std::vector<T,Allocator>::vector

vector();

vector() noexcept(noexcept(Allocator()));

constexpr vector() noexcept(noexcept(Allocator()));

explicit vector( const Allocator& alloc );

explicit vector( const Allocator& alloc ) noexcept;

constexpr explicit vector( const Allocator& alloc ) noexcept;

explicit vector( size_type count,
                 const T& value = T(),
                 const Allocator& alloc = Allocator() );

vector( size_type count,
                 const T& value,
                 const Allocator& alloc = Allocator() );

constexpr vector( size_type count,
                  const T& value,
                  const Allocator& alloc = Allocator() );

explicit vector( size_type count );

explicit vector( size_type count,
                 const Allocator& alloc = Allocator() );

constexpr explicit vector( size_type count,
                           const Allocator& alloc = Allocator() );

template< class InputIt >
vector( InputIt first, InputIt last,
        const Allocator& alloc = Allocator() );

template< class InputIt >
constexpr vector( InputIt first, InputIt last,
                  const Allocator& alloc = Allocator() );

vector( const vector& other );

constexpr vector( const vector& other );

vector( const vector& other, const Allocator& alloc );

constexpr vector( const vector& other, const Allocator& alloc );

vector( vector&& other );

vector( vector&& other ) noexcept;

constexpr vector( vector&& other ) noexcept;

vector( vector&& other, const Allocator& alloc );

constexpr vector( vector&& other, const Allocator& alloc );

vector( std::initializer_list<T> init,
        const Allocator& alloc = Allocator() );

constexpr vector( std::initializer_list<T> init,
                  const Allocator& alloc = Allocator() );

template< container-compatible-range<T> R >
constexpr vector( std::from_range_t, R&& rg,
                  const Allocator& alloc = Allocator() );

Constructs a new container from a variety of data sources, optionally using a user supplied allocator alloc.

Parameters

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.
• 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.

• 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.

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.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}

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;
}

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}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also