"=?gb18030?B?V2VuIFlp?=" <896634148(at)qq(dot)com> writes:
> lseek(STDIN_FILENO, 0, SEEK_SET);
If you are not checking for failure return from a system call,
you are in a state of sin.
> I really don't know, why the buffer's content not be "Hello world\n"?
Probably because a tty input device is not seekable.
regards, tom lane