std::data (3) - Linux Manuals

std::data: std::data

NAME

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!