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NAME
ctermid - generate a pathname for the controlling terminal
SYNOPSIS
#include <stdio.h> char *ctermid(char *s);
DESCRIPTION
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
guaranteed.
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.
RETURN VALUE
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
0.
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.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
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 terminal 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.
#include <stdio.h>
...
char term[L_ctermid];
char *ptr;
ptr = ctermid(term);
APPLICATION USAGE
The difference between ctermid() and ttyname() is that ttyname() must be handed a file descriptor and
return a path of the terminal associated 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.
RATIONALE
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 hypothetical thread-safe version of
ctermid() along with allocating a buffer 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.
FUTURE DIRECTIONS
None.
SEE ALSO
ttyname() , the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>
COPYRIGHT
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 .