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READDIR_R(3) Linux Programmer's Manual READDIR_R(3)
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 un‐
necessary 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 dif‐
ferent 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)
2021-03-22 READDIR_R(3)