https://svn.boost.org/trac10/ticket/9227 <pre class="wiki">#include &lt;boost/regex.hpp&gt; int main(int, char **) { boost::regex r("(a)"); std::cout &lt;&lt; r.mark_count(); return 0; } </pre><p> prints out "2" instead of "1". Both libc++ and libstdc++ print out "1". </p> <p> This was discussed in 2007 as well I believe, but I couldn't find any other mention of the issue: [regex] regex::mark_count() incorrect? (I can't post the link since trac rejects my submission) </p> en-us /htdocs/site/boost.png https://svn.boost.org/trac10/ticket/9227 Trac 1.4.3 John Maddock Sat, 14 Dec 2013 17:44:38 GMT https://svn.boost.org/trac10/ticket/9227#comment:1 https://svn.boost.org/trac10/ticket/9227#comment:1 <ul> <li><strong>status</strong> <span class="trac-field-old">new</span> → <span class="trac-field-new">closed</span> </li> <li><strong>resolution</strong> → <span class="trac-field-new">fixed</span> </li> </ul> <p> Fixed in Git develop </p> Ticket