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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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CTERMID(3P) POSIX Programmer's Manual CTERMID(3P)
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.
ctermid — generate a pathname for the controlling terminal
#include <stdio.h>
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 guaranteed.
The ctermid() function need not be thread-safe if called with a
NULL parameter.
If s is a null pointer, the string shall be generated in an area
that may be static, the address of which shall be returned. The
application shall not modify the string returned. The returned
pointer might be invalidated or the string content might be
overwritten by a subsequent call to ctermid(). The returned
pointer might also be invalidated if the calling thread is
terminated. If s is not a null pointer, 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.
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 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);
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.
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 multiple threads cannot call
ctermid() with NULL as the parameter. 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.
None.
ttyname(3p)
The Base Definitions volume of POSIX.1‐2017, stdio.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 CTERMID(3P)
Pages that refer to this page: stdio.h(0p), unistd.h(0p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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