The ptsname() function shall return the name of the slave pseudo-terminal
device associated with a master pseudo-terminal device. The fildes
argument is a file descriptor that refers to the master device. The
ptsname() function shall return a pointer to a string containing the
pathname of the corresponding slave device.
The ptsname() function need not be reentrant. A function that is not
required to be reentrant is not required to be thread-safe.
Upon successful completion, ptsname() shall return a pointer to a string
which is the name of the pseudo-terminal slave device. Upon failure,
ptsname() shall return a null pointer. This could occur if
fildes is an invalid file descriptor or if the slave device name does
not exist in the file system.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html