std::span<T,Extent>::first
From cppreference.com
| template< std::size_t Count > constexpr std::span<element_type, Count> first() const; |
(since C++20) | |
| constexpr std::span<element_type, std::dynamic_extent> first( size_type Count ) const; |
(since C++20) | |
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().
[edit] 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.
[edit] Example
Run this code
#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); }
Output:
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};[edit] See also
obtains a subspan consisting of the last N elements of the sequence (public member function) | |
| obtains a subspan (public member function) |
