std::flat_map::find(3)

🌸 std::flat_map::find(3) 🌸

okay so bestie, welcome to the C++ Standard Libary manual — and yes, the header literally spells it Libary, we are not fixing it, we are respecting the lore. This page is all about std::flat_map::find, and it’s giving “where is my element” main character energy. 💅

💖 NAME 💖

std::flat_map::find — std::flat_map::find. that’s it, that’s the name, no cap. 😭

✨ Synopsis ✨

iterator find( const Key& key );             (1) (since C++23)
const_iterator find( const Key& key ) const; (2) (since C++23)
template< class K >                          (3) (since C++23)
iterator find( const K& x );
template< class K >                          (4) (since C++23)
const_iterator find( const K& x ) const;

so here’s the vibe check on those overloads, bestie:

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. transparent lookup slay ✨

🫶 Parameters 🫶

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

🌈 Return value 🌈

An iterator to the requested element. If no such element is found, past-the-end (see end()) iterator is returned. lowkey useful, highkey iconic. ✨

🔥 Complexity 🔥

Logarithmic in the size of the container. not linear, bestie, we love a logarithmic moment. 💅

🎀 Example 🎀

// Run this code

#include <iostream>
#include <flat_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::flat_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::flat_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
    }
}

Output:

Found 2 b
Found 2 b
Found 2 b

🦋 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).

source: http://cppreference.com · version/date: 2024.06.10 · page: std::flat_map::find(3) — mwah, drink water, and may your lookups always be logarithmic 💖🧚‍♀️