put">async_read_some_at()</code>, <code class="computeroutput">write_some_at()</code> or <code class="computeroutput">async_write_some_at()</code>
          member functions. However, like the equivalent functions (<code class="computeroutput">read_some()</code>,
          etc.) on streams, these functions are only required to transfer one or
          more bytes in a single operation. Therefore free functions called <a class="link" href="../../reference/read_at.html" title="read_at">read_at()</a>, <a class