C restore stdout to terminal

Question

I am working with a multi-thread program.

First I redirect my stdout to a certain file. No problem there (I used dup2(fd, 1) where fd is t

Answer 1

If the program runs on a Linux environment, you can freopen ("/dev/stdout", "a", stdout).

But if you know that stdout was the terminal, freopen ("/dev/tty", "a", stdout) or the equivalent for other OSs—even Windows.

Answer 2

#include <unistd.h>

...

int saved_stdout;

...

/* Save current stdout for use later */
saved_stdout = dup(1);
dup2(my_temporary_stdout_fd, 1);

... do some work on your new stdout ...

/* Restore stdout */
dup2(saved_stdout, 1);
close(saved_stdout);

Answer 3

Before you do the dup2(fd, STDOUT_FILENO), you should save the current open file descriptor for standard output by doing int saved_stdout = dup(STDOUT_FILENO); (letting dup() choose an available file descriptor number for you). Then, after you've finished with the output redirected to a file, you can do dup2(saved_stdout, STDOUT_FILENO) to restore standard output to where it was before you started all this (and you should close saved_stdout too).

You do need to worry about flushing standard I/O streams (fflush(stdout)) at appropriate times as you mess around with this. That means 'before you switch stdout over'.