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.h> 39 40int 41DB->set_dup_compare(DB *db, 42 int (*dup_compare_fcn)(DB *db, const DBT *dbt, const DBT *dbt2)); </pre> 43 <p> 44 Set the duplicate data item comparison function. The comparison 45 function is called whenever it is necessary to compare a data item 46 specified by the application with a data item currently stored in the 47 database. Calling <code class="methodname">DB->set_dup_compare()</code> implies calling 48 <a class="xref" href="dbset_flags.html" title="DB->set_flags()">DB->set_flags()</a> with the 49 <a class="link" href="dbset_flags.html#dbset_flags_DB_DUPSORT">DB_DUPSORT</a> 50 flag. 51 </p> 52 <p> 53 If no comparison function is specified, the data items are compared 54 lexically, with shorter data items collating before longer data items. 55 </p> 56 <p> 57 The <code class="methodname">DB->set_dup_compare()</code> method may not be called after the 58 <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> method is called. If 59 the database already exists when <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> 60 is called, the information specified to <code class="methodname">DB->set_dup_compare()</code> must be the same as 61 that historically used to create the database or corruption can occur. 62 </p> 63 <p> 64 The <code class="methodname">DB->set_dup_compare()</code> <span> 65 <span> 66 method returns a non-zero error value on failure and 0 on success. 67 </span> 68 69 </span> 70 </p> 71 <div class="sect2" lang="en" xml:lang="en"> 72 <div class="titlepage"> 73 <div> 74 <div> 75 <h3 class="title"><a id="id1644878"></a>Parameters</h3> 76 </div> 77 </div> 78 </div> 79 <div class="sect3" lang="en" xml:lang="en"> 80 <div class="titlepage"> 81 <div> 82 <div> 83 <h4 class="title"><a id="id1644937"></a>dup_compare_fcn</h4> 84 </div> 85 </div> 86 </div> 87 <p> 88 The <span class="bold"><strong>dup_compare_fcn</strong></span> function is the 89 application-specified duplicate data item comparison function. The 90 function takes three arguments: 91 </p> 92 <div class="itemizedlist"> 93 <ul type="disc"> 94 <li> 95 <p> 96 <code class="literal">db</code> 97 </p> 98 <p> 99 The <span class="bold"><strong>db</strong></span> parameter is the enclosing 100 database handle. 101 </p> 102 </li> 103 <li> 104 <p> 105 <code class="literal">dbt1</code> 106 </p> 107 <p> 108 The <span class="bold"><strong>dbt1</strong></span> parameter is a 109 <a class="link" href="dbt.html" title="Chapter��4.�� The DBT Handle">DBT</a> representing the application 110 supplied data item. 111 </p> 112 </li> 113 <li> 114 <p> 115 <code class="literal">dbt2</code> 116 </p> 117 <p> 118 The <span class="bold"><strong>dbt2</strong></span> parameter is a 119 <a class="link" href="dbt.html" title="Chapter��4.�� The DBT Handle">DBT</a> representing the current 120 tree's data item. 121 </p> 122 </li> 123 </ul> 124 </div> 125 <p> 126 The <span class="bold"><strong>dup_compare_fcn</strong></span> function must return an 127 integer value less than, equal to, or greater than zero if the first data item 128 parameter is considered to be respectively less than, equal to, or greater than 129 the second data item parameter. In addition, the comparison function must cause 130 the data items in the set to be <span class="emphasis"><em>well-ordered</em></span>. The 131 comparison function must correctly handle any data item values used by the 132 application (possibly including zero-length data items). The 133 <span class="bold"><strong>data</strong></span> and <span class="bold"><strong>size</strong></span> 134 fields of the <a class="link" href="dbt.html" title="Chapter��4.�� The DBT Handle">DBT</a> are the only fields 135 that may be used for the purposes of this comparison, and no particular 136 alignment of the memory to which the <span class="bold"><strong>data</strong></span> field 137 refers may be assumed. 138 </p> 139 </div> 140 </div> 141 <div class="sect2" lang="en" xml:lang="en"> 142 <div class="titlepage"> 143 <div> 144 <div> 145 <h3 class="title"><a id="id1645136"></a>Errors</h3> 146 </div> 147 </div> 148 </div> 149 <p> 150 The <code class="methodname">DB->set_dup_compare()</code> <span> 151 <span> 152 method may fail and return one of the following non-zero errors: 153 </span> 154 155 </span> 156 </p> 157 <div class="sect3" lang="en" xml:lang="en"> 158 <div class="titlepage"> 159 <div> 160 <div> 161 <h4 class="title"><a id="id1645069"></a>EINVAL</h4> 162 </div> 163 </div> 164 </div> 165 <p> 166 An invalid flag value or parameter was specified. 167 </p> 168 </div> 169 </div> 170 <div class="sect2" lang="en" xml:lang="en"> 171 <div class="titlepage"> 172 <div> 173 <div> 174 <h3 class="title"><a id="id1645070"></a>Class</h3> 175 </div> 176 </div> 177 </div> 178 <p> 179 <a class="link" href="db.html" title="Chapter��2.�� The DB Handle">DB</a> 180 </p> 181 </div> 182 <div class="sect2" lang="en" xml:lang="en"> 183 <div class="titlepage"> 184 <div> 185 <div> 186 <h3 class="title"><a id="id1645144"></a>See Also</h3> 187 </div> 188 </div> 189 </div> 190 <p> 191 <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> 192 </p> 193 </div> 194 </div> 195 <div class="navfooter"> 196 <hr /> 197 <table width="100%" summary="Navigation footer"> 198 <tr> 199 <td width="40%" align="left"><a accesskey="p" href="dbset_create_dir.html">Prev</a>��</td> 200 <td width="20%" align="center"> 201 <a accesskey="u" href="db.html">Up</a> 202 </td> 203 <td width="40%" align="right">��<a accesskey="n" href="dbset_encrypt.html">Next</a></td> 204 </tr> 205 <tr> 206 <td width="40%" align="left" valign="top">DB->set_create_dir()��</td> 207 <td width="20%" align="center"> 208 <a accesskey="h" href="index.html">Home</a> 209 </td> 210 <td width="40%" align="right" valign="top">��DB->set_encrypt()</td> 211 </tr> 212 </table> 213 </div> 214 </body> 215</html> 216