information specified to <code class="methodname">Db::set_dup_compare()</code> must be the same as 64 that historically used to create the database or corruption can occur. 65 </p> 66 <p> 67 The <code class="methodname">Db::set_dup_compare()</code> <span> 68 69 <span> 70 method either returns a non-zero error value or throws an 71 exception that encapsulates a non-zero error value on 72 failure, and returns 0 on success. 73 </span> 74 </span> 75 </p> 76 <div class="sect2" lang="en" xml:lang="en"> 77 <div class="titlepage"> 78 <div> 79 <div> 80 <h3 class="title"><a id="id1645225"></a>Parameters</h3> 81 </div> 82 </div> 83 </div> 84 <div class="sect3" lang="en" xml:lang="en"> 85 <div class="titlepage"> 86 <div> 87 <div> 88 <h4 class="title"><a id="id1645197"></a>dup_compare_fcn</h4> 89 </div> 90 </div> 91 </div> 92 <p> 93 The <span class="bold"><strong>dup_compare_fcn</strong></span> function is the 94 application-specified duplicate data item comparison function. The 95 function takes three arguments: 96 </p> 97 <div class="itemizedlist"> 98 <ul type="disc"> 99 <li> 100 <p> 101 <code class="literal">db</code> 102 </p> 103 <p> 104 The <span class="bold"><strong>db</strong></span> parameter is the enclosing 105 database handle. 106 </p> 107 </li> 108 <li> 109 <p> 110 <code class="literal">dbt1</code> 111 </p> 112 <p> 113 The <span class="bold"><strong>dbt1</strong></span> parameter is a 114 <a class="link" href="dbt.html" title="Chapter 4. The Dbt Handle">Dbt</a> representing the application 115 supplied data item. 116 </p> 117 </li> 118 <li> 119 <p> 120 <code class="literal">dbt2</code> 121 </p> 122 <p> 123 The <span class="bold"><strong>dbt2</strong></span> parameter is a 124 <a class="link" href="dbt.html" title="Chapter 4. The Dbt Handle">Dbt</a> representing the current 125 tree's data item. 126 </p> 127 </li> 128 </ul> 129 </div> 130 <p> 131 The <span class="bold"><strong>dup_compare_fcn</strong></span> function must return an 132 integer value less than, equal to, or greater than zero if the first data item 133 parameter is considered to be respectively less than, equal to, or greater than 134 the second data item parameter. In addition, the comparison function must cause 135 the data items in the set to be <span class="emphasis"><em>well-ordered</em></span>. The 136 comparison function must correctly handle any data item values used by the 137 application (possibly including zero-length data items). The 138 <span class="bold"><strong>data</strong></span> and <span class="bold"><strong>size</strong></span> 139 fields of the <a class="link" href="dbt.html" title="Chapter 4. The Dbt Handle">Dbt</a> are the only fields 140 that may be used for the purposes of this comparison, and no particular 141 alignment of the memory to which the <span class="bold"><strong>data</strong></span> field 142 refers may be assumed. 143 </p> 144 </div> 145 </div> 146 <div class="sect2" lang="en" xml:lang="en"> 147 <div class="titlepage"> 148 <div> 149 <div> 150 <h3 class="title"><a id="id1645452"></a>Errors</h3> 151 </div> 152 </div> 153 </div> 154 <p> 155 The <code class="methodname">Db::set_dup_compare()</code> <span> 156 157 <span> 158 method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a> 159 exception, encapsulating one of the following non-zero errors, or return one 160 of the following non-zero errors: 161 </span> 162 </span> 163 </p> 164 <div class="sect3" lang="en" xml:lang="en"> 165 <div class="titlepage"> 166 <div> 167 <div> 168 <h4 class="title"><a id="id1645363"></a>EINVAL</h4> 169 </div> 170 </div> 171 </div> 172 <p> 173 An invalid flag value or parameter was specified. 174 </p> 175 </div> 176 </div> 177 <div class="sect2" lang="en" xml:lang="en"> 178 <div class="titlepage"> 179 <div> 180 <div> 181 <h3 class="title"><a id="id1645364"></a>Class</h3> 182 </div> 183 </div> 184 </div> 185 <p> 186 <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> 187 </p> 188 </div> 189 <div class="sect2" lang="en" xml:lang="en"> 190 <div class="titlepage"> 191 <div> 192 <div> 193 <h3 class="title"><a id="id1645459"></a>See Also</h3> 194 </div> 195 </div> 196 </div> 197 <p> 198 <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> 199 </p> 200 </div> 201 </div> 202 <div class="navfooter"> 203 <hr /> 204 <table width="100%" summary="Navigation footer"> 205 <tr> 206 <td width="40%" align="left"><a accesskey="p" href="dbset_create_dir.html">Prev</a> </td> 207 <td width="20%" align="center"> 208 <a accesskey="u" href="db.html">Up</a> 209 </td> 210 <td width="40%" align="right"> <a accesskey="n" href="dbset_encrypt.html">Next</a></td> 211 </tr> 212 <tr> 213 <td width="40%" align="left" valign="top">Db::set_create_dir() </td> 214 <td width="20%" align="center"> 215 <a accesskey="h" href="index.html">Home</a> 216 </td> 217 <td width="40%" align="right" valign="top"> Db::set_encrypt()</td> 218 </tr> 219 </table> 220 </div> 221 </body> 222</html> 223