W3cubDocs

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

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

#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: