Switch语句掉线...应该允许吗？ [英] Switch statement fall-through...should it be allowed?

问题描述

只要我记得我就避免使用switch语句掉线。实际上，我不记得它曾经作为一种可能的方式进入我的意识，因为它早在我的脑海中就被深深地钻了出来，因为它只不过是switch语句中的一个错误。但是，今天，我遇到了一些设计上使用它的代码，这让我立即想知道社区中的每个人对switch语句失败的看法。

For as long as I can remember I have avoided using switch statement fall-through. Actually, I can't remember it ever entering my consciousness as a possible way to do things as it was drilled into my head early on that it was nothing more than a bug in the switch statement. However, today I ran across some code that uses it by design, which got me immediately wondering what everyone in the community thinks about switch statement fall-through.

是吗？编程语言应该明确不允许（像C＃一样，尽管它提供了一种解决方法），或者它是任何一种足以使程序员掌握的语言功能吗？

Is it something that a programming language should explicitly not allow (like C# does, though it supplies a workaround) or is it a feature of any language that is powerful enough to leave in the programmer's hands?

编辑：：
我对落空的含义还不够具体。我经常使用这种类型：

I wasn't specific enough to what I meant by fall-through. I use this type a lot:

    switch(m_loadAnimSubCt){
        case 0:
        case 1:
            // Do something
            break;
        case 2:
        case 3:
        case 4:
            // Do something
            break;
   }

但是，我担心这样的事情。

However, I'm concerned about something like this.

   switch(m_loadAnimSubCt){
        case 0:
        case 1:
            // Do something, but fall through to the other cases
            // after doing it.

        case 2:
        case 3:
        case 4:
            // Do something else.
            break;
   }

这样，当大小写为0、1时，它将完成切换中的所有操作声明。我从设计上就已经看到了这一点，但我不知道是否同意以这种方式使用switch语句。我认为第一个代码示例非常有用且安全。第二种似乎很危险。

This way whenever the case is 0, 1 it will do everything in the switch statement. I've seen this by design and I just don't know if I agree that switch statements should be used this way. I think the first code example is a very useful and safe. The second seems kind of dangerous.

推荐答案

这可能取决于您认为的失败之处。我对这种事情没事：

It may depend on what you consider fallthrough. I'm ok with this sort of thing:

switch (value)
{
  case 0:
    result = ZERO_DIGIT;
    break;

  case 1:
  case 3:
  case 5:
  case 7:
  case 9:
     result = ODD_DIGIT;
     break;

  case 2:
  case 4:
  case 6:
  case 8:
     result = EVEN_DIGIT;
     break;
}

但是，如果您有一个case标签，后跟代码可转至另一个case标签，我几乎总是认为那是邪恶的。也许将通用代码移至函数并从两个地方调用都是更好的主意。

But if you have a case label followed by code that falls through to another case label, I'd pretty much always consider that evil. Perhaps moving the common code to a function and calling from both places would be a better idea.

并且请注意，我使用了 C ++常见问题解答 邪恶

And please note that I use the C++ FAQ definition of "evil"

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