C Code "[0 … 255] From ="...What's that?

    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;

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

Source: [here]

What is "..." and "&&l_bad" in this code? I can't search for moles and it's frustrating.

c gcc-extension

2022-09-22 22:18

1 Answers

... is an extension provided by GCC that is used to initialize a specific range to the same value.

If you look at Designated Initiators

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 };

&& is also extension, which is used to determine the address of the label within the function (different from binary op logic AND) If you look at 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;

2022-09-22 22:18

C Code "[0 … 255] From ="...What's that?

1 Answers

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