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'\" t
.\" Copyright (C) 2008, 2016 Michael Kerrisk <mtk.manpages@gmail.com>
.\" and Copyright (C) 2016 Florian Weimer <fweimer@redhat.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH readdir_r 3 2023-07-20 "Linux man-pages 6.05.01"
.SH NAME
readdir_r \- read a directory
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <dirent.h>
.PP
.BI "[[deprecated]] int readdir_r(DIR *restrict " dirp ,
.BI " struct dirent *restrict " entry ,
.BI " struct dirent **restrict " result );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR readdir_r ():
.nf
_POSIX_C_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
This function is deprecated; use
.BR readdir (3)
instead.
.PP
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
.I dirent
structure, see
.BR readdir (3).
.PP
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 .
.PP
It is recommended that applications use
.BR readdir (3)
instead of
.BR readdir_r ().
Furthermore, since glibc 2.24, glibc deprecates
.BR readdir_r ().
The reasons are as follows:
.IP \[bu] 3
On systems where
.B 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 \[bu]
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
.I d_name
field may not be null terminated or may be truncated.
.IP \[bu]
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 \[bu]
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;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR readdir_r ()
T} Thread safety MT-Safe
.TE
.sp 1
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
POSIX.1-2001.
.SH SEE ALSO
.BR readdir (3)
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