#include enum class Level : int { High, Medium, Low }; // this breaks the code inline std::ostream &operator<<(std::ostream &o, const Level &l) { switch(l) { case Level::High: o << "High"; break; case Level::Medium: o << "Medium"; break; case Level::Low: o << "Low"; break; } return o; } int main(int argc, char **argv) { CLI::App app; Level level; // specify string->value mappings std::vector> map{ {"high", Level::High}, {"medium", Level::Medium}, {"low", Level::Low}}; // checked Transform does the translation and checks the results are either in one of the strings or one of the // translations already app.add_option("-l,--level", level, "Level settings") ->required() ->transform(CLI::CheckedTransformer(map, CLI::ignore_case)); CLI11_PARSE(app, argc, argv); // CLI11's built in enum streaming can be used outside CLI11 like this: using namespace CLI::enums; std::cout << "Enum received: " << level << std::endl; return 0; }