READDIR_R
Section: Linux Programmer's Manual (3)
Updated: 2016-03-01
Page Index
NAME
readdir_r - read a directory
SYNOPSIS
#include <dirent.h>
int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
readdir_r():
-
_POSIX_C_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
This function is deprecated; use
readdir(3)
instead.
The
readdir_r()
function was invented as a reentrant version of
readdir(3).
It reads the next directory entry from the directory stream
dirp,
and returns it in the caller-allocated buffer pointed to by
entry.
For details of the
dirent
structure, see
readdir(3).
A pointer to the returned buffer is placed in
*result;
if the end of the directory stream was encountered,
then NULL is instead returned in
*result.
It is recommended that applications use
readdir(3)
instead of
readdir_r().
Furthermore, since version 2.24, glibc deprecates
readdir_r().
The reasons are as follows:
- *
-
On systems where
NAME_MAX
is undefined, calling
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.
- *
-
On some systems,
readdir_r()
can't read directory entries with very long names.
When the glibc implementation encounters such a name,
readdir_r()
fails with the error
ENAMETOOLONG
after the final directory entry has been read.
On some other systems,
readdir_r()
may return a success status, but the returned
d_name
field may not be null terminated or may be truncated.
- *
-
In the current POSIX.1 specification (POSIX.1-2008),
readdir(3)
is not required to be thread-safe.
However, in modern implementations (including the glibc implementation),
concurrent calls to
readdir(3)
that specify different directory streams are thread-safe.
Therefore, the use of
readdir_r()
is generally unnecessary in multithreaded programs.
In cases where multiple threads must read from the same directory stream,
using
readdir(3)
with external synchronization is still preferable to the use of
readdir_r(),
for the reasons given in the points above.
- *
-
It is expected that a future version of POSIX.1
will make
readdir_r()
obsolete, and require that
readdir(3)
be thread-safe when concurrently employed on different directory streams.
RETURN VALUE
The
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,
readdir_r()
returns 0, and returns NULL in
*result.
ERRORS
- EBADF
-
Invalid directory stream descriptor dirp.
- ENAMETOOLONG
-
A directory entry whose name was too long to be read was encountered.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
readdir_r()
| Thread safety | MT-Safe
|
CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
SEE ALSO
readdir(3)
COLOPHON
This page is part of release 5.10 of the Linux
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/.