Error support

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

1. int ret;
2. if ((ret = dbenv->set_cachesize(dbenv, 0, 32 * 1024, 1)) != 0) {
3. fprintf(stderr, "set_cachesize failed: %s\n", db_strerror(ret));
4. return (1);
5. }

There are also two additional error methods: DB_ENV->err() and DB_ENV->errx(). 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 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() method.

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

1. int ret;
2. ...
3. dbenv->set_errpfx(dbenv, program_name);
4. if ((ret = dbenv->open(dbenv, home,
5. DB_CREATE | DB_INIT_LOG | DB_INIT_TXN | DB_USE_ENVIRON, 0))
6. != 0) {
7. dbenv->err(dbenv, ret, "open: %s", home);
8. dbenv->errx(dbenv,
9. "contact your system administrator: session ID was %d",
10. session_id);
11. return (1);
12. }

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:

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