Some differences: the standard doesn't guarantee that C++ bitfields will be densely packed (this is mostly a technicality), you can't have non-const bitfields, and you can't take a pointer to a bitfield. Zig's pointer-to-bitfield is a special type, for obvious reasons, but they can come in handy.

I have no idea if the requirement that each bitfield be reified as its declared type inhibits optimization of that example or not, in practice. Maybe, maybe not.