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[thirdparty/man-pages.git] / man3 / telldir.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 17:48:42 1993 by Rik Faith (faith@cs.unc.edu)
.TH TELLDIR 3 2021-03-22 GNU "Linux Programmer's Manual"
.SH NAME
telldir \- return current location in directory stream
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <dirent.h>
.PP
.BI "long telldir(DIR *" dirp );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR telldir ():
.nf
    _XOPEN_SOURCE
       || /* Glibc since 2.19: */ _DEFAULT_SOURCE
       || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
The
.BR telldir ()
function returns the current location associated with
the directory stream \fIdirp\fP.
.SH RETURN VALUE
On success, the
.BR telldir ()
function returns the current location
in the directory stream.
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EBADF
Invalid directory stream descriptor \fIdirp\fP.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR telldir ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
.SH NOTES
In glibc up to version 2.1.1, the return type of
.BR telldir ()
was
.IR off_t .
POSIX.1-2001 specifies
.IR long ,
and this is the type used since glibc 2.1.2.
.PP
In early filesystems, the value returned by
.BR telldir ()
was a simple file offset within a directory.
Modern filesystems use tree or hash structures, rather than flat tables,
to represent directories.
On such filesystems, the value returned by
.BR telldir ()
(and used internally by
.BR readdir (3))
is a "cookie" that is used by the implementation
to derive a position within a directory.
.\" https://lwn.net/Articles/544298/
Application programs should treat this strictly as an opaque value, making
.I no
assumptions about its contents.
.SH SEE ALSO
.BR closedir (3),
.BR opendir (3),
.BR readdir (3),
.BR rewinddir (3),
.BR scandir (3),
.BR seekdir (3)