Std::data (3) Linux Manual Page

std::data – std::data

Synopsis

Defined in header<iterator>

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

Parameters

c – a container with a data() method
array – an array of arbitrary type
il – an initializer list

Return value

A pointer to the block of memory containing the elements of the container.

Notes

In addition to being included in <iterator>, std::data is guaranteed to become available if any of the following headers are included: <array>, <deque>, <forward_list>, <list>, <map>, <regex>, <set>
, <span>
(since C++20), <string>, <string_view>, <unordered_map>, <unordered_set>, and <vector>.

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> //std::data is guaranteed to be available after inclusion

#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 << "\n";
}

Output:

Hello world!

std::data (3) Linux Manual Page