std::array<T,N>::operator[]
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std::array
array::operator[]
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Deduction guides (C++17)
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.
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. Moreover, if the contract-violation handler returns under "observe" evaluation semantic, the behavior is undefined.
- If the implementation is not hardened, the behavior is undefined.
[edit] Parameters
pos
-
position of the element to return
[edit] Return value
Reference to the requested element.
[edit] Complexity
Constant.
[edit] 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).
[edit] Example
The following code uses operator[] to read from and write to a std::array <int, N>:
Run this code
#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:
Second element: 4 All numbers: 5 4 6 8