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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 <flat_map>
	Defined in header <flat_set>
	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>
	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 std::initializer_list

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

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	      Value    Std		 Feature
	__cpp_lib_nonmember_container_access	201411L   (C++17)   std::size(),
     std::data(), and
							     std::empty()

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

      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 contigu-
     ous range
	(C++20)       (customization point object)

http://cppreference.com 	   2024.06.10			    std::data(3)
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