std::vector<T,Allocator>::vector
(1) | ||
vector(); |
(until C++17) | |
vector() noexcept(noexcept(Allocator())); |
(since C++17) (until C++20) |
|
constexpr vector() noexcept(noexcept(Allocator())); |
(since C++20) | |
(2) | ||
explicit vector( const Allocator& alloc ); |
(until C++17) | |
explicit vector( const Allocator& alloc ) noexcept; |
(since C++17) (until C++20) |
|
constexpr explicit vector( const Allocator& alloc ) noexcept; |
(since C++20) | |
(3) | ||
explicit vector( size_type count, const T& value = T(), |
(until C++11) | |
vector( size_type count, const T& value, |
(since C++11) (until C++20) |
|
constexpr vector( size_type count, const T& value, |
(since C++20) | |
(4) | ||
explicit vector( size_type count ); |
(since C++11) (until C++14) |
|
explicit vector( size_type count, const Allocator& alloc = Allocator() ); |
(since C++14) (until C++20) |
|
constexpr explicit vector( size_type count, const Allocator& alloc = Allocator() ); |
(since C++20) | |
(5) | ||
template< class InputIt > vector( InputIt first, InputIt last, |
(until C++20) | |
template< class InputIt > constexpr vector( InputIt first, InputIt last, |
(since C++20) | |
(6) | ||
vector( const vector& other ); |
(until C++20) | |
constexpr vector( const vector& other ); |
(since C++20) | |
(7) | ||
vector( const vector& other, const Allocator& alloc ); |
(since C++11) (until C++20) |
|
constexpr vector( const vector& other, const Allocator& alloc ); |
(since C++20) | |
(8) | ||
vector( vector&& other ); |
(since C++11) (until C++17) |
|
vector( vector&& other ) noexcept; |
(since C++17) (until C++20) |
|
constexpr vector( vector&& other ) noexcept; |
(since C++20) | |
(9) | ||
vector( vector&& other, const Allocator& alloc ); |
(since C++11) (until C++20) |
|
constexpr vector( vector&& other, const Allocator& alloc ); |
(since C++20) | |
(10) | ||
vector( std::initializer_list<T> init, const Allocator& alloc = Allocator() ); |
(since C++11) (until C++20) |
|
constexpr vector( std::initializer_list<T> init, const Allocator& alloc = Allocator() ); |
(since C++20) | |
template< container-compatible-range<T> R > constexpr vector( std::from_range_t, R&& rg, |
(11) | (since C++23) |
Constructs a new container from a variety of data sources, optionally using a user supplied allocator alloc.
[
first,
last)
.
This constructor has the same effect as vector(static_cast<size_type>(first), static_cast<value_type>(last), a) if |
(until C++11) |
This overload participates in overload resolution only if |
(since C++11) |
The allocator is obtained as if by calling std::allocator_traits<allocator_type>::select_on_container_copy_construction( |
(since C++11) |
During class template argument deduction, only the first argument contributes to the deduction of the container's |
(since C++23) |
other
is not guaranteed to be empty after the move.)
During class template argument deduction, only the first argument contributes to the deduction of the container's |
(since C++23) |
Parameters
alloc | - | allocator to use for all memory allocations of this container |
count | - | the size of the container |
value | - | the value to initialize elements of the container with |
first, last | - | the range [ first, last) to copy the elements from
|
other | - | another container to be used as source to initialize the elements of the container with |
init | - | initializer list to initialize the elements of the container with |
rg | - | a container compatible range, that is, an input_range whose elements are convertible to T
|
Complexity
- If first and last are both forward, bidirectional or random-access iterators,
- The copy constructor of
T
is only called N times, and - No reallocation occurs.
- The copy constructor of
- Otherwise (first and last are just input iterators),
- The copy constructor of
T
is called O(N) times, and - Reallocation occurs O(log N) times.
- The copy constructor of
- If
R
models ranges::forward_range or ranges::sized_range,
- Initializes exactly N elements from the result of dereferencing successive iterators of rg, and
- No reallocation occurs.
- Otherwise (
R
models input range),
- The copy or move constructor of
T
is called O(N) times, and - Reallocation occurs O(log N) times.
- The copy or move constructor of
Exceptions
Calls to Allocator::allocate may throw.
Notes
After container move construction (overload (8)), references, pointers, and iterators (other than the end iterator) to other
remain valid, but refer to elements that are now in *this. The current standard makes this guarantee via the blanket statement in [container.rev.reqmts]/17, and a more direct guarantee is under consideration via LWG issue 2321.
The overload (4) zeroes out elements of non-class types such as int, which is different from the behavior of new[], which leaves them uninitialized. To match the behavior of new[], a custom Allocator::construct
can be provided which leaves such elements uninitialized.
Note that the presence of list-initializing constructor (10) means list initialization and direct initialization do different things:
std::vector<int> b{3}; // creates a 1-element vector holding {3} std::vector<int> d(3); // creates a 3-element vector holding {0, 0, 0} std::vector<int> p{1, 2}; // creates a 2-element vector holding {1, 2} std::vector<int> q(1, 2); // creates a 1-element vector holding {2}
Feature-test macro | Value | Std | Comment |
---|---|---|---|
__cpp_lib_containers_ranges |
202202L | (C++23) | Ranges-aware construction and insertion; overload (11) |
Example
#include <vector> #include <iostream> #include <string> template<typename T> std::ostream& operator<<(std::ostream& s, const std::vector<T>& v) { s.put('{'); char comma[3]{'\0', ' ', '\0'}; for (const auto& e : v) { s << comma << e; comma[0] = ','; } return s << "}\n"; } int main() { // C++11 initializer list syntax: std::vector<std::string> words1{"the", "frogurt", "is", "also", "cursed"}; std::cout << "1: " << words1; // words2 == words1 std::vector<std::string> words2(words1.begin(), words1.end()); std::cout << "2: " << words2; // words3 == words1 std::vector<std::string> words3(words1); std::cout << "3: " << words3; // words4 is {"Mo", "Mo", "Mo", "Mo", "Mo"} std::vector<std::string> words4(5, "Mo"); std::cout << "4: " << words4; }
Output:
1: {the, frogurt, is, also, cursed} 2: {the, frogurt, is, also, cursed} 3: {the, frogurt, is, also, cursed} 4: {Mo, Mo, Mo, Mo, Mo}
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 134 | C++98 | overload (5) allowed up to 2N copy constructor calls in the input iterator case |
changed to O(N) calls |
LWG 868 | C++98 | for overload (4), the elements in the container were default constructed | they are value-initialized |
LWG 2193 | C++11 | the default constructor is explicit | made non-explicit |
See also
assigns values to the container (public member function) | |
assigns values to the container (public member function) |