The C++ driver ensureIndex interface lacks the sparse index option that is available
Add sparse option to ensureIndex
Add Create Index Helper
Other options described in http://docs.mongodb.org/manual/reference/method/db.collection.ensureIndex/ are missing too:
dropDups, and options related to new Text index (2.4).
Currently, the legacy C++ driver is currently only getting critical bug/security fixes, not new features.
We encourage users to migrate to the new 'mongocxx' driver for much greater stability, configurability and support for new MongoDB server features.
See the C++ driver docs site for details on mongocxx.