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<title>Berkeley DB Reference Guide: Error support</title>
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<td><dl><dt>Berkeley DB Reference Guide:<dd>Environment</dl></td>
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Error support
Berkeley DB offers programmatic support for displaying error return values.
The <a href="../../api_c/env_strerror.html">db_strerror</a> function returns a pointer to the error
message corresponding to any Berkeley DB error return. This is similar to the
ANSI C strerror interface, but can handle both system error returns and
Berkeley DB-specific return values.
For example:
<blockquote><pre>int ret;
if ((ret = dbenv-&gt;set_cachesize(dbenv, 0, 32 * 1024, 1)) != 0) {
	fprintf(stderr, "set_cachesize failed: %s\n", db_strerror(ret));
	return (1);
}</pre></blockquote>
There are also two additional error methods: <a href="../../api_c/env_err.html">DB_ENV-&gt;err</a> and
<a href="../../api_c/env_err.html">DB_ENV-&gt;errx</a>. These methods work like the ANSI C printf function,
taking a printf-style format string and argument list, and writing a
message constructed from the format string and arguments.
The <a href="../../api_c/env_err.html">DB_ENV-&gt;err</a> function appends the standard error string to the
constructed message; the <a href="../../api_c/env_err.html">DB_ENV-&gt;errx</a> function does not.
Error messages can be configured always to include a prefix (for
example, the program name) using the <a href="../../api_c/env_set_errpfx.html">DB_ENV-&gt;set_errpfx</a> method.
These functions provide simpler ways of displaying Berkeley DB error messages:
<blockquote><pre>int ret;
dbenv-&gt;set_errpfx(dbenv, program_name);
if ((ret = dbenv-&gt;open(dbenv, home,
 DB_CREATE | DB_INIT_LOG | DB_INIT_TXN | DB_USE_ENVIRON, 0))
 != 0) {
	dbenv-&gt;err(dbenv, ret, "open: %s", home);
	dbenv-&gt;errx(dbenv,
	 "contact your system administrator: session ID was %d",
	 session_id);
	return (1);
}</pre></blockquote>
For example, if the program was called "my_app", and it tried to open
an environment home directory in "/tmp/home" and the open call returned
a permission error, the error messages shown would look like this:
<blockquote><pre>my_app: open: /tmp/home: Permission denied.
my_app: contact your system administrator: session ID was 2</pre></blockquote>
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