NAME¶

std::ranges::data - std::ranges::data

Synopsis¶

Defined in header <ranges>
Defined in header <iterator>
inline namespace /* unspecified */ {

inline constexpr /* unspecified */ data = /* (since C++20)
unspecified */; (customization point object)

}
Call signature
template< class T >

requires /* see below */ (since C++20)
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 T is an array type and std::remove_all_extents_t<std::remove_reference_t<T>> is
incomplete, then the call to ranges::data is ill-formed, no diagnostic required.

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. decay-copy(t.data())
(until C++23)
auto(t.data())
(since C++23), if that expression is valid and its type is a pointer to an
object type.
2. Otherwise, std::to_address(ranges::begin(t)), if the expression ranges::begin(t)
is valid and its type models std::contiguous_iterator.

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.

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.

The C++20 standard requires that if the underlying data function call returns a
prvalue, the return value is move-constructed from the materialized temporary
object. All implementations directly return the prvalue instead. The requirement is
corrected by the post-C++20 proposal P0849R8 to match the implementations.

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