can be used to check if the node referenced by the iterator is still
part of the map, or has been deleted by a call to
If the return value is
then it cannot be relied upon to remain
if other threads may be erasing elements concurrently. Once the return
true for a given
iterator instance, then it will remain
until a new value is assigned to that iterator.
A deleted node may still be accessed through an iterator that refers to it, but it is not reachable from any operation on the map.
bool is_deleted_node() const;
true if the element
referred to by
*this has been removed from the