case 语句中的省略号是标准 C/C++

发布于 2024-11-06 01:29:47 字数 606 浏览 1 评论 0原文

我正在浏览 Linux 内核中的一些代码，遇到了类似 case '0' ... '9': 的语句

。为了尝试这个，我创建了下面的测试程序。

#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;
    }
}

上面的程序确实可以编译，尽管我以前从未在 case 语句构造中遇到过省略号。这是标准的 C 和 C++ 还是 GNU 对该语言的特定扩展？

原文

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?

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半枫 2024-11-13 01:29:47

这是 GNU C 编译器的 case range 扩展，它不是标准 C 或 C++。

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丑疤怪 2024-11-13 01:29:47

那是一个扩展。使用 -pedantic 编译程序会给出：

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 给出更好的警告：

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:
            ^

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:
            ^

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