From: Tor Arntsen <tor@spacetec.no>
Date: Wed, 25 May 2011 20:37:34 GMT
Subject: Re: [PATCH 2/2] Include unistd.h.
Message-ID: <BANLkTim4gPAyA9vLnpBz7qRY+b4RQ7LwNw@mail.gmail.com>
In-Reply-To: <7vd3j64oq6.fsf@alter.siamese.dyndns.org>

On Wed, May 25, 2011 at 20:30, Junio C Hamano <gitster@pobox.com> wrote:
> mduft@gentoo.org writes:
>
>> At least on Interix, NULL is defined in unistd.h, and not including it
>> causes compilation failure.
>>
>> Signed-off-by: Markus Duft <mduft@gentoo.org>
>> ---
>>  compat/fnmatch/fnmatch.c |    1 +
>>  1 files changed, 1 insertions(+), 0 deletions(-)
>>
>> diff --git a/compat/fnmatch/fnmatch.c b/compat/fnmatch/fnmatch.c
>> index 14feac7..0238cca 100644
>> --- a/compat/fnmatch/fnmatch.c
>> +++ b/compat/fnmatch/fnmatch.c
>> @@ -25,6 +25,7 @@
>>  # define _GNU_SOURCE 1
>>  #endif
>>
>> +#include <unistd.h>
>>  #include <errno.h>
>>  #include <fnmatch.h>
>>  #include <ctype.h>
>
> The header stddef.h is where NULL is supposed to be defined, and commonly
> used headers are supposed to define NULL the same way as stddef.h does.
> There is a conditional inclusion of stdlib.h in fnmatch.c and stdlib.h is
> one of those files; probably that is how the upstream pulls in NULL when
> compiling this.

According to POSIX (well, IEEE Std 1003.1, 2004 Edition at least)
unistd.h must define NULL:

"
The following symbolic constant shall be defined:

NULL
    Null pointer
"

> But we don't define STDC_HEADERS nor _LIBC (and we shouldn't), so I don't
> know how the existing users of compat/fnmatch/ gets the defintion of NULL
> from. Output from "gcc -E -dD -DNO_FNMATCH compat/fnmatch/fnmatch.c" does
> not seem to show any NULL defined.
>
> Other platforms (e.g. SunOS, IRIX, HPUX, Windows) use NO_FNMATCH_CASEFOLD
> and compile this file.  How are they getting their NULLs?

IRIX defines NULL in <unistd.h> and <stddef.h> (the latter via
<internal/stddef_core.h>).
Solaris 10 defines NULL in <unistd.h>, but also in <stddef.h> via
<iso/stddef_iso.h>
Tru64 v5.1 in <unistd.h> and <stddef.h> and a bunch of other places
(string.h, stdio,h, stdlib.h, everywhere)
AIX 5.1 in <unistd.h> and <stddef.h> and just about everywhere.
Linux also gets NULL via <unistd.h> because it includes <stddef.h>,
but then stddef.h isn't in /usr/include, at least on my system -
presumably it's in some compiler-provided place.

For all those non-Linu systems it's always a straight-forward no-dependency
#ifndef NULL
#define NULL 0 /* or sometimes 0L */
#endif

-Tor