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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 func-
       tions, 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. Other-
       wise, 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 termi-
       nal 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 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 hypothetical thread-safe
       version of ctermid() along with allocating a buffer is more of a burden than merely  allo-
       cating  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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				       CTERMID(P)
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