C 中的“[0 ... 255] =”语法是什么？

Question

代码语法如下：

    static void *gostruct[] =
    {
        [0 ... 255] = &&l_bad,
        ['\t'] = &&l_loop, [' '] = &&l_loop, ['\r'] = &&l_loop, ['\n'] = &&l_loop,
        ['"'] = &&l_qup,
        [':'] = &&l_loop, [','] = &&l_loop,
        ['['] = &&l_up, [']'] = &&l_down, // tracking [] and {} individually would allow fuller validation but is really messy
        ['{'] = &&l_up, ['}'] = &&l_down,
        ['-'] = &&l_bare, [48 ... 57] = &&l_bare, // 0-9
        [65 ... 90] = &&l_bare, // A-Z
        [97 ... 122] = &&l_bare // a-z
    };

........
.......

l_bad:
    *vlen = cur - json; // where error'd
    return 0;

........
........

谁能解释一下这里发生了什么？语法 [0 ... 255] 和 &&l_bad 在这里做什么？

Answer 1

...是GCC提供的扩展

https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated-Inits

To initialize a range of elements to the same value, write [first ... last] = value. This is a GNU extension. For example,
 int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };

&&是另一个扩展

https://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html#Labels-as-Values

You can get the address of a label defined in the current function (or a containing function) with the unary operator &&. The value has type void *. This value is a constant and can be used wherever a constant of that type is valid. For example:
 void *ptr;
 /* ... */
 ptr = &&foo;

C 中的“[0 ... 255] =”语法是什么？

What is this "[0 ... 255] =" syntax in C?

c

gcc-extensions