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Import BSDDB 4.7.25 (as of svn r89086)

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Zachary Ware
2017-09-04 13:40:25 -05:00
parent 4b29e0458f
commit 8f590873d0
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Transactional Cursors</title>
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
<meta name="generator" content="DocBook XSL Stylesheets V1.62.4" />
<link rel="home" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
<link rel="up" href="usingtxns.html" title="Chapter 3. Transaction Basics" />
<link rel="previous" href="nestedtxn.html" title="Nested Transactions" />
<link rel="next" href="txnindices.html" title="Secondary Indices with Transaction Applications" />
</head>
<body>
<div class="navheader">
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Transactional Cursors</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a> </td>
<th width="60%" align="center">Chapter 3. Transaction Basics</th>
<td width="20%" align="right"> <a accesskey="n" href="txnindices.html">Next</a></td>
</tr>
</table>
<hr />
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="txncursor"></a>Transactional Cursors</h2>
</div>
</div>
<div></div>
</div>
<p>
You can transaction-protect your cursor operations by
specifying a transaction handle at the time that you create
your cursor. Beyond that, you do not ever
provide a transaction handle directly to a cursor method.
</p>
<p>
Note that if you transaction-protect a cursor, then you must
make sure that the cursor is closed before you either commit or
abort the transaction. For example:
</p>
<pre class="programlisting">#include "db_cxx.h"
...
int main(void)
{
// Environment and database opens omitted
...
DbTxn *txn = NULL;
Dbc *cursorp = NULL;
try {
Dbt key, data;
key.set_data(keystr);
key.set_size((strlen(keystr) + 1) * sizeof(char));
key.set_data(datastr);
key.set_size((strlen(datastr) + 1) * sizeof(char));
DbTxn *txn = NULL;
myEnv.txn_begin(NULL, &amp;txn, 0);
try {
// Get our cursor. Note that we pass the transaction handle here.
db.cursor(txn, &amp;cursorp, 0);
// Perform our operations. Note that we do not pass a transaction
// handle here.
char *replacementString = "new string";
while (cursor-&gt;get(&amp;key, &amp;data, DB_NEXT) == 0) {
data.set_data(void *)replacementString);
data.set_size((strlen(replacementString) + 1) * sizeof(char));
cursor-&gt;put(&amp;key, &amp;data, DB_CURRENT);
}
// We're done. Commit the transaction.
cursor-&gt;close();
txn-&gt;commit(0);
} catch (DbException &amp;e) {
std::cerr &lt;&lt; "Error in transaction: "
&lt;&lt; e.what() &lt;&lt; std::endl;
cursor-&gt;close();
txn-&gt;abort();
}
} catch(DbException &amp;e) {
std::cerr &lt;&lt; "Error opening database and environment: "
&lt;&lt; file_name &lt;&lt; ", "
&lt;&lt; envHome &lt;&lt; std::endl;
std::cerr &lt;&lt; e.what() &lt;&lt; std::endl;
}
return (EXIT_SUCCESS);
} </pre>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a> </td>
<td width="20%" align="center">
<a accesskey="u" href="usingtxns.html">Up</a>
</td>
<td width="40%" align="right"> <a accesskey="n" href="txnindices.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">Nested Transactions </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> Secondary Indices with Transaction Applications</td>
</tr>
</table>
</div>
</body>
</html>