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<p>Library Version 18.1.40</p>
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<h2 class="title" style="clear: both"><a id="am_misc_error"></a>Error support</h2>
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<p>
Berkeley DB offers programmatic support for displaying error
return values.
</p>
<p>
The <a href="../api_reference/C/envstrerror.html" class="olink">db_strerror()</a> function returns a pointer to the error
message corresponding to any Berkeley DB error return, similar
to the ANSI C strerror function, but is able to handle both
system error returns and Berkeley DB specific return
values.
</p>
<p>
For example:
</p>
<a id="prog_am25"></a>
<pre class="programlisting">int ret;
...
if ((ret = dbp->put(dbp, NULL, &key, &data, 0)) != 0) {
fprintf(stderr, "put failed: %s\n", db_strerror(ret));
return (1);
}</pre>
<p>
There are also two additional error methods, <a href="../api_reference/C/dberr.html" class="olink">DB->err()</a> and
<code class="methodname">DB->errx()</code>. These methods work
like the ANSI C X3.159-1989 (ANSI C) printf function, taking a
printf-style format string and argument list, and writing a
message constructed from the format string and
arguments.
</p>
<p>
The <a href="../api_reference/C/dberr.html" class="olink">DB->err()</a> method appends the standard error string to the
constructed message; the
<code class="methodname">DB->errx()</code> method does not.
These methods provide simpler ways of displaying Berkeley DB
error messages. For example, if your application tracks
session IDs in a variable called session_id, it can include
that information in its error messages:
</p>
<p>
Error messages can additionally be configured to always
include a prefix (for example, the program name) using the
<a href="../api_reference/C/dbset_errpfx.html" class="olink">DB->set_errpfx()</a> method.
</p>
<a id="prog_am26"></a>
<pre class="programlisting">#define DATABASE "access.db"
int ret;
(void)dbp->set_errpfx(dbp, program_name);
if ((ret = dbp->open(dbp,
NULL, DATABASE, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) {
dbp->err(dbp, ret, "%s", DATABASE);
dbp->errx(dbp,
"contact your system administrator: session ID was %d",
session_id);
return (1);
}</pre>
<p>
For example, if the program were called my_app and the open
call returned an EACCESS system error, the error messages
shown would appear as follows:
</p>
<pre class="programlisting">my_app: access.db: Permission denied.
my_app: contact your system administrator: session ID was 14</pre>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
Equivalent methods exist for informational messages. See
<a href="../api_reference/C/dbmsg.html" class="olink">DB->msg()</a> and <a href="../api_reference/C/dbset_msgpfx.html" class="olink">DB->set_msgpfx()</a> for details.
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