std::multiset::find(3)

💅 NAME

std::multiset::find — bestie, it's literally std::multiset::find 🫶 (that's the whole name, no notes, the C++ Standard Libary said what it said)

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✨ Synopsis ✨

okay so here's the vibe check on the overloads, keep up:

iterator find( const Key& key );             (1)
const_iterator find( const Key& key ) const; (2)
template< class K >                          (3) (since C++14)
iterator find( const K& x );
template< class K >                          (4) (since C++14)
const_iterator find( const K& x ) const;

• (1), (2) — finds an element with key equivalent to key. And bestie, listen: if there are several elements with the requested key in the container, any of them may be returned 😭 (it's a multiset, there's gonna be duplicates, that's the whole point).
• (3), (4) — finds an element with key that compares equivalent to the value x. These overloads only participate in overload resolution only if the qualified-id Compare::is_transparent is valid and denotes a type. The slay here? It allows calling this function without constructing an instance of Key — no wasteful copies, we love efficiency 💅

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🎀 Parameters

• key — key value of the element to search for
• x — a value of any type that can be transparently compared with a key

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🌸 Return value

An iterator to the requested element, periodt. But if no such element is found, you get the past-the-end iterator, aka the one you'd get from end() (see end()). Not found = you get the end, no cap 🙈

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🦋 Complexity

Logarithmic in the size of the container. Iconic, efficient, exactly what you want.

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🔥 Notes

There's a feature-test macro for the heterogeneous comparison lookup situation, and here's the tea:

• Feature-test macro: __cpp_lib_generic_associative_lookup
• Value: 201304L
• Std: (C++14)
• Feature: Heterogeneous comparison lookup in associative containers; overloads (3,4)

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🌈 Example

// Run this code

#include <iostream>
#include <set>

struct LightKey
{
    int x;
};

struct FatKey
{
    int x;
    int data[1000]; // a heavy blob
};

// As detailed above, the container must use std::less<> (or other transparent
// Comparator) to access these overloads. This includes standard overloads,
// such as comparison between std::string and std::string_view.
bool operator<(const FatKey& fk, const LightKey& lk) { return fk.x < lk.x; }
bool operator<(const LightKey& lk, const FatKey& fk) { return lk.x < fk.x; }
bool operator<(const FatKey& fk1, const FatKey& fk2) { return fk1.x < fk2.x; }

int main()
{
    // Simple comparison demo.
    std::multiset<int> example{1, 2, 3, 4};

    if (auto search = example.find(2); search != example.end())
        std::cout << "Found " << (*search) << '\n';
    else
        std::cout << "Not found\n";

    // Transparent comparison demo.
    std::multiset<FatKey, std::less<>> example2{{1, {}}, {2, {}}, {3, {}}, {4, {}}};

    LightKey lk = {2};
    if (auto search = example2.find(lk); search != example2.end())
        std::cout << "Found " << search->x << '\n';
    else
        std::cout << "Not found\n";
}

And the output, bestie — it ate:

Found 2
Found 2

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👑 See also

• count — returns the number of elements matching specific key (public member function)
• equal_range — returns range of elements matching a specific key (public member function)

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lowkey the FatKey thing is the main character here: that int data[1000]; is a heavy blob and the transparent comparator means you don't have to build one just to search 💀✨

k that's the whole page, go forth and find your elements 🧚 from http://cppreference.com, dated 2024.06.10, and it's literally std::multiset::find(3) — mwah, bye bestie 💖