linux文件描述符0 1 2是否不适用于stdin，stdout和stderr? [英] Is it possible that linux file descriptor 0 1 2 not for stdin, stdout and stderr?

问题描述

程序启动时，默认情况下是否接受stdin，stdout和stderr的文件描述符0、1和2?由于已经使用了这些值，因此诸如open(...)，socket(...)之类的API调用是否不会返回0、1和2?在任何情况下，open(...)或socket(...)都将返回0、1或2.并且0、1和2与stdin，stdout和stderr无关.

When a program begins, does it take file descriptors 0, 1 and 2 for stdin, stdout and stderr by default?. And will API calls such as open(...), socket(...) not return 0, 1 and 2 since these values are already taken?. Is there any case in which open(...) or socket(...) would return 0, 1 or 2. And 0, 1 and 2 are not related with stdin, stdout, and stderr.

推荐答案

在文件描述符级别， stdin 定义为文件描述符0 ， stdout 定义为文件描述符1 ；并且 stderr 被定义为文件描述符2 .参见此.

At the file descriptor level, stdin is defined to be file descriptor 0, stdout is defined to be file descriptor 1; and stderr is defined to be file descriptor 2. See this.

即使您的程序或外壳程序发生了更改(例如，使用 dup2(2))什么是文件描述符0，它始终保持为 stdin (因为根据定义，STDIN_FILENO为0).

Even if your program -or the shell- changes (e.g. redirect with dup2(2)) what is file descriptor 0, it always stays stdin (since by definition STDIN_FILENO is 0).

^{因此， stdin 当然可以是管道，套接字或文件(​​而不是终端).如果它是tty，则可以使用 isatty(3)进行测试和/或使用 fstat(2)来获取状态信息}

^{So of course stdin could be a pipe or a socket or a file (not a terminal). You could test with isatty(3) if it is a tty, and/or use fstat(2) to get status information on it.}

系统调用，例如 open(2)或 pipe(2)或

Syscalls like open(2) or pipe(2) or socket(2) may give e.g. STDIN_FILENO (i.e. 0) if that file descriptor is free (e.g. because it has been close(2)-d before). But when that occurs, it is still stdin by definition.

当然，在 stdio(3)中， FILE流 stdin 有点复杂.您的程序可以 fclose(3)，

Of course, in stdio(3), the FILE stream stdin is a bit more complex. Your program could fclose(3), freopen(3), fdopen(3) ...

^{当神奇地启动/sbin/init作为内核时，内核可能会将 stdin ， stdout 和 stderr 文件描述符设置到控制台.第一步.}

^{Probably the kernel sets stdin, stdout, and stderr file descriptors to the console when magically starting /sbin/init as the first process.}

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