std::array(3)

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)