Dbc::get |
#include <db_cxx.h>int Dbc::get(Dbt *key, Dbt *data, u_int32_t flags); int Dbc::pget(Dbt *key, Dbt *pkey, Dbt *data, u_int32_t flags);
The Dbc::get method retrieves key/data pairs from the database. The address and length of the key are returned in the object to which key refers (except for the case of the DB_SET flag, in which the key object is unchanged), and the address and length of the data are returned in the object to which data refers.
When called on a cursor opened on a database that has been made into a secondary index using the Db::associate method, the Dbc::get and Dbc::pget methods return the key from the secondary index and the data item from the primary database. In addition, the Dbc::pget method returns the key from the primary database. In databases that are not secondary indices, the Dbc::pget interface will always fail and return EINVAL.
Modifications to the database during a sequential scan will be reflected in the scan; that is, records inserted behind a cursor will not be returned while records inserted in front of a cursor will be returned.
In Queue and Recno databases, missing entries (that is, entries that were never explicitly created or that were created and then deleted) will be skipped during a sequential scan.
The flags value must be set to one of the following values:
If the cursor key/data pair was deleted, Dbc::get will return DB_KEYEMPTY.
If the cursor is not yet initialized, the Dbc::get method either returns EINVAL or throws an exception that encapsulates EINVAL.
If the database is a Queue or Recno database, Dbc::get using the DB_FIRST (DB_LAST) flags will ignore any keys that exist but were never explicitly created by the application, or were created and later deleted.
If the database is empty, Dbc::get will return DB_NOTFOUND.
When used with the Dbc::pget version of this interface on a secondary index handle, both the secondary and primary keys must be matched by the secondary and primary key item in the database. It is an error to use the DB_GET_BOTH flag with the Dbc::get version of this interface and a cursor that has been opened on a secondary index handle.
For DB_GET_RECNO to be specified, the underlying database must be of type Btree, and it must have been created with the DB_RECNUM flag.
For DB_JOIN_ITEM to be specified, the underlying cursor must have been returned from the Db::join method.
If the database is a Queue or Recno database, Dbc::get using the DB_NEXT (DB_PREV) flag will skip any keys that exist but were never explicitly created by the application, or those that were created and later deleted.
If the cursor is already on the last (first) record in the database, Dbc::get will return DB_NOTFOUND.
If the cursor is not yet initialized, the Dbc::get method either returns EINVAL or throws an exception that encapsulates EINVAL.
If the database is a Queue or Recno database, Dbc::get using the DB_NEXT_NODUP (DB_PREV_NODUP) flags will ignore any keys that exist but were never explicitly created by the application, or those that were created and later deleted.
If no non-duplicate key/data pairs occur after (before) the cursor position in the database, Dbc::get will return DB_NOTFOUND.
In the presence of duplicate key values, Dbc::get will return the first data item for the given key.
If the database is a Queue or Recno database, and the specified key exists, but was never explicitly created by the application or was later deleted, Dbc::get will return DB_KEYEMPTY.
If no matching keys are found, Dbc::get will return DB_NOTFOUND.
For DB_SET_RECNO to be specified, the underlying database must be of type Btree, and it must have been created with the DB_RECNUM flag.
In addition, the following flags may be set by bitwise inclusively OR'ing them into the flags parameter:
If DB_MULTIPLE is specified for the Queue and Recno access methods, the buffer will be filled with as many data records as possible. The record number of the first record will be returned in the key argument. The record number of each subsequent returned record must be calculated from this value.
The buffer to which the data argument refers should be large relative to the page size of the underlying database, aligned for unsigned integer access, and be a multiple of 1024 bytes in size.
The DB_MULTIPLE flag may only be used with the DB_CURRENT, DB_FIRST, DB_GET_BOTH, DB_NEXT, DB_NEXT_DUP, DB_NEXT_NODUP, DB_SET, DB_SET_RANGE, and DB_SET_RECNO options.
The DB_MULTIPLE flag may not be used when accessing databases made into secondary indices using the Db::associate method.
See DB_MULTIPLE_INIT for more information.
The buffer to which the data argument refers should be large relative to the page size of the underlying database, aligned for unsigned integer access, and be a multiple of 1024 bytes in size.
The DB_MULTIPLE_KEY flag may only be used with the DB_CURRENT, DB_FIRST, DB_GET_BOTH, DB_NEXT, DB_NEXT_NODUP, DB_SET, DB_SET_RANGE, and DB_SET_RECNO options. The DB_MULTIPLE_KEY flag may not be used when accessing databases made into secondary indices using the Db::associate method.
See DB_MULTIPLE_INIT for more information.
Otherwise, the Dbc::get method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success.
If Dbc::get fails for any reason, the state of the cursor will be unchanged.
The Dbc::get method may fail and throw an exception or return a non-zero error for the following conditions:
The specified cursor was not currently initialized.
The Dbc::pget interface was called with a cursor that does not refer to a secondary index.
The Dbc::get method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the Dbc::get method may fail and either return DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.