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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 se-
     quence
		(public member function)
	subspan obtains a subspan
		(public member function)

http://cppreference.com 	   2024.06.10		     std::span::first(3)
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