Re: [Boost-users] program_options positional and required arguments

Subject: Re: [Boost-users] program_options positional and required arguments
From: Vladimir Prus (vladimir_at_[hidden])
Date: 2009-11-09 02:56:49

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<vector<wstring> >(), "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<vector<wstring> >()[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