The first form deletes the dictionary from memory, but leaves it on the disk. You do this by passing the FALSE boolean value to the SetDestroyFileOnDelete member function.
// example of using TDiskDictionary::SetDestroyFileOnDelete
dict->SetDestroyFileOnDelete(FALSE); // leave files intact when dict deleted
delete dict;
// example of using TDiskDictionary::SetDestroyFileOnDelete
dict3->SetDestroyFileOnDelete(TRUE);
// remove the files when dict is deleted
delete dict3;