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std::data(3)		      C++ Standard Libary		  std::data(3)

NAME
       std::data - std::data

Synopsis
	  Defined in header <array>
	  Defined in header <deque>
	  Defined in header <forward_list>
	  Defined in header <iterator>
	  Defined in header <list>
	  Defined in header <map>
	  Defined in header <regex>
	  Defined in header <set>
	  Defined		 in		   header		<span>
       (since C++20)
	  Defined in header <string>
	  Defined in header <string_view>
	  Defined in header <unordered_map>
	  Defined in header <unordered_set>
	  Defined in header <vector>
	  template <class  C>						   (1)
       (since C++17)
	  constexpr auto data(C& c) -> decltype(c.data());
	  template  <class  C>						   (2)
       (since C++17)
	  constexpr auto data(const C& c) -> decltype(c.data());
	  template <class T, std::size_t  N>				   (3)
       (since C++17)
	  constexpr T* data(T (&array)[N]) noexcept;
	  template  <class  E>						   (4)
       (since C++17)
	  constexpr const E* data(std::initializer_list<E> il) noexcept;

	  Returns a pointer to the block of memory containing the elements  of
       the range.

	  1,2) returns c.data()
	  3) returns array
	  4) returns il.begin()

Parameters
	  c	- a container or view with a data() member function
	  array	- an array of arbitrary	type
	  il	- an initializer list

Return value
	  A  pointer  to  the  block  of memory	containing the elements	of the
       range.

Exceptions
	  1) May throw implementation-defined exceptions.

Notes
	  The overload for std::initializer_list is necessary because it  does
       not have	a
	  member function data.

	  Feature-test macro: __cpp_lib_nonmember_container_access

Possible implementation
First version
	  template <class C>
	  constexpr auto data(C& c) -> decltype(c.data())
	  {
	      return c.data();
	  }

Second version
	  template <class C>
	  constexpr auto data(const C& c) -> decltype(c.data())
	  {
	      return c.data();
	  }
				  Third	version
	  template <class T, std::size_t N>
	  constexpr T* data(T (&array)[N]) noexcept
	  {
	      return array;
	  }
				 Fourth	version
	  template <class E>
	  constexpr const E* data(std::initializer_list<E> il) noexcept
	  {
	      return il.begin();
	  }

Example
       // Run this code

	#include <string>
	#include <cstring>
	#include <iostream>

	int main()
	{
	    std::string	s {"Hello world!\n"};

	    char a[20];	// storage for a C-style string
	    std::strcpy(a, std::data(s));
	    //	[s.data(),  s.data()  +	 s.size()] is guaranteed to be an NTBS
       since C++11

	    std::cout << a;
	}

Output:
	Hello world!

See also
	  ranges::data	obtains	a pointer to the  beginning  of	 a  contiguous
       range
	  (C++20)	(customization point object)
	  ranges::cdata	obtains	a pointer to the beginning of a	read-only con-
       tiguous range
	  (C++20)	(customization point object)

http://cppreference.com		  2022.07.31			  std::data(3)

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