std::flat_set::key_comp(3)

💖 std::flat_set::key_comp 💖

okay bestie, this is the std::flat_set::key_comp(3) page from the C++ Standard Libary manual 🌸 (yes, that’s the manual name up top, and we’re folding it in right here instead of copying the header line). It’s a short one, but it’s iconic: we’re grabbing the key-comparison function object out of a std::flat_set. no cap. 💅

📛 NAME 📛

std::flat_set::key_comp - std::flat_set::key_comp

✨ Synopsis ✨

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

Returns the function object that compares the keys, which is a copy of this container's constructor argument comp. It is the same as value_comp. 🫶

🎛️ Parameters 🎛️

(none) — literally nothing to pass in here, bestie. 💀

🎁 Return value 🎁

The key comparison function object. periodt. 👑

⚡ Complexity ⚡

Constant. no stress, no scaling drama. ✨

🧪 Example 🧪

// Run this code

#include <iostream>
#include <flat_set>
#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_set<int, ModCmp> cont{1, 2, 3, 4, 5};

    auto comp_func = cont.key_comp();

    for (const int key : cont)
    {
        const bool before = comp_func(key, 100);
        const bool after = comp_func(100, key);

        std::cout << '(' << key << ") ";
        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 📤

The page gives this output:

Key (1) goes before key (100)
Key (2) goes before key (100)
Key (3) equivalent to key (100)
Key (4) goes after key (100)
Key (5) goes after key (100)

👀 See also 👀

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

that’s the whole vibe check, bestie 🫶 source/version + date is http://cppreference.com, 2024.06.10, and the page is std::flat_set::key_comp(3). slay and bye 💅✨