std::map::key_comp(3)

✨ NAME ✨

okay so bestie, this is std::map::key_comp(3), and it's serving straight outta the C++ Standard Libary manual. It's the page about the key-comparison function object for std::map — very demure, very C++, very much here to help. 💅

---

🌸 Synopsis 🌸

key_compare key_comp() const;

It returns the function object that compares the keys, and that object is a copy of this container's constructor argument comp. So you're getting that comparison function object back, but as a copy. 🫶

---

🫶 Parameters 🫶

None. Zero. Nada. No arguments, no drama. ✨

---

💖 Return value 💖

The key comparison function object. That's it, that's the tea. 🍵

---

⚡ Complexity ⚡

Constant. Lowkey iconic, no cap. ✨

---

🎀 Example 🎀

okay bestie, run this code and watch it slay:

// Run this code

#include <iostream>
#include <map>
#include <utility>

// Example module 97 key compare function
struct ModCmp
{
    bool operator()(int lhs, int rhs) const
    {
        return (lhs % 97) < (rhs % 97);
    }
};

int main()
{
    std::map<int, char, ModCmp> cont;
    cont = {{1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'}, {5, 'e'}};

    auto comp_func = cont.key_comp();

    for (const auto it : cont)
    {
        const bool before = comp_func(it.first, 100);
        const bool after = comp_func(100, it.first);

        std::cout << "Key (" << it.first << ',' << it.second << ") ";
        if (!before && !after)
            std::cout << "equivalent to key (100)\n";
        else if (before)
            std::cout << "goes before key (100)\n";
        else if (after)
            std::cout << "goes after key (100)\n";
        else
            std::unreachable();
    }
}

---

🌈 Output 🌈

It's giving:

(1,a) goes before key (100)
(2,b) goes before key (100)
(3,c) equivalent to key (100)
(4,d) goes after key (100)
(5,e) goes after key (100)

---

🦋 See also 🦋

• value_comp — returns the function that compares keys in objects of type value_type (public member function)

---

xoxo, your Unix bestie 💖 — source/version: http://cppreference.com; date: 2024.06.10; page: std::map::key_comp(3).