readdir_r - read a directory
#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
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.
- EBADF
- Invalid directory stream descriptor dirp.
- ENAMETOOLONG
- 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.
readdir(3)