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<title>Berkeley DB Reference Guide: Error support</title>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Access Methods</dl></h3></td>
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<h1 align=center>Error support</h1>
<p>Berkeley DB offers programmatic support for displaying error return values.
<p>The <a href="../../api_c/env_strerror.html">db_strerror</a> interface returns a pointer to the error
message corresponding to any Berkeley DB error return, similar to the ANSI C
strerror interface, but is able to handle both system error returns and
Berkeley DB specific return values.
<p>For example:
<p><blockquote><pre>int ret;
if ((ret = dbp->put(dbp, NULL, &key, &data, 0)) != 0) {
fprintf(stderr, "put failed: %s\n", db_strerror(ret));
return (1);
}</pre></blockquote>
<p>There are also two additional error interfaces, <a href="../../api_c/db_err.html">DB->err</a> and
<a href="../../api_c/db_err.html">DB->errx</a>. These interfaces work like the ANSI C X3.159-1989 (ANSI C) printf
interface, taking a printf-style format string and argument list, and
writing a message constructed from the format string and arguments.
<p>The <a href="../../api_c/db_err.html">DB->err</a> method appends the standard error string to the constructed
message; the <a href="../../api_c/db_err.html">DB->errx</a> method does not. These interfaces 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>Error messages can additionally be configured to always include a prefix
(for example, the program name) using the <a href="../../api_c/db_set_errpfx.html">DB->set_errpfx</a> interface.
<p><blockquote><pre>#define DATABASE "access.db"
<p>
int ret;
<p>
(void)dbp->set_errpfx(dbp, program_name);
<p>
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></blockquote>
<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><blockquote><pre>my_app: access.db: Permission denied.
my_app: contact your system administrator: session ID was 14</pre></blockquote>
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