<?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_nelem()</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_hash.html" title="Db::set_h_hash()" /> <link rel="next" href="dbset_lorder.html" title="Db::set_lorder()" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Db::set_h_nelem()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="dbset_h_hash.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_lorder.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_nelem"></a>Db::set_h_nelem()</h2> </div> </div> </div> <pre class="programlisting">#include <db_cxx.h> int Db::set_h_nelem(u_int32_t h_nelem); </pre> <p> Set an estimate of the final size of the hash table. </p> <p> In order for the estimate to be used when creating the database, the <a class="xref" href="dbset_h_ffactor.html" title="Db::set_h_ffactor()">Db::set_h_ffactor()</a> method must also be called. If the estimate or fill factor are not set or are set too low, hash tables will still expand gracefully as keys are entered, although a slight performance degradation may be noticed. </p> <p> The <code class="methodname">Db::set_h_nelem()</code> method configures a database, not only operations performed using the specified <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> handle. </p> <p> The <code class="methodname">Db::set_h_nelem()</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_nelem()</code> will be ignored. </p> <p> The <code class="methodname">Db::set_h_nelem()</code> <span> <span> method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success. </span> </span> </p> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1648610"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id1648782"></a>h_nelem</h4> </div> </div> </div> <p> The <span class="bold"><strong>h_nelem</strong></span> parameter is an estimate of the final size of the hash table. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1648758"></a>Errors</h3> </div> </div> </div> <p> The <code class="methodname">Db::set_h_nelem()</code> <span> <span> method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a> exception, encapsulating one of the following non-zero errors, or 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="id1648871"></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="id1647124"></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="id1648447"></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_hash.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_lorder.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Db::set_h_hash() </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Db::set_lorder()</td> </tr> </table> </div> </body> </html>