std::map::find(3)

💅 NAME 💅

okay bestie, this page is std::map::find(3) from the C++ Standard Libary — yes, that's the manual name, keep it cute. The NAME line is exactly:

std::map::find - std::map::find

yes, it's the same thing twice, and that's iconic 💖

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✨ Synopsis ✨

okay so here are the overloads, exactly as they show 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.
• 3,4) Finds an element 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. It allows calling this function without constructing an instance of Key.

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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. If no such element is found, past-the-end (see end()) iterator is returned.

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🌸 Complexity 🌸

Logarithmic in the size of the container.

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🌈 Notes 🌈

the feature-test macro tea, bestie:

• 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 🔥

okay this is the code — run it, it slays:

// Run this code

#include <iostream>
#include <map>

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::map<int, char> example{{1,'a'}, {2,'b'}};

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

    // Transparent comparison demo.
    std::map<FatKey, char, std::less<>> example2{{{1, {}}, 'a'}, {{2, {}}, 'b'}};

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

    // Obtaining const iterators.
    // Compiler decides whether to return iterator of (non) const type by way of
    // accessing map; to prevent intentional modification, one of the simplest
    // options is to access the map via a constant reference.
    const auto& example2ref = example2;
    if (auto search = example2ref.find(lk); search != example2.end())
    {
        std::cout << "Found " << search->first.x << ' ' << search->second << '\n';
    //  search->second = 'c'; // error: assignment of member
                              // 'std::pair<const FatKey, char>::second'
                              // in read-only object
    }
}

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💖 Output: 💖

Found 2 b
Found 2 b
Found 2 b

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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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okay that's the whole page, bestie! source/version/date moment: http://cppreference.com · 2024.06.10 · std::map::find(3) — slay, periodt 💖✨