readdir_r(3) — Linux manual page

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:

       •  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.

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)

COLOPHON

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Linux man-pages 6.9.1          2024-05-02                   readdir_r(3)

Pages that refer to this page: readdir(3)

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