mirror of
https://github.com/berkeleydb/libdb.git
synced 2024-11-16 09:06:25 +00:00
111 lines
5.2 KiB
HTML
111 lines
5.2 KiB
HTML
<?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>Tcl error handling</title>
|
||
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
|
||
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
|
||
<link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
|
||
<link rel="up" href="tcl.html" title="Chapter 21. Berkeley DB Extensions: Tcl" />
|
||
<link rel="prev" href="tcl_program.html" title="Tcl API programming notes" />
|
||
<link rel="next" href="tcl_faq.html" title="Tcl FAQ" />
|
||
</head>
|
||
<body>
|
||
<div xmlns="" class="navheader">
|
||
<div class="libver">
|
||
<p>Library Version 11.2.5.3</p>
|
||
</div>
|
||
<table width="100%" summary="Navigation header">
|
||
<tr>
|
||
<th colspan="3" align="center">Tcl error handling</th>
|
||
</tr>
|
||
<tr>
|
||
<td width="20%" align="left"><a accesskey="p" href="tcl_program.html">Prev</a> </td>
|
||
<th width="60%" align="center">Chapter 21.
|
||
Berkeley DB Extensions: Tcl
|
||
</th>
|
||
<td width="20%" align="right"> <a accesskey="n" href="tcl_faq.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="tcl_error"></a>Tcl error handling</h2>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>The Tcl interfaces to Berkeley DB generally return TCL_OK on success and throw
|
||
a Tcl error on failure, using the appropriate Tcl interfaces to provide
|
||
the user with an informative error message. There are some "expected"
|
||
failures, however, for which no Tcl error will be thrown and for which
|
||
Tcl commands will return TCL_OK. These failures include times when a
|
||
searched-for key is not found, a requested key/data pair was previously
|
||
deleted, or a key/data pair cannot be written because the key already
|
||
exists.</p>
|
||
<p>These failures can be detected by searching the Berkeley DB error message that
|
||
is returned. For example, use the following to detect that an attempt
|
||
to put a record into the database failed because the key already
|
||
existed:</p>
|
||
<pre class="programlisting">% berkdb open -create -btree a.db
|
||
db0
|
||
% db0 put dog cat
|
||
0
|
||
% set ret [db0 put -nooverwrite dog newcat]
|
||
DB_KEYEXIST: Key/data pair already exists
|
||
% if { [string first DB_KEYEXIST $ret] != -1 } {
|
||
puts "This was an error; the key existed"
|
||
}
|
||
This was an error; the key existed
|
||
% db0 close
|
||
0
|
||
% exit</pre>
|
||
<p>To simplify parsing, it is recommended that the initial Berkeley DB error name
|
||
be checked; for example, <a href="../api_reference/C/dbcput.html#dbcput_DB_KEYEXIST" class="olink">DB_MULTIPLE</a> in the previous example.
|
||
To ensure that Tcl scripts are not broken by upgrading to new releases
|
||
of Berkeley DB, these values will not change in future releases of Berkeley DB.
|
||
There are currently only three such "expected" error returns:</p>
|
||
<pre class="programlisting">DB_NOTFOUND: No matching key/data pair found
|
||
DB_KEYEMPTY: Nonexistent key/data pair
|
||
DB_KEYEXIST: Key/data pair already exists</pre>
|
||
<p>Finally, sometimes Berkeley DB will output additional error information when
|
||
a Berkeley DB error occurs. By default, all Berkeley DB error messages will be
|
||
prefixed with the created command in whose context the error occurred
|
||
(for example, "env0", "db2", and so on). There are several ways to
|
||
capture and access this information.</p>
|
||
<p>First, if Berkeley DB invokes the error callback function, the additional
|
||
information will be placed in the error result returned from the command
|
||
and in the errorInfo backtrace variable in Tcl.</p>
|
||
<p>Also, the two calls to open an environment and open a database take an
|
||
option, <span class="bold"><strong>-errfile filename</strong></span>, which sets an output file to which
|
||
these additional error messages should be written.</p>
|
||
<p>Additionally, the two calls to open an environment and open a database
|
||
take an option, <span class="bold"><strong>-errpfx string</strong></span>, which sets the error prefix to
|
||
the given string. This option may be useful in circumstances where a
|
||
more descriptive prefix is desired or where a constant prefix indicating
|
||
an error is desired.</p>
|
||
</div>
|
||
<div class="navfooter">
|
||
<hr />
|
||
<table width="100%" summary="Navigation footer">
|
||
<tr>
|
||
<td width="40%" align="left"><a accesskey="p" href="tcl_program.html">Prev</a> </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="u" href="tcl.html">Up</a>
|
||
</td>
|
||
<td width="40%" align="right"> <a accesskey="n" href="tcl_faq.html">Next</a></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="40%" align="left" valign="top">Tcl API programming notes </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="h" href="index.html">Home</a>
|
||
</td>
|
||
<td width="40%" align="right" valign="top"> Tcl FAQ</td>
|
||
</tr>
|
||
</table>
|
||
</div>
|
||
</body>
|
||
</html>
|