C 语言中的“[0... 255] =”语法是什么？

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;


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

有人能解释一下这里做了什么吗? 语法 [0 ... 255]和 &&l_bad在这里做什么？

6561

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最佳答案

... is an extension provided by GCC

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 };

&& is another extension

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;