Yang Zhang wrote:

More usability issues with program_options: I couldn't really find much mention of positional options in the docs. I'm writing a typical command line program: one that takes some set of optional options and a single required positional argument. Currently, I'm doing (where namespace po = boost::program_options):

po::options_description desc("Allowed options"); desc.add_options() ("help,h", "show this help message") ... ("exe", po::wvalue(), "the command line to execute");

po::positional_options_description posopts; posopts.add("exe", -1);

po::variables_map vm; po::store(po::wcommand_line_parser(argc, argv). options(desc).positional(posopts).run(), vm); po::notify(vm); if (vm.count("help") > 0) { cout << desc << endl; return 0; } ... if (vm.count("exe") == 0) { cerr << desc << endl; return 1; } wstring exe(vm["exe"].as()[0]);

I had to add the exe option to the regular (non-positional) options_description as a vector<wstring>, causing it to show up as an option in the usage message.

You can create a hidden options group and put 'exe' there.

Omitting it resulted in errors about the option being unregistered (even after trying to add allow_unregistered). Why would I get this error?

Because you say that all positional options should become values of the 'exe' option -- that you did not define.

Shouldn't the wcommand_line_parser::run method be doing this checking after it has collected all the sets of option descriptions? Can I get rid of this? What's the proper way to express what I want?

Is there a way to require the positional argument occur (1) at least once and

No. There are patches in the works to implement 'required' options, though.

(2) at most once (besides manual checks after parsing)?

psoptions.add("exe", 1) ? - Volodya