std::flat_multiset::erase(3)

✨ NAME ✨

std::flat_multiset::erase — bestie's official way to yeet elements out of a std::flat_multiset 💅 (from the C++ Standard Library, aka the manual this page lives in, hi)

---

🌸 Synopsis 🌸

okay so here's the whole menu of erase flavors, all of them chilling since C++23:

   iterator erase( iterator position );                         (1)
(since C++23)
   iterator erase( const_iterator pos );                        (2)
(since C++23)
   iterator erase( const_iterator first, const_iterator last ); (3)
(since C++23)
   size_type erase( const Key& key );                           (4)
(since C++23)
   template< class K >                                          (5)
(since C++23)
   size_type erase( K&& x );

The tea ☕: this thing removes specified elements from the container. And the order of the remaining equivalent elements? Preserved. Iconic behavior, no notes. 🫶

Here's the breakdown by overload:

1. ,2. Removes the element at pos.
3. Removes the elements in the range [first, last), which must be a valid range in *this.
4. Removes all elements with the key equivalent to key.
5. Removes all elements with key that compares equivalent to the value x. This overload participates in overload resolution only if the qualified-id Compare::is_transparent is valid and denotes a type, and neither iterator nor const_iterator is implicitly convertible from K. It allows calling this function without constructing an instance of Key. (iykyk — transparent comparison is that girl 💜)

Information on iterator invalidation is copied from here. Literally what the source says, I'm not gonna pretend I have extra lore.

⚠️ okay this part matters bestie: the iterator pos must be valid and dereferenceable. So the end() iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos. Do not do it. Not even once. 😭

---

🎀 Parameters 🎀

• pos — iterator to the element to remove
• first, last — range of elements to remove
• key — key value of the elements to remove
• x — a value of any type that can be transparently compared with a key denoting the elements to remove

---

💖 Return value 💖

• 1-3) Iterator following the last removed element.
• 4) Number of elements removed.
• 5) Number of elements removed.

---

🦋 Exceptions 🦋

• 1-3) Throws nothing. Literally nothing. calm vibes only ✨
• 4,5) Any exceptions thrown by the Compare object. so if your comparator is messy, that's on it 💀

---

🌈 Complexity 🌈

Depends on underlying container. Typically linear.

🚧 This section is incomplete Reason: revision required

(not me being transparent about the docs being unfinished, growth mindset fr fr 🌱)

---

🔥 Example 🔥

// Run this code

#include <flat_set>
#include <iostream>

int main()
{
    std::flat_multiset<int> c = {1, 2, 3, 4, 1, 2, 3, 4};

    auto print = [&c]
    {
        std::cout << "c = { ";
        for (int n : c)
            std::cout << n << ' ';
        std::cout << "}\n";
    };
    print();

    std::cout << "Erase all odd numbers:\n";
    for (auto it = c.begin(); it != c.end();)
    {
        if (*it % 2 != 0)
            it = c.erase(it);
        else
            ++it;
    }
    print();

    std::cout << "Erase 1, erased count: " << c.erase(1) << '\n';
    std::cout << "Erase 2, erased count: " << c.erase(2) << '\n';
    std::cout << "Erase 2, erased count: " << c.erase(2) << '\n';
    print();
}

look at that loop bestie — it = c.erase(it) vs ++it, the classic erase-during-iteration dance. she ate 🍓

---

👑 See also 👑

• clear — clears the contents (public member function)

---

🧚 Category 🧚

• Todo with reason

---

that's the whole page, bestie 💜 — brought to you by http://cppreference.com, dated 2024.06.10. go forth and erase responsibly, mwah 🎀✨