220 lines
8.2 KiB
HTML
220 lines
8.2 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Putting Records Using Cursors</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.62.4" />
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<link rel="home" href="index.html" title="Getting Started with Berkeley DB" />
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<link rel="up" href="Cursors.html" title="Chapter 4. Using Cursors" />
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<link rel="previous" href="Positioning.html" title="Getting Records Using the Cursor" />
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<link rel="next" href="DeleteEntryWCursor.html" title="Deleting Records Using Cursors" />
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</head>
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<body>
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<div class="navheader">
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Putting Records Using Cursors</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="Positioning.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 4. Using Cursors</th>
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<td width="20%" align="right"> <a accesskey="n" href="DeleteEntryWCursor.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="PutEntryWCursor"></a>Putting Records Using Cursors</h2>
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</div>
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</div>
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<div></div>
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</div>
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<p>
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You can use cursors to put records into the database. DB's behavior
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when putting records into the database differs depending on the flags
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that you use when writing the record, on the access method that you are
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using, and on whether your database supports sorted duplicates.
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</p>
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<p>
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Note that when putting records to the database using a cursor, the
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cursor is positioned at the record you inserted.
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</p>
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<p>
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You use
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<tt class="methodname">Dbc::put()</tt>
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to put (write) records to the database. You can use the following flags
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with this method:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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<tt class="literal">DB_NODUPDATA</tt>
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</p>
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<p>
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If the provided key already exists
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in the database, then this method returns
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<tt class="literal">DB_KEYEXIST</tt>.
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</p>
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<p>
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If the key does not exist, then the order that the record is put into the database
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is determined by the
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<span>
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insertion order in use by the database. If a comparison
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function has been provided to the database, the record is
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inserted in its sorted location. Otherwise (assuming BTree),
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lexicographical sorting is used, with
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shorter items collating before longer items.
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</span>
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</p>
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<p>
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This flag can only be used for the BTree and Hash access methods,
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and only if the database has been configured to support sorted
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duplicate data items (<tt class="literal">DB_DUPSORT</tt> was specified at
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database creation time).
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</p>
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<p>
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This flag cannot be used with the Queue or Recno access methods.
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</p>
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<p>
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For more information on duplicate records, see
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<a href="btree.html#duplicateRecords">Allowing Duplicate Records</a>.
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</p>
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</li>
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<li>
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<p>
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<tt class="literal">DB_KEYFIRST</tt>
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</p>
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<p>
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For databases that do not support duplicates, this method behaves
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<span>
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exactly the same as if a default insertion was performed.
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</span>
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If the database supports duplicate records,
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<span>
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and a duplicate sort function has been specified, the
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inserted data item is added in its sorted location. If
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the key already exists in the database and no duplicate
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sort function has been specified, the inserted data item
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is added as the first of the data items for that key.
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</span>
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</p>
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</li>
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<li>
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<p>
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<tt class="literal">DB_KEYLAST</tt>
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</p>
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<p>
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Behaves exactly as if
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<tt class="literal">DB_KEYFIRST</tt>
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was used, except that if the key already exists in the database and no
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duplicate sort function has been specified, the
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inserted data item is added as the last of the data
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items for that key.
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</p>
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</li>
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</ul>
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</div>
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<p>For example:</p>
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<a id="cxx_cursor7"></a>
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<pre class="programlisting">#include <db_cxx.h>
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#include <string.h>
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...
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char *key1str = "My first string";
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char *data1str = "My first data";
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char *key2str = "A second string";
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char *data2str = "My second data";
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char *data3str = "My third data";
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Db my_database(NULL, 0);
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Dbc *cursorp;
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try {
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// Set up our DBTs
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Dbt key1(key1str, strlen(key1str) + 1);
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Dbt data1(data1str, strlen(data1str) + 1);
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Dbt key2(key2str, strlen(key2str) + 1);
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Dbt data2(data2str, strlen(data2str) + 1);
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Dbt data3(data3str, strlen(data3str) + 1);
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// Database open omitted
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// Get the cursor
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my_database.cursor(NULL, &cursorp, 0);
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// Assuming an empty database, this first put places
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// "My first string"/"My first data" in the first
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// position in the database
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int ret = cursorp->put(&key1, &data1, DB_KEYFIRST);
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// This put places "A second string"/"My second data" in the
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// the database according to its key sorts against the key
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// used for the currently existing database record. Most likely
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// this record would appear first in the database.
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ret = cursorp->put(&key2, &data2,
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DB_KEYFIRST); /* Added according to sort order */
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// If duplicates are not allowed, the currently existing record that
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// uses "key2" is overwritten with the data provided on this put.
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// That is, the record "A second string"/"My second data" becomes
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// "A second string"/"My third data"
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//
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// If duplicates are allowed, then "My third data" is placed in the
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// duplicates list according to how it sorts against "My second data".
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ret = cursorp->put(&key2, &data3,
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DB_KEYFIRST); // If duplicates are not allowed, record
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// is overwritten with new data. Otherwise,
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// the record is added to the beginning of
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// the duplicates list.
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} catch(DbException &e) {
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my_database.err(e.get_errno(), "Error!");
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} catch(std::exception &e) {
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my_database.errx("Error! %s", e.what());
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}
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// Cursors must be closed
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if (cursorp != NULL)
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cursorp->close();
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my_database.close(0);</pre>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="Positioning.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="Cursors.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="DeleteEntryWCursor.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Getting Records Using the Cursor </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Deleting Records Using Cursors</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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