NAME¶

std::array - std::array

Synopsis¶

Defined in header <array>
template<

class T, (since C++11)
std::size_t N

> struct array;

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*
LegacyRandomAccessIterator and (until C++17)
LegacyContiguousIterator to value_type
LegacyRandomAccessIterator and (since C++17)
iterator LegacyContiguousIterator that is a LiteralType (until C++20)
to value_type
LegacyRandomAccessIterator,
contiguous_iterator, and ConstexprIterator to (since C++20)
value_type
LegacyRandomAccessIterator and (until C++17)
LegacyContiguousIterator to const value_type
LegacyRandomAccessIterator and (since C++17)
const_iterator LegacyContiguousIterator that is a LiteralType (until C++20)
to const value_type
LegacyRandomAccessIterator,
contiguous_iterator, and ConstexprIterator to (since C++20)
const value_type
reverse_iterator std::reverse_iterator<iterator>
const_reverse_iterator std::reverse_iterator<const_iterator>

Member functions¶

Implicitly-defined member functions¶

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

Element access¶

at access specified element with bounds checking
(C++11) (public member function)
operator[] access specified element
(C++11) (public member function)
front access the first element
(C++11) (public member function)
back access the last element
(C++11) (public member function)
data direct access to the underlying array
(C++11) (public member function)

Iterators¶

begin returns an iterator to the beginning
cbegin (public member function)
(C++11)
end returns an iterator to the end
cend (public member function)
(C++11)
rbegin returns a reverse iterator to the beginning
crbegin (public member function)
(C++11)
rend returns a reverse iterator to the end
crend (public member function)
(C++11)

Capacity¶

empty checks whether the container is empty
(C++11) (public member function)
size returns the number of elements
(C++11) (public member function)
max_size returns the maximum possible number of elements
(C++11) (public member function)

Operations¶

fill fill the container with specified value
(C++11) (public member function)
swap swaps the contents
(C++11) (public member function)

Non-member functions¶

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

Helper classes¶

std::tuple_size<std::array> obtains the size of an array
(C++11) (class template specialization)
std::tuple_element<std::array> obtains the type of the elements of array
(C++11) (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}; // double braces 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 << ' ';

// deduction guide for array creation (since C++17)
[[maybe_unused]] std::array a4{3.0, 1.0, 4.0}; // -> std::array<double, 3>
}

Output:¶

3 2 1
a b

See also¶

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