OK, I found the answer to my (stupid) question --- I had to relearn how to use program_options. Which brings us to a IMHO really cool little example, combining lambda with program_options: ,----[ /home/nbecker/boost-program_options/Test1.cc ] | #include <boost/program_options.hpp> | #include <iostream> | #include <cxxabi.h> // demangle | #include <cmath> | | using namespace std; | namespace po = boost::program_options; | | #include <boost/lambda/lambda.hpp> | using namespace boost::lambda; | | int main (int argc, char** argv) { | double angle; | | std::set_terminate(__gnu_cxx::__verbose_terminate_handler); | po::options_description desc("Allowed options"); | desc.add_options() | ("help", "produce help message") | ("angle", po::value<double>()->notifier(var(angle)=180./M_PI*_1), "set | angle") ; | | po::variables_map vm; | | po::store(po::parse_command_line(argc, argv, desc), vm); | | | po::notify(vm); | | if (vm.count("help")) { | cout << desc << "\n"; | return 1; | } | | cout << "angle: " << angle << '\n'; | } `----