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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>Environment</dl></h3></td>
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<h1 align=center>Error support</h1>
<p>Berkeley DB offers programmatic support for displaying error return values.
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. This is similar to
the ANSI C strerror interface, but can handle both system error returns
and Berkeley DB-specific return values.
<p>For example:
<p><blockquote><pre>int ret;
if ((ret = dbenv->set_cachesize(dbenv, 0, 32 * 1024, 1)) != 0) {
fprintf(stderr, "set_cachesize failed: %s\n", db_strerror(ret));
return (1);
}</pre></blockquote>
<p>There are also two additional error interfaces: <a href="../../api_c/env_err.html">DB_ENV->err</a> and
<a href="../../api_c/env_err.html">DB_ENV->errx</a>. These functions work like the 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/env_err.html">DB_ENV->err</a> function appends the standard error string to the
constructed message; the <a href="../../api_c/env_err.html">DB_ENV->errx</a> function does not.
<p>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->set_errpfx</a>
interface.
<p>These functions provide simpler ways of displaying Berkeley DB error messages:
<p><blockquote><pre>int ret;
dbenv->set_errpfx(dbenv, program_name);
if ((ret = dbenv->open(dbenv, home, NULL,
DB_CREATE | DB_INIT_LOG | DB_INIT_TXN | DB_USE_ENVIRON))
!= 0) {
dbenv->err(dbenv, ret, "open: %s", home);
dbenv->errx(dbenv,
"contact your system administrator: session ID was %d",
session_id);
return (1);
}</pre></blockquote>
<p>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:
<p><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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