Section (3) readdir_r
Name
readdir_r — read a directory
Synopsis
#include <dirent.h>
int
readdir_r( |
DIR *dirp, |
struct dirent *entry, | |
struct dirent **result) ; |
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Note | |||
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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, callingreaddir_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_zsingle_quotesz_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 returnedd_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 ofreaddir_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 |
COLOPHON
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