ttyname

Returns a pointer to the null-terminated name of the terminal device associated with file descriptor 0, the default input device (stdin).

#include  <unixio.h>

char *ttyname (void);

This function is provided only for UNIX compatibility and has limited use in the OpenVMS environment.

x	A pointer to a null-terminated string.
0	Indicates that SYS$INPUT is not a TTY device.