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Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary?

From David Brown <david.brown@hesbynett.no>
Newsgroups comp.lang.c++
Subject Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary?
Date 2024-11-22 09:30 +0100
Organization A noiseless patient Spider
Message-ID <vhpffm$13p8k$1@dont-email.me> (permalink)
References (4 earlier) <vhlo4a$9ud2$1@dont-email.me> <vhlt2v$aq3g$2@dont-email.me> <6OG%O.12794$vGnb.894@fx46.iad> <vhnlsi$n457$1@dont-email.me> <FuK%O.36887$IFic.14310@fx12.iad>

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On 21/11/2024 18:55, Scott Lurndal wrote:
> Muttley@DastartdlyHQ.org writes:
>> On Thu, 21 Nov 2024 13:43:30 GMT
>> scott@slp53.sl.home (Scott Lurndal) boring babbled:
>>> "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> writes:
>>>> On 11/20/2024 2:33 PM, Chris M. Thomasson wrote:
>>>>> On 11/20/2024 2:11 PM, Scott Lurndal wrote:
>>>
>>>>
>>>> Actually, for some reason, this makes me think of nullptr = 0 = NULL wrt
>>>> NULL can be 0xdeadbeefbeefdead?
>>>>
>>>
>>> I've worked with systems where the NULL pointer value was not zero.
>>>
>>> That's why C has a symbolic constant for NULL.
>>
>> Thats a bit iffy given the number of devs - and I include myself - who often use
>> !<whatever> in place of <whatever> == NULL and similarly <whatever> instead
>> of <whatever> != NULL.
> 
> No, it's not iffy, that's just bad coding practice on your part.

If you are talking about testing a normal pointer to check for a null 
pointer, it is not "iffy" at all in C++.  If you have "int * p;", then 
"if (p)" is a conversion of "p" to bool, which is defined as false if 
and only if p is a null pointer.  "if (!p)" first converts "p" to bool, 
and then negates it, so it is also entirely well defined.

For C, "(!p)" is defined as "(0 == p)", which will be true if and only 
if "p" is a null pointer.  (An integer constant expression with value 0, 
when converted to a pointer type, is a null pointer constant - 
regardless of representation.)

All of this applies - AFAICS - regardless of whether the implementation 
uses a bit representation of 0 for a null pointer, or anything else.  It 
still applies even if there can be many different representations of 
null pointers, as they must all compare equal.

However, I can't see a justification for claiming that "if (p)" works as 
expected for any C implementation.  I might be missing something, and of 
course real C implementations will support it as you would expect.  In 
C++, "if (p)" converts "p" to bool, but in C, it converts it to "int". 
And while you are guaranteed that converting an integer constant 
expression of value 0 to a pointer type will give you a null pointer, 
you are not guaranteed that a null pointer, converted to an int, will 
give 0.  (And int variables and other expressions of int type which 
happen to contain the value 0, are not guaranteed to give null pointers 
when converting to a pointer type - only /constant/ expressions get that 
treatment.)

So for C, "if (p)" appears to be "iffy" in theory, but fine in practice. 
  "if (!p)" is fine, as is "if (!!p)" and "if ((bool) p)".  For C++, "if 
(p)" is solid.

(If anyone can point to what I am missing that makes "if (p)" safe in C, 
I'd be glad to hear about it.)


What counts as "bad coding practice" is a much more subjective matter.

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Thread

Is EXIT_SUCCESS/EXIT_FAILURE necessary? wij <wyniijj5@gmail.com> - 2024-11-20 11:02 +0800
  Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Paavo Helde <eesnimi@osa.pri.ee> - 2024-11-20 09:22 +0200
    Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastartdlyHQ.org - 2024-11-20 08:27 +0000
      Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-20 13:47 +0000
        Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastartdlyHQ.org - 2024-11-20 15:05 +0000
          Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-20 15:45 +0000
            Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastartdlyHQ.org - 2024-11-20 16:41 +0000
    Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-20 13:37 -0800
      Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-20 22:11 +0000
        Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-20 14:33 -0800
          Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-20 23:03 +0000
            Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-20 15:57 -0800
          Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-20 15:58 -0800
            Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-21 13:43 +0000
              Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastartdlyHQ.org - 2024-11-21 16:07 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-21 17:55 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? David Brown <david.brown@hesbynett.no> - 2024-11-22 09:30 +0100
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Ross Finlayson <ross.a.finlayson@gmail.com> - 2024-11-22 11:10 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@dastardlyhq.com - 2024-11-23 11:36 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-22 12:26 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-22 12:49 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-22 23:26 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? David Brown <david.brown@hesbynett.no> - 2024-11-23 13:07 +0100
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-25 13:55 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-01 20:57 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastartdlyHQ.org - 2024-11-22 09:55 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-11-26 04:21 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-22 11:57 -0500
              Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-22 11:31 -0500
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-22 12:36 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-22 16:53 -0500
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? wij <wyniijj5@gmail.com> - 2024-11-24 12:57 +0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-25 14:03 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? wij <wyniijj5@gmail.com> - 2024-11-26 12:21 +0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? wij <wyniijj5@gmail.com> - 2024-11-27 16:23 +0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastartdlyHQ.org - 2024-11-27 08:26 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? wij <wyniijj5@gmail.com> - 2024-11-27 18:48 +0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Paavo Helde <eesnimi@osa.pri.ee> - 2024-11-27 15:39 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastardlyHQ.org - 2024-11-27 13:54 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Michael S <already5chosen@yahoo.com> - 2024-11-27 17:24 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastardlyHQ.org - 2024-11-27 16:12 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Richard Damon <richard@damon-family.org> - 2024-11-27 13:00 -0500
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastardlyHQ.org - 2024-11-28 08:23 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Michael S <already5chosen@yahoo.com> - 2024-11-28 15:06 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Richard Damon <richard@damon-family.org> - 2024-11-28 08:08 -0500
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-27 14:58 -0500
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Ross Finlayson <ross.a.finlayson@gmail.com> - 2024-11-27 19:46 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastardlyHQ.org - 2024-11-28 08:26 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Paavo Helde <eesnimi@osa.pri.ee> - 2024-11-28 13:03 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Ralf Fassel <ralfixx@gmx.de> - 2024-11-28 12:15 +0100
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Paavo Helde <eesnimi@osa.pri.ee> - 2024-11-28 13:36 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Ralf Fassel <ralfixx@gmx.de> - 2024-11-28 14:12 +0100
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Richard Damon <richard@damon-family.org> - 2024-11-28 07:50 -0500
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Michael S <already5chosen@yahoo.com> - 2024-11-28 15:19 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastardlyHQ.org - 2024-11-28 15:12 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Michael S <already5chosen@yahoo.com> - 2024-11-28 17:36 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? David Brown <david.brown@hesbynett.no> - 2024-11-28 16:43 +0100
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastardlyHQ.org - 2024-11-28 15:59 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Ross Finlayson <ross.a.finlayson@gmail.com> - 2024-11-28 10:19 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Paavo Helde <eesnimi@osa.pri.ee> - 2024-11-28 22:41 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Michael S <already5chosen@yahoo.com> - 2024-11-29 00:21 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Paavo Helde <eesnimi@osa.pri.ee> - 2024-11-29 00:59 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Michael S <already5chosen@yahoo.com> - 2024-11-29 01:20 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-28 17:18 -0500
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Paavo Helde <eesnimi@osa.pri.ee> - 2024-11-27 19:01 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastardlyHQ.org - 2024-11-28 08:22 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Ross Finlayson <ross.a.finlayson@gmail.com> - 2024-11-27 11:00 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-27 14:57 -0500
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Muttley@DastardlyHQ.org - 2024-11-27 13:52 +0000
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-27 14:54 -0500
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Michael S <already5chosen@yahoo.com> - 2024-11-28 15:27 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Michael S <already5chosen@yahoo.com> - 2024-11-27 15:30 +0200
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-28 18:32 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-25 14:00 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-25 14:15 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-01 21:00 -0800
                Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-11-26 04:26 -0800
          Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-20 23:20 -0500
        Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Ross Finlayson <ross.a.finlayson@gmail.com> - 2024-11-20 17:32 -0800
          Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? red floyd <no.spam.here@its.invalid> - 2024-11-20 22:56 -0800
            Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-21 13:52 +0000
          Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-21 13:51 +0000
  Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-20 13:44 +0000
    Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? wij <wyniijj5@gmail.com> - 2024-11-20 22:57 +0800
      Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Michael S <already5chosen@yahoo.com> - 2024-11-20 17:23 +0200
  Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-20 23:09 -0500
    Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? scott@slp53.sl.home (Scott Lurndal) - 2024-11-21 13:52 +0000
    Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? wij <wyniijj5@gmail.com> - 2024-11-21 22:45 +0800
  Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Rosario19 <Ros@invalid.invalid> - 2024-11-25 22:20 +0100
    Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? "Fred. Zwarts" <F.Zwarts@HetNet.nl> - 2024-11-26 10:20 +0100
      Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Rosario19 <Ros@invalid.invalid> - 2024-11-30 16:52 +0100
  Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary? Andrey Tarasevich <noone@noone.net> - 2025-02-15 16:21 -0800

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