std::ranges::data

 

C++

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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

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Technical Specifications

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range primitives
iterator_tsentinel_t	range_size_trange_difference_t	range_value_t	range_reference_trange_rvalue_reference_t
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Semiregular wrapper
Factories
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	views::counted
Adaptors
views::all_tviews::all join_viewviews::join take_viewviews::take basic_istream_viewistream_view	ref_view                                split_viewviews::split take_while_viewviews::take_while elements_viewviews::elements	common_viewviews::common transform_viewviews::transform drop_viewviews::drop keys_viewviews::keys	reverse_viewviews::reverse filter_viewviews::filter drop_while_viewviews::drop_while values_viewviews::values

 

Defined in header <ranges>
inline namespace /*unspecified*/ {     inline constexpr /*unspecified*/ data = /*unspecified*/; }		(since C++20) (customization point object)
Call signature
template< class T >     requires /* see below */ constexpr std::remove_reference_t<ranges::range_reference_t<T>>* data(T&& t);

Returns a pointer to the first element of a contiguous range.

If the argument is an lvalue or ranges::enable_borrowed_range<std::remove_cv_t<T>> is true, a call to ranges::data is expression-equivalent to:

1. std::forward<T>(t).data(), if that expression is valid, and its return type is a pointer to an object type.
2. Otherwise, std::to_address(ranges::begin(std::forward<T>(t))), if ranges::begin(std::forward<T>(t)) is valid and returns a type that models std::contiguous_iterator.

   If std::remove_all_extents_t<std::remove_reference_t<T>> is incomplete, then ranges::data(std::forward<T>(t)) is ill-formed, no diagnostic required.

In all other cases, a call to ranges::data is ill-formed, which can result in substitution failure when ranges::data(e) appears in the immediate context of a template instantiation.

Expression-equivalent

Expression e is expression-equivalent to expression f, if e and f have the same effects, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

Customization point objects

The name ranges::data denotes a customization point object, which is a const function object of a literal semiregular class type (denoted, for exposition purposes, as data_ftor). All instances of data_ftor are equal. Thus, ranges::data can be copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to ranges::data above, data_ftor will satisfy std::invocable<const data_ftor&, Args...>. Otherwise, no function call operator of data_ftor participates in overload resolution.

Notes

If the argument is an rvalue (i.e. T is an object type) and ranges::enable_borrowed_range<std::remove_cv_t<T>> is false, the call to ranges::data is ill-formed, which also results in substitution failure.

If ranges::data(e) is valid for an expression e, then it returns a pointer to an object.

Example

Run this code

#include <cstring>
#include <iostream>
#include <ranges>
#include <string>
 
int main()
{
    std::string s {"Hello world!\n"};
 
    char a[20]; // storage for a C-style string
    std::strcpy(a, std::ranges::data(s));
    // [data(s), data(s) + size(s)] is guaranteed to be an NTBS
 
    std::cout << a;
}

Output:

Hello world!

See also

ranges::cdata (C++20)	obtains a pointer to the beginning of a read-only contiguous range (customization point object)
ranges::begin (C++20)	returns an iterator to the beginning of a range (customization point object)
data (C++17)	obtains the pointer to the underlying array (function template)