stdout和STDOUT_FILENO之间的区别 [英] The difference between stdout and STDOUT_FILENO

问题描述

我想知道Linux C中 stdout 和 STDOUT_FILENO 之间的区别.

I was wondering the difference between stdout and STDOUT_FILENO in Linux C.

经过一些搜索工作，我得出以下结论.您能帮我查看一下并更正其中的任何错误吗?谢谢

After some searching work, I draw the following conclusion. Could you help me review it and correct any mistake in it? Thanks

• stdout 属于C语言的标准I/O流；类型为FILE *并在stdio.h中定义的

• stdout belongs to standard I/O stream of C language; whose type is FILE* and defined in stdio.h

STDOUT_FILENO 在 unistd.h 处定义.它是LINUX系统的文件描述符.在 unistd.h 中，解释如下:

STDOUT_FILENO, possessing an int type, is defined at unistd.h. It's a file descriptor of LINUX system. In unistd.h, it's explained as below:

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.

因此，我认为 STDOUT_FILENO 属于系统级调用，并且在某种程度上类似于系统API. STDOUT_FILENO 可用于描述系统中的任何设备.

So, in my opinion, the STDOUT_FILENO belongs system-level calling and, to some extent, like a system API. STDOUT_FILENO can be used to describe any device in system.

stdout 位于较高的级别(用户级别?)，并且实际上封装了 STDOUT_FILENO 的详细信息. stdout 具有I/O缓冲区.

The stdout locates in a higher level (user level?) and actually encapsulate the details of STDOUT_FILENO. stdout has I/O buffer.

我了解他们之间的区别.谢谢您的任何评论或纠正.

That's my understand about their difference. Any comment or correction is appreciated, thanks.

推荐答案

stdout 是 FILE * "constant"，提供标准输出流.因此，显然 fprintf(stdout，"x =％d \ n"，x); 具有与 printf("x =％d \ n"，x);相同的行为>;您将 stdout 用于< stdio.h> 函数，例如 fprintf ， fputs 等.

stdout is 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 stdout for <stdio.h> functions like fprintf, fputs etc..

STDOUT_FILENO 是一个整数文件描述符(实际上是整数1).您可以将其用于 write 系统调用.

STDOUT_FILENO is an integer file descriptor (actually, the integer 1). You might use it for write syscall.

两者之间的关系是 STDOUT_FILENO == fileno(stdout)

^{(除了在执行诸如 fclose(stdout); 之类的怪异事情之后，或者在某些 fclose(stdin) freopen 之外，>，您几乎应该永远不要这样做！请参见此.com/users/4279/jf-sebastian> JFSebastian )}

^{(Except after you do weird things like fclose(stdout);, or perhaps some freopen after some fclose(stdin), which you should almost never do! See this, as commented by J.F.Sebastian)}

您通常更喜欢 FILE * 东西，因为它们是经过缓冲的(因此通常表现良好).有时，您可能需要调用 fflush 刷新缓冲区.

You usually prefer the FILE* things, because they are buffered (so usually perform well). Sometimes, you may want to call fflush to flush buffers.

您可以为系统调用使用文件描述符编号，例如投票(2).但是使用系统调用很麻烦.它可能会给您带来很好的效率(但是很难编写代码)，但是 stdio 库通常足够好(并且更易于移植).

You could use file descriptor numbers for syscalls like write(2) (which is used by the stdio library), 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 stdio library is good enough (and more portable).

(当然，对于stdio函数，您应该 #include< stdio.h> ，以及 #include< unistd.h> -和其他一些标头-对于像 write 这样的系统调用，并且stdio函数是通过syscalls实现的，因此 fprintf 可以调用 write ).

(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 fprintf may call write).

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