# std::span<T,Extent>::back

From cppreference.com
< cpp‎ | container‎ | span

constexpr reference back() const; |  | (since C++20)

Returns a reference to the last element in the span.

Calling `back` on an empty span results in undefined behavior.

### Parameters

(none)

### Return value

A reference to the back element.

### Complexity

Constant

### Notes

For a span `c`, the expression c.back() is equivalent to *(c.end() - 1).

### Example

Run this code

    #include <iostream>
    #include <span>

    void print_forward(std::span<const int> const span)
    {
        for (auto n { span.size() }; n != 0; --n )
            std::cout << span.last(n).front() << ' ';
        std::cout << '\n';
    }

    void print_backward(std::span<const int> const span)
    {
        for (auto n { span.size() }; n != 0; --n)
            std::cout << span.first(n).back() << ' ';
        std::cout << '\n';
    }

    int main()
    {
        constexpr int numbers[] { 0, 1, 2, 3, 4 };
        print_forward(numbers);
        print_backward(numbers);
    }

Output:

    0 1 2 3 4
    4 3 2 1 0

### See also

front (C++20) | access the first element (public member function)

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