Table of Contents
In Berkeley DB, a database is a collection of records. Records, in turn, consist of key/data pairings.
Conceptually, you can think of a
database
as containing a two-column table where column 1 contains a key and column 2
contains data. Both the key and the data are managed using
Dbt
class instances
(see Database Records for details on this
class
).
So, fundamentally, using a DB
database
involves putting, getting, and deleting database records, which in turns involves efficiently
managing information
encapsulated by
Dbt
objects.
The next several chapters of this book are dedicated to those activities.
You open a database by instantiating a Db object
and then calling its open() method.
Note that by default, DB does not create databases if they do not already exist.
To override this behavior, specify the
DB_CREATE flag on the
open() method.
The following code fragment illustrates a database open:
#include <db_cxx.h>
...
Db db(NULL, 0); // Instantiate the Db object
u_int32_t oFlags = DB_CREATE; // Open flags;
try {
// Open the database
db.open(NULL, // Transaction pointer
"my_db.db", // Database file name
NULL, // Optional logical database name
DB_BTREE, // Database access method
oFlags, // Open flags
0); // File mode (using defaults)
// DbException is not subclassed from std::exception, so
// need to catch both of these.
} catch(DbException &e) {
// Error handling code goes here
} catch(std::exception &e) {
// Error handling code goes here
}