std::array<T,N>::operator[]

reference operator[]( size_type pos );	(1)	(since C++11) (constexpr since C++17)
const_reference operator[]( size_type pos ) const;	(2)	(since C++11) (constexpr since C++14)

Returns a reference to the element at specified location pos. No bounds checking is performed, unless the implementation is hardened(since C++26).

If pos < size() is false, the behavior is undefined.

(until C++26)

If pos < size() is false:

If the implementation is hardened, a contract violation occurs.
If the implementation is not hardened, the behavior is undefined.

(since C++26)

Parameters

pos

position of the element to return

Return value

Reference to the requested element.

Complexity

Constant.

Notes

Unlike std::map::operator[], this operator never inserts a new element into the container. Accessing a nonexistent element through this operator is undefined behavior, unless the implementation is hardened(since C++26).

Example

The following code uses operator[] to read from and write to a std::array<int,N>:

#include <array>
#include <iostream>

int main()
{
    std::array<int, 4> numbers{2, 4, 6, 8};
    
    std::cout << "Second element: " << numbers[1] << '\n';
    
    numbers[0] = 5;
    
    std::cout << "All numbers:";
    for (auto i : numbers)
        std::cout << ' ' << i;
    std::cout << '\n';
}

Output: