Difference between revisions of "cpp/container/vector"

Revision as of 14:53, 12 September 2023

Defined in header `<vector>`
template< class T, class Allocator = std::allocator<T> > class vector;

std::vector is a sequence container that encapsulates dynamic size arrays.

The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets on regular pointers to elements. This means that a pointer to an element of a vector may be passed to any function that expects a pointer to an element of an array.

The storage of the vector is handled automatically, being expanded and contracted as needed. Vectors usually occupy more space than static arrays, because more memory is allocated to handle future growth. This way a vector does not need to reallocate each time an element is inserted, but only when the additional memory is exhausted. The total amount of allocated memory can be queried using capacity() function. Extra memory can be returned to the system via a call to shrink_to_fit()(C++11).

Reallocations are usually costly operations in terms of performance. reserve() function can be used to eliminate reallocations if the number of elements is known beforehand.

The complexity (efficiency) of common operations on vectors is as follows:

Random access - constant $O(1)$
Insertion or removal of elements at the end - amortized constant $O(1)$
Insertion or removal of elements - linear in distance to the end of the vector $O(n)$

The requirements that are imposed on the elements depend on the actual operations performed on the container. Generally, it is required that element type meets the requirements of Erasable, but many member functions impose stricter requirements. This container (but not its members) can be instantiated with an incomplete element type if the allocator satisfies the allocator completeness requirements.

Feature-test macro	Value	Std	Feature
`__cpp_lib_incomplete_container_elements`	201505L	(C++17)	Minimal incomplete type support

(since C++17)

[edit]

Allocator - An allocator that is used to acquire/release memory and to construct/destroy the elements in that memory. The type must meet the requirements of Allocator. The behavior is undefined(until C++20)The program is ill-formed(since C++20) if Allocator::value_type is not the same as T.[edit]

Specializations

The standard library provides a specialization of std::vector for the type bool, which is optimized for space efficiency.

vector<bool>

space-efficient dynamic bitset
(class template specialization) [edit]

Member types

Member type Definition

value_type T[edit]

allocator_type Allocator[edit]

size_type Unsigned integer type (usually std::size_t)[edit]

difference_type Signed integer type (usually std::ptrdiff_t)[edit]

reference value_type&[edit]

const_reference const value_type&[edit]

pointer

`Allocator::pointer`	(until C++11)
std::allocator_traits<Allocator>::pointer	(since C++11)

[edit]

const_pointer

`Allocator::const_pointer`	(until C++11)
std::allocator_traits<Allocator>::const_pointer	(since C++11)

[edit]

iterator

LegacyRandomAccessIterator and LegacyContiguousIterator to `value_type`	(until C++20)
LegacyRandomAccessIterator, `contiguous_iterator`, and ConstexprIterator to `value_type`	(since C++20)

[edit]

const_iterator

LegacyRandomAccessIterator and LegacyContiguousIterator to const value_type	(until C++20)
LegacyRandomAccessIterator, `contiguous_iterator`, and ConstexprIterator to const value_type	(since C++20)

[edit]

reverse_iterator std::reverse_iterator<iterator>[edit]

const_reverse_iterator std::reverse_iterator<const_iterator>[edit]

Member functions

(constructor)	constructs the `vector` (public member function) [edit]
(destructor)	destructs the `vector` (public member function) [edit]
operator=	assigns values to the container (public member function) [edit]
assign	assigns values to the container (public member function) [edit]
get_allocator	returns the associated allocator (public member function) [edit]
Element access
at	access specified element with bounds checking (public member function) [edit]
operator[]	access specified element (public member function) [edit]
front	access the first element (public member function) [edit]
back	access the last element (public member function) [edit]
data	direct access to the underlying contiguous storage (public member function) [edit]
Iterators
begincbegin (C++11)	returns an iterator to the beginning (public member function) [edit]
endcend (C++11)	returns an iterator to the end (public member function) [edit]
rbegincrbegin (C++11)	returns a reverse iterator to the beginning (public member function) [edit]
rendcrend (C++11)	returns a reverse iterator to the end (public member function) [edit]
Capacity
empty	checks whether the container is empty (public member function) [edit]
size	returns the number of elements (public member function) [edit]
max_size	returns the maximum possible number of elements (public member function) [edit]
reserve	reserves storage (public member function) [edit]
capacity	returns the number of elements that can be held in currently allocated storage (public member function) [edit]
shrink_to_fit (DR*)	reduces memory usage by freeing unused memory (public member function) [edit]
Modifiers
clear	clears the contents (public member function) [edit]
insert	inserts elements (public member function) [edit]
emplace (C++11)	constructs element in-place (public member function) [edit]
erase	erases elements (public member function) [edit]
push_back	adds an element to the end (public member function) [edit]
emplace_back (C++11)	constructs an element in-place at the end (public member function) [edit]
pop_back	removes the last element (public member function) [edit]
resize	changes the number of elements stored (public member function) [edit]
swap	swaps the contents (public member function) [edit]

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)	lexicographically compares the values of two `vector`s (function template) [edit]
std::swap(std::vector)	specializes the std::swap algorithm (function template) [edit]

@@ Line 1: / Line 1: @@
 {{cpp/title|vector}}
 {{cpp/container/vector/navbar}}
-{{dcl begin}}
+{{ddcl | header=vector |
-{{dcl header|vector}}
-{{dcl|num=1|1=
 template<
      class T,
-     class Allocator = std::allocator<T>
+     class Allocator {{=}} std::allocator<T>
 > class vector;
 }}
-{{dcl|since=c++17|num=2|1=
-namespace pmr {
-    template< class T >
-    using vector = std::vector<T, std::pmr::polymorphic_allocator<T>>;
-}
-}}
-{{dcl end}}
-@1@ {{tt|std::vector}} is a sequence container that encapsulates dynamic size arrays.
+{{tt|std::vector}} is a sequence container that encapsulates dynamic size arrays.
-@2@ {{tt|std::pmr::vector}} is an alias template that uses a [[cpp/memory/polymorphic_allocator|polymorphic allocator]].
-The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets to regular pointers to elements. This means that  a pointer to an element of a vector may be passed to any function that expects a pointer to an element of an array.
+The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets on regular pointers to elements. This means that  a pointer to an element of a vector may be passed to any function that expects a pointer to an element of an array.
-The storage of the vector is handled automatically, being expanded as needed. Vectors usually occupy more space than static arrays, because more memory is allocated to handle future growth. This way a vector does not need to reallocate each time an element is inserted, but only when the additional memory is exhausted. The total amount of allocated memory can be queried using {{lc|capacity()}} function. Extra memory can be returned to the system via a call to {{lc|shrink_to_fit()}}<ref>In libstdc++, {{tt|shrink_to_fit()}} is [https://gcc.gnu.org/onlinedocs/libstdc++/manual/strings.html#strings.string.shrink not available] in C++98 mode.</ref>.
+The storage of the vector is handled automatically, being expanded and contracted as needed. Vectors usually occupy more space than static arrays, because more memory is allocated to handle future growth. This way a vector does not need to reallocate each time an element is inserted, but only when the additional memory is exhausted. The total amount of allocated memory can be queried using {{lc|capacity()}} function. Extra memory can be returned to the system via a call to {{lc|shrink_to_fit()}}{{mark c++11}}.
-Reallocations are usually costly operations in terms of performance. The {{lc|reserve()}} function can be used to eliminate reallocations if the number of elements is known beforehand.
+Reallocations are usually costly operations in terms of performance. {{lc|reserve()}} function can be used to eliminate reallocations if the number of elements is known beforehand.
 The complexity (efficiency) of common operations on vectors is as follows:
-* Random access - constant {{math|𝓞(1)}}.
+* Random access - constant {{math|O(1)}}
-* Insertion or removal of elements at the end - amortized constant {{math|𝓞(1)}}.
+* Insertion or removal of elements at the end - amortized constant {{math|O(1)}}
-* Insertion or removal of elements - linear in the distance to the end of the vector {{math|𝓞(n)}}.
+* Insertion or removal of elements - linear in distance to the end of the vector {{math|O(n)}}
-{{tt|std::vector}} (for {{tt|T}} other than {{c/core|bool}}) meets the requirements of {{named req|Container}}{{rev inl|since=c++11|, {{named req|AllocatorAwareContainer}}}}, {{named req|SequenceContainer}}{{rev inl|since=c++17|, {{named req|ContiguousContainer}}}} and {{named req|ReversibleContainer}}.
-{{rrev|since=c++20|
-Member functions of {{tt|std::vector}} are {{c/core|constexpr}}: it is possible to create and use {{tt|std::vector}} objects in the evaluation of a constant expression.
-However, {{tt|std::vector}} objects generally cannot be {{c/core|constexpr}}, because any dynamically allocated storage must be released in the same evaluation of constant expression.
-}}
-<references/>
 ===Template parameters===
 {{par begin}}
-{{par inc|cpp/container/param list T|vector}}
+{{par inc | cpp/container/param list T | vector}}
-{{par inc|cpp/container/param list Allocator|vector}}
+{{par inc | cpp/container/param list Allocator | vector}}
 {{par end}}
 ===Specializations===
-The standard library provides a specialization of {{tt|std::vector}} for the type {{c/core|bool}}, which may be optimized for space efficiency.
+The standard library provides a specialization of {{tt|std::vector}} for the type {{c|bool}}, which is optimized for space efficiency.
 {{dsc begin}}
-{{dsc inc|cpp/container/dsc vector bool}}
+{{dsc inc | cpp/container/dsc vector_bool}}
 {{dsc end}}
-===Iterator invalidation===
-{|class="dsctable" style="font-size:0.9em"
-!Operations
-!Invalidated
-|-
-|All read only operations
-|Never
-|-
-|{{lc|swap}}, {{lc|std::swap}}
-|{{lc|end()}}
-|-
-|{{lc|clear}}, {{lc|1=operator=}}, {{lc|assign}}
-|Always
-|-
-|{{lc|reserve}}, {{lc|shrink_to_fit}}
-|If the vector changed capacity, all of them. If not, none.
-|-
-|{{lc|erase}}
-|Erased elements and all elements after them (including {{lc|end()}})
-|-
-|{{lc|push_back}}, {{lc|emplace_back}}
-|If the vector changed capacity, all of them. If not, only {{lc|end()}}.
-|-
-|{{lc|insert}}, {{lc|emplace}}
-|If the vector changed capacity, all of them.<br>If not, only those at or after the insertion point (including {{lc|end()}}).
-|-
-|{{lc|resize}}
-|If the vector changed capacity, all of them. If not, only {{lc|end()}} and any elements erased.
-|-
-|{{lc|pop_back}}
-|The element erased and {{lc|end()}}.
-|}
 ===Member types===
 {{dsc begin}}
-{{dsc hitem|Member type|Definition}}
+{{dsc hitem | Member type | Definition}}
-{{dsc inc|cpp/container/dsc value_type|vector}}
+{{dsc inc | cpp/container/dsc value_type | vector}}
-{{dsc inc|cpp/container/dsc allocator_type|vector}}
+{{dsc inc | cpp/container/dsc allocator_type | vector}}
-{{dsc inc|cpp/container/dsc size_type|vector}}
+{{dsc inc | cpp/container/dsc size_type | vector}}
-{{dsc inc|cpp/container/dsc difference_type|vector}}
+{{dsc inc | cpp/container/dsc difference_type | vector}}
-{{dsc inc|cpp/container/dsc reference|vector}}
+{{dsc inc | cpp/container/dsc reference | vector}}
-{{dsc inc|cpp/container/dsc const_reference|vector}}
+{{dsc inc | cpp/container/dsc const_reference | vector}}
-{{dsc inc|cpp/container/dsc pointer|vector}}
+{{dsc inc | cpp/container/dsc pointer | vector}}
-{{dsc inc|cpp/container/dsc const_pointer|vector}}
+{{dsc inc | cpp/container/dsc const_pointer | vector}}
-{{dsc inc|cpp/container/dsc iterator|vector}}
+{{dsc inc | cpp/container/dsc iterator | vector}}
-{{dsc inc|cpp/container/dsc const_iterator|vector}}
+{{dsc inc | cpp/container/dsc const_iterator | vector}}
-{{dsc inc|cpp/container/dsc reverse_iterator|vector}}
+{{dsc inc | cpp/container/dsc reverse_iterator | vector}}
-{{dsc inc|cpp/container/dsc const_reverse_iterator|vector}}
+{{dsc inc | cpp/container/dsc const_reverse_iterator | vector}}
 {{dsc end}}
 ===Member functions===
 {{dsc begin}}
-{{dsc inc|cpp/container/dsc constructor|vector}}
+{{dsc inc | cpp/container/dsc constructor | vector}}
-{{dsc inc|cpp/container/dsc destructor|vector}}
+{{dsc inc | cpp/container/dsc destructor | vector}}
-{{dsc inc|cpp/container/dsc operator{{=}}|vector}}
+{{dsc inc | cpp/container/dsc operator{{=}} | vector}}
-{{dsc inc|cpp/container/dsc assign|vector}}
+{{dsc inc | cpp/container/dsc assign | vector}}
-{{dsc inc|cpp/container/dsc assign_range|vector}}
+{{dsc inc | cpp/container/dsc get_allocator | vector}}
-{{dsc inc|cpp/container/dsc get_allocator|vector}}
-{{dsc h2|Element access}}
+{{dsc h2 | Element access}}
-{{dsc inc|cpp/container/dsc at|vector}}
+{{dsc inc | cpp/container/dsc at | vector}}
-{{dsc inc|cpp/container/dsc operator_at|vector}}
+{{dsc inc | cpp/container/dsc operator_at | vector}}
-{{dsc inc|cpp/container/dsc front|vector}}
+{{dsc inc | cpp/container/dsc front | vector}}
-{{dsc inc|cpp/container/dsc back|vector}}
+{{dsc inc | cpp/container/dsc back | vector}}
-{{dsc inc|cpp/container/dsc data|vector}}
+{{dsc inc | cpp/container/dsc data | vector}}
-{{dsc h2|Iterators}}
+{{dsc h2 | Iterators}}
-{{dsc inc|cpp/container/dsc begin|vector}}
+{{dsc inc | cpp/container/dsc begin | vector}}
-{{dsc inc|cpp/container/dsc end|vector}}
+{{dsc inc | cpp/container/dsc end | vector}}
-{{dsc inc|cpp/container/dsc rbegin|vector}}
+{{dsc inc | cpp/container/dsc rbegin | vector}}
-{{dsc inc|cpp/container/dsc rend|vector}}
+{{dsc inc | cpp/container/dsc rend | vector}}
-{{dsc h2|Capacity}}
+{{dsc h2 | Capacity}}
-{{dsc inc|cpp/container/dsc empty|vector}}
+{{dsc inc | cpp/container/dsc empty | vector}}
-{{dsc inc|cpp/container/dsc size|vector}}
+{{dsc inc | cpp/container/dsc size | vector}}
-{{dsc inc|cpp/container/dsc max_size|vector}}
+{{dsc inc | cpp/container/dsc max_size | vector}}
-{{dsc inc|cpp/container/dsc reserve|vector}}
+{{dsc inc | cpp/container/dsc reserve | vector}}
-{{dsc inc|cpp/container/dsc capacity|vector}}
+{{dsc inc | cpp/container/dsc capacity | vector}}
-{{dsc inc|cpp/container/dsc shrink_to_fit|vector}}
+{{dsc inc | cpp/container/dsc shrink_to_fit | vector}}
-{{dsc h2|Modifiers}}
+{{dsc h2 | Modifiers}}
-{{dsc inc|cpp/container/dsc clear|vector}}
+{{dsc inc | cpp/container/dsc clear | vector}}
-{{dsc inc|cpp/container/dsc insert|vector}}
+{{dsc inc | cpp/container/dsc insert | vector}}
-{{dsc inc|cpp/container/dsc insert_range|vector}}
+{{dsc inc | cpp/container/dsc emplace | vector}}
-{{dsc inc|cpp/container/dsc emplace|vector}}
+{{dsc inc | cpp/container/dsc erase | vector}}
-{{dsc inc|cpp/container/dsc erase|vector}}
+{{dsc inc | cpp/container/dsc push_back | vector}}
-{{dsc inc|cpp/container/dsc push_back|vector}}
+{{dsc inc | cpp/container/dsc emplace_back | vector}}
-{{dsc inc|cpp/container/dsc emplace_back|vector}}
+{{dsc inc | cpp/container/dsc pop_back | vector}}
-{{dsc inc|cpp/container/dsc append_range|vector}}
+{{dsc inc | cpp/container/dsc resize | vector}}
-{{dsc inc|cpp/container/dsc pop_back|vector}}
+{{dsc inc | cpp/container/dsc swap | vector}}
-{{dsc inc|cpp/container/dsc resize|vector}}
-{{dsc inc|cpp/container/dsc swap|vector}}
 {{dsc end}}
 ===Non-member functions===
 {{dsc begin}}
-{{dsc inc|cpp/container/dsc operator_cmp|vector}}
+{{dsc inc | cpp/container/dsc operator_cmp | vector}}
-{{dsc inc|cpp/container/dsc swap2|vector}}
+{{dsc inc | cpp/container/dsc swap2 | vector}}
-{{dsc inc|cpp/container/dsc erase seq|vector}}
 {{dsc end}}
-{{rrev|noborder=true|since=c++17|{{=}}{{=}}{{=}}{{rl|deduction guides|Deduction guides}}{{=}}{{=}}{{=}}}}
+[[de:cpp/container/vector]]
+[[es:cpp/container/vector]]
-===Notes===
+[[fr:cpp/container/vector]]
-{{ftm begin|std=1|comment=1}}
+[[it:cpp/container/vector]]
-{{ftm|__cpp_lib_containers_ranges|value=202202L|std=C++23|Ranges construction and insertion for containers}}
+[[ja:cpp/container/vector]]
-{{ftm end}}
+[[ko:cpp/container/vector]]
+[[pt:cpp/container/vector]]
-===Example===
+[[ru:cpp/container/vector]]
-{{example
+[[zh:cpp/container/vector]]
-|code=
-#include <iostream>
-#include <vector>
-int main()
-{
-    // Create a vector containing integers
-    std::vector<int> v = {8, 4, 5, 9};
-    // Add two more integers to vector
-    v.push_back(6);
-    v.push_back(9);
-    // Overwrite element at position 2
-    v[2] = -1;
-    // Print out the vector
-    for (int n : v)
-        std::cout << n << ' ';
-    std::cout << '\n';
-}
-|output=
-4 -1 9 6 9
-}}
-===Defect reports===
-{{dr list begin}}
-{{dr list item|wg=lwg|dr=69|std=C++98|before=contiguity of the storage for elements of {{tt|vector}} was not required|after=required}}
-{{dr list item|wg=lwg|dr=230|std=C++98|before={{tt|T}} was not required to be {{named req|CopyConstructible}}<br>(an element of type {{tt|T}} might not be able to be constructed)|after={{tt|T}} is also required to<br>be {{named req|CopyConstructible}}}}
-{{dr list item|wg=lwg|dr=464|std=C++98|before=access to the underlying storage of an empty {{tt|vector}} resulted in UB|after={{tt|data}} function provided}}
-{{dr list end}}
-{{langlinks|cs|de|es|fr|it|ja|ko|pl|pt|ru|zh}}

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Difference between revisions of "cpp/container/vector"

Revision as of 14:53, 12 September 2023

Contents

Template parameters

Specializations

Member types

Member functions

Element access

Iterators

Capacity

Modifiers

Non-member functions

Navigation

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