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)):
_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
the end of the directory stream was encountered, then NULL is instead
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.
Invalid directory stream descriptor
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).
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