88 lines
4.0 KiB
HTML
88 lines
4.0 KiB
HTML
<!--$Id: db_set_dup_compare.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
|
|
<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
|
|
<!--See the file LICENSE for redistribution information.-->
|
|
<html>
|
|
<head>
|
|
<title>Berkeley DB: DB->set_dup_compare</title>
|
|
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
|
|
<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
|
|
</head>
|
|
<body bgcolor=white>
|
|
<table width="100%"><tr valign=top>
|
|
<td>
|
|
<b>DB->set_dup_compare</b>
|
|
</td>
|
|
<td align=right>
|
|
<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></td>
|
|
</tr></table>
|
|
<hr size=1 noshade>
|
|
<tt>
|
|
<b><pre>
|
|
#include <db.h>
|
|
<p>
|
|
int
|
|
DB->set_dup_compare(DB *db,
|
|
int (*dup_compare_fcn)(DB *, const DBT *, const DBT *));
|
|
</pre></b>
|
|
<hr size=1 noshade>
|
|
<b>Description: DB->set_dup_compare</b>
|
|
<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 DB->set_dup_compare implies calling
|
|
<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>
|
|
<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 DB->set_dup_compare method may not be called after the <a href="../api_c/db_open.html">DB->open</a> method is called.
|
|
If the database already exists when
|
|
<a href="../api_c/db_open.html">DB->open</a> is called, the information specified to DB->set_dup_compare must
|
|
be the same as that historically used to create the database or
|
|
corruption can occur.</p>
|
|
<p>The DB->set_dup_compare method
|
|
returns a non-zero error value on failure
|
|
and 0 on success.
|
|
</p>
|
|
<b>Parameters</b> <br>
|
|
<b>dup_compare_fcn</b><ul compact><li>The <b>dup_compare_fcn</b> function is the application-specified
|
|
duplicate data item comparison function. The function takes three
|
|
arguments:
|
|
<br>
|
|
<b><b>db</b></b><ul compact><li>The <b>db</b> parameter is the enclosing database handle.</ul>
|
|
<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
|
|
supplied data item.</ul>
|
|
<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
|
|
tree's data item.</ul>
|
|
<br>
|
|
<p>The <b>dup_compare_fcn</b> 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 <i>well-ordered</i>. The
|
|
comparison function must correctly handle any data item values used by
|
|
the application (possibly including zero-length data items). The
|
|
<b>data</b> and <b>size</b> fields of the <a href="../api_c/dbt_class.html">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 <b>data</b> field
|
|
refers may be assumed.</p></ul>
|
|
<br>
|
|
<br><b>Errors</b>
|
|
<p>The DB->set_dup_compare method
|
|
may fail and return one of the following non-zero errors:</p>
|
|
<br>
|
|
<b>EINVAL</b><ul compact><li>An
|
|
invalid flag value or parameter was specified.</ul>
|
|
<br>
|
|
<hr size=1 noshade>
|
|
<br><b>Class</b>
|
|
<a href="../api_c/db_class.html">DB</a>
|
|
<br><b>See Also</b>
|
|
<a href="../api_c/db_list.html">Databases and Related Methods</a>
|
|
</tt>
|
|
<table width="100%"><tr><td><br></td><td align=right>
|
|
<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>
|
|
</td></tr></table>
|
|
<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
|
|
</body>
|
|
</html>
|