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From cppreference.com
< cpp‎ | iterator
 
 
Iterator library
Iterator concepts
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
Utilities
Iterator adaptors
Stream iterators
Iterator customization points
Iterator operations
(C++11)
(C++11)
Range access
(C++11)(C++14)
(C++11)(C++14)
(C++17)(C++20)
(C++14)(C++14)
(C++14)(C++14)
(C++17)
data
(C++17)
 
Defined in header <array>
Defined in header <deque>
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>
(since C++20)
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>
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()

Contents

[edit] Parameters

c - a container with a data() member function
array - an array of arbitrary type
il - an initializer list

[edit] Return value

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

[edit] 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();
}

[edit] Example

#include <string>
#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;
}

Output:

Hello world!