https://en.cppreference.com/w/cpp/utility/optional std::optional - cppreference.com template class optional; (since C++17) The class template std::optional manages an optional contained value, i.e. a value that may or may not be present. A common use case for optional is the return value of a function that may fail. As opposed en.cppreference.com optional. 값이 존재할 수도 있고, 존재하지 않을 수도 있는 ..