C switch case 中的多个标签值 [英] multiple label value in C switch case

问题描述

以下是 Dennis M Ritchie 的书 ANSI C 的摘录:

Following is the excerpt from Dennis M Ritchie's book, ANSI C:

每种情况都由一个或多个整数值常量或常量表达式标记.

Each case is labeled by one or more integer-valued constants or constant expressions.

我无法想出一个开关案例的例子，其中我们有带有多个标签的案例.

I could not come up with an example of a switch case where we have case with more than one label.

任何说明上述属性的示例都会有所帮助.

Any example illustrating the above property will be helpful.

推荐答案

这是我在检查选项的程序中找到的示例:

Here's an example I found in a program which checks options:

switch (optionChar) {
    case 'a': case 'A':
    case 'f': case 'F':
    case 'q': case 'Q':
    case 'z': case 'Z': optionsOk = TRUE;  break;
    default:            optionsOk = FALSE; break;
}

这可能不是我编写代码的方式^(a) 但它肯定是有效的.当使用 case 导致代码比长组 || 连词更短时，通常会使用它来满足需要基本相似操作的条件:

It's probably not how I would have written the code^(a) but it's certainly valid. It's often used when the use of case results in shorter code than a long seties of || conjunctions for conditions that need substantially similar actions:

if (optionChar == 'a' || optionChar == 'A' || ...

<小时>

而且，事实上，K&R 本身就有一个例子，就在你提到的引用之后.它在计算不同字符类的代码中:

---

And, in fact, K&R itself has an example, right after the quote you mention. It's in the code for counting different character classes:

while ((c = getchar()) != EOF) {
    switch (c) {
    case '0': case '1': case '2': case '3': case '4':
    case '5': case '6': case '7': case '8': case '9':
        ndigit[c-'0']++;
        break;
    case ' ': case '\n': case '\t':
        nwhite++;
        break;
    default:
        nother++;
        break;
    }
}

<小时>

^(a) 我可能会做一些类似的事情:

---

^(a) I probably would have done something along the lines of:

optionsOk = (strchr("aAfFqQzZX", optionChar) != NULL);

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