Date: Sun, 11 Jan 2004 02:03:50 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Stefan Farfeleder <stefan@fafoe.narf.at> Cc: freebsd-standards@freebsd.org Subject: Re: Fwd: Re: ports/52016: New port: lang/harbour -AClipper-compatible compiler Message-ID: <20040111014013.I22846@gamplex.bde.org> In-Reply-To: <20040109164241.GA596@wombat.fafoe.narf.at> References: <200401081510.39015.linimon@lonesome.com> <20040110012527.S18300@gamplex.bde.org> <20040109164241.GA596@wombat.fafoe.narf.at>
index | next in thread | previous in thread | raw e-mail
On Fri, 9 Jan 2004, Stefan Farfeleder wrote: > On Sat, Jan 10, 2004 at 02:03:57AM +1100, Bruce Evans wrote: > > > - at least old standards seem to permit feature test macros to have no > > value (they may be empty, or perhaps more bizarre). The "+ 0" in the > > above is to handle this case, so that feature test with an empty value > > work the same as ones with value 0. > > [...] > > > #if _POSIX_SYNCHRONIZED_IO + 0 > 0 > > Undefined identifiers are replaced with 0 in a #if directive. Maybe > some ancient pre-C90 compilers didn't do that, but I think they can be > ignored these days. I know :-), and consider it a style bug to not depend on this feature, but the above is to handle the case where _POSIX_SYNCHRONIZED_IO is defined to be <nothing>. Then "_POSIX_SYNCHRONIZED_IO > 0" would expand to " > 0", which is a syntax error. I think this possibility is fixed in POSIX.1-2001. It clearly says that the feature test constants "shall be defined with a value" if they are defined at all. POSIX.1-1990 seems to only say what happens if they are defined with a value or are undefined, leaving open the possibility that they are defined to a non-value. Hmm, POSIX.1-2001 doesn't seem to require the value to be integral, except tacitly since they would not be usable in cpp expressions if they were floating point. Brucehome | help
Want to link to this message? Use this
URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20040111014013.I22846>