std::span<T,Extent>::back
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Tables
std::span
span::back
(C++26)
(C++23)
(C++23)
(C++23)
(C++23)
constexpr reference back() const;
(since C++20)
Returns a reference to the last element in the span.
If empty() is true, the behavior is undefined.
If empty() is true:
- 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.
Contents
[edit] Return value
A reference to the back element.
[edit] Complexity
Constant.
[edit] Notes
For a span c, the expression c.back() is equivalent to *(c.end() - 1).
[edit] Example
Run this code
#include <iostream> #include <span> void print_forward(const std::span <const int> span) { for (auto n{span.size()}; n != 0; --n) std::cout << span.last(n).front() << ' '; std::cout << '\n'; } void print_backward(const std::span <const int> 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