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Difference between revisions of "cpp/container"

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Revision as of 23:52, 22 September 2022

 
C++
 
Containers library
 

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.

Contents

Sequence containers

Sequence containers implement data structures which can be accessed sequentially.

(C++11)
 fixed-sized inplace contiguous array
(class template) [edit]
dynamic contiguous array
(class template) [edit]
double-ended queue
(class template) [edit]
(C++11)
 singly-linked list
(class template) [edit]
doubly-linked list
(class template) [edit]

Associative containers

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

collection of unique keys, sorted by keys
(class template) [edit]
collection of key-value pairs, sorted by keys, keys are unique
(class template) [edit]
collection of keys, sorted by keys
(class template) [edit]
collection of key-value pairs, sorted by keys
(class template) [edit]

Unordered associative containers (since C++11)

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

(C++11)
 collection of unique keys, hashed by keys
(class template) [edit]
(C++11)
 collection of key-value pairs, hashed by keys, keys are unique
(class template) [edit]
(C++11)
 collection of keys, hashed by keys
(class template) [edit]
(C++11)
 collection of key-value pairs, hashed by keys
(class template) [edit]

Container adaptors

Container adaptors provide a different interface for sequential containers.

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

Views

span(since C++20) and mdspan(since C++23) are non-owning views over a contiguous sequence of objects, the storage of which is owned by some other object.

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

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.

(since C++11)

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

  1. 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.
  2. 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.
  3. 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).
  4. 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.
  5. 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.
  6. 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

- 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

This section is incomplete
Reason: This table is incomplete: add span and mdspan
Sequence containers Associative containers Unordered associative containers Container adaptors
Header <array> <vector> <deque> <forward_list> <list> <set> <map> <unordered_set> <unordered_map> <stack> <queue> <flat_set> <flat_map>
Container
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
(constructor)
(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)
(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
operator=
(implicit)
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_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
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
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
operator[]
operator[]
operator[]
operator[]
operator[]
operator[]
operator[]
data
data
data
front
front
front
front
front
front
front
top
back
back
back
back
back
top
back
Capacity
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
empty
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
resize
resize
resize
resize
resize
capacity
capacity
bucket_count
bucket_count
bucket_count
bucket_count
reserve
reserve
reserve
reserve
reserve
reserve
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
insert
insert
insert
insert_after
insert
insert
insert
insert
insert
insert
insert
insert
insert
insert
insert
insert
insert
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_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_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
erase
erase
erase
erase_after
erase
erase
erase
erase
erase
erase
erase
erase
erase
erase
erase
erase
erase
push_front
push_front
push_front
push_front
prepend_range
prepend_range
prepend_range
prepend_range
emplace_front
emplace_front
emplace_front
emplace_front
pop_front
pop_front
pop_front
pop_front
pop
pop
push_back
push_back
push_back
push_back
push
push
push
append_range
append_range
append_range
append_range
push_range
push_range
push_range
emplace_back
emplace_back
emplace_back
emplace_back
emplace
emplace
emplace
pop_back
pop_back
pop_back
pop_back
pop
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
extract
extract
extract
extract
extract
extract
extract
extract
extract
List operations
splice
splice_after
splice
remove
remove
remove
remove_if
remove_if
remove_if
reverse
reverse
reverse
unique
unique
unique
sort
sort
sort
Lookup
count
count
count
count
count
count
count
count
count
count
count
count
count
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
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
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
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
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
Adaptors
extract
extract
extract
extract
extract
replace
replace
replace
replace
replace
Container
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
Sequence containers Associative containers Unordered associative containers Container adaptors
  • note: functions in two different 'extract' lines have different meanings

Non-member function table

Sequence containers Associative containers Unordered associative containers Container adaptors
Header <array> <vector> <deque> <forward_list> <list> <set> <map> <unordered_set> <unordered_map> <stack> <queue> <flat_set> <flat_map>
Container
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
Non-member function
operator==
operator==
operator==
operator==
operator==
operator==
operator==
operator==
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< (removed in C++20)
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> (removed in C++20)
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<=>
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
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
Container
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
Sequence containers Associative containers Unordered associative containers Container adaptors

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:

numeric arrays, array masks and array slices
(class template) [edit]
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