Reading Unicode characters from command line arguments using boost::program_options in Windows

Question

I have several Windows applications that read a file path from command-line arguments. Everything works flawlessly, except when passing paths with non-ANSI characters. I expected this, but don't know how to deal with it. Probably an entry-level question but that is driving me crazy.

My current code looks like:

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

    po::options_description po_desc("Allowed options");
    po_desc.add_options()
        ("file", po::value<std::string>(), "path to file");

    po::variables_map po_vm;
    try {
        po::store(po::parse_command_line(argc, argv, po_desc), po_vm);
        po::notify(po_vm);
    } catch (...) {
        std::cout << po_desc << std::endl;
        return false;
    }

    const std::string file_path = po_vm["file"].as<std::string>();

    // ...
}

I've found that if I replace the type of file_path from std::string to boost::filesystem::path, some paths are now read. I don't know exactly why but can deduce that it has to be with a translation from the Latin1 charset.

For example, having following files:

malaga.txt
málaga.txt
mąlaga.txt

The first is always read correctly, while the second one fails when using std::string file_path but not boost::filesystem::path file_path. The third one always fails.

I've tried switching the main function to int main(int argc, wchar_t* argv) and using std::wstring for the argument type, but it is not compatible with boost::program_options parser.

How can I correctly read such Unicode file names?