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

Obtains a span that is a view over the first Count elements of this span. The program is ill-formed if Count > Extent . The behavior is undefined if Count > size ( ) .

Return value

A span r that is a view over the first Count elements of * this , such that r. data ( ) == this - > data ( ) && r. size ( ) == Count .

Example

#include <iostream>
#include <ranges>
#include <span>
#include <string_view>
 
void print(std::string_view const title,
           std::ranges::forward_range auto const& container)
{
    auto size{std::size(container)};
    std::cout << title << '[' << size << "]{";
    for (auto const& elem : container)
        std::cout << elem << (--size ? ", " : "");
    std::cout << "};\n";
}
 
void run_game(std::span<const int> span)
{
    print("span: ", span);
 
    std::span<const int, 5> span_first = span.first<5>();
    print("span.first<5>(): ", span_first);
 
    std::span<const int, std::dynamic_extent> span_first_dynamic = span.first(4);
    print("span.first(4): ", span_first_dynamic);
}
 
int main()
{
    int a[8]{1, 2, 3, 4, 5, 6, 7, 8};
    print("int a", a);
    run_game(a);
}

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

See also