std::vector<T,Allocator>::vector
(1) | ||
vector(); |
(until C++17) | |
vector() noexcept(noexcept(Allocator())); |
(since C++17) (constexpr since C++20) |
|
(2) | ||
explicit vector( const Allocator& alloc ); |
(until C++17) | |
explicit vector( const Allocator& alloc ) noexcept; |
(since C++17) (constexpr 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) (constexpr 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) | |
template< class InputIt > vector( InputIt first, InputIt last, |
(5) | (constexpr since C++20) |
vector( const vector& other ); |
(6) | (constexpr since C++20) |
vector( const vector& other, const Allocator& alloc ); |
(7) | (since C++11) (constexpr since C++20) |
vector( vector&& other ); |
(8) | (since C++11) (noexcept since C++17) (constexpr since C++20) |
vector( vector&& other, const Allocator& alloc ); |
(9) | (since C++11) (constexpr since C++20) |
vector( std::initializer_list<T> init, const Allocator& alloc = Allocator() ); |
(10) | (since C++11) (constexpr 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) |
Contents |
[edit] 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
|
[edit] 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
[edit] Exceptions
Calls to Allocator::allocate may throw.
[edit] 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.reqmts]/67, 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 | Feature |
---|---|---|---|
__cpp_lib_containers_ranges |
202202L | (C++23) | Ranges-aware construction and insertion; overload (11) |
[edit] Example
#include <iostream> #include <string> #include <vector> template<typename T> std::ostream& operator<<(std::ostream& s, const std::vector<T>& v) { s.put('{'); for (char comma[]{'\0', ' ', '\0'}; 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; auto const rg = {"cat", "cow", "crow"}; #ifdef __cpp_lib_containers_ranges std::vector<std::string> words5(std::from_range, rg); // overload (11) #else std::vector<std::string> words5(rg.begin(), rg.end()); // overload (5) #endif std::cout << "5: " << words5; }
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} 5: {cat, cow, crow}
[edit] 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 |
[edit] See also
assigns values to the container (public member function) | |
assigns values to the container (public member function) |