std::data

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Iterator library

Iterator primitives
iterator_traits
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tag
iterator
Iterator adaptors
reverse_iterator move_iterator (C++11) back_insert_iterator front_insert_iterator insert_iterator	make_reverse_iterator (C++14) make_move_iterator (C++11) back_inserter front_inserter inserter
Stream iterators
istream_iterator
ostream_iterator
istreambuf_iterator
ostreambuf_iterator
Iterator operations
advance
distance
prev (C++11)
next (C++11)
Range access
begincbegin (C++11)(C++14)
endcend (C++11)(C++14)
rbegincrbegin (C++14)(C++14)
rendcrend (C++14)(C++14)
Container access
sizessize (C++17)(C++20)
empty (C++17)
data (C++17)

 

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

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!