How to get the real name of the controlling terminal?

How can one get the real name of the controlling terminal (if there is one, else an error) as a pathname? By "real name", I mean not /dev/tty, which cannot be used by other arbitrary processes to refer to the same terminal. I prefer the answer as a simple shell code (like the example below) if possible, otherwise as a C function. Note that this must work even if the standard input is redirected, so that the tty utility cannot be used: one would get a not a tty error in such a case, since tty just prints the file name of the terminal connected to standard input. Under Linux, one can use: echo "/dev/ps -p $$ -o tty | tail -n 1" but this is not portable, as according to POSIX, [the format of the terminal name is unspecified](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/ps.html#tag_20_96_18) . Concerning C functions, ctermid (NULL) returns /dev/tty, which is useless here. **Note:** according to the zsh documentation, one should be able to do zsh -c 'echo $TTY' but this currently (version 5.0.7) fails when both the standard input and the standard output are redirected: $ zsh -c 'echo $TTY > /dev/tty' /dev/tty' /dev/null /dev/tty