# std::queue<T,Container>::queue

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< cpp‎ | container‎ | queue

queue() : queue(Container()) { } | (1) | (since C++11)
| (2) |
explicit queue( const Container& cont = Container() ); |  | (until C++11)
explicit queue( const Container& cont ); |  | (since C++11)
explicit queue( Container&& cont ); | (3) | (since C++11)
queue( const queue& other ); | (4) |
queue( queue&& other ); | (5) | (since C++11)
template< class Alloc > explicit queue( const Alloc& alloc ); | (6) | (since C++11)
template< class Alloc > queue( const Container& cont, const Alloc& alloc ); | (7) | (since C++11)
template< class Alloc > queue( Container&& cont, const Alloc& alloc ); | (8) | (since C++11)
template< class Alloc > queue( const queue& other, const Alloc& alloc ); | (9) | (since C++11)
template< class Alloc > queue( queue&& other, const Alloc& alloc ); | (10) | (since C++11)

Constructs new underlying container of the container adaptor from a variety of data sources.

1) Default constructor. Value-initializes the container.
2) Copy-constructs the underlying container `c` with the contents of `cont`. This is also the default constructor. (until C++11)
3) Move-constructs the underlying container `c` with std::move(cont).
4) Copy constructor. The adaptor is copy-constructed with the contents of other.c. (implicitly declared)
5) Move constructor. The adaptor is constructed with std::move(other.c). (implicitly declared)
6-10) The following constructors are only defined if std::uses_allocator<container_type, Alloc>::value == true, that is, if the underlying container is an allocator-aware container (true for all standard library containers that can be used with `queue`).
6) Constructs the underlying container using `alloc` as allocator, as if by c(alloc).
7) Constructs the underlying container with the contents of `cont` and using `alloc` as allocator, as if by c(cont, alloc).
8) Constructs the underlying container with the contents of `cont` using move semantics while utilizing `alloc` as allocator, as if by c(std::move(cont), alloc).
9) Constructs the adaptor with the contents of `other.c` and using `alloc` as allocator, as if by c(other.c, alloc).
10) Constructs the adaptor with the contents of `other` using move semantics while utilizing `alloc` as allocator, as if by c(std::move(other.c), alloc).

### Parameters

alloc | - | allocator to use for all memory allocations of the underlying container
other | - | another container adaptor to be used as source to initialize the underlying container
cont | - | container to be used as source to initialize the underlying container
first, last | - | range of elements to initialize with
Type requirements
- `Alloc` must meet the requirements of Allocator.
- `Container` must meet the requirements of Container. The constructors (5-10) are only defined if `Container` meets the requirements of AllocatorAwareContainer
- `InputIt` must meet the requirements of LegacyInputIterator.

### Complexity

Same as the corresponding operation on the wrapped container.

### Defect reports

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

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
P0935R0 | C++11 | default constructor was explicit | made implicit

### Example

Run this code

    #include <queue>
    #include <deque>
    #include <iostream>

    int main()
    {
        std::queue<int> c1;
        c1.push(5);
        std::cout << c1.size() << '\n';

        std::queue<int> c2(c1);
        std::cout << c2.size() << '\n';

        std::deque<int> deq {3, 1, 4, 1, 5};
        std::queue<int> c3(deq);
        std::cout << c3.size() << '\n';
    }

Output:

    1
    1
    5

### See also

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

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