如果在while循环的条件后放置分号，会发生什么情况? [英] What happens when one places a semi-colon after a while loop's condition?

问题描述

我遇到过几次这样的情况:

I've come across a situation like this a few times:

while (true) {

while (age == 5); //What does this semi-colon indicate?
//Code
//Code
//Code

}

while(true)表示这是一个无限循环，但是我很难理解while条件完成后的分号，这不等于吗?:

The while(true) indicates that this is an infinite loop, but I have trouble understanding what the semi-colon after the while condition accomplishes, isn't it equivalent to this?:

while (age == 5) { }

//Code
//Code

换句话说，这是否意味着while循环是无用的，因为它永远不会进入该块?

In other words, does it mean that the while loop is useless as it never enters the block?

推荐答案

while (age == 5);     // empty statement

等同于

while (age == 5) { }  // empty block

更新:即使没有要执行的主体，也不意味着循环终止.取而代之的是，它将简单地反复遍历条件(可能具有或依赖于副作用)，直到满足条件为止.这是带有goto的等效形式:

Update: Even if there is no body to execute, doesn't mean that the loop terminates. Instead it will simply loop repeatedly over the conditional (which may have or rely upon side-effects) until it is satisfied. Here is the equivalent form with a goto:

loop:
if (age == 5)
  goto loop;

此结构有时 用作繁忙循环等待标志被线程代码已更改. (确切的使用和有效性因语言，算法和执行环境而异.)

This construct is sometimes used as a busy-loop waiting on a flag to be changed in threaded code. (The exact use and validity varies a good bit by language, algorithm, and execution environment.)

我发现使用;表示空块" 空语句是一个可使用的可疑构造，因为这样的问题:

I find the use of ; for an "empty block" empty statement a questionable construct to use because of issues like this:

while (age == 5); {
   Console.WriteLine("I hate debugging");
}

(添加新代码时，我已经多次见过该错误.)

(I have seen this bug several times before, when new code was added.)

快乐的编码.

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