Categories of Iterator

STL includes many kinds of iterators, including random access iterators, reverse iterators, and IOStream iterators. Iterators are grouped into the following categories.

Input iterators-Read one item at a time in a forward direction only
Output iterators-Write one item at a time in a forward direction only
Forward iterators-Read or write one item at a time in a forward direction (combines the characteristics of input and output iterators)
Bidirectional iterators-Read or write one item at a time in either a forward or backward direction
Random access iterators-Read or write one item at a time in either a forward or backward direction, and can jump by an arbitrary distance

These iterator categories and their interfaces can be arranged in a hierarchical fashion, as shown in the following diagram.

In addition to these basic types of iterators, other iterators have special characteristics, such as the ability to move in a reverse fashion through a collection, as well as const versions of the iterators that can iterate through read-only collections.