std::flat_set::rbegin,(3)

✨ std::flat_set::rbegin,(3) ✨

Bestie, this is the std::flat_set::rbegin, page from the C++ Standard Libary manual — yes, Libary, that's how it's spelled on the page, leave it 💅 — and it's all about reverse iterators. Group-chat summary: it gives you the reverse-iterator beginning of a flat_set, and it is very much giving "last element first" energy. 🦋

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🎀 NAME 🎀

std::flat_set::rbegin, - std::flat_set::rbegin, — that's the name, repeated, no notes.

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🌸 Synopsis 🌸

          reverse_iterator rbegin() noexcept;              (1) (since C++23)
          const_reverse_iterator rbegin() const noexcept;  (2) (since C++23)
          const_reverse_iterator crbegin() const noexcept; (3) (since C++23)

Okay so these return a reverse iterator to the first element of the reversed flat_set. It corresponds to the last element of the non-reversed flat_set. If the flat_set is empty, the returned iterator is equal to rend(). That's the whole plot. 🫶

Also there's a diagram situation: range-rbegin-rend.svg.

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🫶 Parameters 🫶

None. Zero. Nada. No arguments, bestie.

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💖 Return value 💖

A reverse iterator to the first element. That's it, that's the return.

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⚡ Complexity ⚡

Constant. Snappy. Done.

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💀 Notes 💀

Because both iterator and const_iterator are constant iterators (and may in fact be the same type), it is not possible to mutate the elements of the container through an iterator returned by any of these member functions. So like... no sneaky edits through these iterators, periodt. 🙈

The underlying iterator of the returned reverse iterator is the end iterator. Hence the returned iterator is invalidated if and when the end iterator is invalidated.

That invalidation bit is important, bestie — respect the iterator lifecycle 😭.

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🌈 Example 🌈

       // Run this code

        #include <iostream>
        #include <flat_set>

        int main()
        {
            std::flat_set<unsigned> rep{1, 2, 3, 4, 1, 2, 3, 4};

            for (auto it = rep.crbegin(); it != rep.crend(); ++it)
            {
                for (auto n = *it; n > 0; --n)
                    std::cout << "⏼" << ' ';
                std::cout << '\n';
            }
        }

Output:

        ⏼ ⏼ ⏼ ⏼
        ⏼ ⏼ ⏼
        ⏼ ⏼
        ⏼

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👑 See also 👑

• rend — returns a reverse iterator to the end
• crend — (public member function)
• rbegin — returns a reverse iterator to the beginning of a container or array
• crbegin — (function template) (C++14)

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Source / version / date check, because bestie deserves receipts: http://cppreference.com, 2024.06.10, page std::flat_set::rbegin,(3). Bye babes, go reverse-iterate responsibly 🫶💅✨