C++ In a Nutshell

Iterators

An iterator is an abstraction of a pointer used for pointing into containers and other sequences. An ordinary pointer can point to different elements in an array. The ++ operator advances the pointer to the next element, and the * operator dereferences the pointer to return a value from the array. Iterators generalize the concept so that the same operators have the same behavior for any container, even trees and lists. See the <iterator> section of Chapter 13 for more details.

Iterator Categories

There are five categories of iterators:

Input

Permits you to read a sequence in one pass. The increment (++) operator advances to the next element, but there is no decrement operator. The dereference (*) operator returns an rvalue, not an lvalue, so you can read elements but not modify them.

Output

Permits you to write a sequence in one pass. The increment (++) operator advances to the next element, but there is no decrement operator. You can dereference an element only to assign a value to it. You cannot compare output iterators.

Forward

Permits unidirectional access to a sequence. You can refer to and assign to an item as many times as you want. You can use a forward iterator wherever an input iterator is required or wherever an output iterator is required.

Bidirectional

Similar to a forward iterator but also supports the -- (decrement) operator to move the iterator back one position.

Random access

Similar to a bidirectional iterator but also supports the [] (subscript) operator to access ...