Thanks, I meant to mention that the order of the fields is important for the list of field names. (I've added an update mentioning that.) I considered using tied hashes that preserve order, but thought that would be less clear.

If I just needed to preserve the order of the unpack spec, I could also use the "@0 n @2 n @4 N @8 a16 ..." form of unpack() specs, but the fieldname order is also useful to us.