On a whim, I tried changing 'boost::cmatch' to 'boost::smatch'. That fixed my problem.

I'd appreciate it if someone would tell me what was going on, though.

Yes: smatch is match_resultsstd::string::const_iterator and cmatch is match_results, with some std libs these are the same thing, on others not. You are correct to be using smatch when matching a std::string. John.