Namespaces
Variants
Actions

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

From cppreference.com
< cpp‎ | container‎ | span
 
C++
 
Containers library
 
std::span
 
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.

(until C++26)

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.
(since C++26)

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

[edit] See also

 access the first element
(public member function) [edit]
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/container/span/back&oldid=182278"

Follow Lee on X/Twitter - Father, Husband, Serial builder creating AI, crypto, games & web tools. We are friends :) AI Will Come To Life!

Check out: eBank.nz (Art Generator) | Netwrck.com (AI Tools) | Text-Generator.io (AI API) | BitBank.nz (Crypto AI) | ReadingTime (Kids Reading) | RewordGame | BigMultiplayerChess | WebFiddle | How.nz | Helix AI Assistant