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std::vector::vector(3) C++ Standard Libary std::vector::vector(3) NAME std::vector::vector - std::vector::vector Synopsis vector(); (until C++17) (since vector() C++17) noexcept(noexcept(Allocator())); (until C++20) constexpr vector() (since noexcept(noexcept(Allocator())); C++20) explicit vector( const (until Allocator& alloc ); C++17) (since explicit vector( const C++17) Allocator& alloc ) noexcept; (until C++20) constexpr ex- plicit vector( const (since Allocator& alloc ) noexcept; C++20) explicit vector( size_type count, (until const T& value = T(), C++11) const Allocator& alloc = Allocator()); vector( size_type count, (since const T& value, C++11) (until const Al- locator& alloc = C++20) Allocator()); constexpr vector( size_type count, (since const T& value, C++20) const Allocator& alloc = Allocator()); (since explicit vector( size_type count C++11) ); (until C++14) explicit vector( size_type (since count, const Allocator& alloc = C++14) Allocator() ); (until C++20) constexpr explicit vector( size_type count, (since const Allocator& alloc = C++20) Allocator() ); (1) template< class InputIt > vector( InputIt first, InputIt (until last, (2) C++20) const Allocator& alloc = Allocator() ); template< class InputIt > (3) constexpr vector( InputIt first, (since InputIt last, C++20) const Allocator& alloc = Allocator() ); vector( const vector& other ); (until C++20) constexpr vector( const vector& (since other ); (4) C++20) (since vector( const vector& other, C++11) const Allocator& alloc ); (until C++20) constexpr vector( const vector& (since other, const Allocator& alloc ); (5) C++20) (since vector( vector&& other ); C++11) (un- til C++17) (since vector( vector&& other ) C++17) noexcept; (6) (until C++20) constexpr vector( vector&& other (7) (since ) noexcept; C++20) (since vector( vector&& other, const (8) C++11) Allocator& alloc ); (until C++20) constexpr vector( vector&& (since other, const Allocator& alloc ); C++20) vector( std::initializer_list<T> (9) (since init, C++11) const Allocator& alloc = (until Allocator() ); (10) C++20) constexpr vector( std::initializer_list<T> init, (since const Allocator& alloc = C++20) Allocator() ); Constructs a new container from a variety of data sources, option- ally using a user supplied allocator alloc. 1) Default constructor. Constructs an empty container with a de- fault-constructed allocator. 2) Constructs an empty container with the given allocator alloc. 3) Constructs the container with count copies of elements with value value. 4) Constructs the container with count default-inserted instances of T. No copies are made. 5) Constructs the container with the contents of the range [first, last). This constructor has the same effect as vector(static_cast<size_type>(first), static_cast<value_type>(last), (until C++11) a) if InputIt is an integral type. This overload participates in overload resolution only if InputIt satisfies LegacyInputIterator, to avoid ambiguity with the overload (since C++11) (3). 6) Copy constructor. Constructs the container with the copy of the contents of other. The allocator is obtained as if by calling (since std::allocator_traits<allocator_type>::select_on_container_copy_con- struction( C++11) other.get_allocator()). 7) Constructs the container with the copy of the contents of other, using alloc as the allocator. The template parameter Allocator is only deduced from the first (since C++23) argument while used in class template argument deduction. 8) Move constructor. Constructs the container with the contents of other using move semantics. Allocator is obtained by move-construction from the allo- cator belonging to other. After the move, other is guaranteed to be empty(). 9) Allocator-extended move constructor. Using alloc as the allocator for the new container, moving the contents from other; if alloc != other.get_al- locator(), this results in an element-wise move. (In that case, other is not guaran- teed to be empty after the move.) The template parameter Allocator is only deduced from the first (since C++23) argument while used in class template argument deduction. 10) Constructs the container with the contents of the initializer list init. 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 Complexity 1-2) Constant 3-4) Linear in count 5) Linear in distance between first and last 6-7) Linear in size of other 8) Constant. 9) Linear if alloc != other.get_allocator(), otherwise constant. 10) Linear in size of init. Exceptions Calls to Allocator::allocate may throw. Notes After container move construction (overload (8)), references, point- ers, 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.requirements.general]/12, 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 uninitial- ized. 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} Example // Run this code #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] Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct be- havior LWG 2193 C++11 the default constructor is explicit made non-ex- plicit See also assign assigns values to the container (public member function) operator= assigns values to the container (public member function) http://cppreference.com 2022.07.31 std::vector::vector(3)
NAME | Synopsis | Parameters | Complexity | Exceptions | Notes | Example | Output: | See also
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