</span> <span class="special">=</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">read_some</span><span class="special">(</span><span class="identifier">mb</span><span class="special">,</span> <span class="identifier">ec</span><span class="special">);</span>
<span class="keyword">if</span> <span class="special">(</span><span class="identifier">ec</span><span class="special">)</span> <span class="keyword">throw</span> <span class="identifier">system_error</span><s