CTERMID(3P) POSIX Programmer's Manual CTERMID(3P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAMEctermid - generate a pathname for the controlling terminal
char *ctermid(char *s);
The ctermid() function shall generate a string that, when used as a
pathname, refers to the current controlling terminal for the current
process. If ctermid() returns a pathname, access to the file is not
If the application uses any of the _POSIX_THREAD_SAFE_FUNCTIONS or
_POSIX_THREADS functions, it shall ensure that the ctermid() function
is called with a non-NULL parameter.
If s is a null pointer, the string shall be generated in an area that
may be static (and therefore may be overwritten by each call), the
address of which shall be returned. Otherwise, s is assumed to point to
a character array of at least L_ctermid bytes; the string is placed in
this array and the value of s shall be returned. The symbolic constant
L_ctermid is defined in <stdio.h>, and shall have a value greater than
The ctermid() function shall return an empty string if the pathname
that would refer to the controlling terminal cannot be determined, or
if the function is unsuccessful.
No errors are defined.
The following sections are informative.
Determining the Controlling Terminal for the Current Process
The following example returns a pointer to a string that identifies the
controlling terminal for the current process. The pathname for the ter‐
minal is stored in the array pointed to by the ptr argument, which has
a size of L_ctermid bytes, as indicated by the term argument.
ptr = ctermid(term);
The difference between ctermid() and ttyname() is that ttyname() must
be handed a file descriptor and return a path of the terminal associ‐
ated with that file descriptor, while ctermid() returns a string (such
as "/dev/tty" ) that refers to the current controlling terminal if used
as a pathname.
L_ctermid must be defined appropriately for a given implementation and
must be greater than zero so that array declarations using it are
accepted by the compiler. The value includes the terminating null byte.
Conforming applications that use threads cannot call ctermid() with
NULL as the parameter if either _POSIX_THREAD_SAFE_FUNCTIONS or
_POSIX_THREADS is defined. If s is not NULL, the ctermid() function
generates a string that, when used as a pathname, refers to the current
controlling terminal for the current process. If s is NULL, the return
value of ctermid() is undefined.
There is no additional burden on the programmer-changing to use a hypo‐
thetical thread-safe version of ctermid() along with allocating a buf‐
fer is more of a burden than merely allocating a buffer. Application
code should not assume that the returned string is short, as some
implementations have more than two pathname components before reaching
a logical device name.
SEE ALSOttyname(), the Base Definitions volume of IEEE Std 1003.1-2001,
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 .
IEEE/The Open Group 2003 CTERMID(3P)