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

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(P)
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