It seems that xpressive's blank isn't matched properly to a space when used with wide strings. Here is a short example: #include <boost/xpressive/xpressive_static.hpp> #include <string> #include <iostream> #if 1 // 1 for wide character, 0 for normal. # define REGEX_TYPE boost::xpressive::wsregex # define REGEX_ITER_TYPE boost::xpressive::wsregex_iterator # define REGEX_MATCH_TYPE boost::xpressive::wsmatch # define STR_TYPE std::wstring # define STREAM_TYPE std::wcout # define STR(s) L##s #else # define REGEX_TYPE boost::xpressive::sregex # define REGEX_ITER_TYPE boost::xpressive::sregex_iterator # define REGEX_MATCH_TYPE boost::xpressive::smatch # define STR_TYPE std::string # define STREAM_TYPE std::cout # define STR(s) s #endif int main() { using namespace boost::xpressive; REGEX_TYPE expr = ( s1= ( STR("something") >> +( (*blank >> +alpha) ) ) ) ; STR_TYPE strings[] = { STR("something"), STR("something "), STR("somethingelse"), STR("something else") }; const int numStrings(sizeof(strings) / sizeof(strings[0])); for(int i(0); numStrings != i; ++i) { const STR_TYPE & s(strings[i]); STREAM_TYPE << "String \"" << s << "\":" << std::endl; for(REGEX_ITER_TYPE current(s.begin(), s.end(), expr), end; current != end; ++current) { const REGEX_MATCH_TYPE & what(*current); const STR_TYPE match(what[1]); STREAM_TYPE << "\t" << match << std::endl; } } return 0; } I would expect the last string to match (as it does with simple characters) but it doesn't. Using space instead, or using (set= STR(' '),STR('\t')) seems to work in both cases. I'm using MSVC 2005 SP1. I'm not sure if the problem is in the compiler's char traits and how blank uses them (if it does) or somewhere in the bowels of xpressive. Thanks, JF