Iterators

An iterator is a design pattern, but interestingly, the STL work started much before
Gang of Four published their design patterns-related work to the software community. Iterators themselves are objects that allow traversing the containers to access, modify, and manipulate the data stored in the containers. Iterators do this so magically that we don't realize or need to know where and how the data is stored and retrieved.

The following image visually represents an iterator:

From the preceding image, you can understand that every iterator supports the begin() API, which returns the first element position, and the end() API returns one position past the last element in the container.

The STL broadly supports the following five types of iterators:

• Input iterators
• Output iterators
• Forward iterators
• Bidirectional iterators 
• Random-access iterators

The container implements the iterator to let us easily retrieve and manipulate the data, without delving much into the technical details of a container. 

The following table explains each of the five iterators: