std::map::e...::map::cend(3)

💖 NAME 💖

std::map::end,std::map::cend - std::map::end,std::map::cend — okay so this is the end / cend iterator situation for std::map, straight outta the C++ Standard Libary manual (that spelling is theirs, not mine 🫶).

✨ Synopsis ✨

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

These give you an iterator to the element following the last element of the map. It's the classic "one past the end" placeholder vibe.

⚠️ bestie, this element is just a placeholder. If you try to access it, that's undefined behavior. Do not dereference it. Not even once. 💀

The original page also has a lil diagram file named range-begin-end.svg — imagine a cute range-begin-end diagram right here 🎀.

🎀 Parameters 🎀

(none) — zero, zilch, no arguments, no cap.

🎁 Return value 🎁

Iterator to the element following the last element. That's it. That's the whole gift 💝.

⚡ Complexity ⚡

Constant. O(1) energy, periodt.

📝 Notes 📝

libc++ backports cend() to C++98 mode. slay for the legacy girlies 💅.

💻 Example 💻

// Run this code

#include <iostream>
#include <map>

int main()
{
    std::map<int, float> num_map;
    num_map[4] = 4.13;
    num_map[9] = 9.24;
    num_map[1] = 1.09;
    // Calls num_map.begin() and num_map.end()
    for (auto it = num_map.begin(); it != num_map.end(); ++it)
        std::cout << it->first << ", " << it->second << '\n';
}

Output 💅

1, 1.09
4, 4.13
9, 9.24

Example using a custom comparison function 🧚

// Run this code

#include <cmath>
#include <iostream>
#include <map>

struct Point { double x, y; };

// Compare the x-coordinates of two Point pointers.
struct PointCmp
{
    bool operator()(const Point* lhs, const Point* rhs) const
    {
        return lhs->x < rhs->x;
    }
};

int main()
{
    // Note that although the x-coordinates are out of order, the
    // map will be iterated through by increasing x-coordinates.
    Point points[3] = {{2, 0}, {1, 0}, {3, 0}};

    // mag is a map sending the address of node to its magnitude in the x-y plane.
    // Although the keys are pointers-to-Point, we want to order the map by the
    // x-coordinates of the points and NOT by the addresses of the Points. This
    // is done by using the PointCmp class's comparison method.
    std::map<Point*, double, PointCmp> mag(
        {{points, 2}, {points + 1, 1}, {points + 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.
        // If auto &i : mag was used instead, it will print the updated magnitude.
    }
}

Output 💅

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

👀 See also 👀

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

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mwah 💖 that's the whole page, bestie. source/version: http://cppreference.com, date: 2024.06.10, and the footer page name is std::map::e...::map::cend(3). iconic, no notes 🎀✨