osx man page for ttyname

TTYNAME(3)						   BSD Library Functions Manual 						TTYNAME(3)

NAME
     isatty, ttyname, ttyslot -- get name of associated terminal (tty) from file descriptor

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     int
     isatty(int fildes);

     char *
     ttyname(int fildes);

     int
     ttyslot(void);

DESCRIPTION
     These functions operate on the system file descriptors for terminal type devices.	These descriptors are not related to the standard I/O FILE
     typedef, but refer to the special device files found in /dev and named /dev/ttyxx and for which an entry exists in the initialization file
     /etc/ttys.  (See ttys(5).)

     The isatty() function determines if the file descriptor fildes refers to a valid terminal type device.

     The ttyname() function gets the related device name of a file descriptor for which isatty() is true.

     The ttyslot() function fetches the current process' control terminal number from the ttys(5) file entry.

RETURN VALUES
     The ttyname() function returns the null terminated name if the device is found and isatty() is true; otherwise, a NULL pointer is returned.

     The ttyslot() function returns the unit number of the device file if found; otherwise, the value zero is returned.

FILES
     /dev/*
     /etc/ttys

SEE ALSO
     ioctl(2), ttys(5)

HISTORY
     A isatty(), ttyname(), and ttyslot() function appeared in Version 7 AT&T UNIX.

BUGS
     The ttyname() function leaves its result in an internal static object and returns a pointer to that object.  Subsequent calls to ttyname()
     will modify the same object.

BSD
								   June 4, 1993 							       BSD