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 overwritten 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 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 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,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications 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
       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 .