1<!--$Id: db_set_dup_compare.so,v 10.50 2004/08/13 03:38:56 bostic Exp $--> 2<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 3<!--See the file LICENSE for redistribution information.--> 4<html> 5<head> 6<title>Berkeley DB: DB->set_dup_compare</title> 7<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 8<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 9</head> 10<body bgcolor=white> 11<table width="100%"><tr valign=top> 12<td> 13<b>DB->set_dup_compare</b> 14</td> 15<td align=right> 16<a href="/api_c/api_core.html"><img src="/images/api.gif" alt="API"></a> 17<a href="/ref/toc.html"><img src="/images/ref.gif" alt="Ref"></a></td> 18</tr></table> 19<hr size=1 noshade> 20<tt> 21<b><pre> 22#include <db.h> 23<p> 24int 25DB->set_dup_compare(DB *db, 26 int (*dup_compare_fcn)(DB *, const DBT *, const DBT *)); 27</pre></b> 28<hr size=1 noshade> 29<b>Description: DB->set_dup_compare</b> 30<p>Set the duplicate data item comparison function. The comparison 31function is called whenever it is necessary to compare a data item 32specified by the application with a data item currently stored in the 33database. Calling DB->set_dup_compare implies calling 34<a href="/api_c/db_set_flags.html">DB->set_flags</a> with the <a href="/api_c/db_set_flags.html#DB_DUPSORT">DB_DUPSORT</a> flag.</p> 35<p>If no comparison function is specified, the data items are compared 36lexically, with shorter data items collating before longer data items.</p> 37<p>The DB->set_dup_compare method may not be called after the <a href="/api_c/db_open.html">DB->open</a> method is called. 38If the database already exists when 39<a href="/api_c/db_open.html">DB->open</a> is called, the information specified to DB->set_dup_compare must 40be the same as that historically used to create the database or 41corruption can occur.</p> 42<p>The DB->set_dup_compare method 43returns a non-zero error value on failure 44and 0 on success. 45</p> 46<b>Parameters</b> <br> 47 <b>dup_compare_fcn</b><ul compact><li>The <b>dup_compare_fcn</b> function is the application-specified 48duplicate data item comparison function. The function takes three 49arguments: 50<br> 51<b><b>db</b></b><ul compact><li>The <b>db</b> parameter is the enclosing database handle.</ul> 52<b><b>dbt1</b></b><ul compact><li>The <b>dbt1</b> parameter is a <a href="/api_c/dbt_class.html">DBT</a> representing the application 53supplied data item.</ul> 54<b><b>dbt2</b></b><ul compact><li>The <b>dbt2</b> parameter is a <a href="/api_c/dbt_class.html">DBT</a> representing the current 55tree's data item.</ul> 56<br> 57<p>The <b>dup_compare_fcn</b> function must return an integer value less 58than, equal to, or greater than zero if the first data item parameter 59is considered to be respectively less than, equal to, or greater than 60the second data item parameter. In addition, the comparison function 61must cause the data items in the set to be <i>well-ordered</i>. The 62comparison function must correctly handle any data item values used by 63the application (possibly including zero-length data items). The 64<b>data</b> and <b>size</b> fields of the <a href="/api_c/dbt_class.html">DBT</a> are the only 65fields that may be used for the purposes of this comparison, and no 66particular alignment of the memory to which the <b>data</b> field 67refers may be assumed.</p></ul> 68<br> 69<br><b>Errors</b> 70<p>The DB->set_dup_compare method 71may fail and return one of the following non-zero errors:</p> 72<br> 73<b>EINVAL</b><ul compact><li>An 74invalid flag value or parameter was specified.</ul> 75<br> 76<hr size=1 noshade> 77<br><b>Class</b> 78<a href="/api_c/db_class.html">DB</a> 79<br><b>See Also</b> 80<a href="/api_c/db_list.html">Databases and Related Methods</a> 81</tt> 82<table width="100%"><tr><td><br></td><td align=right> 83<a href="/api_c/api_core.html"><img src="/images/api.gif" alt="API"></a><a href="/ref/toc.html"><img src="/images/ref.gif" alt="Ref"></a> 84</td></tr></table> 85<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> 86</body> 87</html> 88
