C++ Boost program options with json file

Question

It is possible with boost program options library: http://www.boost.org/doc/libs/1_64_0/doc/html/program_options.html

to read json formatted file as an input file here?

Or if I have some config in json like file, I need to parse it myself, with for example: http://www.boost.org/doc/libs/1_64_0/doc/html/property_tree.html

Answer 1

I've met the same problem. Here is my implementation of JSON parser for program_options library, based on property_tree:

template <class charT> void parseChildren(std::string prefix, boost::property_tree::ptree& tree, boost::program_options::parsed_options& options)
{
    if (tree.size() == 0)
    {
        //cut first dot
        std::basic_string<charT> name = prefix.substr(1);
        std::basic_string<charT> value = tree.data();

        boost::program_options::basic_option<charT> opt;
        opt.string_key = name;
        opt.value.push_back(value);
        opt.unregistered = (options.description->find_nothrow(name, false) == nullptr);
        opt.position_key = -1;
        options.options.push_back(opt);
    }
    else
    {
        for (auto it = tree.begin(); it != tree.end(); ++it)
        {
            parseChildren<charT>(prefix + "." + it->first, it->second, options);
        }
    }
}

template <class charT>
void parseJsonOptions(std::basic_istream<charT>& is, boost::program_options::parsed_options& options)
{
        boost::property_tree::basic_ptree<std::basic_string<charT>, std::basic_string<charT>> pt;
        boost::property_tree::read_json(is, pt);

        parseChildren<charT>(std::basic_string<charT>(), pt, options);
}

template <class charT>
boost::program_options::basic_parsed_options<charT> parse_json_config_file(std::basic_istream<charT>& is, const boost::program_options::options_description& desc, bool allow_unregistered = false)
{     
    // do any option check here

    boost::program_options::parsed_options result(&desc);
    parseJsonOptions(is, result);

    return boost::program_options::basic_parsed_options<charT>(result);
}

Use it like:

po::variables_map vm;
std::ifstream configFileStream(configFilePath_.generic_string());

store(parse_json_config_file(configFileStream, algorithmsDesc_), vm);
notify(vm);