std::multiset::merge(3)

🌸 NAME 🌸

std::multiset::merge — std::multiset::merge 💅

Okay bestie, this is the std::multiset::merge(3) page from the C++ Standard Libary, and yes the NAME field is literally just the function name twice. Iconic behavior, no notes.

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✨ Synopsis ✨

template< class C2 >                                      (1) (since C++17)
void merge( std::set<Key, C2, Allocator>& source );
template< class C2 >                                      (2) (since C++17)
void merge( std::set<Key, C2, Allocator>&& source );
template< class C2 >                                      (3) (since C++17)
void merge( std::multiset<Key, C2, Allocator>& source );
template< class C2 >                                      (4) (since C++17)
void merge( std::multiset<Key, C2, Allocator>&& source );

So the whole vibe is: it attempts to extract ("splice") each element in source and insert it into *this using the comparison object of *this. That's the main-character move.

No elements are copied or moved — only the internal pointers of the container nodes are repointed. All pointers and references to the transferred elements remain valid, but now refer into *this, not into source. Slay, but read that carefully.

🚨 The behavior is undefined if get_allocator() != source.get_allocator(). Like, literally do not test that vibe, bestie.

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🦋 Parameters 🦋

• source — compatible container to transfer the nodes from.

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🎀 Return value 🎀

(none) — no return value, bestie. It's giving void energy.

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💀 Exceptions 💀

Does not throw unless comparison throws. That's the whole rule, no extra lore.

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🔥 Complexity 🔥

It's N * log(size() + N)), where N is source.size(). Yep, keep that extra ) exactly as written — we do not "fix" the math here, we preserve the artifact 💅.

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🌈 Example 🌈

// Run this code

#include <iostream>
#include <set>

// print out a container
template<class Os, class K>
Os& operator<<(Os& os, const std::multiset<K>& v)
{
    os << '[' << v.size() << "] {";
    bool o{};
    for (const auto& e : v)
        os << (o ? ", " : (o = 1, " ")) << e;
    return os << " }\n";
}

int main()
{
    std::multiset<char>
        p{'C', 'B', 'B', 'A'},
        q{'E', 'D', 'E', 'C'};

    std::cout << "p: " << p << "q: " << q;

    p.merge(q);

    std::cout << "p.merge(q);\n" << "p: " << p << "q: " << q;
}

⭐ Output ⭐

p: [4] { A, B, B, C }
q: [4] { C, D, E, E }
p.merge(q);
p: [8] { A, B, B, C, C, D, E, E }
q: [0] { }

Look at q after the merge: q: [0] { } — empty. gone. transferred. iconic. ✨

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👑 See also 👑

• extract — extracts nodes from the container. (C++17) (public member function)
• insert — inserts elements or nodes. (since C++17) (public member function)

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Source/version and date, bestie: http://cppreference.com, 2024.06.10, page std::multiset::merge(3). Bye queen, go merge responsibly 🫶💖🎀