C++ boost::regex_match strange behaviour

Trying boost::regex_match and got a strange behaviour.

boost::cmatch what;
std::string fn_re_str = R"(\.sig\|\|([a-zA-Z0-9$]+)\()";
boost::regex fn_re(fn_re_str);
if (boost::regex_match("{var d=a[c];if(d.sig||d.s){var e=d.sig||qt(d.", what, fn_re)) {
    std::cout << what[1] << std::endl;
} else {
    std::cerr << "not found" << std::endl;
}

qt is expected to be found.

Here http://ift.tt/1Kai95K it is found.

Why boost::regex_match can't find it? Do I miss something?