Don't forget about an alignment. If the first character is not one of '@', '=', '<', '>' or '!', '@' is assumed, which means native byte order, type sizes and alignments. If the 'f' format character require 4-byte alignment, 2 padding bytes are inserted before the first 'f' item.

Add the '=' character at the start of the format string if you need native byte order, "standard" type sizes and no alignments. Add the '<' or '>' characters if you need some specific byte order.