> 
Determine the number of bytes available
          for reading.
        </p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">available</span><span class="special">(</span>
    <span class="keyword">const</span> <span class="identifier">implementation_type</span> <span class="special">&amp;</span> <span class="identifier">impl</span><span class="special">,</span>
    <span class="identifier">boost<