They're not any use for pulling sub-byte fields out of network packets in portable code, because everything about the precise layout of bitfields is entirely im

They're not any use for pulling sub-byte fields out of network packets in portable code, because everything about the precise layout of bitfields is entirely implementation-defined. Portable code has to use masking-and-shifting. The only portable uses of bitfields are to potentially save a little memory, and to get "modulo-power-of-2" behaviour. Bitfields are a classic "not as useful as they first appear" feature.