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DIRFD(3P)                  POSIX Programmer's Manual                 DIRFD(3P)
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
       dirfd -- extract the file descriptor used by a DIR stream
SYNOPSIS
       #include <dirent.h>
       int dirfd(DIR *dirp);
DESCRIPTION
       The dirfd() function shall return a file descriptor  referring  to  the
       same  directory  as  the  dirp  argument. This file descriptor shall be
       closed by a call to closedir().  If any attempt is made  to  close  the
       file  descriptor, or to modify the state of the associated description,
       other than by means of closedir(), readdir(), readdir_r(), rewinddir(),
       or seekdir(), the behavior is undefined.
RETURN VALUE
       Upon  successful completion, the dirfd() function shall return an inte-
       ger which contains a file descriptor for the stream pointed to by dirp.
       Otherwise, it shall return -1 and may set errno to indicate the error.
ERRORS
       The dirfd() function may fail if:
       EINVAL The dirp argument does not refer to a valid directory stream.
       ENOTSUP
              The  implementation  does  not support the association of a file
              descriptor with a directory.
       The following sections are informative.
EXAMPLES
       None.
APPLICATION USAGE
       The dirfd() function is intended to be a mechanism by which an applica-
       tion may obtain a file descriptor to use for the fchdir() function.
RATIONALE
       This  interface  was  introduced because the Base Definitions volume of
       POSIX.1-2008 does not make public the DIR data structure.  Applications
       tend  to  use  the fchdir() function on the file descriptor returned by
       this interface, and this has proven useful  for  security  reasons;  in
       particular,  it is a better technique than others where directory names
       might change.
       The description uses the term ``a file descriptor'' rather  than  ``the
       file  descriptor''.  The implication intended is that an implementation
       that does not use an fd for opendir() could still open() the  directory
       to  implement  the  dirfd()  function. Such a descriptor must be closed
       later during a call to closedir().
       An implementation that does not support file descriptors  referring  to
       directories may fail with [ENOTSUP].
       If  it  is  necessary  to  allocate an fd to be returned by dirfd(), it
       should be done at the time of a call to opendir().
FUTURE DIRECTIONS
       None.
SEE ALSO
       closedir(), fchdir(), fdopendir(), fileno(), open(), readdir()
       The Base Definitions volume of POSIX.1-2008, <dirent.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 Electri-
       cal 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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                            DIRFD(3P)