c++ - Why do I always get default values when passing positional arguments? -


i'm trying familiarize myself boost::program_options, , i'm running problem positional arguments.

here's main function, set options passed through command line. please note po namespace alias boost::program_options.

int main(int argc, char** argv) {     int retval = success;     try     {         // define , parse program options         po::options_description desc("options");         desc.add_options()           ("help", "print messages")           ("mode,m", po::value<std::string>()->default_value("ecb"), "cipher mode of operation")           ("keyfile,f", po::value<bool>(), "use keyfile")           ("key,k", po::value<std::string>(), "ascii key")           ("infile", po::value<std::string>()->default_value("plaintext.txt"), "input file")           ("outfile", po::value<std::string>()->default_value("ciphertext.txt"), "output file");          po::positional_options_description pargd;         pargd.add("infile", 1);         pargd.add("outfile", 2);      po::variables_map vm;     try     {         po::store(po::parse_command_line(argc, argv, desc), vm); // can throw        // --help option       if ( vm.count("help")  )       {         std::cout << "basic command line parameter app" << std::endl                   << desc << std::endl;         return success;       }          po::notify(vm); // throws on error, after in case                       // there problems     }     catch(po::error& e)     {         std::cerr << "error: " << e.what() << std::endl << std::endl;         std::cerr << desc << std::endl;         return error_in_command_line;     }      ///application code here     retval = application(vm);      }     catch(std::exception& e)     {         std::cerr << "unhandled exception reached top of main: "                   << e.what() << ", application exit" << std::endl;         return error_unhandled_exception;     }      return retval; } // main

when try print positional argument of vm (the variable_map) cout << wm["infile"].as<std::string>();, default value "infile" parameter.

i'm calling executable ./a.out in.file out.file test.

what doing wrong?

i figured out!

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

should be...

po::store(po::command_line_parser(argc, argv).options(desc).positional(pargd).run(), vm);

although i'm not sure understand why yet...


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