Re: signed vs unsigned and gcc -Wsign-conversion

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c
Subject	Re: signed vs unsigned and gcc -Wsign-conversion
Date	2025-10-21 22:56 +0200
Organization	A noiseless patient Spider
Message-ID	<10d8s2q$6up0$1@dont-email.me> (permalink)
References	<10d5j0v$3kdmk$1@dont-email.me> <10d5thm$3ciil$1@dont-email.me> <20251020125218.835@kylheku.com> <10d7o2d$3riat$1@dont-email.me> <10d8kau$26bqh$3@dont-email.me>

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On 21/10/2025 20:44, James Kuyper wrote:
> On 2025-10-21 06:42, David Brown wrote:
>> On 20/10/2025 22:09, Kaz Kylheku wrote:
>>> On 2025-10-20, David Brown <david.brown@hesbynett.no> wrote:
>>>> On 20/10/2025 17:03, pozz wrote:
> ...>> However using unsigned types due to them being safe is often poorly
>>> considered because if something goes wrong contrary to the programmer's
>>> intent, there likely will be undefined behavior somewhere.
>>
>> Exactly.  Unsigned types are not somehow "safer" than signed types, just
>> because signed types have UB on overflow.  Don't overflow your signed
>> types, then you have no UB.  And if you overflow your unsigned types
>> without that being an intentional and understood part of your code, you
>> will at the very least get unexpected behaviour - a bug - and just like
>> UB, there are no limits to how bad that can get.
> 
> No, there are limits on unexpected behavior: being unexpected, you might
> not know what they are, but it is still the case that the behavior
> starts out with having nothing more than an expression with an
> unexpected but valid value. That's pretty bad, and your code might make
> it worse, for example by promoting the unexpected value into undefined
> behavior. However, unless and until it actually does so, the behavior is
> somewhat more restricted than UB.

The effect of "unexpected behaviour" - something that has well-defined 
behaviour according to the C standard or the implementation, but was not 
what the programmer had intended or expected - is clear at the point it 
happens.  Your unsigned arithmetic overflows in a defined and specified 
manner.  But the knock-on effects are, in general, unpredictable - there 
are no specific limits for how bad things can get.  It is not unlikely 
that you'll end up with "real" UB.  In theory, real UB can lead to 
launching of nasal daemons, while unexpected behaviour, if it does not 
lead to real UB, cannot launch nasal daemons unless you have nasal 
daemon launch procedures in your program.  In practice, real UB can more 
often lead to a quick crash and perhaps "nicer" bad behaviour (via OS 
memory protections and the like), while the unexpected behaviour can 
continue on, quietly causing future havoc and problems that are harder 
to find and debug.  Either way, I think we can agree that bad things can 
happen!

Thread

signed vs unsigned and gcc -Wsign-conversion pozz <pozzugno@gmail.com> - 2025-10-20 17:03 +0200
  Re: signed vs unsigned and gcc -Wsign-conversion Bonita Montero <Bonita.Montero@gmail.com> - 2025-10-20 17:38 +0200
  Re: signed vs unsigned and gcc -Wsign-conversion Michael S <already5chosen@yahoo.com> - 2025-10-20 19:43 +0300
    Re: signed vs unsigned and gcc -Wsign-conversion Bonita Montero <Bonita.Montero@gmail.com> - 2025-10-20 19:07 +0200
    Re: signed vs unsigned and gcc -Wsign-conversion scott@slp53.sl.home (Scott Lurndal) - 2025-10-20 18:01 +0000
      Re: signed vs unsigned and gcc -Wsign-conversion Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-21 04:27 +0200
      Re: signed vs unsigned and gcc -Wsign-conversion David Brown <david.brown@hesbynett.no> - 2025-10-21 09:13 +0200
    Re: signed vs unsigned and gcc -Wsign-conversion BGB <cr88192@gmail.com> - 2025-10-20 17:44 -0500
    Re: signed vs unsigned and gcc -Wsign-conversion Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-10-20 23:36 +0000
      Re: signed vs unsigned and gcc -Wsign-conversion Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-20 23:52 +0000
      Re: signed vs unsigned and gcc -Wsign-conversion Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-20 16:58 -0700
  Re: signed vs unsigned and gcc -Wsign-conversion David Brown <david.brown@hesbynett.no> - 2025-10-20 20:03 +0200
    Re: signed vs unsigned and gcc -Wsign-conversion Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-20 20:09 +0000
      Re: signed vs unsigned and gcc -Wsign-conversion rbowman <bowman@montana.com> - 2025-10-21 01:43 +0000
      Re: signed vs unsigned and gcc -Wsign-conversion David Brown <david.brown@hesbynett.no> - 2025-10-21 12:42 +0200
        Re: signed vs unsigned and gcc -Wsign-conversion James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-10-21 14:44 -0400
          Re: signed vs unsigned and gcc -Wsign-conversion David Brown <david.brown@hesbynett.no> - 2025-10-21 22:56 +0200
  Re: signed vs unsigned and gcc -Wsign-conversion Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-20 14:48 -0700
    Re: signed vs unsigned and gcc -Wsign-conversion Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-20 17:13 -0700
      Re: signed vs unsigned and gcc -Wsign-conversion Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-21 01:45 +0000
        Re: signed vs unsigned and gcc -Wsign-conversion antispam@fricas.org (Waldek Hebisch) - 2025-10-21 03:52 +0000
  Re: signed vs unsigned and gcc -Wsign-conversion Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-10-20 23:35 +0000
    Re: signed vs unsigned and gcc -Wsign-conversion Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-10-20 23:38 +0000
      Re: signed vs unsigned and gcc -Wsign-conversion Bonita Montero <Bonita.Montero@gmail.com> - 2025-10-21 09:57 +0200
        Re: signed vs unsigned and gcc -Wsign-conversion Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-10-21 19:45 +0000
  Re: signed vs unsigned and gcc -Wsign-conversion antispam@fricas.org (Waldek Hebisch) - 2025-10-21 04:42 +0000
  Re: signed vs unsigned and gcc -Wsign-conversion Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-12-15 00:25 -0800

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