From: thiago.adams@gmail.com
On 10/23/2025 4:12 AM, David Brown wrote:
> On 22/10/2025 20:22, Kaz Kylheku wrote:
>> On 2025-10-22, Thiago Adams wrote:
>>> On 10/22/2025 8:44 AM, Richard Harnden wrote:
>>> ....
>>>>> 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 ...
>>>>
>>>> $ cat x.c
>>>> #include
>>>>
>>>> enum x {A, B, C};
>>>>
>>>> int main(void)
>>>> {
>>>> enum x x = C;
>>>>
>>>> switch (x)
>>>> {
>>>> case A:
>>>> printf("A\n");
>>>> break;
>>>>
>>>> case B:
>>>> printf("B\n");
>>>> break;
>>>> }
>>>>
>>>> return 0;
>>>> }
>>>>
>>>> $ gcc -Wall x.c
>>>> x.c: In function ‘main’:
>>>> x.c:9:9: warning: enumeration value ‘C’ not handled in switch [-
>>>> Wswitch]
>>>> 9 | switch (x)
>>>> | ^~~~~~
>>>>
>>>>
>>>
>>> The problem with this GCC approach is when there are many enumerators
>>> but only a few are used.
>>
>> The problem with the C and GCC approach is that there is no
>> one-size-fits all solution.
>>
>> Some switches are intended to be exhaustive, such that
>> missing a case is a bug.
>>
>> Some are not.
>>
>> You need an "eswitch" for the exhaustively handled enumerations, and
>> switch for the others.
>>
>> GCC can turn on diagnostics over ranges of a file with pragma
>> and there is also _Pragram, but it's all too clumsy.
>>
>
> The gcc approach works fine in almost all situations - use "-
> Wswitch=error", and add a default case if your switch is not meant to
> handle all enumeration values. If the default should do nothing, it's
> just "default: // Not all cases need handling". If the default should
> never happen, "default: __builtin_unreachable();" or "default:
> __builtin_trap();" might be appropriate.
>
>
>
But then instead a compiler time error (like I suggest) you leave it for
runtime.
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