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

    From cppreference.com
     
    C++
     
    Containers library
     
    std::span
     
    template< std::size_t Count > constexpr std::span<element_type, Count> last() const;
    		 (1) (since C++20)
    constexpr std::span<element_type, std::dynamic_extent> last( size_type count ) const;
    		 (2) (since C++20)
    See More

    Obtains a subview over the last Count or count elements of this span.

    1) The element count is provided as a template argument, and the subview has a static extent.
    If Count > Extent is true, the program is ill-formed.
    2) The element count is provided as a function argument, and the subview has a dynamic extent.

    If Count > size() or count > size() is true, the behavior is undefined.

    		(until C++26)

    If Count > size() or count > size() 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)

    Parameters

    count - the number of the elements of the subview

    Return value

    1) std::span<element_type, Count>{data() + (size() - Count), Count}
    2) std::span<element_type, std::dynamic_extent>{data() + (size() - count), count}

    Example

    Run this code
    #include <iostream>
#include <span>
#include <string_view>

void println(const std::string_view title, const auto& container)
{
    std::cout << title << '[' << std::size(container) << "]{ ";
    for (const auto& elem : container)
        std::cout << elem << ", ";
    std::cout << "};\n";
};

void run(std::span<const int> span)
{
    println("span: ", span);
    
    std::span<const int, 3> span_last = span.last<3>();
    println("span.last<3>(): ", span_last);
    
    std::span<const int, std::dynamic_extent> span_last_dynamic = span.last(2);
    println("span.last(2): ", span_last_dynamic);
}

int main()
{
    int a[8]{1, 2, 3, 4, 5, 6, 7, 8};
    println("int a", a);
    run(a);
}

    Output: 

    int a[8]{ 1, 2, 3, 4, 5, 6, 7, 8, };
span: [8]{ 1, 2, 3, 4, 5, 6, 7, 8, };
span.last<3>(): [3]{ 6, 7, 8, };
span.last(2): [2]{ 7, 8, };

    See also

    		 obtains a subspan consisting of the first N elements of the sequence
    (public member function) [edit]
    		obtains a subspan
    (public member function) [edit]