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.
seekdir — set the position of a directory stream
void seekdir(DIR *dirp, long loc);
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 seekdir() function shall not return a value.
No errors are defined.
The following sections are informative.
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.
fdopendir(), readdir(), telldir()
The Base Definitions volume of POSIX.1‐2017,
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 .
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