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 contiguous range
   (C++20) (customization point object)