std::vector...ctor::crend(3)

🌸 std::vector::rend,std::vector::crend 🌸

okay bestie, real talk: this page lives in the C++ Standard Libary (yes, that's how the header spells it, no cap) and the man-page header is std::vector...ctor::crend(3). We're talking about reverse iterators on std::vector, and it's giving end-of-the-reverse-line energy. 💅

💖 NAME 💖

std::vector::rend,std::vector::crend — std::vector::rend,std::vector::crend

🫶 Synopsis 🫶

reverse_iterator rend();                       (1) (noexcept since C++11)
                                               (constexpr since C++20)
const_reverse_iterator rend() const;           (2) (noexcept since C++11)
                                               (constexpr since C++20)
const_reverse_iterator crend() const noexcept; (3) (since C++11)
                                               (constexpr since C++20)

So what does it actually do? It returns a reverse iterator to the element following the last element of the reversed vector. It corresponds to the element preceding the first element of the non-reversed vector. That element is literally just a placeholder, bestie — attempting to access it results in undefined behavior. 😭

There's a diagram placeholder here: range-rbegin-rend.svg.

🎀 Parameters 🎀

(none) — fr fr, zero parameters. She takes nothing.

🦋 Return value 🦋

Reverse iterator to the element following the last element.

⭐ Complexity ⭐

Constant. periodt.

💜 Notes 💜

libc++ backports crend() to C++98 mode.

🌈 Example 🌈

// Run this code

#include <algorithm>
#include <iostream>
#include <numeric>
#include <string>
#include <vector>

int main()
{
    std::vector<int> nums{1, 2, 4, 8, 16};
    std::vector<std::string> fruits{"orange", "apple", "raspberry"};
    std::vector<char> empty;

    // Print vector.
    std::for_each(nums.rbegin(), nums.rend(), [](const int n) {
       std::cout << n << ' '; });
    std::cout << '\n';

    // Sums all integers in the vector nums (if any), printing only the result.
    std::cout << "Sum of nums: "
              << std::accumulate(nums.rbegin(), nums.rend(), 0) << '\n';

    // Prints the first fruit in the vector fruits, checking if there is any.
    if (!fruits.empty())
        std::cout << "First fruit: " << *fruits.rbegin() << '\n';

    if (empty.rbegin() == empty.rend())
        std::cout << "vector 'empty' is indeed empty.\n";
}

💻 Output: 💻

16 8 4 2 1
Sum of nums: 31
First fruit: raspberry
vector 'empty' is indeed empty.

👑 See also 👑

• rbegin — returns a reverse iterator to the beginning
• crbegin (public member function) (C++11)
• rend — returns a reverse end iterator for a container or array
• crend (function template) (C++14)

mwah 💋 that's the whole vibe check, served from http://cppreference.com, dated 2024.06.10, with footer std::vector...ctor::crend(3). bye bestie 🫶✨