What does this syntax of switch case mean?

Question

I saw some C code like this:

int check = 10:

switch(check) {
            case 1...9: printf("It is 2 to 9");break;
            case 10: printf("It is 10");break;
}

What does this case 1...9: mean? Is it standard?

thank you man, I basically can guess what does this mean, but I need to get confirmed and know whether this is standarded? — user2131316, Jul 17 '13 at 12:36
@user2131316 As I noted below you can use `gcc -std=c99 -pedantic` to check against a specific standard — Shafik Yaghmour, Jul 17 '13 at 12:39
Does this answer your question? [What is "..." in switch-case in C code](https://stackoverflow.com/questions/18853502/what-is-in-switch-case-in-c-code) — phuclv, Jan 22 '20 at 07:22
[Are Elipses in case statements standard C/C++](https://stackoverflow.com/q/5924681/995714) — phuclv, Jan 22 '20 at 07:23

score 8 · Accepted Answer · answered Jul 17 '13 at 12:27

8

It's a GNU C extension called case range.

As noted in the document, you have to put spaces between the low and high value of the range.

case 1 ... 9:
    statement;

is equivalent to:

case 1:
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
case 9:
    statement;

answered Jul 17 '13 at 12:27

ouah

ok, thank you, but this GNU C is standard C or is it supported by C99 or what? – user2131316 Jul 17 '13 at 12:29
As far as I can tell `1...9` is a syntax error, there needs to be a space. – Shafik Yaghmour Jul 17 '13 at 12:30
@user2131316 GNU C is not C. It is an extension to C. – ouah Jul 17 '13 at 12:30
then can we use it as normal or we need to install something in order to build it? – user2131316 Jul 17 '13 at 12:32
@user2131316 by default `gcc` is c89 + GNU extensions. – ouah Jul 17 '13 at 12:32

score 1 · Answer 2 · answered Jul 17 '13 at 12:33

This is gcc extension, they easiest way to usually figure this out with gcc at least is to use -pedantic argument:

gcc -pedantic

will warn:

warning: range expressions in switch statements are non-standard [-pedantic]

and if you wanted to check against a specific standard, for example c99, you do as follows:

 gcc -std=c99 -pedantic

Also, this is not correct:

case 1...9:

you need spaces between the dots and numbers:

case 1 ... 9:

as noted in the document:

Be careful: Write spaces around the ..., for otherwise it may be parsed wrong when you use it with integer values.

2 Answers2