Are Elipses in case statements standard C/C++

Question

I was browsing some code in the linux kernel and I came across the statements like case '0' ... '9':

To try this out I created the test program below.

#include <iostream>

int main()
{
    const int k = 15;

    switch (k)
    {
    case 0 ... 10:
        std::cout << "k is less than 10" << std::endl;
        break;
    case 11 ... 100:
        std::cout << "k is between 11 and 100" << std::endl;
        break;
    default:    
        std::cout << "k greater than 100" << std::endl;
        break;
    }
}   

The program above does compile although I have never come across the elipses in case statement construct before. Is this standard C and C++ or is this a GNU specific extension to the language?

Answer 1

That is the case range extension of the GNU C compiler, it is not standard C or C++.

Answer 2

That's an extension. Compiling your program with -pedantic gives:

example.cpp: In function ‘int main()’:
example.cpp:9: error: range expressions in switch statements are non-standard
example.cpp:12: error: range expressions in switch statements are non-standard

clang gives even better warnings:

example.cpp:9:12: warning: use of GNU case range extension [-Wgnu]
    case 0 ... 10:
           ^
example.cpp:12:13: warning: use of GNU case range extension [-Wgnu]
    case 11 ... 100:
            ^

Answer 3

This is a GCC extension to C, mentioned in this answer to what is basically a duplicate question, and confirmed in the GCC documentation.