As already mentioned,
map allows to iterate over the elements in a sorted way, but
unordered_map does not. This is very important in many situations, for example displaying a collection (e.g. address book). This also manifests in other indirect ways like: (1) Start iterating from the iterator returned by
find(), or (2) existence of member functions like
Also, I think there is some difference in the worst case search complexity.
map, it is O( lg N )
unordered_map, it is O( N ) [This may happen when the hash function is not good leading to too many hash collisions.]
The same is applicable for worst case deletion complexity.