Description

   The opendir function opens the directory specified by dir_name
   and associates a directory stream with it. The dir_name argument
   can be specified in OpenVMS style or UNIX style. The directory
   stream is positioned at the first entry. The type DIR, defined
   in the <dirent.h> header file, represents a directory stream.
   A directory stream is an ordered sequence of all the directory
   entries in a particular directory.

   The opendir function also returns a pointer to identify the
   directory stream in subsequent operations. The NULL pointer is
   returned when the directory named by dir_name cannot be accessed,
   or when not enough memory is available to hold the entire stream.

                                 NOTES

      o  An open directory must always be closed with the closedir
         function to ensure that the next attempt to open that
         directory is successful. The opendir function should be
         used with readdir, closedir, and rewinddir to examine the
         contents of the directory.

      o  The opendir function supports UNIX style path name
         specifications.