Can't match a hex sequence with std::regex and :xdigit:

Question

I have this code:

try
{
    std::string input = "00179d006d000174";

    std::regex pattern("[[:xdigit:]]{16}");

    if(std::regex_match(input, pattern))
        std::cout << "Full match" << std::endl;
}
catch(const std::exception& e)
{
    std::cerr << e.what() << std::endl;
}

But can't understand two things:

• why does it throw a regex_error
• if I add the std::regex::basic flag to the the regex it no longer throws the error but still doesn't print "full match"
• how would I match a simple sequence of 16 hex digits like the one in the example?