readdir_r — read a directory


        #include <dirent.h>
int readdir_r( DIR *dirp,
  struct dirent *entry,
  struct dirent **result);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_POSIX_C_SOURCE || /* Glibc versions <= 2.19:


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.


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.



Invalid directory stream descriptor dirp.


A directory entry whose name was too long to be read was encountered.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
readdir_r() Thread safety MT-Safe


POSIX.1-2001, POSIX.1-2008.




This page is part of release 4.12 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−pages/.

  Copyright (C) 2008, 2016 Michael Kerrisk <>
and Copyright (C) 2016 Florian Weimer <>

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

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.