READDIR_R(3) Linux Programmer's Manual READDIR_R(3)NAMEreaddir_r - read a directory
SYNOPSIS
#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
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
*result.
It is recommended that applications use readdir(3) instead of read‐
dir_r(). Furthermore, since version 2.24, glibc deprecates read‐
dir_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
*result.
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 │
└────────────┴───────────────┴─────────┘
CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
SEE ALSOreaddir(3)COLOPHON
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2016-03-01 READDIR_R(3)
