From: janis_papanagnou+ng@hotmail.com

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.

Janis

>
> $ 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)
>       |         ^~~~~~
>
>
>

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