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NAME
readdir_r - read a directory
SYNOPSIS
#include <dirent.h>
int readdir_r(DIR *restrict dirp, struct dirent *restrict entry,
struct dirent **restrict result);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
readdir_r():
_POSIX_C_SOURCE
|| /* Glibc <= 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
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found at https://www.kernel.org/doc/man-pages/.
2021-03-22 READDIR_R(3)