Date: Mon, 16 Jan 2006 15:05:05 -0500
From: Christopher Faylor <cgf-no-personal-reply-please AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Define _POSIX_SOURCE in cygwin's features.h?
Message-ID: <20060116200504.GA16164@trixie.casa.cgf.cx>
Reply-To: cygwin AT cygwin DOT com
References: <20060112173104 DOT GA30011 AT trixie DOT casa DOT cgf DOT cx> <43C7BD94 DOT 7090704 AT byu DOT net>
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On Fri, Jan 13, 2006 at 07:47:48AM -0700, Eric Blake wrote:
>>P.S.  I know that Cygwin isn't fully compliant with POSIX
>>specifications.
>
>One other thing to be aware of.  If cygwin does define _POSIX2_VERSION
>in its headers, programs will assume that all features specified by
>POSIX are available.  Coreutils, in particular, makes a compile-time
>decision about the default behavior of some of its apps, based on the
>value of _POSIX2_VERSION (of course, this decision is overridable at
>runtime by redefining _POSIX2_VERSION in the environment).  An example
>of this would be that right now on cygwin, with coreutils 5.93, "tail
>+4" defaults to the 1992 POSIX semantics of "tail -n +4", because
>_POSIX2_VERSION was not detected at configure time.  But if you start
>adding _POSIX* macros to features.h, to be more like Linux, and choose
>to move to the 2001 version of POSIX, then a recompilation of "tail +4"
>would default to the semantics of "tail ./+4".

I was just reviewing this thread to begin thinking about preparing a
plan of attack for this problem and I see that I forgot to thank you for
this insight.  This is exactly the kind of feedback I was hoping for.
While I suspect that turning on _POSIX_SOURCE in cygwin's feature.h and
cleaning up the fallout from that action in the header files may make
some programs easier to port, I was wondering what the other
side-effects would be.

So, it sounds like the effect would be to make some applications behave
more like linux, which is theoretically a good thing.  But, since it
will be a change in visible behavior, we may see some complaints.

Actually, strike the "may" and substitute "will".

cgf

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