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_h_nelem()</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_h_hash.html" title="Db::set_h_hash()" /> 12 <link rel="next" href="dbset_lorder.html" title="Db::set_lorder()" /> 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_h_nelem()</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="dbset_h_hash.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_lorder.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_h_nelem"></a>Db::set_h_nelem()</h2> 35 </div> 36 </div> 37 </div> 38 <pre class="programlisting">#include <db_cxx.h> 39 40int 41Db::set_h_nelem(u_int32_t h_nelem); </pre> 42 <p> 43 Set an estimate of the final size of the hash table. 44 </p> 45 <p> 46 In order for the estimate to be used when creating the database, the 47 <a class="xref" href="dbset_h_ffactor.html" title="Db::set_h_ffactor()">Db::set_h_ffactor()</a> 48 method must also be called. If the estimate or fill factor are not 49 set or are set too low, hash tables will still expand gracefully as 50 keys are entered, although a slight performance degradation may be 51 noticed. 52 </p> 53 <p> 54 The <code class="methodname">Db::set_h_nelem()</code> method configures a database, not only 55 operations performed using the specified <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> 56 handle. 57 </p> 58 <p> 59 The <code class="methodname">Db::set_h_nelem()</code> method may not be called after the 60 <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> method is called. If 61 the database already exists when <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> 62 is called, the information specified to <code class="methodname">Db::set_h_nelem()</code> will be ignored. 63 </p> 64 <p> 65 The <code class="methodname">Db::set_h_nelem()</code> <span> 66 67 <span> 68 method either returns a non-zero error value or throws an 69 exception that encapsulates a non-zero error value on 70 failure, and returns 0 on success. 71 </span> 72 </span> 73 </p> 74 <div class="sect2" lang="en" xml:lang="en"> 75 <div class="titlepage"> 76 <div> 77 <div> 78 <h3 class="title"><a id="id1648610"></a>Parameters</h3> 79 </div> 80 </div> 81 </div> 82 <div class="sect3" lang="en" xml:lang="en"> 83 <div class="titlepage"> 84 <div> 85 <div> 86 <h4 class="title"><a id="id1648782"></a>h_nelem</h4> 87 </div> 88 </div> 89 </div> 90 <p> 91 The <span class="bold"><strong>h_nelem</strong></span> parameter is an estimate 92 of the final size of the hash table. 93 </p> 94 </div> 95 </div> 96 <div class="sect2" lang="en" xml:lang="en"> 97 <div class="titlepage"> 98 <div> 99 <div> 100 <h3 class="title"><a id="id1648758"></a>Errors</h3> 101 </div> 102 </div> 103 </div> 104 <p> 105 The <code class="methodname">Db::set_h_nelem()</code> <span> 106 107 <span> 108 method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a> 109 exception, encapsulating one of the following non-zero errors, or return one 110 of the following non-zero errors: 111 </span> 112 </span> 113 </p> 114 <div class="sect3" lang="en" xml:lang="en"> 115 <div class="titlepage"> 116 <div> 117 <div> 118 <h4 class="title"><a id="id1648871"></a>EINVAL</h4> 119 </div> 120 </div> 121 </div> 122 <p> 123 If the method was called after <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> 124 was called; or if an invalid flag value or parameter was specified. 125 </p> 126 </div> 127 </div> 128 <div class="sect2" lang="en" xml:lang="en"> 129 <div class="titlepage"> 130 <div> 131 <div> 132 <h3 class="title"><a id="id1647124"></a>Class</h3> 133 </div> 134 </div> 135 </div> 136 <p> 137 <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> 138 </p> 139 </div> 140 <div class="sect2" lang="en" xml:lang="en"> 141 <div class="titlepage"> 142 <div> 143 <div> 144 <h3 class="title"><a id="id1648447"></a>See Also</h3> 145 </div> 146 </div> 147 </div> 148 <p> 149 <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> 150 </p> 151 </div> 152 </div> 153 <div class="navfooter"> 154 <hr /> 155 <table width="100%" summary="Navigation footer"> 156 <tr> 157 <td width="40%" align="left"><a accesskey="p" href="dbset_h_hash.html">Prev</a> </td> 158 <td width="20%" align="center"> 159 <a accesskey="u" href="db.html">Up</a> 160 </td> 161 <td width="40%" align="right"> <a accesskey="n" href="dbset_lorder.html">Next</a></td> 162 </tr> 163 <tr> 164 <td width="40%" align="left" valign="top">Db::set_h_hash() </td> 165 <td width="20%" align="center"> 166 <a accesskey="h" href="index.html">Home</a> 167 </td> 168 <td width="40%" align="right" valign="top"> Db::set_lorder()</td> 169 </tr> 170 </table> 171 </div> 172 </body> 173</html> 174