案例中的三个点(案例'0' ... '9':) 是有效的C 语言切换语法吗? [英] Are triple dots inside a case (case '0' ... '9':) valid C language switch syntax?

问题描述

我在 DRBD 软件 (user/drbdtool_common.c)

const char* shell_escape(const char* s)
{
    /* ugly static buffer. so what. */
    static char buffer[1024];
    char *c = buffer;

    if (s == NULL)
        return s;

    while (*s) {
        if (buffer + sizeof(buffer) < c+2)
            break;

        switch(*s) {
        /* set of 'clean' characters */
        case '%': case '+': case '-': case '.': case '/':
        case '0' ... '9':
        case ':': case '=': case '@':
        case 'A' ... 'Z':
        case '_':
        case 'a' ... 'z':
            break;
        /* escape everything else */
        default:
            *c++ = '\';
        }
        *c++ = *s++;
    }
    *c = '';
    return buffer;
}

我以前从未在 C 中见过这种三点"结构(case '0' ... '9':).它是一种有效的标准 C 语言吗?或者这是某种预处理器魔法?这里发生了什么?

I have never seen this "triple dot" construction (case '0' ... '9':) in C before. Is it a valid standard C language? Or is that some kind of preprocessor magic? What's going on here?

推荐答案

正如其他人所说，这是一个特定于编译器的扩展.使用正确的选项(例如，gcc -std=c99 -pedantic)调用编译器，它应该会发出警告.

As others have said, this is a compiler-specific extension. Invoke the compiler with the right options (say, gcc -std=c99 -pedantic), and it should warn you about it.

我还要指出，它的使用具有潜在的危险，除了另一个编译器可能不会实现它.'a' ... 'z' 表示 26 个小写字母——但 C 标准不保证它们的值是连续的.例如，在EBCDIC中，字母之间有标点符号.

I'll also point out that its use is potentially dangerous, apart from the fact that another compiler might not implement it. 'a' ... 'z' denotes the 26 lowercase letters -- but the C Standard doesn't guarantee that their values are contiguous. In EBCDIC, for example, there are punctuation characters among the letters.

另一方面，我怀疑 gcc 或 Sun C 是否支持使用字母 不 连续的字符集的系统.(它们是 ASCII 及其所有派生词，包括 Latin-1、Windows-1252 和 Unicode.)

On the other hand, I doubt that either gcc or Sun C supports systems that use a character set in which the letters aren't contiguous. (They are in ASCII and all its derivatives, including Latin-1, Windows-1252, and Unicode.)

另一方面，它不包括重音字母.(取决于 DRBD 的使用方式，这可能是也可能不是问题.)

On the other other hand, it excludes accented letters. (Depending on how DRBD is used, that may or may not be an issue.)

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