From: david.brown@hesbynett.no
On 23/10/2025 13:03, Thiago Adams wrote:
> 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.
>
>
As I said - use "-Wswitch=error". That gives you a compile-time error -
not merely a warning, as you had suggested. But /if/ your switch is not
meant to handle all cases, which was what Kaz was complaining about,
then you add a default case. I agree with you that a compile-time error
is best when possible, which is why that was my suggestion.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
|
