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.
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.
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.
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
IEEE/The Open Group 2013 SEEKDIR(3P)