UnQLite C/C++ API Reference - Transaction Manager.
Rollback a write-transaction on the specified database handle.
If a write transaction is open, then all changes made within the transaction are reverted and the current write-transaction is closed (Dropping all exclusive locks on the target database, deletion of the journal file, etc.). Otherwise this routine is a no-op.
A pointer to a unQLite Database Handle.
UNQLITE_READ_ONLY: Read-only database.
UNQLITE_BUSY: Another thread or process have an exclusive lock on the database. In this case, the caller should wait until the lock holder relinquish it.
UNQLITE_IOERR: OS specific error.
UNQLITE_NOMEM: Out of memory (An unlikely scenario).
UNQLITE_ABORT: Another thread have released the database handle.
For a human-readable error message, you can extract the database error log via unqlite_config() with a configuration verb set to UNQLITE_CONFIG_ERR_LOG.