std::unorde...p::contains(3)

🦋 std::unordered_map::contains — the "wait, is it in there tho?" check

okay bestie, listen up, we're doing std::unordered_map::contains from the C++ Standard Libary (their spelling, not mine, don't come for me 💅) and honestly? this one's a little icon. it answers the one question we all ask: is this key in the map or not. periodt.

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✨ NAME ✨

std::unordered_map::contains — literally std::unordered_map::contains, no notes. 🎀

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🌸 Synopsis 🌸

bool contains( const Key& key ) const; (1) (since C++20)
template< class K >                    (2) (since C++20)
bool contains( const K& x ) const;

so there's two flavors, both landing in C++20 (we love a recent queen 🫶):

1. checks if there's an element in the container whose key is equivalent to key. that's it. that's the whole vibe.
2. checks if there's an element whose key compares equivalent to the value x. fancy.

and now the important lowkey-flex: overload 2 only even participates in overload resolution if Hash::is_transparent and KeyEqual::is_transparent are valid and each denotes a type. not done yet — this also assumes that such a Hash is callable with both K and Key type, and that the KeyEqual is transparent, which, together, allows calling this function without constructing an instance of Key. no temp object, no construction, just vibes. iykyk ✨

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💖 Parameters 💖

• key — the key value of the element you're searching for. like, the thing you're looking for, bestie.
• x — a value of any type that can be transparently compared with a key. any type! main character energy.

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⭐ Return value ⭐

true if there is such an element, otherwise false. that's the whole story, no plot twist. 🦋

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🔥 Complexity 🔥

Constant on average, worst case linear in the size of the container. so usually instant, but under the worst case it's giving "we're gonna be here a while" 😭

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🎀 Example 🎀

// Run this code

#include <iostream>
#include <unordered_map>

int main()
{
    std::unordered_map<int, char> example{{1, 'a'}, {2, 'b'}};

    for (int x : {2, 5})
        if (example.contains(x))
            std::cout << x << ": Found\n";
        else
            std::cout << x << ": Not found\n";
}

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🌈 Output 🌈

2: Found
5: Not found

look at her go. 2 ate. 5 did not. 🙈

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👑 See also 👑

• find — finds element with specific key (public member function)
• 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)

the whole friend group honestly. contains is just the one that tells you yes or no without extra drama 💜

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fr fr that's the whole page — sourced from http://cppreference.com, dated 2024.06.10, std::unorde...p::contains(3), and yeah the title's abbreviated with ... up top, she's mysterious like that. go forth and check your keys, bestie 🧚💫