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().  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.1‐2008, <stdio.h>

COPYRIGHT

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

IEEE/The Open Group                                   2013                                       CTERMID(3POSIX)