#include <db_cxx.h> int Db::fd(int *fdp);
         The Db::fd() method provides access to a file descriptor
         representative of the underlying database.  A file descriptor
         referring to the same file will be returned to all processes that call
         Db::open()  with the same
         file parameter.
    
This file descriptor may be safely used as a parameter to the fcntl(2) and flock(2) locking functions.
         The Db::fd() method only supports a coarse-grained form of locking.
         Applications should instead use the Berkeley DB lock manager where
         possible.
    
         The Db::fd() 
            
            
                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.