# std::array

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Defined in header `<array>` |  |
template< class T, std::size_t N > struct array; |  | (since C++11)

`std::array` is a container that encapsulates fixed size arrays.

This container is an aggregate type with the same semantics as a struct holding a C-style array T[N] as its only non-static data member. Unlike a C-style array, it doesn't decay to T* automatically. As an aggregate type, it can be initialized with aggregate-initialization given at most `N` initializers that are convertible to `T`: std::array<int, 3> a = {1,2,3};.

The struct combines the performance and accessibility of a C-style array with the benefits of a standard container, such as knowing its own size, supporting assignment, random access iterators, etc.

`std::array` satisfies the requirements of Container and ReversibleContainer except that default-constructed array is not empty and that the complexity of swapping is linear, satisfies the requirements of ContiguousContainer, (since C++17) and partially satisfies the requirements of SequenceContainer.

There is a special case for a zero-length array (`N == 0`). In that case, array.begin() == array.end(), which is some unique value. The effect of calling front() or back() on a zero-sized array is undefined.

An array can also be used as a tuple of `N` elements of the same type.

### Iterator invalidation

As a rule, iterators to an array are never invalidated throughout the lifetime of the array. One should take note, however, that during swap, the iterator will continue to point to the same array element, and will thus change its value.

### Member types

Member type | Definition
`value_type` | `T`
`size_type` | std::size_t
`difference_type` | std::ptrdiff_t
`reference` | `value_type&`
`const_reference` | `const value_type&`
`pointer` | `value_type*`
`const_pointer` | `const value_type*`
`iterator` | LegacyRandomAccessIterator and ConstexprIterator (since C++20)that is a LiteralType (since C++17)
`const_iterator` | Constant LegacyRandomAccessIterator and ConstexprIterator (since C++20)that is a LiteralType (since C++17)
`reverse_iterator` | std::reverse_iterator<iterator>
`const_reverse_iterator` | std::reverse_iterator<const_iterator>

### Member functions

##### Implicitly-defined member functions

(constructor) (implicitly declared) | initializes the array following the rules of aggregate initialization (note that default initialization may result in indeterminate values for non-class `T`) (public member function)
(destructor) (implicitly declared) | destroys every element of the array (public member function)
operator= (implicitly declared) | overwrites every element of the array with the corresponding element of another array (public member function)

##### Element access

at | access specified element with bounds checking (public member function)
operator[] | access specified element (public member function)
front | access the first element (public member function)
back | access the last element (public member function)
data | direct access to the underlying array (public member function)

##### Iterators

begin cbegin | returns an iterator to the beginning (public member function)
end cend | returns an iterator to the end (public member function)
rbegin crbegin | returns a reverse iterator to the beginning (public member function)
rend crend | returns a reverse iterator to the end (public member function)

##### Capacity

empty | checks whether the container is empty (public member function)
size | returns the number of elements (public member function)
max_size | returns the maximum possible number of elements (public member function)

##### Operations

fill | fill the container with specified value (public member function)
swap | swaps the contents (public member function)

### Non-member functions

operator==operator!=operator<operator<=operator>operator>= | lexicographically compares the values in the array (function template)
std::get(std::array) | accesses an element of an `array` (function template)
std::swap(std::array) (C++11) | specializes the std::swap algorithm (function template)

### Helper classes

std::tuple_size<std::array> | obtains the size of an `array` (class template specialization)
std::tuple_element<std::array> | obtains the type of the elements of `array` (class template specialization)

### Deduction guides(since C++17)

### Example

Run this code

    #include <string>
    #include <iterator>
    #include <iostream>
    #include <algorithm>
    #include <array>

    int main()
    {
        // construction uses aggregate initialization
        std::array<int, 3> a1{ {1, 2, 3} }; // double-braces required in C++11 prior to the CWG 1270 revision
                                            // (not needed in C++11 after the revision and in C++14 and beyond)
        std::array<int, 3> a2 = {1, 2, 3};  // never required after =
        std::array<std::string, 2> a3 = { std::string("a"), "b" };

        // container operations are supported
        std::sort(a1.begin(), a1.end());
        std::reverse_copy(a2.begin(), a2.end(),
                          std::ostream_iterator<int>(std::cout, " "));

        std::cout << '\n';

        // ranged for loop is supported
        for(const auto& s: a3)
            std::cout << s << ' ';
    }

Output:

    3 2 1
    a b

### See also

make_array | Creates a std::array object whose size and optionally element type are deduced from the arguments (function template)
to_array | Creates a std::array object from a built-in array (function template)

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