Steven Bosscher wrote: > Of course, the semantics of "int : 0" are not defined by C99 for packed > structs. As far as I can tell, extend.texi doesn't discuss this case, > so we need to come up with something that makes sense.
The semantics of zero-width bitfields (outside of packed structures) are part of the ABI for each system. They very somewhat from system-to-system, but, in general, they are interpreted as alignment directives. > We discussed this briefly on IRC. We have only two options AFAICT: > 1) ignore the ": 0" field completely. This is what we seem to do > since Jason's patch was commited. > 2) when we see :0 align to the next unit, which seems to be the > behavior of GCC pre-3.4. > > Jason suggested that it looks like they want it to mean "align the > next field despite pragma pack". So that is option (2), Yes, I think we should do option (2). There's otherwise no point at all in putting a zero-width bitfield into a packed structure; it seems better to assume the user had a purpose in having the zero-width bitfield. -- Mark Mitchell CodeSourcery, LLC [EMAIL PROTECTED] (916) 791-8304
