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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 (consult 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 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);
APPLICATION USAGE
       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.
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 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.
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 .

IEEE/The Open Group                  2003                          CTERMID(3P)