Defining bit values (and other externally defined magic numbers) explicitly in e.g. a defined-to-be-canonical header file (which might be just those 8 #defines)

Defining bit values (and other externally defined magic numbers) explicitly in e.g. a defined-to-be-canonical header file (which might be just those 8 #defines) is much safer and easier to debug/maintain I'm all for modern C++, but this is correct, at least IME with embedded systems. You're overall better off sticking with C-style if working at an abstraction level where the interface itself uses bitmasks. At this point you're manipulating memory manually which is (a) C's wheelhouse and (b) where type safety becomes largely irrelevant. There is a lot to be said for using custom enum class implementations (e.g. http://www.drdobbs.com/when-enum-just-isnt-enough-enumeration-c/184403955 http://www.drdobbs.com/when-enum-just-isnt-enough-enumeratio...) but it isn't clear to me how this kind of thing benefits bitmasks when the goal is presumably absolute maximum efficiency.