#include <db_cxx.h>
extern "C" {
typedef int (*compare_fcn_type)(DB *db, const DBT *dbt1,
const DBT *dbt2, size_t *locp);
};
int
Db::set_h_compare(compare_fcn_type compare_fcn);
Set the Hash key comparison function. The comparison function is called whenever it is necessary to compare a key specified by the application with a key currently stored in the database.
If no comparison function is specified, a byte-by-byte comparison is performed.
The Db::set_h_compare() method configures operations performed using
the specified Db handle,
not all operations performed on the underlying database.
The Db::set_h_compare() method may not be called after the
Db::open()
method is called. If
the database already exists when
Db::open()
is called, the information specified to Db::set_h_compare()
must be the same as that historically used to create the database or corruption can occur.
The Db::set_h_compare()
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.
The compare_fcn function is the application-specified Hash comparison function. The comparison function takes four parameters:
db
The db parameter is the enclosing database handle.
dbt1
The dbt1 parameter is the Dbt representing the application supplied key.
dbt2
The dbt2 parameter is the Dbt representing the current database's key.
locp
The locp parameter is currently unused, and must be set to NULL or corruption can occur.
The compare_fcn function must return an integer value less than, equal to, or greater than zero if the first key parameter is considered to be respectively less than, equal to, or greater than the second key parameter. The comparison function must correctly handle any key values used by the application (possibly including zero-length keys). The data and size fields of the Dbt are the only fields that may be used for the purposes of this comparison, and no particular alignment of the memory to which by the data field refers may be assumed.
The Db::set_h_compare()
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.