<iterator>

Iterator definitions

Aniterator is any object that, pointing to some element in a range of elements (such as an array or acontainer), 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 apointer: 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, eachcontainer type (such as alist) has a specificiterator 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 andoutput iterators are the most limited types of iterators: they can perform sequential single-pass input or output operations.

Forward iterators have all the functionality ofinput iterators and -if they are notconstant iterators- also the functionality ofoutput iterators, although they are limited to one direction in which to iterate through a range (forward). Allstandard containers support at least forward iterator types.

Bidirectional iterators are likeforward iterators but can also be iterated through backwards.

Random-access iterators implement all the functionality ofbidirectional 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 anddestructible	`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 anrvalue	`*a a->m`
			Output	Can be dereferenced as anlvalue (only formutable 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]`

WhereX is an iterator type,a andb are objects of this iterator type,t is an object of the type pointed by the iterator type, andn is an integer value.

For more details, see the references forinput iterator,output iterator,forward iterator,bidirectional iterator andrandom-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)

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functions