Berkeley DB Reference Guide: Environment

Error support

Berkeley DB offers programmatic support for displaying error return values. The db_strerror 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.

For example:

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);
}

There are also two additional error interfaces: DB_ENV->err and DB_ENV->errx. 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.

The DB_ENV->err function appends the standard error string to the constructed message; the DB_ENV->errx function does not.

Error messages can be configured always to include a prefix (for example, the program name) using the DB_ENV->set_errpfx interface.

These functions provide simpler ways of displaying Berkeley DB error messages:

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);
}

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:

my_app: open: /tmp/home: Permission denied.
my_app: contact your system administrator: session ID was 2

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