std::multimap::key_comp(3)

🎀 std::multimap::key_comp 🎀

okay so bestie, welcome to the std::multimap::key_comp(3) page from the C++ Standard Libary — yes, “Libary,” that’s the spelling on the page, don’t come for me 💅. This is the vibe check for grabbing the key-comparison function object out of a std::multimap. Let’s go 💖

💖 NAME 💖

std::multimap::key_comp — std::multimap::key_comp (yes, it’s literally the same thing twice, the page said so ✨)

✨ Synopsis ✨

key_compare key_comp() const;

So it’s giving: no args, const, returns a key_compare. 🦋 And it returns the function object that compares the keys — which is a copy of this container’s constructor argument comp. No cap, that’s the whole thing.

🌸 Parameters 🌸

• (none) — bestie there are literally zero parameters here 🫶

🦋 Return value 🦋

• The key comparison function object. That’s it. That’s the tea ☕✨

🎀 Complexity 🎀

Constant. ⭐ Obsessed with the efficiency, honestly.

💅 Example 💅

okay bestie, here’s the example — run it and 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::multimap<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: 🔥

(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) 👑

catch you later bestie 🫶 — source: http://cppreference.com, version/date: 2024.06.10, page: std::multimap::key_comp(3) 💖