e number of
       bytes of data returned.  If -1 is returned, the caller must next call
       <a class="xref" href="libpq-copy.html#LIBPQ-PQENDCOPY"><code class="function">PQendcopy</code></a>, and then return to normal processing.
      </p><p>
       The data returned will not extend beyond a data-row boundary.  If possible
       a whole row will be returned at one time.  But if the buffer offered by
       the caller is too small to hold a row sent by the server, then a partial
       data row will be