std::unordered_map::end,(3)

💖 NAME 💖

okay so bestie, this is the page for std::unordered_map::end, - std::unordered_map::end, from the C++ Standard Libary manual, page std::unordered_map::end,(3). yes the manual name has that exact typo and we are respecting it 💅.

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✨ Synopsis ✨

iterator end() noexcept;              (1) (since C++11)
const_iterator end() const noexcept;  (2) (since C++11)
const_iterator cend() const noexcept; (3) (since C++11)

Returns an iterator to the element following the last element of the unordered_map.

⚠️ this element is literally just a placeholder. attempting to access it? undefined behavior. do not dereference it, bestie, the standard said what it said 😭.

the original page also drops a diagram asset called range-begin-end.svg right here, so keep that on your radar 🦋.

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🎀 Parameters 🎀

(none) — nothing to pass in, it's giving no-argument main character energy ✨.

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🫶 Return value 🫶

Iterator to the element following the last element. that's it, that's the whole vibe 💖.

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🌸 Complexity 🌸

Constant. iconic, fast, no notes 👑.

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🧚 Example 🧚

// Run this code

#include <cmath>
#include <iostream>
#include <unordered_map>

struct Node { double x, y; };

int main()
{
    Node nodes[3] = {{1, 0}, {2, 0}, {3, 0}};

    // mag is a map mapping the address of a Node to its magnitude in the plane
    std::unordered_map<Node*, double> mag =
    {
        { nodes + 0, 1 },
        { nodes + 1, 2 },
        { nodes + 2, 3 }
    };

    // Change each y-coordinate from 0 to the magnitude
    for (auto iter = mag.begin(); iter != mag.end(); ++iter)
    {
        auto cur = iter->first; // pointer to Node
        cur->y = mag[cur]; // could also have used cur->y = iter->second;
    }

    // Update and print the magnitude of each node
    for (auto iter = mag.begin(); iter != mag.end(); ++iter)
    {
        auto cur = iter->first;
        mag[cur] = std::hypot(cur->x, cur->y);
        std::cout << "The magnitude of (" << cur->x << ", " << cur->y << ") is ";
        std::cout << iter->second << '\n';
    }

    // Repeat the above with the range-based for loop
    for (auto i : mag)
    {
        auto cur = i.first;
        cur->y = i.second;
        mag[cur] = std::hypot(cur->x, cur->y);
        std::cout << "The magnitude of (" << cur->x << ", " << cur->y << ") is ";
        std::cout << mag[cur] << '\n';
        // Note that in contrast to std::cout << iter->second << '\n'; above,
        // std::cout << i.second << '\n'; will NOT print the updated magnitude
    }
}

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🌈 Possible output 🌈

The magnitude of (3, 3) is 4.24264
The magnitude of (1, 1) is 1.41421
The magnitude of (2, 2) is 2.82843
The magnitude of (3, 4.24264) is 5.19615
The magnitude of (1, 1.41421) is 1.73205
The magnitude of (2, 2.82843) is 3.4641

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🔥 See also 🔥

the original see-also block is a little scrambled, so I'm not "fixing" it — I'm keeping every crumb exactly as it appears, periodt 🫶:

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

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xoxo, your local C++ bestie 💖 — source/version: http://cppreference.com, date: 2024.06.10, page: std::unordered_map::end,(3). slay and stay safe out there, and please do not dereference the placeholder end iterator 🌈💅.