PQfinish in transactions

What happens if PQfinish() is called from within a transaction PRIOR
to either committing or rolling back the transaction?

Does the transaction get committed? rolled back? left in an
undefined state?

Also, in the normal case of a begin/commit sequence, does the
transaction end at the commit (i.e., is begin/commit/commit an error)
or does the transaction continue until the connection is closed?

Thanks for your help.

Cheers,
Brook