int Db::get(DbTxn *txnid, Dbt *key, Dbt *data, u_int32_t flags);
The Db::get method retrieves key/data pairs from the database. The address and length of the data associated with the specified key are returned in the structure referenced by data.
In the presence of duplicate key values, Db::get will return the first data item for the designated key. Duplicates are sorted by insert order except where this order has been overridden by cursor operations. Retrieval of duplicates requires the use of cursor operations. See Dbc::get for details.
If the file is being accessed under transaction protection, the txnid parameter is a transaction ID returned from DbTxnMgr::begin, otherwise, NULL.
The flags parameter must be set to 0 or one of the following values:
The data field of the specified key must be a pointer to a logical record number (i.e., a db_recno_t). This record number determines the record to be retrieved.
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 value may be set by logically OR'ing it into the flags parameter:
If the database is a recno database and the requested key exists, but was never explicitly created by the application or was later deleted, the Db::get method returns DB_KEYEMPTY. Otherwise, if the requested key is not in the database, the Db::get function returns DB_NOTFOUND. Otherwise, the Db::get method either returns errno or throws an exception that encapsulates an errno on failure, and 0 on success.
The Db::get method may fail and throw an exception for any of the errors specified for the following Berkeley DB and C library functions: Db::cursor, DBcursor->c_close(3), Dbc::get, fflush(3), fprintf(3), vfprintf(3), and vsnprintf(3).
In addition, the Db::get method may fail and throw an exception or return errno for the following conditions:
The DB_THREAD flag was specified to the Db::open method and neither the DB_DBT_MALLOC or DB_DBT_USERMEM flags were set in the Dbt.
A record number of 0 was specified.