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.\" Copyright (C) 2008, 2016 Michael Kerrisk <mtk.manpages@gmail.com>
.\" and Copyright (C) 2016 Florian Weimer <fweimer@redhat.com>
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.TH READDIR_R 3 2016-03-01 "" "Linux Programmer's Manual"
.SH NAME
readdir_r \- read a directory
.SH SYNOPSIS
.nf
.B #include <dirent.h>
.sp
.BI "int readdir_r(DIR *" dirp ", struct dirent *" entry \
", struct dirent **" result );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.ad l
.in
.sp
.BR readdir_r ():
.RS 4
_POSIX_C_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.ad b
.SH DESCRIPTION
This function is deprecated; use
.BR readdir (3)
instead.
The
.BR readdir_r ()
function was invented as a reentrant version of
.BR readdir (3).
It reads the next directory entry from the directory stream
.IR dirp ,
and returns it in the caller-allocated buffer pointed to by
.IR entry .
For details of the
.IR dirent
structure, see
.BR readdir (3).
A pointer to the returned buffer is placed in
.IR *result ;
if the end of the directory stream was encountered,
then NULL is instead returned in
.IR *result .
It is recommended that applications use
.BR readdir (3)
instead of
.BR readdir_r ().
Furthermore, since version 2.24, glibc deprecates
.BR readdir_r ().
The reasons are as follows:
.IP * 3
On systems where
.BR NAME_MAX
is undefined, calling
.BR readdir_r ()
may be unsafe because the interface does not allow the caller to specify
the length of the buffer used for the returned directory entry.
.IP *
On some systems,
.BR readdir_r ()
can't read directory entries with very long names.
When the glibc implementation encounters such a name,
.BR readdir_r ()
fails with the error
.B ENAMETOOLONG
.IR "after the final directory entry has been read" .
On some other systems,
.BR readdir_r ()
may return a success status, but the returned
.IR d_name
field may not be null terminated or may be truncated.
.IP *
In the current POSIX.1 specification (POSIX.1-2008),
.BR readdir (3)
is not required to be thread-safe.
However, in modern implementations (including the glibc implementation),
concurrent calls to
.BR readdir (3)
that specify different directory streams are thread-safe.
Therefore, the use of
.BR readdir_r ()
is generally unnecessary in multithreaded programs.
In cases where multiple threads must read from the same directory stream,
using
.BR readdir (3)
with external synchronization is still preferable to the use of
.BR readdir_r (),
for the reasons given in the points above.
.IP *
It is expected that a future version of POSIX.1
.\" FIXME .
.\" http://www.austingroupbugs.net/view.php?id=696
will make
.BR readdir_r ()
obsolete, and require that
.BR readdir (3)
be thread-safe when concurrently employed on different directory streams.
.SH RETURN VALUE
The
.BR readdir_r ()
function returns 0 on success.
On error, it returns a positive error number (listed under ERRORS).
If the end of the directory stream is reached,
.BR readdir_r ()
returns 0, and returns NULL in
.IR *result .
.SH ERRORS
.TP
.B EBADF
Invalid directory stream descriptor \fIdirp\fP.
.TP
.B ENAMETOOLONG
A directory entry whose name was too long to be read was encountered.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface Attribute Value
T{
.BR readdir_r ()
T} Thread safety MT-Safe
.TE
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
.SH SEE ALSO
.BR readdir (3)
.SH COLOPHON
This page is part of release 4.10 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
|
