Berkeley DB: Db::cursor
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++

### Db::cursor |

`

###

    #include <db_cxx.h>

    int
    Db::cursor(DbTxn *txnid, Dbc **cursorp, u_int32_t flags);

### Description: Db::cursor

The Db::cursor method returns a created database cursor.

Cursors may span threads, but only serially, that is, the application must serialize access to the cursor handle.

The Db::cursor 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.

### Parameters

cursorp
  The cursorp parameter references memory into which a pointer to the allocated cursor is copied.
flags
  The flags parameter must be set to 0 or by bitwise inclusively OR'ing together one or more of the following values:
  DB_READ_COMMITTED
    Configure a transactional cursor to have degree 2 isolation. This ensures the stability of the current data item read by this cursor but permits data read by this cursor to be modified or deleted prior to the commit of the transaction for this cursor.
  DB_READ_UNCOMMITTED
    Configure a transactional cursor to have degree 1 isolation. Read operations performed by the cursor may return modified but not yet committed data. Silently ignored if the DB_READ_UNCOMMITTED flag was not specified when the underlying database was opened.
  DB_WRITECURSOR
    Specify that the cursor will be used to update the database. The underlying database environment must have been opened using the DB_INIT_CDB flag.
  DB_TXN_SNAPSHOT
    Configure a transactional cursor to operate with read-only snapshot isolation. For databases with the DB_MULTIVERSION flag set, data values will be read as they are when the cursor is opened, without taking read locks. This flag implicitly begins a transaction that is committed when the cursor is closed. Silently ignored if DB_MULTIVERSION not set on the underlying database or if a transaction is supplied in the txnid parameter.
txnid
  Cursor operations are not automatically transaction-protected, even if the DB_AUTO_COMMIT flag is specified to the DbEnv::set_flags or Db::open methods. If cursor operations are to be transaction-protected, the txnid parameter must be a transaction handle returned from DbEnv::txn_begin; otherwise, NULL. To transaction-protect cursor operations, cursors must be opened and closed within the context of a transaction, and the txnid parameter specifies the transaction context in which the cursor may be used.

### Errors

The Db::cursor method may fail and throw DbException, encapsulating one of the following non-zero errors, or return one of the following non-zero errors:

DB_REP_HANDLE_DEAD
  The database handle has been invalidated because a replication election unrolled a committed transaction.
DB_REP_LOCKOUT
  The operation was blocked by client/master synchronization.

EINVAL
  An invalid flag value or parameter was specified.

### Class

Dbc

### See Also

Database Cursors and Related Methods`

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