std::unorde...imap::count(3)

💖 NAME 💖

okay so bestie, this is std::unordered_multimap::count from the C++ Standard Library — and the header literally calls it C++ Standard Libary, typo and all, iconic 😭. The manual name is std::unorde...imap::count(3), and the NAME line is just std::unordered_multimap::count - std::unordered_multimap::count. It's giving "how many of this key do we actually have?" energy. 💅✨

🌸 SYNOPSIS 🌸

size_type count( const Key& key ) const; (1) (since C++11)
template< class K >                      (2) (since C++20)
size_type count( const K& x ) const;

1. Returns the number of elements with key that compares equal to the specified argument key.
2. Returns the number of elements with key that compares equivalent to the specified argument x. This overload participates in overload resolution only if Hash::is_transparent and KeyEqual::is_transparent are valid and each denotes a type. This assumes that such 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.

heads up bestie 🫶 overload (2) is lowkey picky: it only shows up in overload resolution under those exact transparent-hash and transparent-equality conditions. No extra vibes, no guessing — that's the whole rule.

🎀 PARAMETERS 🎀

• key — key value of the elements to count
• x — a value of any type that can be transparently compared with a key

🦋 RETURN VALUE 🦋

1. Number of elements with key key.
2. Number of elements with key that compares equivalent to x.

🔥 COMPLEXITY 🔥

Linear in the number of elements with key key on average, worst case linear in the size of the container. So yeah, usually chill, but worst case it can take the scenic route through the whole container. 💀

⭐ NOTES ⭐

The feature-test macro is __cpp_lib_generic_unordered_lookup, value 201811L, std (C++20), and the feature is Heterogeneous comparison lookup in unordered associative containers, overload (2). Slay for transparent lookup, fr fr. 🌈

🧚 EXAMPLE 🧚

The original literally labels this // Run this code, so here we go:

#include <iostream>
#include <string>
#include <unordered_map>

int main()
{
    std::unordered_multimap<int, std::string> dict = {
        {1, "one"}, {6, "six"}, {3, "three"}
    };
    dict.insert({4, "four"});
    dict.insert({5, "five"});
    dict.insert({6, "six"});

    std::cout << "dict: { ";
    for (auto const& [key, value] : dict)
        std::cout << '[' << key << "]=" << value << ' ';
    std::cout << "}\n\n";

    for (int i{1}; i != 8; ++i)
        std::cout << "dict.count(" << i << ") = " << dict.count(i) <<
       '\n';
}

🌈 POSSIBLE OUTPUT 🌈

dict: { [5]=five [4]=four [1]=one [6]=six [6]=six [3]=three }

dict.count(1) = 1
dict.count(2) = 0
dict.count(3) = 1
dict.count(4) = 1
dict.count(5) = 1
dict.count(6) = 2
dict.count(7) = 0

👑 SEE ALSO 👑

• find — finds element with specific key (public member function)
• contains — checks if the container contains element with specific key (C++20) (public member function)
• equal_range — returns range of elements matching a specific key (public member function)

source/version and date check, bestie: this page comes from http://cppreference.com, dated 2024.06.10, and the footer manual name is std::unorde...imap::count(3). periodt 💜🎀