From: david.brown@hesbynett.no

On 22/10/2025 16:05, Janis Papanagnou wrote:
> On 22.10.2025 15:41, David Brown 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?
>>
>> 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.
>>
>>>>
>>>> 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.
>>
>> I don't think it is normally appropriate to add a default case unless
>> you actually need it
>
> Yes I was saying that I want it; I "need" it once errors slip in and
> such a message or error log immediately clears the issue! (You might
> be excluding some "needs" from your repertoire of necessities, okay.)
>
>> - code that exists but can never be reached is
>> untestable and can be confusing to people reading the code.  But
>> sometimes it can be useful to add a "default : printf("Internal
>> error...");" for debugging, however.
>
> This printf error message or log entry is what I suggested. It isn't
> confusing because it even _documents_ what's the case here. Rather,
> a missing default leaves the reader with an unnecessary uncertainty.
> YMMV.
>

Indeed YMMV.  But when I see a printf call that says something has gone
horribly wrong, I wonder /how/ that could happen.  I don't put such
statements into my code without it being a possible execution path.  I
agree, of course, that a good error message here makes the code somewhat
self-documenting in terms of what it does.  But it does nothing to help
say how it happened to run.  A printf call that never runs is not free -
it costs in many different ways, and should not be there unless it is
worth those costs.

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