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Re: NULL versus 0

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On 29/09/2021 05:34, Keith Thompson wrote:
> Branimir Maksimovic <branimir.maksimovic@gmail.com> writes:
>> On 2021-09-26, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
>>> Branimir Maksimovic <branimir.maksimovic@gmail.com> writes:
>>>> On 2021-09-26, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
>>>>>> #define NULL (void*)0 
>>>>>> simple, problem is that in C++, one have to cast from void
>>>>>> and that does not works, and this is BuG in C++.
>>>>>
>>>>> That's not a valid definition of NULL in either C or C++.
>>>>>
>>>>> In C or C++, the definition has to be parenthesized to avoid parsing
>>>>> errors in some contexts;
>>>>>
>>>>>     #define NULL ((void*0)
>>>>>
>>>>> I'm not sure what you mean by "this is BuG in C++".  A C++
>>>>> implementation that defined NULL that way would be non-conforming.
>>>>>
>>>> Exactly, that is why it is Bug.
>>>> Thanks for correction, BTW.
>>>
>>> To be clear, you're saying that if any C++ implementation actually
>>> defined NULL that way, it would be a bug in that implementation.
>>> That's true, but I'm not aware of any implementation that actually
>>> has that hypothetical bug.  It can require some trivial extra work
>>> for an implementation that shares headers between C and C++, but
>>> implementers are well aware of the issue.
>>>
>> We have problem off overoading resolution then with constant zero.
>> Still, despite nullptr. You  can accidentally mean 0 the integer
>> and have overload with pointer argument, and hav COMPILER BUG.
>> This should be corrected in future standard...
> 
> I don't know what "COMPILER BUG" you're talking about.
> 
> Using 0 as a null pointer constant in the presence of overloaded
> functions can lead to a *programming* bug.  I'm not aware of any C++
> compiler that has a bug in this area (i.e., handles it in a way that's
> inconsistent with what the language requires).
> 
> That kind of programming bug can be avoided by using nullptr rather than
> 0 (something that wasn't possible before C++11).
> 
> If you're suggesting changing the language so that 0 is no longer a null
> pointer constant, that would break tons of existing code.

Yes.  But if you want that effect, some compilers will give you it with
the right flags (-Werror=zero-as-null-pointer-constant in gcc).

The downside of backwards compatibility in C and C++ is that it is hard
to remove features, even if they have been shown to be dangerous or
replaced by significantly better alternatives.  Look how long it has
taken C to get rid of non-prototype function declarations - 33 years,
assuming C23 comes out on plan.

It would be nice if there were some way to standardise options like this
in a cross-compiler fashion (perhaps with pragmas rather than compiler
flags, so that they are included in the source code).  The C++ and C
committees [[attributes]] to standardise common extensions (gcc/clang
__attribute__, MSVC declspec).  So I live in hope!


> 
> Programming bugs, compiler bugs, and language bugs are three very
> different things.
> 

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Thread

NULL versus 0 "das...@gmail.com" <dashley@gmail.com> - 2021-09-25 11:03 -0700
  Re: NULL versus 0 Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 18:16 +0000
  Re: NULL versus 0 Paavo Helde <myfirstname@osa.pri.ee> - 2021-09-25 21:20 +0300
    Re: NULL versus 0 Paavo Helde <myfirstname@osa.pri.ee> - 2021-09-25 21:32 +0300
      Re: NULL versus 0 "das...@gmail.com" <dashley@gmail.com> - 2021-09-25 12:08 -0700
    Re: NULL versus 0 Juha Nieminen <nospam@thanks.invalid> - 2021-09-27 05:47 +0000
      Re: NULL versus 0 Bo Persson <bo@bo-persson.se> - 2021-09-27 08:32 +0200
        Re: NULL versus 0 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-09-26 23:37 -0700
        Re: NULL versus 0 "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-09-27 10:32 +0200
          Re: NULL versus 0 Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-27 11:32 -0700
      Re: NULL versus 0 James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-27 15:03 -0400
  Re: NULL versus 0 "see.my....@gmail.com" <see.my.homepage@gmail.com> - 2021-09-25 13:05 -0700
    Re: NULL versus 0 Jorgen Grahn <grahn+nntp@snipabacken.se> - 2021-09-26 06:58 +0000
      Re: NULL versus 0 Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-26 07:47 +0000
        Re: NULL versus 0 Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-26 02:15 -0700
          Re: NULL versus 0 Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-26 09:38 +0000
            Re: NULL versus 0 Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-26 15:03 -0700
              Re: NULL versus 0 Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-29 02:29 +0000
                Re: NULL versus 0 Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-28 20:34 -0700
                Re: NULL versus 0 David Brown <david.brown@hesbynett.no> - 2021-09-29 08:52 +0200
        Re: NULL versus 0 Bo Persson <bo@bo-persson.se> - 2021-09-26 13:54 +0200
          Re: NULL versus 0 Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-26 15:17 -0700
          Re: NULL versus 0 Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-29 02:26 +0000
      Re: NULL versus 0 Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-26 02:17 -0700
      Re: NULL versus 0 HorseyWorsey@the_stables.com - 2021-09-26 14:20 +0000
  Re: NULL versus 0 James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-09-25 17:36 -0400
  Re: NULL versus 0 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-09-26 23:05 -0700

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