Opening databases within the environment
Prev | Chapter 9. The Berkeley DB Environment | Next

## Opening databases within the environment

Once the environment has been created, database handles may be created and then opened within the environment. This is done by calling the db_create() function and specifying the appropriate environment as an argument.

File naming, database operations, and error handling will all be done as specified for the environment. For example, if the DB_INIT_LOCK or DB_INIT_CDB flags were specified when the environment was created or joined, database operations will automatically perform all necessary locking operations for the application.

The following is a simple example of opening two databases within a database environment:

        DB_ENV *dbenv;
        DB *dbp1, *dbp2;
        int ret;

        dbenv = NULL;
        dbp1 = dbp2 = NULL;

        /*
         * Create an environment and initialize it for additional error
         * reporting.
         */
        if ((ret = db_env_create(&dbenv, 0)) != 0) {
            fprintf(errfp, "%s: %s\n", progname, db_strerror(ret));
            return (ret);
        }

        dbenv->set_errfile(dbenv, errfp);
        dbenv->set_errpfx(dbenv, progname);

        /* Open an environment with just a memory pool. */
        if ((ret =
            dbenv->open(dbenv, home, DB_CREATE | DB_INIT_MPOOL, 0)) != 0) {
            dbenv->err(dbenv, ret, "environment open: %s", home);
            goto err;
        }

        /* Open database #1. */
        if ((ret = db_create(&dbp1, dbenv, 0)) != 0) {
            dbenv->err(dbenv, ret, "database create");
            goto err;
        }
        if ((ret = dbp1->open(dbp1,
            NULL, DATABASE1, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) {
            dbenv->err(dbenv, ret, "DB->open: %s", DATABASE1);
            goto err;
        }

        /* Open database #2. */
        if ((ret = db_create(&dbp2, dbenv, 0)) != 0) {
            dbenv->err(dbenv, ret, "database create");
            goto err;
        }
        if ((ret = dbp2->open(dbp2,
            NULL, DATABASE2, NULL, DB_HASH, DB_CREATE, 0664)) != 0) {
            dbenv->err(dbenv, ret, "DB->open: %s", DATABASE2);
            goto err;
        }

        return (0);

    err:    if (dbp2 != NULL)
            (void)dbp2->close(dbp2, 0);
        if (dbp1 != NULL)
            (void)dbp1->close(dbp1, 0);
        (void)dbenv->close(dbenv, 0);
        return (1);
    }

Prev | Up | Next
Creating a database environment | Home | Error support