std::ranges...erface::data(3)

🎀 std::ranges::view_interface::data 🎀

okay bestie, this page is from the C++ Standard Libary manual — yes, that's the manual name — and it's all about std::ranges::view_interface::data, page (3). It's giving default data() member function energy, and we're gonna get into it. 💅

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🌸 NAME 🌸

std::ranges::view_interface::data — literally std::ranges::view_interface::data, the member function. That's the name, no cap. 🫶

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✨ Synopsis ✨

Here are the two overloads, with their requires clauses doing main character work:

constexpr auto data()                                          (1)
(since C++20)
       requires std::contiguous_iterator<ranges::iterator_t<D>>;
   constexpr auto data() const

       requires ranges::range<const D> &&                         (2)
(since C++20)

           std::contiguous_iterator<ranges::iterator_t<const D>>;

So the default implementation of the data() member function obtains the address denoted by the beginning iterator via std::to_address, and that is also the lowest address of the contiguous storage (implied by contiguous_iterator) referenced by the view of the derived type when the view is not empty. Lowkey precise, highkey iconic. ✨

1. Let derived be static_cast<D&>(*this). Equivalent to return std::to_address(ranges::begin(derived));.
2. Same as (1), except that derived is static_cast<const D&>(*this).

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💖 Parameters 💖

(none) — literally none. Zero parameters. Not a single one, bestie. 🫶

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🫶 Return value 🫶

The address denoted by the beginning iterator. That's it, that's the tea. 🍵

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🧚 Notes 🧚

These derived types may use the default implementation of data():

• std::ranges::common_view
• std::ranges::drop_view
• std::ranges::drop_while_view
• std::ranges::ref_view
• std::ranges::subrange
• std::ranges::take_view
• std::ranges::take_while_view

And these types are derived from std::ranges::view_interface and do not declare their own data() member function, but they cannot use the default implementation, because their iterator types never satisfy contiguous_iterator:

• std::ranges::basic_istream_view
• std::ranges::elements_view
• std::ranges::filter_view
• std::ranges::iota_view
• std::ranges::join_view
• std::ranges::lazy_split_view
• std::ranges::reverse_view
• std::ranges::split_view
• std::ranges::transform_view

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🍓 Example 🍓

// Run this code

#include <array>
#include <iostream>
#include <ranges>
#include <string_view>

int main() {
    constexpr std::string_view str { "Hello, C++20!" };
    std::cout << (str | std::views::drop(7)).data() << '\n';
    constexpr static std::array a { 1,2,3,4,5 };
    constexpr auto v { a | std::views::take(3) };
    static_assert( &a[0] == v.data() );
}

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💜 Output 💜

C++20!

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🌈 See also 🌈

• data — obtains the pointer to the underlying array (C++17) (function template)
• ranges::data — obtains a pointer to the beginning of a contiguous range (C++20) (customization point object)
• ranges::cdata — obtains a pointer to the beginning of a read-only contiguous range (C++20) (customization point object)
• to_address — obtains a raw pointer from a pointer-like type (C++20) (function template)

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source/version/date: http://cppreference.com · 2024.06.10 · std::ranges...erface::data(3) — byeee bestie, go check that contiguous storage 💖✨