er">Traits</span><span class="special">,</span> <span class="identifier">A</span><span class="special">&gt;&amp;</span> <span class="identifier">sub</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
   <span class="identifier">string_type</span> <a class="link" href="match_results.html#boost_regex.match_results.str">str</a><span class="special">(</span><span class="keyword">int</span> <span class="identifier">sub</span> <span class="special">=</span> <span