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.

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

RETURN VALUE

       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().   The  returned
       pointer  might also be invalidated if the calling thread is terminated.  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 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 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 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 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 POSIX.1‐2017, <stdio.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                       CTERMID(3POSIX)