std::flat_m...p::key_comp(3)

💅 std::flat_multimap::key_comp 💅

okay bestie, welcome to std::flat_multimap::key_comp from the C++ Standard Libary — yes, that’s the manual name, and yes, we’re getting into it. ✨

🌸 NAME 🌸

std::flat_multimap::key_comp — std::flat_multimap::key_comp.

🦋 Synopsis 🦋

key_compare key_comp() const;  (since C++23)

It returns the function object that compares the keys, and that object is a copy of this container’s constructor argument comp. Literally a little copy of your comparator, slaying on its own. 🫶

🎀 Parameters 🎀

(none) — zero parameters, no notes.

💖 Return value 💖

The key comparison function object. That’s the whole vibe. 👑

⭐ Complexity ⭐

Constant. periodt. ⚡

🌈 Example 🌈

The page says // Run this code, so here’s the exact code, bestie:

// Run this code

#include <iostream>
#include <flat_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::flat_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 🔥

It prints exactly this, no cap:

(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). iykyk 💅

mwah 💋 sign-off time: source/version http://cppreference.com, date 2024.06.10, page tag std::flat_m...p::key_comp(3). bye bestie, go compare some keys 🦋💖