CTERMID(3P)               POSIX Programmer's Manual              CTERMID(3P)

PROLOG         top

       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         top

       ctermid — generate a pathname for the controlling terminal

SYNOPSIS         top

       #include <stdio.h>

       char *ctermid(char *s);

DESCRIPTION         top

       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

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

RETURN VALUE         top

       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         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top

   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

           #include <stdio.h>
           char term[L_ctermid];
           char *ptr;

           ptr = ctermid(term);


       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         top

       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

       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.



SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2008, stdio.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                         CTERMID(3P)