readdir_r(3) Library Functions Manual readdir_r(3)
NAME
readdir_r - read a directory
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <dirent.h>
[[deprecated]] 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 read-
dir(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 *re-
sult.
It is recommended that applications use readdir(3) instead of read-
dir_r(). Furthermore, since glibc 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 direc-
tory entry has been read. On some other systems, readdir_r() may re-
turn 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 pro-
grams. In cases where multiple threads must read from the same di-
rectory 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 concur-
rently 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 direc-
tory stream is reached, readdir_r() returns 0, and returns NULL in *re-
sult.
ERRORS
EBADF Invalid directory stream descriptor dirp.
ENAMETOOLONG
A directory entry whose name was too long to be read was encoun-
tered.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│ readdir_r() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
POSIX.1-2008.
HISTORY
POSIX.1-2001.
SEE ALSO
readdir(3)
Linux man-pages 6.9.1 2024-05-02 readdir_r(3)
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