VMS Help CC, Language topics, Storage Class Modifiers, _align  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The _align modifier allows you to align objects of any of the
  Compaq C data types on a specified storage boundary.  Use the
  _align modifier in a data declaration or definition.

  When specifying the boundary of the data alignment, you can use a
  predefined constant:  BYTE or byte, WORD or word, LONGWORD or
  longword, QUADWORD or quadword, OCTAWORD or octaword, and PAGE or
  page.

  You can also specify an integer value that is a power of two.  The
  power of two tells Compaq C the number of bytes to pad in order to
  align the data:

    For OpenVMS VAX systems, specify a constant 0, 1, 2, 3, 4, or 9.

    For OpenVMS Alpha systems, specify any constant from 0 to 16.