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:

  1. DB_ENV *dbenv;
  2.     DB *dbp1, *dbp2;
  3.     int ret;
  5.     dbenv = NULL;
  6.     dbp1 = dbp2 = NULL;
  7.     /*
  8.      * Create an environment and initialize it for additional error
  9.      * reporting.
  10.      */
  11.     if ((ret = db_env_create(&dbenv, 0)) != 0) {
  12.         fprintf(errfp, "%s: %s\n", progname, db_strerror(ret));
  13.         return (ret);
  14.     }
  16.     dbenv->set_errfile(dbenv, errfp);
  17.     dbenv->set_errpfx(dbenv, progname);
  19.     /* Open an environment with just a memory pool. */
  20.     if ((ret =
  21.         dbenv->open(dbenv, home, DB_CREATE | DB_INIT_MPOOL, 0)) != 0) {
  22.         dbenv->err(dbenv, ret, "environment open: %s", home);
  23.         goto err;
  24.     }
  26.     /* Open database #1. */
  27.     if ((ret = db_create(&dbp1, dbenv, 0)) != 0) {
  28.         dbenv->err(dbenv, ret, "database create");
  29.         goto err;
  30.     }
  31.     if ((ret = dbp1->open(dbp1,
  32.         NULL, DATABASE1, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) {
  33.         dbenv->err(dbenv, ret, "DB->open: %s", DATABASE1);
  34.         goto err;
  35.     }
  37.     /* Open database #2. */
  38.     if ((ret = db_create(&dbp2, dbenv, 0)) != 0) {
  39.         dbenv->err(dbenv, ret, "database create");
  40.         goto err;
  41.     }
  42.     if ((ret = dbp2->open(dbp2,
  43.         NULL, DATABASE2, NULL, DB_HASH, DB_CREATE, 0664)) != 0) {
  44.         dbenv->err(dbenv, ret, "DB->open: %s", DATABASE2);
  45.         goto err;
  46.     }
  48.     return (0);
  50. err:    if (dbp2 != NULL)
  51.         (void)dbp2->close(dbp2, 0);
  52.     if (dbp1 != NULL)
  53.         (void)dbp1->close(dbp1, 0);
  54.     (void)dbenv->close(dbenv, 0);
  55.     return (1);
  56. }