Containers library

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

flat_set (C++23)

flat_multiset (C++23)

flat_map (C++23)

flat_multimap (C++23)

Views

span (C++20)

mdspan (C++23)

Iterator invalidation

Member function table

Non-member function table

 

The Containers library is a generic collection of class templates and algorithms that allow programmers to easily implement common data structures like queues, lists and stacks. There are two (until C++11)three (since C++11) classes of containers:

• sequence containers,
• associative containers, and

unordered associative containers,

(since C++11)

each of which is designed to support a different set of operations.

The container manages the storage space that is allocated for its elements and provides member functions to access them, either directly or through iterators (objects with properties similar to pointers).

Most containers have at least several member functions in common, and share functionalities. Which container is the best for the particular application depends not only on the offered functionality, but also on its efficiency for different workloads.

Sequence containers

Sequence containers implement data structures which can be accessed sequentially.

array (C++11)	static contiguous array (class template)
vector	dynamic contiguous array (class template)
deque	double-ended queue (class template)
forward_list (C++11)	singly-linked list (class template)
list	doubly-linked list (class template)

Associative containers

Associative containers implement sorted data structures that can be quickly searched (O(log n) complexity).

set	collection of unique keys, sorted by keys (class template)
map	collection of key-value pairs, sorted by keys, keys are unique (class template)
multiset	collection of keys, sorted by keys (class template)
multimap	collection of key-value pairs, sorted by keys (class template)

Unordered associative containers (since C++11)

Unordered associative containers implement unsorted (hashed) data structures that can be quickly searched (O(1) average, O(n) worst-case complexity).

unordered_set (C++11)	collection of unique keys, hashed by keys (class template)
unordered_map (C++11)	collection of key-value pairs, hashed by keys, keys are unique (class template)
unordered_multiset (C++11)	collection of keys, hashed by keys (class template)
unordered_multimap (C++11)	collection of key-value pairs, hashed by keys (class template)

Container adaptors

Container adaptors provide a different interface for sequential containers.

stack	adapts a container to provide stack (LIFO data structure) (class template)
queue	adapts a container to provide queue (FIFO data structure) (class template)
priority_queue	adapts a container to provide priority queue (class template)
flat_set (C++23)	adapts a container to provide a collection of unique keys, sorted by keys (class template)
flat_map (C++23)	adapts two containers to provide a collection of key-value pairs, sorted by unique keys (class template)
flat_multiset (C++23)	adapts a container to provide a collection of keys, sorted by keys (class template)
flat_multimap (C++23)	adapts two containers to provide a collection of key-value pairs, sorted by keys (class template)

Views

Views provide flexible facilities for interacting with one- or multi-dimensional views over a non-owning array of elements.

span (C++20)	a non-owning view over a contiguous sequence of objects (class template)
mdspan (C++23)	a multi-dimensional non-owning array view (class template)

Iterator invalidation

Read-only methods never invalidate iterators or references. Methods which modify the contents of a container may invalidate iterators and/or references, as summarized in this table.

Category	Container	After insertion, are...		After erasure, are...		Conditionally
		iterators valid?	references valid?	iterators valid?	references valid?
Sequence containers	array	N/A		N/A
	vector	No		N/A		Insertion changed capacity
		Yes		Yes		Before modified element(s) (for insertion only if capacity didn't change)
		No		No		At or after modified element(s)
	deque	No	Yes	Yes, except erased element(s)		Modified first or last element
			No	No		Modified middle only
	list	Yes		Yes, except erased element(s)
	forward_list	Yes		Yes, except erased element(s)
Associative containers	set multiset map multimap	Yes		Yes, except erased element(s)
Unordered associative containers	unordered_set unordered_multiset unordered_map unordered_multimap	No	Yes	N/A		Insertion caused rehash
		Yes		Yes, except erased element(s)		No rehash

Here, insertion refers to any method which adds one or more elements to the container and erasure refers to any method which removes one or more elements from the container.

• Examples of insertion methods are std::set::insert, std::map::emplace, std::vector::push_back, and std::deque::push_front.

Note that std::unordered_map::operator[] also counts, as it may insert an element into the map.

(since C++11)

• Examples of erasure methods are std::set::erase, std::vector::pop_back, std::deque::pop_front, and std::map::clear.
  • clear invalidates all iterators and references. Because it erases all elements, this technically complies with the rules above.

Unless otherwise specified (either explicitly or by defining a function in terms of other functions), passing a container as an argument to a library function never invalidate iterators to, or change the values of, objects within that container.

The past-the-end iterator deserves particular mention. In general this iterator is invalidated as though it were a normal iterator to a non-erased element. So std::set::end is never invalidated, std::unordered_set::end is invalidated only on rehash (since C++11), std::vector::end is always invalidated (since it is always after the modified elements), and so on.

There is one exception: an erasure which deletes the last element of a std::deque does invalidate the past-the-end iterator, even though it is not an erased element of the container (or an element at all). Combined with the general rules for std::deque iterators, the net result is that the only modifying operation which does not invalidate std::deque::end is an erasure which deletes the first element, but not the last.

Thread safety All container functions can be called concurrently by different threads on different containers. More generally, the C++ standard library functions do not read objects accessible by other threads unless those objects are directly or indirectly accessible via the function arguments, including the this pointer. All const member functions can be called concurrently by different threads on the same container. In addition, the member functions begin(), end(), rbegin(), rend(), front(), back(), data(), find(), lower_bound(), upper_bound(), equal_range(), at(), and, except in associative containers, operator[], behave as const for the purposes of thread safety (that is, they can also be called concurrently by different threads on the same container). More generally, the C++ standard library functions do not modify objects unless those objects are accessible, directly or indirectly, via the function's non-const arguments, including the this pointer. Different elements in the same container can be modified concurrently by different threads, except for the elements of std::vector<bool> (for example, a vector of std::future objects can be receiving values from multiple threads). Iterator operations (e.g. incrementing an iterator) read, but do not modify the underlying container, and may be executed concurrently with operations on other iterators on the same container, with the const member functions, or reads from the elements. Container operations that invalidate any iterators modify the container and cannot be executed concurrently with any operations on existing iterators even if those iterators are not invalidated. Elements of the same container can be modified concurrently with those member functions that are not specified to access these elements. More generally, the C++ standard library functions do not read objects indirectly accessible through their arguments (including other elements of a container) except when required by its specification. In any case, container operations (as well as algorithms, or any other C++ standard library functions) may be parallelized internally as long as this does not change the user-visible results (e.g. std::transform may be parallelized, but not std::for_each which is specified to visit each element of a sequence in order).

(since C++11)

Function table

Note: std::basic_string is not treated as a container by the standard but behaves much like one due to its similarity. It is listed as 'Pseudo container' here for convenience.

	- functions present in C++03
	- functions present since C++11
	- functions present since C++17
	- functions present since C++20
	- functions present since C++23

Member function table

		Pseudo container	Sequence containers					Associative containers				Unordered associative containers				Container adaptors
Header		<string>	<array>	<vector>	<deque>	<forward_list>	<list>	<set>		<map>		<unordered_set>		<unordered_map>		<stack>	<queue>		<flat_set>		<flat_map>		Header
Container		basic_string	array	vector	deque	forward_list	list	set	multiset	map	multimap	unordered_set	unordered_multiset	unordered_map	unordered_multimap	stack	queue	priority_queue	flat_set	flat_multiset	flat_map	flat_multimap	Container
	(constructor)	basic_string	(implicit)	vector	deque	forward_list	list	set	multiset	map	multimap	unordered_set	unordered_multiset	unordered_map	unordered_multimap	stack	queue	priority_queue	flat_set	flat_multiset	flat_map	flat_multimap	(constructor)
	(destructor)	~basic_string	(implicit)	~vector	~deque	~forward_list	~list	~set	~multiset	~map	~multimap	~unordered_set	~unordered_multiset	~unordered_map	~unordered_multimap	~stack	~queue	~priority_queue	~flat_set	~flat_multiset	~flat_map	~flat_multimap	(destructor)
	operator=	operator=	(implicit)	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=	operator=
	assign	assign		assign	assign	assign	assign																assign
	assign_range	assign_range		assign_range	assign_range	assign_range	assign_range																assign_range
Iterators	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin				begin cbegin	begin cbegin	begin cbegin	begin cbegin	begin cbegin	Iterators
	end cend	end cend	end cend	end cend	end cend	end cend	end cend	end cend	end cend	end cend	end cend	end cend	end cend	end cend	end cend				end cend	end cend	end cend	end cend	end cend
	rbegin crbegin	rbegin crbegin	rbegin crbegin	rbegin crbegin	rbegin crbegin		rbegin crbegin	rbegin crbegin	rbegin crbegin	rbegin crbegin	rbegin crbegin								rbegin crbegin	rbegin crbegin	rbegin crbegin	rbegin crbegin	rbegin crbegin
	rend crend	rend crend	rend crend	rend crend	rend crend		rend crend	rend crend	rend crend	rend crend	rend crend								rend crend	rend crend	rend crend	rend crend	rend crend
Element access	at	at	at	at	at					at				at							at		at	Element access
	operator[]	operator[]	operator[]	operator[]	operator[]					operator[]				operator[]							operator[]		operator[]
	data	data	data	data																			data
	front	front	front	front	front	front	front										front	top					front
	back	back	back	back	back		back									top	back						back
Capacity	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	empty	Capacity
	size	size	size	size	size		size	size	size	size	size	size	size	size	size	size	size	size	size	size	size	size	size
	max_size	max_size	max_size	max_size	max_size	max_size	max_size	max_size	max_size	max_size	max_size	max_size	max_size	max_size	max_size				max_size	max_size	max_size	max_size	max_size
	resize	resize		resize	resize	resize	resize																resize
	capacity	capacity		capacity																			capacity
	reserve	reserve		reserve								reserve	reserve	reserve	reserve								reserve
	shrink_to_fit	shrink_to_fit		shrink_to_fit	shrink_to_fit																		shrink_to_fit
Modifiers	clear	clear		clear	clear	clear	clear	clear	clear	clear	clear	clear	clear	clear	clear				clear	clear	clear	clear	clear	Modifiers
	insert	insert		insert	insert	insert_after	insert	insert	insert	insert	insert	insert	insert	insert	insert				insert	insert	insert	insert	insert
	insert_range	insert_range		insert_range	insert_range	insert_range_after	insert_range	insert_range	insert_range	insert_range	insert_range	insert_range	insert_range	insert_range	insert_range				insert_range	insert_range	insert_range	insert_range	insert_range
	insert_or_assign									insert_or_assign				insert_or_assign							insert_or_assign		insert_or_assign
	emplace			emplace	emplace	emplace_after	emplace	emplace	emplace	emplace	emplace	emplace	emplace	emplace	emplace				emplace	emplace	emplace	emplace	emplace
	emplace_hint							emplace_hint	emplace_hint	emplace_hint	emplace_hint	emplace_hint	emplace_hint	emplace_hint	emplace_hint				emplace_hint	emplace_hint	emplace_hint	emplace_hint	emplace_hint
	try_emplace									try_emplace				try_emplace							try_emplace		try_emplace
	erase	erase		erase	erase	erase_after	erase	erase	erase	erase	erase	erase	erase	erase	erase				erase	erase	erase	erase	erase
	push_front				push_front	push_front	push_front																push_front
	prepend_range				prepend_range	prepend_range	prepend_range																prepend_range
	emplace_front				emplace_front	emplace_front	emplace_front																emplace_front
	pop_front				pop_front	pop_front	pop_front										pop	pop					pop_front
	push_back	push_back		push_back	push_back		push_back									push	push	push					push_back
	append_range	append_range		append_range	append_range		append_range									push_range	push_range	push_range					append_range
	emplace_back			emplace_back	emplace_back		emplace_back									emplace	emplace	emplace					emplace_back
	pop_back	pop_back		pop_back	pop_back		pop_back									pop							pop_back
	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap
	merge					merge	merge	merge	merge	merge	merge	merge	merge	merge	merge								merge
	extract							extract	extract	extract	extract	extract	extract	extract	extract								extract
List operations	splice					splice_after	splice																splice	List operations
	remove					remove	remove																remove
	remove_if					remove_if	remove_if																remove_if
	reverse					reverse	reverse																reverse
	unique					unique	unique																unique
	sort					sort	sort																sort
Bucket and Hash	begin(size_type) cbegin(size_type)											begin(size_type) cbegin(size_type)	begin(size_type) cbegin(size_type)	begin(size_type) cbegin(size_type)	begin(size_type) cbegin(size_type)								begin(size_type) cbegin(size_type)	Bucket and Hash
	end(size_type) cend(size_type)											end(size_type) cend(size_type)	end(size_type) cend(size_type)	end(size_type) cend(size_type)	end(size_type) cend(size_type)								end(size_type) cend(size_type)
	bucket_count											bucket_count	bucket_count	bucket_count	bucket_count								bucket_count
	max_bucket_count											max_bucket_count	max_bucket_count	max_bucket_count	max_bucket_count								max_bucket_count
	bucket_size											bucket_size	bucket_size	bucket_size	bucket_size								bucket_size
	bucket											bucket	bucket	bucket	bucket								bucket
	load_factor											load_factor	load_factor	load_factor	load_factor								load_factor
	max_load_factor											max_load_factor	max_load_factor	max_load_factor	max_load_factor								max_load_factor
	rehash											rehash	rehash	rehash	rehash								rehash
Lookup	count							count	count	count	count	count	count	count	count				count	count	count	count	count	Lookup
	find	find						find	find	find	find	find	find	find	find				find	find	find	find	find
	contains	contains						contains	contains	contains	contains	contains	contains	contains	contains				contains	contains	contains	contains	contains
	lower_bound							lower_bound	lower_bound	lower_bound	lower_bound								lower_bound	lower_bound	lower_bound	lower_bound	lower_bound
	upper_bound							upper_bound	upper_bound	upper_bound	upper_bound								upper_bound	upper_bound	upper_bound	upper_bound	upper_bound
	equal_range							equal_range	equal_range	equal_range	equal_range	equal_range	equal_range	equal_range	equal_range				equal_range	equal_range	equal_range	equal_range	equal_range
Observers	key_comp							key_comp	key_comp	key_comp	key_comp								key_comp	key_comp	key_comp	key_comp	key_comp	Observers
	value_comp							value_comp	value_comp	value_comp	value_comp								value_comp	value_comp	value_comp	value_comp	value_comp
	hash_function											hash_function	hash_function	hash_function	hash_function								hash_function
	key_eq											key_eq	key_eq	key_eq	key_eq								key_eq
Allocator	get_allocator	get_allocator		get_allocator	get_allocator	get_allocator	get_allocator	get_allocator	get_allocator	get_allocator	get_allocator	get_allocator	get_allocator	get_allocator	get_allocator								get_allocator	Allocator
Adaptors	extract																		extract	extract	extract	extract	extract	Adaptors
	replace																		replace	replace	replace	replace	replace
Container		basic_string	array	vector	deque	forward_list	list	set	multiset	map	multimap	unordered_set	unordered_multiset	unordered_map	unordered_multimap	stack	queue	priority_queue	flat_set	flat_multiset	flat_map	flat_multimap	Container
Header		<string>	<array>	<vector>	<deque>	<forward_list>	<list>	<set>		<map>		<unordered_set>		<unordered_map>		<stack>	<queue>		<flat_set>		<flat_map>		Header
		Pseudo container	Sequence containers					Associative containers				Unordered associative containers				Container adaptors

• Note: functions in two different extract lines have different meanings and syntax:

Non-member function table

		Pseudo container	Sequence containers					Associative containers				Unordered associative containers				Container adaptors
Header		<string>	<array>	<vector>	<deque>	<forward_list>	<list>	<set>		<map>		<unordered_set>		<unordered_map>		<stack>	<queue>		<flat_set>		<flat_map>		Header
Container		basic_string	array	vector	deque	forward_list	list	set	multiset	map	multimap	unordered_set	unordered_multiset	unordered_map	unordered_multimap	stack	queue	priority_queue	flat_set	flat_multiset	flat_map	flat_multimap	Container
Non-member function	operator==	operator==	operator==	operator==	operator==	operator==	operator==	operator==	operator==	operator==	operator==	operator==	operator==	operator==	operator==	operator==	operator==		operator==	operator==	operator==	operator==	operator==	Non-member function
	operator!= (removed in C++20)	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=	operator!=						operator!= (removed in C++20)
	operator< (removed in C++20)	operator<	operator<	operator<	operator<	operator<	operator<	operator<	operator<	operator<	operator<					operator<	operator<						operator< (removed in C++20)
	operator<= (removed in C++20)	operator<=	operator<=	operator<=	operator<=	operator<=	operator<=	operator<=	operator<=	operator<=	operator<=					operator<=	operator<=						operator<= (removed in C++20)
	operator> (removed in C++20)	operator>	operator>	operator>	operator>	operator>	operator>	operator>	operator>	operator>	operator>					operator>	operator>						operator> (removed in C++20)
	operator>= (removed in C++20)	operator>=	operator>=	operator>=	operator>=	operator>=	operator>=	operator>=	operator>=	operator>=	operator>=					operator>=	operator>=						operator>= (removed in C++20)
	operator<=>	operator<=>	operator<=>	operator<=>	operator<=>	operator<=>	operator<=>	operator<=>	operator<=>	operator<=>	operator<=>					operator<=>	operator<=>		operator<=>	operator<=>	operator<=>	operator<=>	operator<=>
	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap	swap
	erase	erase		erase	erase	erase	erase																erase
	erase_if	erase_if		erase_if	erase_if	erase_if	erase_if	erase_if	erase_if	erase_if	erase_if	erase_if	erase_if	erase_if	erase_if				erase_if	erase_if	erase_if	erase_if	erase_if
Container		basic_string	array	vector	deque	forward_list	list	set	multiset	map	multimap	unordered_set	unordered_multiset	unordered_map	unordered_multimap	stack	queue	priority_queue	flat_set	flat_multiset	flat_map	flat_multimap	Container
Header		<string>	<array>	<vector>	<deque>	<forward_list>	<list>	<set>		<map>		<unordered_set>		<unordered_map>		<stack>	<queue>		<flat_set>		<flat_map>		Header
		Pseudo container	Sequence containers					Associative containers				Unordered associative containers				Container adaptors

The <, <=, >, >=, and != operators are synthesized from operator<=> and operator== respectively.

(since C++20)

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 51	C++98	container iterators might be invalidated by arbitrary library operation	they are only invalidated when specified

See also

C++ named requirements:

• Container
• SequenceContainer
• ContiguousContainer
• ReversibleContainer
• AssociativeContainer
• AllocatorAwareContainer
• UnorderedAssociativeContainer

valarray	numeric arrays, array masks and array slices (class template)
basic_string	stores and manipulates sequences of characters (class template)
basic_string_view (C++17)	read-only string view (class template)