Typedef struct {
     double re;   /*real part */
     double im;   /*imaginary part */
  } complex_t;

  complex_t tmp;  /*used only to compute offsets */
  hid_t complex_id = H5Tcreate (H5T_COMPOUND, sizeof tmp);
  H5Tinsert (complex_id, "real", HOFFSET(tmp,re),
            H5T_NATIVE_DOUBLE);
  H5Tinsert (complex_id, "imaginary", HOFFSET(tmp,im),
            H5T_NATIVE_DOUBLE);