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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

       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.

	      #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 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.


       ttyname(),  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)

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