Iterator Categories

Supported operations

Now that we have a better understanding of how a range is defined and how we can know when we have reached the end of a sequence, it’s time to look more closely at the operations that iterators can support in order to navigate, read, and write values.

Iterator navigation in a sequence can be done with the following operations:

• Step forward: std::next(it) or ++it
• Step backward: std::prev(it) or --it
• Jump to an arbitrary position: std::advance(it, n) or it += n

Reading and writing a value at the position that the iterator represents is done by dereferencing the iterator. Here is how it looks:

• Read: auto value = *it
• Write: *it = value

These are the most common operations for iterators that are exposed by containers. But in addition, iterators might operate on data sources where a write or read implies a step forward. Examples of such data sources could be user input, a network connection, or a file. These data sources require the following operations:

• Read only and step forward: auto value = *it; ++it;
• Write only and step forward: *it = value; ++it;