<?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_dup_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_create_dir.html" title="DB->set_create_dir()" /> <link rel="next" href="dbset_encrypt.html" title="DB->set_encrypt()" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">DB->set_dup_compare()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="dbset_create_dir.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_encrypt.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_dup_compare"></a>DB->set_dup_compare()</h2> </div> </div> </div> <pre class="programlisting">#include <db.h> int DB->set_dup_compare(DB *db, int (*dup_compare_fcn)(DB *db, const DBT *dbt, const DBT *dbt2)); </pre> <p> Set the duplicate data item comparison function. The comparison function is called whenever it is necessary to compare a data item specified by the application with a data item currently stored in the database. Calling <code class="methodname">DB->set_dup_compare()</code> implies calling <a class="xref" href="dbset_flags.html" title="DB->set_flags()">DB->set_flags()</a> with the <a class="link" href="dbset_flags.html#dbset_flags_DB_DUPSORT">DB_DUPSORT</a> flag. </p> <p> If no comparison function is specified, the data items are compared lexically, with shorter data items collating before longer data items. </p> <p> The <code class="methodname">DB->set_dup_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_dup_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_dup_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="id1644878"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id1644937"></a>dup_compare_fcn</h4> </div> </div> </div> <p> The <span class="bold"><strong>dup_compare_fcn</strong></span> function is the application-specified duplicate data item comparison function. The function takes three arguments: </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 a <a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> representing the application supplied data item. </p> </li> <li> <p> <code class="literal">dbt2</code> </p> <p> The <span class="bold"><strong>dbt2</strong></span> parameter is a <a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> representing the current tree's data item. </p> </li> </ul> </div> <p> The <span class="bold"><strong>dup_compare_fcn</strong></span> function must return an integer value less than, equal to, or greater than zero if the first data item parameter is considered to be respectively less than, equal to, or greater than the second data item parameter. In addition, the comparison function must cause the data items in the set to be <span class="emphasis"><em>well-ordered</em></span>. The comparison function must correctly handle any data item values used by the application (possibly including zero-length data items). 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 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="id1645136"></a>Errors</h3> </div> </div> </div> <p> The <code class="methodname">DB->set_dup_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="id1645069"></a>EINVAL</h4> </div> </div> </div> <p> 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="id1645070"></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="id1645144"></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_create_dir.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_encrypt.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">DB->set_create_dir() </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> DB->set_encrypt()</td> </tr> </table> </div> </body> </html>