allow multiple occurrences of custom type using Boost::program_options

Question

Is there any way I can allow multiple occurrences of custom type (struct) in boost::program_options? I found the various sources specifying this can be done using std::vector but I wanted to achieve the same using custom data type. However this struct do contain a std::vector where I want to store the data.

Answer 1

A code sample would really help a lot.

But, since your struct will contain the vector, why not bind that vector?

Simple example:

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#include <boost/program_options.hpp>
#include <boost/program_options/variables_map.hpp>
#include <boost/program_options/cmdline.hpp>
#include <iostream>
#include <vector>

struct my_custom_type {
    std::vector<std::string> values;

    friend std::ostream& operator<<(std::ostream& os, my_custom_type const& mct) {
        std::copy(mct.values.begin(), mct.values.end(), std::ostream_iterator<std::string>(os << "{ ", ", "));
        return os << "}";
    };
};

int main(int argc, char** argv) {
    namespace po = boost::program_options;

    my_custom_type parse_into;

    po::options_description desc;
    desc.add_options()
        ("item", po::value<std::vector<std::string> >(&parse_into.values), "One or more items to be parsed")
        ;

    try {
        po::variables_map vm;
        po::store(po::parse_command_line(argc, argv, desc, po::command_line_style::default_style), vm);
        vm.notify();

        std::cout << "Parsed custom struct: " << parse_into << "\n";
    } catch(std::exception const& e) {
        std::cerr << "Error: " << e.what() << "\n";
    }
}

When called with 26 arguments, like ./test --item={a..z} it prints:

Parsed custom struct: { a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z, }

If you want to "automatically" treat the conversions in a "special" way, you can look at

• custom validators (http://www.boost.org/doc/libs/1_59_0/doc/html/program_options/howto.html#idp343336928)
• custom notifiers (see e.g. Example 63.1 for a simple example).