Signature:

      SUBROUTINE h5tconvert_f(src_id, dst_id, nelmts, buf, hdferr, background, plist_id)
        INTEGER(HID_T) , INTENT(IN)               :: src_id
        INTEGER(HID_T) , INTENT(IN)               :: dst_id
        INTEGER(SIZE_T), INTENT(IN)               :: nelmts
        TYPE(C_PTR)    , INTENT(INOUT)            :: buf
        INTEGER        , INTENT(OUT)              :: hdferr
        TYPE(C_PTR)    , INTENT(INOUT), OPTIONAL  :: background
        INTEGER(HID_T) , INTENT(IN)   , OPTIONAL  :: plist_id

Inputs:

      src_id     - Identifier for the source datatype.
      dst_id     - Identifier for the destination datatype.
      nelmts     - Size of array buf.
      buf        - Array containing pre-conversion values.
      background - Optional background buffer.
      plist_id   - Dataset transfer property list identifier.

Outputs:

      buf        - Array containing post-conversion values.
      hdferr     - error code:
                     0 on success and -1 on failure