std::array

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C++
 
Containers library
 
std::array
 
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 LegacyContiguousIterator to value_type

(until C++17)

LegacyRandomAccessIterator and LegacyContiguousIterator that is a LiteralType to value_type

(since C++17)
(until C++20)

LegacyRandomAccessIterator, contiguous_iterator, and ConstexprIterator to value_type

(since C++20)
const_iterator

LegacyRandomAccessIterator and LegacyContiguousIterator to const value_type

(until C++17)

LegacyRandomAccessIterator and LegacyContiguousIterator that is a LiteralType to const value_type

(since C++17)
(until C++20)

LegacyRandomAccessIterator, contiguous_iterator, and ConstexprIterator to const value_type

(since C++20)
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
(C++11)
 access specified element with bounds checking
(public member function)
(C++11)
 access specified element
(public member function)
(C++11)
 access the first element
(public member function)
(C++11)
 access the last element
(public member function)
(C++11)
 direct access to the underlying array
(public member function)
Iterators
(C++11)
 returns an iterator to the beginning
(public member function)
(C++11)
 returns an iterator to the end
(public member function)
(C++11)
 returns a reverse iterator to the beginning
(public member function)
(C++11)
 returns a reverse iterator to the end
(public member function)
Capacity
(C++11)
 checks whether the container is empty
(public member function)
(C++11)
 returns the number of elements
(public member function)
(C++11)
 returns the maximum possible number of elements
(public member function)
Operations
(C++11)
 fill the container with specified value
(public member function)
(C++11)
 swaps the contents
(public member function)

Non-member functions

(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)
 lexicographically compares the values in the array
(function template)
(C++11)
 accesses an element of an array
(function template)
(C++11)
 specializes the std::swap algorithm
(function template)
(C++20)
 creates a std::array object from a built-in array
(function template)

Helper classes

(C++11)
 obtains the size of an array
(class template specialization)
(C++11)
 obtains the type of the elements of array
(class template specialization)

Deduction guides

 (since C++17)

Example

Run this code
#include <algorithm>
#include <array>
#include <iostream>
#include <iterator>
#include <string>
 
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}; // double braces never required after =
 
    std::array<std::string, 2> a3 = { std::string("E"), "\u018E" };
 
    // container operations are supported
    std::sort(a1.begin(), a1.end());
    std::ranges::reverse_copy(a2, std::ostream_iterator<int>(std::cout, " "));
    std::cout << '\n';
 
    // ranged for loop is supported
    for (const auto& s: a3)
        std::cout << s << ' ';
 
    // deduction guide for array creation (since C++17)
    [[maybe_unused]] std::array a4{3.0, 1.0, 4.0}; // std::array<double, 3>
 
    // Corner cases:
    [[maybe_unused]] std::array<int, 2> a5; // a5[0] and a5[1] are default initialized
    [[maybe_unused]] std::array<int, 2> a6 = {}; // a6[0] and a6[1] are 0
    [[maybe_unused]] std::array<int, 2> a7 = {1}; // a7[0] == 1, a7[1] == 0
}

Output: 

3 2 1
E Ǝ

See also

(library fundamentals TS v2)
 creates a std::array object whose size and optionally element type are deduced from the arguments
(function template)
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