什么时候cout flush？ [英] When does cout flush?

问题描述

我知道 endl 或调用 flush（）会清除它。我也知道当你在 cout 后调用 cin 时，它也会刷新。并且当程序退出时。还有其他情况， cout 刷新吗？

I know endl or calling flush() will flush it. I also know that when you call cin after cout, it flushes too. And also when the program exit. Are there other situations that cout flushes?

我只是写了一个简单的循环， ，但我可以看到它正在打印到屏幕上。为什么？谢谢！

I just wrote a simple loop, and I didn't flush it, but I can see it being printed to the screen. Why? Thanks!

for (int i =0; i<399999; i++) {

        cout<<i<<"\n";

}

此外，完成时间与 endl 两者约7秒。

Also the time for it to finish is same as withendl both about 7 seconds.

for (int i =0; i<399999; i++) {

        cout<<i<<endl;

}

推荐答案

没有标准的严格规则 - 只有 endl 将冲洗，但实施可以随时刷新喜欢。

There is no strict rule by the standard - only that endl WILL flush, but the implementation may flush at any time it "likes".

当然，在400K以下的所有数字的总和是6 * 400K = 2.4MB，这不太可能适合缓冲区，并且循环快足够运行，你不会注意到每个输出之间需要一段时间。尝试这样：

And of course, the sum of all digits in under 400K is 6 * 400K = 2.4MB, and that's very unlikely to fit in the buffer, and the loop is fast enough to run that you won't notice if it takes a while between each output. Try something like this:

 for(int i = 0; i < 100; i++)
 {
   cout<<i<<"\n";
   Sleep(1000);
 }

（如果您使用的是基于Unix的操作系统，请使用 sleep（1）改为 - 或添加一个需要一些时间的循环等）

(If you are using a Unix based OS, use sleep(1) instead - or add a loop that takes some time, etc)

编辑：应该注意，这不是保证显示任何差异。我知道在我的Linux机器上，如果你没有在这种特定类型的场景中刷新，它不会输出任何东西 - 但是，一些系统可能会冲洗\\\
或类似的东西。

It should be noted that this is not guaranteed to show any difference. I know that on my Linux machine, if you don't have a flush in this particular type of scenario, it doesn't output anything - however, some systems may do "flush on \n" or something similar.

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