<?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_h_hash()</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_h_ffactor.html" title="DB->set_h_ffactor()" /> <link rel="next" href="dbset_h_nelem.html" title="DB->set_h_nelem()" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">DB->set_h_hash()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="dbset_h_ffactor.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_h_nelem.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_h_hash"></a>DB->set_h_hash()</h2> </div> </div> </div> <pre class="programlisting">#include <db.h> int DB->set_h_hash(DB *db, u_int32_t (*h_hash_fcn)(DB *dbp, const void *bytes, u_int32_t length)); </pre> <p> Set a user-defined hash function; if no hash function is specified, a default hash function is used. Because no hash function performs equally well on all possible data, the user may find that the built-in hash function performs poorly with a particular data set. </p> <p> The <code class="methodname">DB->set_h_hash()</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_h_hash()</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_h_hash()</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_h_hash()</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="id1647806"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id1647748"></a>h_hash_fcn</h4> </div> </div> </div> <p> The <span class="bold"><strong>h_hash_fcn</strong></span> parameter is the application-specified hash function. </p> <p> Application-specified hash functions take a pointer to a byte string and a length as parameters, and return a value of type <span class="bold"><strong>u_int32_t</strong></span>. The hash function must handle any key values used by the application (possibly including zero-length keys). </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1648010"></a>Errors</h3> </div> </div> </div> <p> The <code class="methodname">DB->set_h_hash()</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="id1647923"></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="id1648002"></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="id1647889"></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_h_ffactor.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_h_nelem.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">DB->set_h_ffactor() </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> DB->set_h_nelem()</td> </tr> </table> </div> </body> </html>