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std::span::first(3) C++ Standard Libary std::span::first(3) NAME std::span::first - std::span::first Synopsis template< std::size_t Count > (since C++20) constexpr std::span<element_type, Count> first() const; constexpr std::span<element_type, std::dynamic_extent> first( (since C++20) size_type Count ) const; 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 // 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}; See also last obtains a subspan consisting of the last N elements of the sequence (public member function) subspan obtains a subspan (public member function) http://cppreference.com 2024.06.10 std::span::first(3)
NAME | Synopsis | Return value | Example | Output: | See also
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