LINUX C中stdout和STDOUT_FILENO的区别
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The difference between stdout and STDOUT_FILENO in LINUX C
提问by Bing Lu
I was wondering the difference between stdoutand STDOUT_FILENOin Linux C.
我想知道Linux C 中stdout和之间的区别STDOUT_FILENO。
After some searching work, I draw the following conclusion. Could you help me review it and correct any mistake in it? Thanks
经过一番搜索工作，我得出以下结论。你能帮我检查一下并纠正其中的任何错误吗？谢谢
stdoutbelongs to standard I/O stream of C language; whose type is FILE* and defined in stdio.hSTDOUT_FILENO, possessing an int type, is defined atunistd.h. It's a file descriptor of LINUX system. Inunistd.h, it's explained as below:
stdout属于C语言的标准I/O流；其类型为 FILE* 并在 stdio.h 中定义STDOUT_FILENO，拥有一个 int 类型，在 处定义unistd.h。它是LINUX系统的文件描述符。中unistd.h，解释如下：
The following symbolic constants shall be defined for file streams: STDERR_FILENO File number of stderr; 2. STDIN_FILENO File number of stdin; 0. STDOUT_FILENO File number of stdout; 1.
The following symbolic constants shall be defined for file streams: STDERR_FILENO File number of stderr; 2. STDIN_FILENO File number of stdin; 0. STDOUT_FILENO File number of stdout; 1.
So, in my opinion, the STDOUT_FILENObelongs system-level calling and, to some extent, like a system API. STDOUT_FILENOcan be used to describe any device in system.
所以，在我看来，它STDOUT_FILENO属于系统级调用，在某种程度上，就像一个系统 API。STDOUT_FILENO可用于描述系统中的任何设备。
The stdoutlocates in a higher level (user level?) and actually encapsulate the details of STDOUT_FILENO. stdouthas I/O buffer.
在stdout较高的水平（用户级？），实际所处封装的细节STDOUT_FILENO。stdout有 I/O 缓冲区。
That's my understand about their difference. Any comment or correction is appreciated, thanks.
这就是我对它们差异的理解。任何意见或更正表示赞赏，谢谢。
采纳答案by Basile Starynkevitch
stdoutis a FILE*"constant" giving the standard outout stream. So obviously fprintf(stdout, "x=%d\n", x);has the same behavior as printf("x=%d\n", x);; you use stdoutfor <stdio.h>functions like fprintf, fputsetc..
stdout是FILE*给出标准输出流的“常量”。所以显然fprintf(stdout, "x=%d\n", x);具有相同的行为printf("x=%d\n", x);；您stdout用于,等<stdio.h>功能。fprintffputs
STDOUT_FILENOis an integer file descriptor (actually, the integer 1). You might use it for writesyscall.
STDOUT_FILENO是一个整数文件描述符（实际上是整数 1）。您可以将它用于write系统调用。
The relation between the two is STDOUT_FILENO == fileno(stdout)
两者的关系是 STDOUT_FILENO == fileno(stdout)
(Except after you do weird things like fclose(stdout);, or perhaps some freopenafter some fclose(stdin), which you should almost never do! See this, as commented by J.F.Sebastian)
（除了在你做了一些奇怪的事情之后fclose(stdout);，或者一些freopen之后fclose(stdin)，你几乎不应该做的事情！看到这个，正如JFSebastian评论的那样）
You usually prefer the FILE*things, because they are buffered (so usually perform well). Sometimes, you may want to call fflushto flush buffers.
你通常更喜欢这些FILE*东西，因为它们是缓冲的（所以通常表现良好）。有时，您可能想要调用fflush刷新缓冲区。
You could use file descriptor numbers for syscallslike write(2)(which is used by the stdiolibrary), or poll(2). But using syscalls is clumpsy. It may give you very good efficiency (but that is hard to code), but very often the stdiolibrary is good enough (and more portable).
您可以将文件描述符编号用于系统调用，例如write(2)（由stdio库使用）或poll(2)。但是使用系统调用是笨拙的。它可能会给您带来非常好的效率（但这很难编码），但通常该stdio库已经足够好（并且更便携）。
(Of course you should #include <stdio.h>for the stdio functions, and #include <unistd.h>-and some other headers- for the syscalls like write. And the stdio functions are implemented with syscalls, so fprintfmay call write).
（当然，您应该#include <stdio.h>针对 stdio 函数，以及#include <unistd.h>- 以及其他一些标头 - 用于系统调用，例如write。并且 stdio 函数是使用系统调用实现的，因此fprintf可以调用write）。
