std::data

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Diagnostics library

Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

Execution control library (C++26)

Technical specifications

Symbols index

External libraries

 

Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) is-integer-like is-signed-integer-like (C++20)(C++20)	sentinel_for (C++20) sized_sentinel_for (C++20) input_iterator (C++20) output_iterator (C++20) input_or_output_iterator (C++20)	forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)	iterator (deprecated in C++17) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (C++20)
Algorithm concepts and utilities
Indirect callable concepts
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)	indirect_unary_predicate (C++20) indirect_binary_predicate (C++20)	indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
Common algorithm requirements
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20)	indirectly_copyable_storable (C++20)   indirectly_swappable (C++20) indirectly_comparable (C++20)	permutable (C++20) mergeable (C++20) sortable (C++20)
Utilities
indirect_result_t (C++20)	projected (C++20)	projected_value_t (C++26)
Iterator adaptors
reverse_iterator make_reverse_iterator (C++14) move_iterator (C++11) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)	front_insert_iterator back_insert_iterator inserter insert_iterator front_inserter back_inserter move_sentinel (C++20)	common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) make_const_iterator (C++23) make_const_sentinel (C++23)
Stream iterators istream_iterator    ostream_iterator istreambuf_iterator ostreambuf_iterator	Iterator customization points ranges::iter_move (C++20) ranges::iter_swap (C++20)
Iterator operations advance distance prev (C++11)   next (C++11) ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)	Range access begincbegin (C++11)(C++14) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) empty (C++17) data (C++17)

 

Defined in header <array>
Defined in header <deque>
Defined in header <flat_map>		(since C++23)
Defined in header <flat_set>		(since C++23)
Defined in header <forward_list>
Defined in header <inplace_vector>		(since C++26)
Defined in header <iterator>
Defined in header <list>
Defined in header <map>
Defined in header <optional>		(since C++26)
Defined in header <regex>
Defined in header <set>
Defined in header <span>		(since C++20)
Defined in header <stacktrace>		(since C++23)
Defined in header <string>
Defined in header <string_view>
Defined in header <unordered_map>
Defined in header <unordered_set>
Defined in header <valarray>
Defined in header <vector>

template< class C > constexpr auto data( C& c ) noexcept(noexcept(c.data())) -> decltype(c.data());	(1)	(since C++17)
template< class C > constexpr auto data( const C& c ) noexcept(noexcept(c.data())) -> 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)

Returns a pointer to the block of memory containing the elements of the range.

1,2) Returns c.data().

3) Returns array.

Parameters

c	-	a container or view with a data() member function
array	-	an array of arbitrary type

Return value

1,2) c.data()

3) array

Exceptions

1,2) What and when the underlying c.data() call throws.

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_nonmember_container_access	201411L	(C++17)	std::size(), std::data(), and std::empty()
__cpp_lib_initializer_list	202511L	(C++26) (DR11)	data and empty member functions of std::initializer_list; removing unnecessary free functions for std::initializer_list

Possible implementation

First version
template<class C> constexpr auto data(C& c) noexcept(noexcept(c.data())) -> decltype(c.data()) { return c.data(); }
Second version
template<class C> constexpr auto data(const C& c) noexcept(noexcept(c.data())) -> decltype(c.data()) { return c.data(); }
Third version
template<class T, std::size_t N> constexpr T* data(T (&array)[N]) noexcept { return array; }

Example

Run this code

#include <cstring>
#include <iostream>
#include <string>

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!

Defect report

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
P3016R6	C++17	1) non-member std::data overload was provided for std::initializer_list 2) std::data was not required to propagate exception specification	1) removed 2) required

See also

ranges::data (C++20)	obtains a pointer to the beginning of a contiguous range (customization point object)
ranges::cdata (C++20)	obtains a pointer to the beginning of a read-only contiguous range (customization point object)