# std::deque<T,Allocator>::deque

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< cpp‎ | container‎ | deque

deque(); explicit deque( const Allocator& alloc ); | (1) |
| (2) |
explicit deque( size_type count, const T& value = T(), const Allocator& alloc = Allocator()); |  | (until C++11)
deque( size_type count, const T& value, const Allocator& alloc = Allocator()); |  | (since C++11)
| (3) |
explicit deque( size_type count ); |  | (since C++11) (until C++14)
explicit deque( size_type count, const Allocator& alloc = Allocator() ); |  | (since C++14)
template< class InputIt > deque( InputIt first, InputIt last, const Allocator& alloc = Allocator() ); | (4) |
deque( const deque& other ); | (5) |
deque( const deque& other, const Allocator& alloc ); | (5) | (since C++11)
deque( deque&& other ); | (6) | (since C++11)
deque( deque&& other, const Allocator& alloc ); | (7) | (since C++11)
deque( std::initializer_list <T> init, const Allocator& alloc = Allocator() ); | (8) | (since C++11)

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

1) Default constructor. Constructs an empty container. If no allocator is supplied, allocator is obtained from a default-constructed instance.
2) Constructs the container with `count` copies of elements with value `value`.
3) Constructs the container with `count` default-inserted instances of `T`. No copies are made.
4) Constructs the container with the contents of the range `[first, last)`.

This constructor has the same effect as deque(static_cast<size_type>(first), static_cast<value_type>(last), a) if `InputIt` is an integral type. | (until C++11)
This overload only participates in overload resolution if `InputIt` satisfies LegacyInputIterator, to avoid ambiguity with the overload (2). | (since C++11)

5) Copy constructor. Constructs the container with the copy of the contents of `other`. If `alloc` is not provided, allocator is obtained as if by calling std::allocator_traits <allocator_type>::select_on_container_copy_construction(other.get_allocator()).
6) Move constructor. Constructs the container with the contents of `other` using move semantics. Allocator is obtained by move-construction from the allocator belonging to `other`.
7) Allocator-extended move constructor. Using `alloc` as the allocator for the new container, moving the contents from `other`; if alloc != other.get_allocator(), this results in an element-wise move.
8) 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) Constant
2-3) Linear in `count`
4) Linear in distance between `first` and `last`
5) Linear in size of `other`
6) Constant.
7) Linear if alloc != other.get_allocator(), otherwise constant.
8) Linear in size of `init`.

### Exceptions

Calls to `Allocator::allocate` may throw.

### Notes

After container move construction (overload (6)), 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 §23.2.1[container.requirements.general]/12, and a more direct guarantee is under consideration via LWG 2321.

### Example

Run this code

    #include <deque>
    #include <string>
    #include <iostream>

    template<typename T>
    std::ostream& operator<<(std::ostream& s, const std::deque<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::deque<std::string> words1 {"the", "frogurt", "is", "also", "cursed"};
        std::cout << "words1: " << words1 << '\n';

        // words2 == words1
        std::deque<std::string> words2(words1.begin(), words1.end());
        std::cout << "words2: " << words2 << '\n';

        // words3 == words1
        std::deque<std::string> words3(words1);
        std::cout << "words3: " << words3 << '\n';

        // words4 is {"Mo", "Mo", "Mo", "Mo", "Mo"}
        std::deque<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 retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2193 | C++11 | the default constructor is explicit | made non-explicit

### See also

assign | assigns values to the container (public member function)
operator= | assigns values to the container (public member function)

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