def h3_to_string(h3_index)
      h3_str = FFI::MemoryPointer.new(:char, H3_TO_STR_BUF_SIZE)
      Bindings::Private.h3_to_string(h3_index, h3_str, H3_TO_STR_BUF_SIZE)
      h3_str.read_string
    end
def h3_to_string(h3_index)
      h3_str = FFI::MemoryPointer.new(:char, H3_TO_STR_BUF_SIZE)
      Bindings::Private.h3_to_string(h3_index, h3_str, H3_TO_STR_BUF_SIZE)
      h3_str.read_string
    end
Derives the hexadecimal string representation for a given H3 index.

 @param [Integer] h3_index A valid H3 index.

 @example Derive the given hexadecimal form for the H3 index
   H3.h3_to_string(617700169958293503)
   "89283470dcbffff"

 @return [String] H3 index in hexadecimal form.