Message-Id: <m0yHr2p-000S3eC@inti.gov.ar>
Comments: Authenticated sender is <salvador AT natacha DOT inti DOT gov DOT ar>
From: "Salvador Eduardo Tropea (SET)" <salvador AT inti DOT gov DOT ar>
Organization: INTI
To: "Andris Pavenis" <pavenis AT laima DOT acad DOT latnet DOT lv>,
        Peter Palotas <blizzar AT hem1 DOT passagen DOT se>, djgpp AT delorie DOT com,
        djgpp-workers AT delorie DOT com
Date: Wed, 25 Mar 1998 11:23:45 +0000
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Subject: Re: NULL redefined! :(
In-reply-to: <199803251406.QAA57422@ieva06.lanet.lv>
References: <3518F995 DOT 6AEA AT rug DOT ac DOT be>
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"Andris Pavenis" <pavenis AT laima DOT acad DOT latnet DOT lv> wrote:

> > Date:          Wed, 25 Mar 1998 13:33:25 +0100
> > From:          Vik Heyndrickx <Vik DOT Heyndrickx AT rug DOT ac DOT be>
> > Subject:       Re: NULL redefined! :(
> 
> > Salvador Eduardo Tropea (SET) wrote:
> > > But perhaps we must investigate if the __null have some advantage and:
> > > 
> > > 1) Define NULL conditionally (no redefinition)
> > > 2) If not defined:
> > > a) Test the gcc version, if 2.8.0 define with __null
> > > b) if prior define with 0.
> > 
> > Conditional redefinition is dangerous since this way NULL might get two
> > values that do not compare equal, even when compiled with the same
> > compiler version.
> > An unconditional #define is best (i.e. preceded with #undef) as it only
> > disadvantages programs which are at fault.
> > 
> > Checking whether gcc's version is 2.8.0, won't help a bit:
> > for instance the libc library can have been defined using gcc-2.7.2.1
> > and hence NULL would be 0. A program compiled with 2.8.0 would then
> > define NULL as __null. Like DJ mentionned, a library function like fopen
> > can return NULL (=0) and it must be possible that a program compares it
> > with NULL (=__null).
> > 
> 
> I suggest to copy definition of NULL to .h files that conflicts
> with ones from gcc 2.8.0 (%DJDIR%/lang/cxx/libio.h vai
> %DJDIR%/lang/cxx/streambuf.h)
> 
> -------------------------------------------------------
> #ifndef NULL
> # if defined __GNUG__ && \
>     (__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 8))
> #  define NULL (__null)
> # else
> #  if !defined(__cplusplus)
> #   define NULL ((void*)0)
> #  else
> #   define NULL (0)
> #  endif
> # endif
> #endif
> -------------------------------------------------------
> 
> I did so and don't have any problems yet. 

I agree and that's just what I propossed at first (conditional definition 
taking care of the gcc version).
The only doubt about this piece of code: 
I think that it needs an extra test for C++ because __null doesn't exist in C, 
perhaps:

#ifndef NULL
// Not NULL defined
#ifdef __cplusplus
// C++ case
# if defined __GNUC__ && \
     (__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 8))
#  define NULL (__null)
# else
#  define NULL ((void *)0)
#else
// C case
#  define NULL (0)
#endif
#endif

SET
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