SEEKDIR
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
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
seekdir
--- set the position of a directory stream
SYNOPSIS
#include <dirent.h>
void seekdir(DIR *dirp, long loc);
DESCRIPTION
The
seekdir()
function shall set the position of the next
readdir()
operation on the directory stream specified by
dirp
to the position specified by
loc.
The value of
loc
should have been returned from an earlier call to
telldir()
using the same directory stream. The new position reverts to the one
associated with the directory stream when
telldir()
was performed.
If the value of
loc
was not obtained from an earlier call to
telldir(),
or if a call to
rewinddir()
occurred between the call to
telldir()
and the call to
seekdir(),
the results of subsequent calls to
readdir()
are unspecified.
RETURN VALUE
The
seekdir()
function shall not return a value.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
The original standard developers perceived that there were restrictions
on the use of the
seekdir()
and
telldir()
functions related to implementation details, and for that reason these
functions need not be supported on all POSIX-conforming systems. They
are required on implementations supporting the XSI option.
One of the perceived problems of implementation is that returning to a
given point in a directory is quite difficult to describe formally, in
spite of its intuitive appeal, when systems that use B-trees, hashing
functions, or other similar mechanisms to order their directories are
considered. The definition of
seekdir()
and
telldir()
does not specify whether, when using these interfaces, a given
directory entry will be seen at all, or more than once.
On systems not supporting these functions, their capability can
sometimes be accomplished by saving a filename found by
readdir()
and later using
rewinddir()
and a loop on
readdir()
to relocate the position from which the filename was saved.
FUTURE DIRECTIONS
None.
SEE ALSO
fdopendir(),
readdir(),
telldir()
The Base Definitions volume of POSIX.1-2017,
<dirent.h>,
<sys_types.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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 .
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 .