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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

       The  ctermid()  function	 need not be thread-safe if called with a NULL

       If s is a null pointer, the string shall be generated in an  area  that
       may  be static, the address of which shall be returned. The application
       shall not modify the string returned. The  returned  pointer  might  be
       invalidated  or the string content might be overwritten by a subsequent
       call to ctermid().  If s is not a null pointer, 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  con‐
       stant 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.

       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 multiple threads cannot call ctermid()
       with NULL as the parameter. 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.



       The Base Definitions volume of POSIX.1‐2008, <stdio.h>

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal and Electronics Engineers,  Inc  and	 The  Open  Group.   (This  is
       POSIX.1-2008  with  the	2013  Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			   CTERMID(3P)

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