- usage_error(const std::string &w, const std::string &h = std::string()): std::runtime_error(w), help_(h) { }
- ~usage_error() throw() { }
+ usage_error(const std::string &w, const std::string &h = std::string()): std::runtime_error(w), m_help(h) { }
+ virtual ~usage_error() throw() = default;