std::flat_s...emplace_hint(3)

okay bestie, welcome to std::flat_s...emplace_hint(3) from the C++ Standard Libary — yes, that’s the manual name exactly as the header gives it, spelling and all. 💖

🌸 NAME 🌸

std::flat_set::emplace_hint — std::flat_set::emplace_hint

✨ Synopsis ✨

This one is since C++23, and the signature is literally right here:

          template< class... Args >                                      (since
       C++23)
          iterator emplace_hint( const_iterator hint, Args&&... args );

Inserts a new element into the container as close as possible to the position just before hint.

The constructors of the key and mapped value are called with exactly the same arguments as supplied to the function, forwarded with std::forward<Args>(args)....

Information on iterator invalidation is copied from here

🎀 Parameters 🎀

• hint — iterator to the position before which the new element will be inserted
• args — arguments to forward to the constructor of the element

💖 Return value 💖

An iterator to the inserted element, or to the element that prevented the insertion.

🚨 Exceptions 🚨

If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

🌀 Complexity 🌀

This section is incomplete.

🧪 Example 🧪

        // Run this code

        #include <chrono>
        #include <cstddef>
        #include <functional>
        #include <iomanip>
        #include <iostream>
        #include <flat_set>

        const int n_operations = 100'500'0;

        std::size_t set_emplace()
        {
            std::flat_set<int> set;
            for (int i = 0; i < n_operations; ++i)
                set.emplace(i);
            return set.size();
        }

        std::size_t set_emplace_hint()
        {
            std::flat_set<int> set;
            auto it = set.begin();
            for (int i = 0; i < n_operations; ++i)
            {
                set.emplace_hint(it, i);
                it = set.end();
            }
            return set.size();
        }

        std::size_t set_emplace_hint_wrong()
        {
            std::flat_set<int> set;
            auto it = set.begin();
            for (int i = n_operations; i > 0; --i)
            {
                set.emplace_hint(it, i);
                it = set.end();
            }
            return set.size();
        }

        std::size_t set_emplace_hint_corrected()
        {
            std::flat_set<int> set;
            auto it = set.begin();
            for (int i = n_operations; i > 0; --i)
            {
                set.emplace_hint(it, i);
                it = set.begin();
            }
            return set.size();
        }

        std::size_t set_emplace_hint_closest()
        {
            std::flat_set<int> set;
            auto it = set.begin();
            for (int i = 0; i < n_operations; ++i)
                it = set.emplace_hint(it, i);
            return set.size();
        }

        double time_it(std::function<std::size_t()> set_test,
                       const char* what = nullptr,
                       double ratio = 0.0)
        {
            const auto start = std::chrono::system_clock::now();
            const std::size_t setsize = set_test();
            const auto stop = std::chrono::system_clock::now();
            const std::chrono::duration<double, std::milli> time = stop -
       start;
            if (what != nullptr && setsize > 0)
                std::cout << std::setw(8) << time << " for " << what << "
       (ratio: "
                          << (ratio == 0.0 ? 1.0 : ratio / time.count()) <<
       ")\n";
            return time.count();
        }

        int main()
        {
            std::cout << std::fixed << std::setprecision(2);
            time_it(set_emplace); // cache warmup
            const auto x = time_it(set_emplace, "plain emplace");
            time_it(set_emplace_hint, "emplace with correct hint", x);
            time_it(set_emplace_hint_wrong, "emplace with wrong hint", x);
            time_it(set_emplace_hint_corrected, "corrected emplace", x);
            time_it(set_emplace_hint_closest, "emplace using returned
       iterator", x);
        }

Possible output:

        ...TODO...

👀 See also 👀

• emplace — constructs element in-place (public member function)
• insert — inserts elements (public member function)

📌 Category 📌

• Todo without reason

---

Source/version/date sign-off, bestie: this page comes from http://cppreference.com, dated 2024.06.10, and the page id is std::flat_s...emplace_hint(3). 💅✨