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std::data

Defined in header <iterator> 
template <class C> 
constexpr auto data(C& c) -> decltype(c.data());
 (1) (since C++17) 
template <class C> 
constexpr auto data(const C& c) -> decltype(c.data());
 (2) (since C++17) 
template <class T, std::size_t N> 
constexpr T* data(T (&array)[N]) noexcept;
 (3) (since C++17) 
template <class E>
constexpr const E* data(std::initializer_list<E> il) noexcept;
 (4) (since C++17)

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

#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!

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