开关案例陈述中的分号

Question

Is there any significance to adding a semicolon in the case statement that is part of a fall-through ? I see that the fall-through works as expected and guess the semicolon is interpreted as an empty statement. But are there pros/cons to having the semicolon ? Is there a certain best practice that is recommended ? In the javascript example below, see the semicolon in the first case statement.

    switch(a) {
        case 2:;
        case 3: alert('hello'); break;
        default: alert('default hello');
    }

I am also interested in knowing about the best practices related to the above in C, C++ and Java. I also saw some documentation that C# throws a compilation error if a case statement part of a fall-through has a statement. Will an empty statement like the above trigger an error in C#?

Answer 1

No, it does not make any difference.

I recommend you not to use it since it makes the code less clear, in my opinion.

In C# it's an error though. D does not allow ; as an empty statement too, you have to use {} .

Answer 2

; does nothing for you in C, C++, and Java. If you don't need it, don't use it. But do throw future readers of your code a bone if you are implementing Duff's Device or a variant and leave them "fall through" or "no break" comments.

In C#

switch(a) {
    case 2:;
    case 3: Console.WriteLine("hello"); break;
    default: Console.WriteLine("default hello");
}

prevents cases 2 and 3 executing the same code by interrupting the little bit of fall through C# does allow.

switch(a) {
    case 2:
    case 3: Console.WriteLine("hello"); break;
    default: Console.WriteLine("default hello"); break;
}

Would be valid with cases 2 and 3 executing the same code.

Answer 3

best practice

Is usually not to use an empty statement.

Will an empty statement like the above trigger an error in C#?

Yes.

Answer 4

Syntactically it's the same

It's bound to confuse someone though so I'd recommend against using it