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<iterator>

Iterator definitions

An iterator is any object that, pointing to some element in a range of elements (such as an array or a container), has the ability to iterate through the elements of that range using a set of operators (with at least the increment (++) and dereference (*) operators).

The most obvious form of iterator is a pointer: A pointer can point to elements in an array, and can iterate through them using the increment operator (++). But other kinds of iterators are possible. For example, each container type (such as a list) has a specific iterator type designed to iterate through its elements.

Notice that while a pointer is a form of iterator, not all iterators have the same functionality of pointers; Depending on the properties supported by iterators, they are classified into five different categories:

Iterator categories

Iterators are classified into five categories depending on the functionality they implement:

Input and output iterators are the most limited types of iterators: they can perform sequential single-pass input or output operations.

Forward iterators have all the functionality of input iterators and -if they are not constant iterators- also the functionality of output iterators, although they are limited to one direction in which to iterate through a range (forward). All standard containers support at least forward iterator types.

Bidirectional iterators are like forward iterators but can also be iterated through backwards.

Random-access iterators implement all the functionality of bidirectional iterators, and also have the ability to access ranges non-sequentially: distant elements can be accessed directly by applying an offset value to an iterator without iterating through all the elements in between. These iterators have a similar functionality to standard pointers (pointers are iterators of this category).

The properties of each iterator category are:

category				properties	valid expressions
all categories				copy-constructible, copy-assignable and destructible	`X b(a); b = a;`
all categories				Can be incremented	`++a a++`
Random Access	Bidirectional	Forward	Input	Supports equality/inequality comparisons	`a == b a != b`
			Input	Can be dereferenced as an rvalue	`*a a->m`
			Output	Can be dereferenced as an lvalue (only for mutable iterator types)	`a = t a++ = t`
				default-constructible	`X a; X()`
				Multi-pass: neither dereferencing nor incrementing affects dereferenceability	`{ b=a; a++; b; }`
				Can be decremented	`--a a-- *a--`
				Supports arithmetic operators `+` and `-`	`a + n n + a a - n a - b`
				Supports inequality comparisons (`<`, `>`, `<=` and `>=`) between iterators	`a < b a > b a <= b a >= b`
				Supports compound assignment operations `+=` and `-=`	`a += n a -= n`
				Supports offset dereference operator (`[]`)	`a[n]`

Where X is an iterator type, a and b are objects of this iterator type, t is an object of the type pointed by the iterator type, and n is an integer value.

For more details, see the references for input iterator, output iterator, forward iterator, bidirectional iterator and random-access iterator.

Functions

Iterator operations:

advance: Advance iterator (function template )

distance: Return distance between iterators (function template )

begin: Iterator to beginning (function template )

end: Iterator to end (function template )

prev: Get iterator to previous element (function template )

next: Get iterator to next element (function template )

Iterator generators:

back_inserter: Construct back insert iterator (function template )

front_inserter: Constructs front insert iterator (function template )

inserter: Construct insert iterator (function template )

make_move_iterator: Construct move iterator (function template )

Classes

iterator: Iterator base class (class template )

iterator_traits: Iterator traits (class template )

Predefined iterators

reverse_iterator: Reverse iterator (class template )

move_iterator: Move iterator (class template )

back_insert_iterator: Back insert iterator (class template )

front_insert_iterator: Front insert iterator (class template )

insert_iterator: Insert iterator (class template )

istream_iterator: Istream iterator (class template )

ostream_iterator: Ostream iterator (class template )

istreambuf_iterator: Input stream buffer iterator (class template )

ostreambuf_iterator: Output stream buffer iterator (class template )

Category tags

input_iterator_tag: Input iterator category (class )

output_iterator_tag: Output iterator category (class )

forward_iterator_tag: Forward iterator category (class )

bidirectional_iterator_tag: Bidirectional iterator category (class )

random_access_iterator_tag: Random-access iterator category (class )

iterator
iterator_traits
functions:
- advance
- back_inserter
- begin
- distance
- end
- front_inserter
- inserter
- make_move_iterator
- next
- prev
iterator categories:
predefined iterators:

<iterator>

Iterator categories

Functions

Classes

Predefined iterators

Category tags

C++

Reference

C library:

Containers:

Input/Output:

Multi-threading:

Other:

<iterator>

functions:

iterator categories:

predefined iterators: