#includeIn this code snippet, the P_ITEM macro is used to define a default compression level of 6 for a command-line option. The P_ITEM macro is a part of the Boost library.namespace po = boost::program_options; po::options_description desc("Allowed options"); desc.add_options() ("compression", po::value ()->default_value(P_ITEM(6)), "compression level"); po::variables_map vm; po::store(po::parse_command_line(argc, argv, desc), vm); po::notify(vm);