用C刷新缓冲区 [英] Flushing buffers in C
问题描述
应该 fflush（）不能用来刷新缓冲区，即使它是一个输出流？
Should fflush() not be used to flush a buffer even if it is an output stream?
这是什么用呢？我们如何在一般刷新缓冲区？
What is it useful for? How do we flush a buffer in general?
推荐答案
我从来没有听说过不刷新输出缓冲区，我很想听到你的上源。刷新输出缓冲器：
I've never heard not to flush the output buffer, and I would be interested to hear your source on that. Flushing the output buffers:
printf("Buffered, will be flushed");
fflush(stdout); // Prints to screen or whatever your standard out is
或
fprintf(fd, "Buffered, will be flushed");
fflush(fd); //Prints to a file
可以是一个非常有用的技术。你为什么要刷新输出缓冲区？通常，当我做到这一点，那是因为code崩溃，我要调试的东西。该标准缓冲液将不打印每次你打电话的printf（）等待，直到它满了一次转储一堆。所以，如果你尝试检查，如果你做它在崩溃之前一个函数调用，它有助于的printf 类似来到这里！，有时缓冲撞击发生之前没有被刷新，你不能告诉你真正得到多远。
Can be a very helpful technique. Why would you want to flush an output buffer? Usually when I do it, it's because the code is crashing and I'm trying to debug something. The standard buffer will not print everytime you call printf() it waits until it's full then dumps a bunch at once. So if you're trying to check if you're making it to a function call before a crash, it's helpful to printf something like "got here!", and sometimes the buffer hasn't been flushed before the crash happens and you can't tell how far you've really gotten.
另外，它是有帮助的，时间是在多进程和多线程code。同样，缓冲区并不总是刷新到一个呼叫的printf（），所以如果你想知道多进程的执行真正秩序应该fflush缓冲区以后每隔打印。
Another time that it's helpful, is in multi-process or multi-thread code. Again, the buffer doesn't always flush on a call to a printf(), so if you want to know the true order of execution of multiple processes you should fflush the buffer after every print.
我做一个习惯，这样做，它节省了我调试了很多头痛。我能想到的这样做唯一的缺点是，的printf（）是一个昂贵的操作（这就是为什么它默认情况下不刷新缓冲区）。
I make a habit to do it, it saves me a lot of headache in debugging. The only downside I can think of to doing so is that printf() is an expensive operation (which is why it doesn't by default flush the buffer).
至于刷新输入缓冲区（标准输入），你不应该这样做。法拉盛标准输入是根据C11标准定义的操作§7.21.5.2第2部分：
As far as flushing the input buffer (stdin), you should not do that. Flushing stdin is undefined behavior according to the C11 standard §7.21.5.2 part 2:
如果流点到输出流... fflush函数导致该流的任何未写入的数据...要写入该文件;否则，行为是不确定的。
If stream points to an output stream ... the fflush function causes any unwritten data for that stream ... to be written to the file; otherwise, the behavior is undefined.
在某些系统，Linux是一个作为你可以在 fflush手册页看到（） ，有一个定义的行为，但它依赖于系统，使您的code将不可移植。
On some systems, Linux being one as you can see in the man page for fflush(), there's a defined behavior but it's system dependent so your code will not be portable.
现在，如果你在你可以使用 fpurge（）上输入缓冲区很担心垃圾套牢。
请参见 fflush（）和 fpurge（）
Now if you're worried about garbage "stuck" in the input buffer you can use fpurge() on that.
See here for more on fflush() and fpurge()
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