Date: Wed, 30 Nov 2011 20:49:44 -0500 From: David Schultz <das@FreeBSD.ORG> To: John Baldwin <jhb@FreeBSD.ORG> Cc: Zack Kirsch <zack@FreeBSD.ORG>, mdf@FreeBSD.ORG, freebsd-arch@FreeBSD.ORG Subject: Re: Use of bool / stdbool.h in kernel Message-ID: <20111201014944.GA78010@zim.MIT.EDU> In-Reply-To: <201111301032.04102.jhb@freebsd.org> References: <CAMBSHm_Be0hCimgg0KpCFs24MHOW=LBczJbFZ3F1cOaCgrS8LA@mail.gmail.com> <20111130154604.B949@besplex.bde.org> <201111301032.04102.jhb@freebsd.org>
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On Wed, Nov 30, 2011, John Baldwin wrote: > On Wednesday, November 30, 2011 12:13:53 am Bruce Evans wrote: > > On Tue, 29 Nov 2011 mdf@freebsd.org wrote: > > > > > At $WORK we have a hack in one of the *.mk files to allow including > > > stdbool.h in the kernel and we use it extensively. This is not > > > allowed by style(9), as far as I can tell, because the file is in > > > include/stdbool.h and those files are not allowed to be included in > > > kernel sources. > > > > Including stdbool.h in the kernel is not a style bug, but unsupported. > > > > > What I want to check on is, would it be acceptable to move stdbool.h > > > from include/stdbool.h to sys/sys/stdbool.h (i.e. like errno.h) and > > > then include it in the kernel as <sys/stdbool.h>? That is, is the > > > > Would be a larger style bug, especially if it were actually used. > > Even its spellings of TRUE and FALSE are strange. Even in userland > > stdbool.h is considered so useful that it is never used in src/bin > > and is only used a few times on other src/*bin. src/bin never uses > > TRUE of FALSE either. > > I suspect there is some bias here though due to the fact that there wasn't > a standard bool type when most of this code was written. :) I don't think > that means we have to forgo use of the new type now that it is in fact > standardized in C99. I would be happy to have 'bool' available and the > lowercase 'true' and 'false' are fine with me. The lowercase 'true' and 'false' are intended to mimic C++, where they are keywords. Regardless of how you prefer to capitalize them, using them instead of 0 and 1 makes the intent much clearer. This is especially true in the kernel, where non-zero could mean true, or it could be an error code. Unfortunately, the "new type" is mostly useless, aside from improving readability. Unlike modern languages, C doesn't consider it a compile-time error to mix up bools and ints.
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