#include <db_cxx.h> int Db::set_append_recno(int (*db_append_recno_fcn)(DB *dbp, Dbt *data, db_recno_t recno));
When using the DB_APPEND
option of the Db::put() method, it may be
useful to modify the stored data based on the generated key. If a
callback function is specified using the
Db::set_append_recno()
method, it will be called after the record number has been selected,
but before the data has been stored.
The Db::set_append_recno() method configures operations performed
using the specified Db
handle, not all operations performed on the underlying database.
The Db::set_append_recno() method may not be called after the
Db::open() method is called.
The Db::set_append_recno()
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.
Berkeley DB is not re-entrant. Callback functions should not attempt to make library calls (for example, to release locks or close open handles). Re-entering Berkeley DB is not guaranteed to work correctly, and the results are undefined.
The db_append_recno_fcn parameter is a function to call after the record number has been selected but before the data has been stored into the database. The function takes three parameters:
dbp
The dbp parameter is the enclosing database handle.
data
The data parameter is the data Dbt to be stored.
recno
The recno parameter is the generated record number.
The called function may modify the data
Dbt. If the function needs to allocate
memory for the data field, the
flags field of
the returned Dbt
should be set to DB_DBT_APPMALLOC, which indicates that
Berkeley DB should free the memory when it is done with it.
The callback function must return 0 on success and errno or a value outside of the Berkeley DB error name space on failure.
The Db::set_append_recno()
method may fail and throw a DbException
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
If the method was called after Db::open() was called; or if an invalid flag value or parameter was specified.