Boost program options detect whether default value was used

Question

I'm using Boost program_options with an argument that has a ->default_value(). Is there any way to tell whether the value that results was specified by the user on the command line, or by the default value?

Answer 1

There is a way - variable_value::defaulted():

  po::variables_map vm;
  try {
    po::store(po::parse_command_line(argc, argv, desc), vm);
  } catch (std::exception& e) {
    std::cerr << "error parsing command line: " << e.what() << "\n";
    return 1;
  }

  // Needed to set default arguments.
  po::notify(vm);

  if (vm["myparam"].defaulted())
     ...