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Groups > comp.lang.c > #394669
| From | Janis Papanagnou <janis_papanagnou+ng@hotmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: bugprone-switch-missing-default-case |
| Date | 2025-10-23 04:39 +0200 |
| Organization | A noiseless patient Spider |
| Message-ID | <10dc4gn$15ir6$1@dont-email.me> (permalink) |
| References | <10da67g$3q59f$1@dont-email.me> <10da8bo$hker$1@dont-email.me> <10dag3d$jkju$1@dont-email.me> <10danqv$ltmu$1@dont-email.me> <10dat1m$nfjr$2@dont-email.me> |
On 22.10.2025 17:25, David Brown wrote:
> On 22/10/2025 15:56, Janis Papanagnou wrote:
>> 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?
>>>>
>>>> Your program fragment is well defined.
>>>>
>>>> What the poster certainly tried to express was that in case you
>>>> haven't implemented a complete list of all possible cases and
>>>> also not provided a 'default' to catch all non-specified cases,
>>>> then you might get in troubles with your program, probably by
>>>> possible oversights, future extensions, new data, and whatnot.
>>>>
>>>> Personally I have the habit to always define a default branch,
>>>> and even if that default is impossible to reach you'll find an
>>>> error message (like "internal error with unexpected value...")
>>>> generated at that place.
>>>>
>>> Use an enum, and the compiler will warn you ...
>>
>> Maybe. Although I don't recall that the "C"-compilers I formerly
>> used checked enums as you've shown below. - But anyway...
>>
>> Enums don't help if you use and compare against (for example)
>> characters that are (for example) got from an external source.
>>
>> char * cmds = "CMDQ"; // 'D' maybe added later
>> char cmd;
>> ...some n lines of code...
>> ...get input cmd...
>> ...optionally verify cmd with cmds...
>> ...some more m lines of code...
>> switch (cmd) {
>> case 'C': ...;
>> case 'M': ...;
>> default: printf ("Error: uncaught cmd '%c'\n", cmd);
>> }
>>
>> It's good to take precautions and define the 'default' case. YMMV.
>>
>
> That's not "taking precautions". If the "...optionally verify cmd" part
> does a good job, then the default line is worse than useless because it
> is code that never runs. [...]
Not sure what you expect in that line. I've had something like
strchr (cmds, cmd) in mind. And the 'switch' is independent
of that, so you could miss adding the switch branch of a later
added command character.
The point was that mistakes can be made, not only in the initial
implementation but also if it gets extended later, and probably
by other folks than the original implementer. I also gave a hint
with "...some more m lines of code..." that such omissions may
also be hard to spot.
It is experience from professional real life projects that such
things happen. And blaming anyone that he's not done "a good job"
may be the appropriate diagnosis and important point if what you
want is primarily to blame someone, but if you want software to
get developed reliably, one element is to quickly spot the place
of such omissions.
Janis
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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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