boost::program_options::collect_unrecognized
// In header: <boost/program_options/parsers.hpp> template<typename charT> (basic_option< options, mode);
Collects the original tokens for all named options with 'unregistered' flag set. If 'mode' is 'include_positional' also collects all positional options. Returns the vector of origianl tokens for all collected options.