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 (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

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 declara-
       tions 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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                   CTERMID(3P)