#include <db.h>
int
DB->set_dup_compare(DB *db, int (*dup_compare_fcn)(DB *db,
const DBT *dbt1, const DBT *dbt2, size_t *locp));
Set the duplicate data item comparison function. The comparison
function is called whenever it is necessary to compare a data item
specified by the application with a data item currently stored in the
database. Calling DB->set_dup_compare() implies calling
DB->set_flags()
with the
DB_DUPSORT
flag.
If no comparison function is specified, the data items are compared lexically, with shorter data items collating before longer data items.
The DB->set_dup_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_dup_compare() must be the same as
that historically used to create the database or corruption can occur.
The DB->set_dup_compare()
method returns a non-zero error value on failure and 0 on success.
The dup_compare_fcn function is the application-specified duplicate data item comparison function. The function takes four arguments:
db
The db parameter is the enclosing database handle.
dbt1
The dbt1 parameter is a DBT representing the application supplied data item.
dbt2
The dbt2 parameter is a DBT representing the current tree's data item.
locp
The locp parameter is currently unused, and must be set to NULL or corruption can occur.
The dup_compare_fcn function must return an integer value less than, equal to, or greater than zero if the first data item parameter is considered to be respectively less than, equal to, or greater than the second data item parameter. In addition, the comparison function must cause the data items in the set to be well-ordered. The comparison function must correctly handle any data item values used by the application (possibly including zero-length data items). 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 the data field refers may be assumed.
The DB->set_dup_compare()
method may fail and return one of the following non-zero errors: