If you want an object with automatic storage that has optional semantics (i.e. may or may not exist), you can use boost::optional.
boost::optional<T> is a container that can have zero or one elements. If it is empty, it doesn’t store a T object, just like an empty vector doesn’t store any object. In fact, you can think of boost::optional<T> as as std::vector<T> whose capacity is always 1 and cannot grow. And since the storage size required for this is fixed and known at compile-time (it’s sizeof(T)), boost::optional doesn’t need any dynamic allocation.