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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 dif-
       fer (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 over-
       written 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  termi-
       nal 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 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 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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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)