program_options

【program_options】

　　The program_options library allows program developers to obtain program options, that is (name, value) pairs from the user, via conventional methods such as command line and config file.

1、添加 options_description.

// Declare the supported options.
po::options_description desc("Allowed options");
desc.add_options()
    ("help", "produce help message")
    ("compression", po::value<int>(), "set compression level")
;

po::variables_map vm;
po::store(po::parse_command_line(ac, av, desc), vm);
po::notify(vm);

if (vm.count("help")) {
    cout << desc << "
";
    return 1;
}

if (vm.count("compression")) {
    cout << vm["compression"].as<int>() << ".
";
}

　　使用示例：

　　

2、po::value

int opt;
po::options_description desc("Allowed options");
desc.add_options()
    ("help", "produce help message")
    ("optimization", po::value<int>(&opt)->default_value(10), 
  "optimization level")
    ("include-path,I", po::value< vector<string> >(), 
  "include path")
    ("input-file", po::value< vector<string> >(), "input file")
;

　　使用示例：
　　

3、po::positional_options_description

po::positional_options_description p;
p.add("input-file", -1);

po::variables_map vm;
po::store(po::command_line_parser(ac, av).
          options(desc).positional(p).run(), vm);
po::notify(vm);

　　

4、config file

　　　　　int opt;
        string config_file;
    
        // Declare a group of options that will be 
        // allowed only on command line
        po::options_description generic("Generic options");
        generic.add_options()
            ("version,v", "print version string")
            ("help", "produce help message")
            ("config,c", po::value<string>(&config_file)->default_value("multiple_sources.cfg"),
                  "name of a file of a configuration.")
            ;
    
        // Declare a group of options that will be 
        // allowed both on command line and in
        // config file
        po::options_description config("Configuration");
        config.add_options()
            ("optimization", po::value<int>(&opt)->default_value(10), 
                  "optimization level")
            ("include-path,I", 
                 po::value< vector<string> >()->composing(), 
                 "include path")
            ;

        // Hidden options, will be allowed both on command line and
        // in config file, but will not be shown to the user.
        po::options_description hidden("Hidden options");
        hidden.add_options()
            ("input-file", po::value< vector<string> >(), "input file")
            ;

        
        po::options_description cmdline_options;
        cmdline_options.add(generic).add(config).add(hidden);

        po::options_description config_file_options;
        config_file_options.add(config).add(hidden);

        po::options_description visible("Allowed options");
        visible.add(generic).add(config);
        
        po::positional_options_description p;
        p.add("input-file", -1);
        
        po::variables_map vm;
        store(po::command_line_parser(ac, av).
              options(cmdline_options).positional(p).run(), vm);
        notify(vm);
        
        ifstream ifs(config_file.c_str());
        if (!ifs){
            cout << "can not open config file: " << config_file << "
";
            return 0;
        }
        else{
            store(parse_config_file(ifs, config_file_options), vm);
            notify(vm);
        }
    
        if (vm.count("help")) {
            cout << visible << "
";
            return 0;
        }

        if (vm.count("version")) {
            cout << "Multiple sources example, version 1.0
";
            return 0;
        }

        if (vm.count("include-path")){
            cout << vm["include-path"].as< vector<string> >() << "
";
        }

        if (vm.count("input-file")){
            cout << vm["input-file"].as< vector<string> >() << "
";
        }

        cout << opt << "
";      

　　

参考：

1、https://www.boost.org/doc/libs/1_69_0/doc/html/program_options.html