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
       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 glibc 2.24, glibc deprecates
       readdir_r().  The reasons are as follows:

       o  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.

       o  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.

       o  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.

       o  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.

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 |
       +--------------------------------------------+---------------+---------+
STANDARDS
       POSIX.1-2008.

HISTORY
       POSIX.1-2001.

SEE ALSO
       readdir(3)

Linux man-pages 6.7               2023-10-31                      readdir_r(3)