create backup file descriptor?

Question

  stdinBackup = 4;
  dup2(0, stdinBackup);

Currently I am doing the above to 'backup' stdin so that it can be restored from backup later after it has been redirected somewhere else. I have a feeling that I am doing a lot wrong? (eg arbitrarily assigning 4 is surely not right). Anyone point me in the right direction?

Answer 1

If you just want to make a general copy for your own use, there is no need to use dup2(). Just use a plain dup():

#include <stdio.h>

int stdinBackup = dup(STDIN_FILENO);

You only need to use dup2() when you care about the duplicate's actual value.

See here for the definition of the symbolic constant STDIN_FILENO, which is far better than using a naked 0 in the code.