C++ Primer, Fifth Edition

Using an Unordered Container

Aside from operations that manage the hashing, the unordered containers provide the same operations (find, insert, and so on) as the ordered containers. That means that the operations we’ve used on map and set apply to unordered_map and unordered_set as well. Similarly for the unordered versions of the containers that allow multiple keys.

As a result, we can usually use an unordered container in place of the corresponding ordered container, and vice versa. However, because the elements are not stored in order, the output of a program that uses an unordered container will (ordinarily) differ from the same program using an ordered container.

For example, we can rewrite our original word-counting program from § 11.1 ...