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Groups > comp.lang.c > #394663
| From | Keith Thompson <Keith.S.Thompson+u@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: bugprone-switch-missing-default-case |
| Date | 2025-10-22 12:41 -0700 |
| Organization | None to speak of |
| Message-ID | <87frbaohaa.fsf@example.invalid> (permalink) |
| References | <10da67g$3q59f$1@dont-email.me> <10da8bo$hker$1@dont-email.me> <10dag3d$jkju$1@dont-email.me> <10damv3$ku01$1@dont-email.me> |
David Brown <david.brown@hesbynett.no> writes:
> On 22/10/2025 13:44, Richard Harnden wrote:
>> On 22/10/2025 10:32, Janis Papanagnou wrote:
>>> On 22.10.2025 10:56, pozz wrote:
>>>>> Switch statements without a default case can lead to unexpected
>>>>> behavior and incomplete handling of all possible cases. When a switch
>>>>> statement lacks a default case, if a value is encountered that does
>>>>> not match any of the specified cases, the program will continue
>>>>> execution without any defined behavior or handling.
>>>>
>>>> Maybe I misunderstood that sentence caused by my bad English. I knew
>>>> that in case the switch value is not present in any case inside the
>>>> switch, the program continues without doing anything (in the switch) and
>>>> without any problem.
>>>>
>>>> int x = 3;
>>>> switch(x) {
>>>> case 1: printf("Hello");break;
>>>> case 2: printf("World");break;
>>>> }
>>>>
>>>> Will the program execution continue without any defined behaviour?
>
> Presumably you meant "without any undefined behaviour" ? The code is
> fine - if no cases match and there is no default case, execution
> continues from the end of the switch statement. Like most warnings,
> this is about a possible bug in the code - not a definite one.
No, pozz meant "without any defined behavior", which is a direct quote
from the cited document.
That document is poorly written. The phrase "without any defined
behavior" strongly implies that the behavior is undefined, which is
simply wrong.
It says:
When a switch statement lacks a default case, if a value is
encountered that does not match any of the specified cases, the
program will continue execution without any defined behavior or
handling.
It would be more accurate to say:
When a switch statement lacks a default case, if a value is
encountered that does not match any of the specified cases, the
switch statement will do nothing and the program will continue
execution without handling the value.
A warning might be warranted, but the behavior is well defined.
Note that the documentation is for the add-on tool clang-tidy, not for
the clang compiler.
I've submitted a bug report :
https://github.com/llvm/llvm-project/issues/164699
--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */
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bugprone-switch-missing-default-case pozz <pozzugno@gmail.com> - 2025-10-22 10:56 +0200
Re: bugprone-switch-missing-default-case Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-22 11:32 +0200
Re: bugprone-switch-missing-default-case Richard Harnden <richard.nospam@gmail.invalid> - 2025-10-22 12:44 +0100
Re: bugprone-switch-missing-default-case Thiago Adams <thiago.adams@gmail.com> - 2025-10-22 10:05 -0300
Re: bugprone-switch-missing-default-case Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-22 18:22 +0000
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-23 09:12 +0200
Re: bugprone-switch-missing-default-case Thiago Adams <thiago.adams@gmail.com> - 2025-10-23 08:03 -0300
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-23 17:06 +0200
Re: bugprone-switch-missing-default-case Thiago Adams <thiago.adams@gmail.com> - 2025-10-23 13:15 -0300
Re: bugprone-switch-missing-default-case bart <bc@freeuk.com> - 2025-10-23 17:46 +0100
Re: bugprone-switch-missing-default-case Thiago Adams <thiago.adams@gmail.com> - 2025-10-23 14:12 -0300
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-23 22:40 +0200
Re: bugprone-switch-missing-default-case scott@slp53.sl.home (Scott Lurndal) - 2025-10-23 20:51 +0000
Re: bugprone-switch-missing-default-case Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-23 16:21 -0700
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-24 08:59 +0200
Re: bugprone-switch-missing-default-case scott@slp53.sl.home (Scott Lurndal) - 2025-10-24 15:51 +0000
Re: bugprone-switch-missing-default-case tTh <tth@none.invalid> - 2025-10-23 23:57 +0200
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-24 09:22 +0200
Re: bugprone-switch-missing-default-case antispam@fricas.org (Waldek Hebisch) - 2025-10-23 23:23 +0000
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-24 09:53 +0200
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-22 15:41 +0200
Re: bugprone-switch-missing-default-case Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-22 16:05 +0200
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-22 17:23 +0200
Re: bugprone-switch-missing-default-case Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-23 04:54 +0200
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-23 09:30 +0200
Re: bugprone-switch-missing-default-case antispam@fricas.org (Waldek Hebisch) - 2025-10-23 22:40 +0000
Re: bugprone-switch-missing-default-case Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-22 12:41 -0700
Re: bugprone-switch-missing-default-case pozz <pozzugno@gmail.com> - 2025-10-23 08:47 +0200
Re: bugprone-switch-missing-default-case Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-23 16:17 -0700
Re: bugprone-switch-missing-default-case Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-23 19:13 -0700
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-23 10:44 +0200
Re: bugprone-switch-missing-default-case Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-22 15:56 +0200
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-22 17:25 +0200
Re: bugprone-switch-missing-default-case Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-23 04:39 +0200
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-23 09:08 +0200
Re: bugprone-switch-missing-default-case Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-23 16:31 -0700
Re: bugprone-switch-missing-default-case David Brown <david.brown@hesbynett.no> - 2025-10-24 10:09 +0200
Re: bugprone-switch-missing-default-case Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-22 18:13 +0000
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