ctermid(3p) — Linux manual page


CTERMID(3P)             POSIX Programmer's Manual            CTERMID(3P)

PROLOG         top

       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.

NAME         top

       ctermid — generate a pathname for the controlling terminal

SYNOPSIS         top

       #include <stdio.h>

       char *ctermid(char *s);

DESCRIPTION         top

       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.

RETURN VALUE         top

       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.

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top

   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.

RATIONALE         top

       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

       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.



SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2017, stdio.h(0p)

COPYRIGHT         top

       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)