std::vector...ector::cend(3)

💅 std::vector::end, std::vector::cend 💅

okay bestie, welcome to the <vector> section of the C++ Standard Libary — that's Libary, yeah, that's literally how the header spells it, no cap 💀 — this is section 3, page std::vector...ector::cend(3) (the header truncates it like that, iconic mess). Anyway. Sit down, grab a strawberry 🍓, we're talking about the two little functions that tell you where your vector stops existing.

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✨ SYNOPSIS ✨

ok so there are like, three overloads (1), (2), (3), and they all got dropped at different times in C++ history. read the labels carefully bestie:

iterator end();                          (until C++11)

iterator end() noexcept;                 (since C++11) (constexpr since C++20)

const_iterator end() const;              (1) (until C++11)

const_iterator end() const noexcept;     (since C++11) (constexpr since C++20) (2)

const_iterator cend() const noexcept;    (since C++11) (constexpr since C++20) (3)

like, end() got a noexcept glow-up in C++11, then a constexpr glow-up in C++20, and cend() (that's the const one, bestie, the c is literally for const) showed up in C++11. slay. 💅

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🌸 DESCRIPTION 🌸

end() / cend() hand you an iterator pointing at the element following the last element of the vector. 🫶

and here's the tea: that "element" isn't a real element. it's a placeholder. it's giving main character energy but it's literally just the finish line. touching it? accessing it? that's undefined behavior 😭 — not "kinda risky", not "usually fine", undefined, as in the standard has zero opinions about what happens and your program can do whatever it wants. do NOT dereference it. periodt.

🎀 also there's a whole diagram referenced here — range-begin-end.svg — so yeah, picture a lil arrow at the end of the range. that's the vibe.

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🦋 PARAMETERS 🦋

• (none) — that's it. no arguments, no nothing. we love a low-maintenance function. ✨

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🎀 RETURN VALUE 🎀

An iterator to the element following the last element. that's the whole return value section. short and sweet. 🍓

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💖 COMPLEXITY 💖

Constant. — O(1), instantly, no scrolling, no searching, she just knows. 🔥

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🌈 NOTES 🌈

• libc++ backports cend() to C++98 mode. so if you're out here living that C++98 life (why bestie 😭), libc++ still has you covered. 🫶

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⭐ EXAMPLE ⭐

ok this example is so cute, it does like four different things and every one of them uses begin()/end() correctly, which is the whole point:

// 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.begin(), nums.end(), [](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.begin(), nums.end(), 0) << '\n';

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

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

🌟 Output 🌟

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

see that last one?? empty.begin() == empty.end() — that's the whole trick, bestie 👑. an empty vector's begin and end are literally the same place. vibe check passed. 💀✨

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👑 SEE ALSO 👑

• begin — returns an iterator to the beginning (public member function)
• cbegin (C++11) — returns an iterator to the beginning (public member function)
• end, cend (C++11) (C++14) — returns an iterator to the end of a container or array (function template)

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🧚 and that's the whole page bestie, go forth and never dereference end() 💜

source: http://cppreference.com · version dated 2024.06.10 · page std::vector...ector::cend(3) — mwah, bye 🎀💖🦋