dir_spec

    A valid OpenVMS or UNIX style directory specification that may
    contain a device name. For example:

    DBA0:[BAY.WINDOWS]     /*    OpenVMS      */
    /dba0/bay/windows      /*   UNIX style    */

    This specification cannot contain a node name, filename, file
    extension, file version, or a wildcard character. The same
    restriction applies to the UNIX style directory specifications.

 mode

    A file protection. See the chmod function in this section for
    information about the specific file protections.

    The file protection of the new directory is derived from the
    mode argument, the process's file protection mask (see the umask
    function), and the parent-directory default protections.

    In a manner consistent with the OpenVMS behavior for creating
    directories, mkdir never applies delete access to the directory.
    An application that needs to set delete access should use an
    explicit call to chmod to set write permission.

    See the Description section of this function for more information
    about how the file protection is set for the newly created
    directory.

  . . .

    Represents the following optional arguments. These arguments have
    fixed position in the argument list, and cannot be arbitrarily
    placed.

       unsigned int uic
       The user identification code (UIC) that identifies the
       owner of the created directory. If this argument is 0, the
       C RTL gives the created directory the UIC of the parent
       directory. If this argument is not specified, the C RTL
       gives the created directory your UIC. This optional argument
       is specific to the C RTL and is not portable.

       unsigned short max_versions
       The maximum number of file versions to be retained in the
       created directory. The system automatically purges the
       directory keeping, at most, max_versions number of every file.

       If this argument is 0, the C RTL does not place a limit
       on the maximum number of file versions.

       If this argument is not specified, the C RTL gives
       the created directory the default version limit of the parent
       directory.

       This optional argument is specific to the C RTL and is
       not portable.

       unsigned short r_v_number
       The volume (device) on which to place the created directory
       if the device is part of a volume set. If this argument is
       not specified, the C RTL arbitrarily places the created
       directory within the volume set. This optional argument is
       specific to the C RTL and is not portable.