Method string get_usage

include/CLI/App.hpp:1179–1181

Generate and return the usage.

    /// Generate and return the usage.
    CLI11_NODISCARD std::string get_usage() const {
        return (usage_callback_) ? usage_callback_() + '\n' + usage_ : usage_;
    }

    /// Generate and return the footer.
    CLI11_NODISCARD std::string get_footer() const {