96 lines
4.5 KiB
HTML
96 lines
4.5 KiB
HTML
<!--$Id: db_set_bt_compare.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<!--See the file LICENSE for redistribution information.-->
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<html>
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<head>
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<title>Berkeley DB: Db::set_bt_compare</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
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</head>
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<body bgcolor=white>
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<table width="100%"><tr valign=top>
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<td>
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<b>Db::set_bt_compare</b>
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</td>
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<td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db_cxx.h>
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<p>
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extern "C" {
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typedef int (*bt_compare_fcn_type)(DB *db, const DBT *dbt1, const DBT *dbt2);
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};
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int
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Db::set_bt_compare(bt_compare_fcn_type bt_compare_fcn);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: Db::set_bt_compare</b>
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<p>Set the Btree key comparison function. The comparison function is
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called whenever it is necessary to compare a key specified by the
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application with a key currently stored in the tree.</p>
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<p>If no comparison function is specified, the keys are compared lexically,
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with shorter keys collating before longer keys.</p>
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<p>The Db::set_bt_compare method configures operations performed using the specified
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<a href="../api_cxx/db_class.html">Db</a> handle, not all operations performed on the underlying
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database.</p>
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<p>The Db::set_bt_compare method may not be called after the <a href="../api_cxx/db_open.html">Db::open</a> method is called.
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If the database already exists when
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<a href="../api_cxx/db_open.html">Db::open</a> is called, the information specified to Db::set_bt_compare must
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be the same as that historically used to create the database or
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corruption can occur.</p>
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<p>The Db::set_bt_compare method
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either returns a non-zero error value
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or throws an exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>bt_compare_fcn</b><ul compact><li>The <b>bt_compare_fcn</b> function is the application-specified Btree
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comparison function. The comparison function takes three parameters:
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<br>
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<b><b>db</b></b><ul compact><li>The <b>db</b> parameter is the enclosing database handle.</ul>
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<b><b>dbt1</b></b><ul compact><li>The <b>dbt1</b> parameter is the <a href="../api_cxx/dbt_class.html">Dbt</a> representing the
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application supplied key.</ul>
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<b><b>dbt2</b></b><ul compact><li>The <b>dbt2</b> parameter is the <a href="../api_cxx/dbt_class.html">Dbt</a> representing the
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current tree's key.</ul>
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<br></ul>
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<p>The <b>bt_compare_fcn</b> function must return an integer value less
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than, equal to, or greater than zero if the first key parameter is
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considered to be respectively less than, equal to, or greater than the
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second key parameter. In addition, the comparison function must cause
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the keys in the database to be <i>well-ordered</i>. The comparison
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function must correctly handle any key values used by the application
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(possibly including zero-length keys). In addition, when Btree key
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prefix comparison is being performed (see <a href="../api_cxx/db_set_bt_prefix.html">Db::set_bt_prefix</a> for
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more information), the comparison routine may be passed a prefix of any
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database key. The <b>data</b> and <b>size</b> fields of the
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<a href="../api_cxx/dbt_class.html">Dbt</a> are the only fields that may be used for the purposes of
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this comparison, and no particular alignment of the memory to which by
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the <b>data</b> field refers may be assumed.</p>
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<br>
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<br><b>Errors</b>
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<p>The Db::set_bt_compare method
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may fail and throw
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<a href="../api_cxx/except_class.html">DbException</a>,
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encapsulating one of the following non-zero errors, or return one of
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the following non-zero errors:</p>
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<br>
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<b>EINVAL</b><ul compact><li>If the method was called after <a href="../api_cxx/db_open.html">Db::open</a> was called; or if an
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invalid flag value or parameter was specified.</ul>
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<br>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_cxx/db_class.html">Db</a>
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<br><b>See Also</b>
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<a href="../api_cxx/db_list.html">Databases and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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</body>
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</html>
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