From: david.brown@hesbynett.no
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.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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