A company called JezUK has released Taggle, which is a straight port of TagSoup 1.2 to C++. It's a part of Arabica, a C++ XML toolkit providing SAX, DOM, XPath, and partial XSLT. I have no connection with JezUK (except apparently as source of inspiration).
The author says the code is alpha-quality now, so he'd appreciate lots of testers to shake out bugs. C++ users, go to it! Having a C++ port will be a real enhancement for TagSoup.
The code is currently in public Subversion: you can fetch it with svn co svn://jezuk.dnsalias.net/jezuk/arabica/branches/tagsoup-port.