Question

Boost.Program_options provides a facility to pass multiple tokens via command line arguments as follows:

std::vector<int> nums;    

po::options_description desc("Allowed options");
desc.add_options()
    ("help", "Produce help message.")
    ("nums", po::value< std::vector<int> >(&nums)->multitoken(), "Numbers.")
;

po::variables_map vm;
po::store(po::parse_command_line(argc, argv, desc), vm);
po::notify(vm);

However, what is the preferred way of accepting only a fixed number of arguments? The only solution I could come is to manually assign values:

int nums[2];    

po::options_description desc("Allowed options");
desc.add_options()
    ("help", "Produce help message.")
    ("nums", "Numbers.")
;

po::variables_map vm;
po::store(po::parse_command_line(argc, argv, desc), vm);

if (vm.count("nums")) {
   // Assign nums
}

This feels a bit clumsy. Is there a better solution?

Answer 1

The boost library only provides the predefined mechanisms. A quick search didn’t find something with a fixed number of values. But you can create this yourself. The po::value< std::vector<int> >(&nums)->multitoken() is just a specialized value_semantic class. As you can see, this class offers the methods min_tokens and max_tokens, which seems to do exactly what you want. If you look at the definition of class typed_value ( this is the object that gets created, when you call po::value< std::vector<int> >(&nums)->multitoken()) you can get the grasp of how the methods should be overridden.