2011-09-13 17:44:24 +00:00
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Error support</title>
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="am_misc.html" title="Chapter 4. Access Method Wrapup" />
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<link rel="prev" href="am_misc_perm.html" title="Retrieved key/data permanence for C/C++" />
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<link rel="next" href="am_misc_stability.html" title="Cursor stability" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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2012-11-14 21:35:20 +00:00
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<p>Library Version 11.2.5.3</p>
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2011-09-13 17:44:24 +00:00
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Error support</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="am_misc_perm.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 4.
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Access Method Wrapup
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="am_misc_stability.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="am_misc_error"></a>Error support</h2>
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</div>
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</div>
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</div>
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<p>Berkeley DB offers programmatic support for displaying error return values.</p>
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<p>The <a href="../api_reference/C/envstrerror.html" class="olink">db_strerror()</a> function returns a pointer to the error
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message corresponding to any Berkeley DB error return, similar to the ANSI C
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strerror function, but is able to handle both system error returns and
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Berkeley DB specific return values.</p>
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<p>For example:</p>
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<a id="prog_am25"></a>
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<pre class="programlisting">int ret;
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...
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if ((ret = dbp->put(dbp, NULL, &key, &data, 0)) != 0) {
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fprintf(stderr, "put failed: %s\n", db_strerror(ret));
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return (1);
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}</pre>
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<p>There are also two additional error methods, <a href="../api_reference/C/dberr.html" class="olink">DB->err()</a> and
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<code class="methodname">DB->errx()</code>. These methods work like the ANSI C X3.159-1989 (ANSI C) printf
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function, taking a printf-style format string and argument list, and
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writing a message constructed from the format string and arguments.</p>
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<p>The <a href="../api_reference/C/dberr.html" class="olink">DB->err()</a> method appends the standard error string to the
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constructed message; the <code class="methodname">DB->errx()</code> method does not. These methods
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provide simpler ways of displaying Berkeley DB error messages. For example,
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if your application tracks session IDs in a variable called session_id,
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it can include that information in its error messages:</p>
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<p>Error messages can additionally be configured to always include a prefix
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(for example, the program name) using the <a href="../api_reference/C/dbset_errpfx.html" class="olink">DB->set_errpfx()</a> method.</p>
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<a id="prog_am26"></a>
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<pre class="programlisting">#define DATABASE "access.db"
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int ret;
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(void)dbp->set_errpfx(dbp, program_name);
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if ((ret = dbp->open(dbp,
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NULL, DATABASE, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) {
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dbp->err(dbp, ret, "%s", DATABASE);
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dbp->errx(dbp,
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"contact your system administrator: session ID was %d",
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session_id);
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return (1);
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}</pre>
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<p>For example, if the program were called my_app and the open call returned
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an EACCESS system error, the error messages shown would appear as follows:</p>
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<pre class="programlisting">my_app: access.db: Permission denied.
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my_app: contact your system administrator: session ID was 14</pre>
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<td width="40%" align="left"><a accesskey="p" href="am_misc_perm.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="am_misc.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="am_misc_stability.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">Retrieved key/data permanence for C/C++ </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"> Cursor stability</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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