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, similar to the ANSI C strerror function, but is able to handle both system error returns and Berkeley DB specific return values.
For example:
int ret; ... if ((ret = dbp->put(dbp, NULL, &key, &data, 0)) != 0) { fprintf(stderr, "put failed: %s\n", db_strerror(ret)); return (1); }
There are also two additional error methods, DB->err() and
DB->errx()
. These methods work
like the ANSI C X3.159-1989 (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->err() method appends the standard error string to the
constructed message; the
DB->errx()
method does not.
These methods 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:
Error messages can additionally be configured to always include a prefix (for example, the program name) using the DB->set_errpfx() method.
#define DATABASE "access.db" int ret; (void)dbp->set_errpfx(dbp, program_name); 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); }
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:
my_app: access.db: Permission denied. my_app: contact your system administrator: session ID was 14
Equivalent methods exist for informational messages. See DB->msg() and DB->set_msgpfx() for details.