Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c++ > #120981

Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary?

Path csiph.com!weretis.net!feeder9.news.weretis.net!news.quux.org!eternal-september.org!feeder2.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups comp.lang.c++
Subject Re: Is EXIT_SUCCESS/EXIT_FAILURE necessary?
Date Fri, 22 Nov 2024 12:26:51 -0800
Organization None to speak of
Lines 65
Message-ID <875xofnhf8.fsf@nosuchdomain.example.com> (permalink)
References <8463694f3a751b287c857fca181451f36eeee982.camel@gmail.com> <vhk2mv$2aq09$1@dont-email.me> <vhlkqd$9bih$3@dont-email.me> <C8t%O.3354$YSkc.1098@fx40.iad> <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> <vhpffm$13p8k$1@dont-email.me>
MIME-Version 1.0
Content-Type text/plain
Injection-Date Fri, 22 Nov 2024 21:26:52 +0100 (CET)
Injection-Info dont-email.me; posting-host="97b7796438caeea427903e521fd90ebb"; logging-data="1402854"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/zJrr45GUSn6eW9Ss79lwr"
User-Agent Gnus/5.13 (Gnus v5.13)
Cancel-Lock sha1:h+46MlUwF+ZbgSCZhWg/+w1j9Uw= sha1:hH8m0n9eUHF0i2NjgIP6J5FiFOY=
Xref csiph.com comp.lang.c++:120981

Show key headers only | View raw

David Brown <david.brown@hesbynett.no> writes:
[...]
> 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.)

Yes, you're missing something.

    some_type *p;
    if (p) do_something();

N1570 6.8.4: `do_something();` is executed if p "compares unequal to 0",
so `if (p)` is equivalent to `if (p != 0)`.

N1570 6.5.10: "If one operand is a pointer and the other is a null
pointer constant, the null pointer constant is converted to the type of
the pointer."  0 is a null pointer constant, so it's converted to type
`some_type*`, yielding a null pointer value of that type.

In `if (p)`, p is not converted to int.  It's compared for inequality to
0, and the result of that comparison is of type int.

> 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.

Indeed.  I would write `if (foo)` only if foo is of type bool/_Bool (or
is "logically Boolean", such as a C int value with no meaninful
distinction among non-zero values).  I would write:

    - `if (foo != NULL)` or `if (foo != nullptr)` for a pointer;
    - `if (foo != '\0')` for a character (or '\0L');
    - `if (foo != 0)` for an integer that doesn't denote a character or
      boolean value (or possibly `0L` et al);
    - `if (foo != 0.0)` for a floating-point value (or possibly
      0.0f or 0.0L).

But that's my own preference, and I don't have any problem reading code
written by people with different preferences.  I recognize that more
agressive use of `if (foo)` is a common idiom, one I'll follow myself if
I'm subjected to a coding standard that requires it.

(C tends to use int for character and Boolean values.  C++ tends not to
do that as much, though you can still write C-style code in C++, and C++
includes (most of) the C standard library.)

I didn't cross-post this to comp.lang.c, but we might consider doing so
if the discussion continues into C-specific content.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */

Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web