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) | |
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 vector'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 vector'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 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 |
[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
[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.rev.reqmts]/17, and a more direct guarantee is under consideration via LWG 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> a(3); // creates a 3-element vector holding {0, 0, 0} std::vector<int> d{1, 2}; // creates a 2-element vector holding {1, 2} std::vector<int> c(1, 2); // creates a 1-element vector holding {2}
[edit] Example
#include <vector> #include <string> #include <iostream> 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 << ']'; } int main() { // C++11 initializer list syntax: std::vector<std::string> words1 {"the", "frogurt", "is", "also", "cursed"}; std::cout << "words1: " << words1 << '\n'; // words2 == words1 std::vector<std::string> words2(words1.begin(), words1.end()); std::cout << "words2: " << words2 << '\n'; // words3 == words1 std::vector<std::string> words3(words1); std::cout << "words3: " << words3 << '\n'; // words4 is {"Mo", "Mo", "Mo", "Mo", "Mo"} std::vector<std::string> words4(5, "Mo"); std::cout << "words4: " << words4 << '\n'; }
Output:
words1: [the, frogurt, is, also, cursed] words2: [the, frogurt, is, also, cursed] words3: [the, frogurt, is, also, cursed] words4: [Mo, Mo, Mo, Mo, Mo]
[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 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) |