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 en-
try. 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 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
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. There-
fore, the use of readdir_r() is generally unnecessary in multi-
threaded programs. In cases where multiple threads must read from
the same directory stream, using readdir(3) with external synchro-
nization is still preferable to the use of readdir_r(), for the rea-
sons given in the points above.
• It is expected that a future version of POSIX.1 will make read-
dir_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 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 attrib-
utes(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 6.7 2023-10-31 readdir_r(3)
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