[shannongreen]

> It is possible to define a struct type in C with bit-fields for the individual elements, however the C standard does not guarantee the layout and order of the individual fields.

As a professional embedded developer who uses bitfields to access registers every day, this doesn't really make a practical difference. On any bare-metal or embedded project you will rely on the behaviour of your compiler, and portability is largely irrelevant if you're accessing memory-mapped registers. Probably, the manufacturer has already provided register maps using bitfields anyway.

[hashmash]

Having direct control over this type of thing is important when updating the fields of a persistent data structure. I've had to deal with mistake before, where the original developer thought the layout matched what they specified, but the actual layout that got persisted didn't match. For compatibility, the broken layout stuck around forever, and special rules were required to detect this.