CODEWITHSUNDEEP
cswitch-statement
Kartik
Kartik

Reputation: 53

Having a switch statement case label without a value

I was working around with the Switch statement when I accidentally wrote the following piece of code(on gcc in C)

        int a = 2;
        switch(a)
        {
                default:
                        printf("Default\n");
                case 1:
                        printf("One\n");          
                case2 :
                        printf("Two\n");
        }

The output I got was:

Default

One

Two

I am able to understand how this output came about, however I don't understand why this does not throw up an error, I mean I clearly don't have a case label (in case2) right? Also I have observed the same result if I right "case2" as "casex" for example. Whereas if I don't put in any case label it gives a compile time error.

Any help would be appreciated, thanks!

Upvotes: 2

Views: 1645

Answers (3)

John Bollinger
John Bollinger

Reputation: 180316

I am able to understand how this output came about, however I don't understand why this does not throw up an error, I mean I clearly don't have a case label (in case2) right?

Yes, case2 : is not a case label, but it is a valid valid ordinary label. Any statement may be preceded by such a label. Since you're using GCC, you could consider turning on the -Wall option (or specifically -Wunused-label), in which case GCC should warn that that label is unused (because it is not the target of any goto statement).

Also I have observed the same result if I right "case2" as "casex" for example.

Well, sure. casex : is also a valid ordinary label.

Whereas if I don't put in any case label it gives a compile time error.

I suppose you must mean that you leave the colon, but remove the whole label text (case2 / casex). That would indeed yield invalid code. If you removed the whole line, however, then of course that would be fine.

Upvotes: 4

bruno
bruno

Reputation: 32596

you missed the break so the execution continue after each case (but with a != 1 to have these 3 outputs)

note case2: is considered as a label (for a goto) so is not an error

Upvotes: 2

CIsForCookies
CIsForCookies

Reputation: 12817

What happens here is you got to the default label, and because you had no break, you followed through to all other cases.

Upvotes: -1

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