A small addition to the article on the use of boost::program_options .
In this appendix I will describe how to use enum enums. Because immediately they do not work. By default, boost::program_options work only with basic types and some types from the standard library, for example std::string .
Suppose we have a class that contains an enum .
class Logger { public: explicit Logger(); enum VerboseLevel { E_DEBUG = 0 E_INFO, E_WARNING, E_CRITICAL, }; };
It is logical that we would like to use this enumeration in the command line menu to set the level of detail of the output in the console or in a file for example.
That is, we want to configure our boost::program_options like this.
m_desc.add_options() (MENU_ITEM_HELP.c_str(), "produce help message") ("level", po::value<Logger::VerboseLevel>(&m_verboseLevel)->default_value(Logger::E_WARNING), "set verbose level of logging, default level is Info\nLevels: \n0) Debug \n1) Info \n2) Warning \n3) Critical") ; po::store(po::parse_command_line(argc, argv, m_desc), m_vm); po::notify(m_vm);
But when building we get an error
Error C2338 Target type is neither std::istream`able nor std::wistream`able
In this case, we need to do an overload on operator>> in order to be able to set the values we need.
The simplest option might look like this.
std::istream& operator>>(std::istream& in, Logger::VerboseLevel& verboseLevel) { std::string token; in >> token; if (token == "0") verboseLevel = Logger::VerboseLevel::E_DEBUG; else if (token == "1") verboseLevel = Logger::VerboseLevel::E_INFO; else if (token == "2") verboseLevel = Logger::VerboseLevel::E_WARNING; else if (token == "3") verboseLevel = Logger::VerboseLevel::E_CRITICAL; else in.setstate(std::ios_base::failbit); return in; }