[PATCH] Fixes sentinel warnings on GCC4

[Derek Atkins]

Quoting Chris Shoemaker <c.shoemaker at cox.net>:

> On Mon, Dec 05, 2005 at 04:38:40PM -0500, Derek Atkins wrote:
>> If you were on IRC you'd have more information on this.
>>
>> Yes, it is 64-bit only.  The problem is that on some versions of gcc4
>> stddef.h #defined NULL as (int)0 which causes a compiler warning when
>> passing that into a char*.
>
> I'm no expert, and I don't actually know what gcc #defines NULL to,
> but I don't think this is quite right.  I don't think this is a gcc
> problem.  No compiler can infer the correct type for variadic
> arguments.  In a variadic argument list, a compiler *must* interpret
> an unqualified "0" (which is probably what NULL is) as integer type.
> Our code is just wrong for any machine where the null pointer is not a
> 32 bit zero, even if it's some (imaginary) 32-bit machine.

The problem is that you cannot pass a 32-bit integer into a 64-bit adddress.
On my system (32-bit, gcc-3.4.3) NULL is either defined as 0, (void*)0, or
__null depending on other #ifdefs (which I didn't go examine).  However
if the callee is expecting a 64-bit pointer and you pass it a 32-bit
integer, the compiler WILL (and SHOULD) complain.  With -Werror this
causes the build to blow out.

>> The fix (which David is working on -- which you'd know if you were in
>> IRC) is to #define GNC_NULL ((gpointer)0) and then use that instead of
>> NULL in these places.
>
> Hmm.  Seems a bit heavy-handed to me, but it would work.  I hope it
> doesn't result in gratuitous use of GNC_NULL in the 99% of places
> where NULL is fine.

I think it would only be used in the particular cases where this is an
issue.  HOWEVER....

> IMHO, it's better that programmers remain aware that the use of NULL
> as a sentinel is "special".  IOW, *not* hiding this behavior gives a
> better picture of what the code actually does, which tends to make for
> better code and better programmers in the long run.  One problem I see
> with GNC_NULL, is visibility.  If it's too visible, people use it
> gratuitously; if it's not visible enough, people forget to use it when
> they should; How to choose?  Better just to /understand/ what's going
> on.

... we're still trying to analyze the issue and figure out what's really
going on.  I.e., there's no plan to make any changes until we understand
the problem.  David just went and tried to reproduce this on an amd64
machine and could not reproduce it.  Then we hear back that these errors
are on a 32-bit machine..  (all this is on IRC, and all in the last
few minutes)..   So..  We're still trying to figure out what the REAL
problem is before we consider this a gnucash  bug.

I agree with you that this SHOULDN'T be a problem, and we SHOULDN'T
need to make this change.

> -chris

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
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