bionic (3) ctermid.3posix.gz

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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>


       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 .