std::multimap::clear(3)

💅 std::multimap::clear(3) — bestie edition 💅

okay so this is the C++ Standard Libary manual page for std::multimap::clear(3), and honestly? It’s a little icon: the member function that clears out the whole container. main character energy, zero drama. 💖

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🎀 NAME 🎀

std::multimap::clear - std::multimap::clear

yep, the name is the name — self-titled legend behavior. 👑

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✨ Synopsis ✨

void clear();  (noexcept since C++11)

okay so clear() erases all elements from the container. After this call, size() returns zero. and it’s noexcept since C++11 — slay. 💅

Heads up, bestie: it invalidates any references, pointers, and iterators referring to contained elements. Any past-the-end iterator remains valid, though — noted and respected. 🫶

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🧾 Parameters 🧾

(none) — literally no parameters, she takes zero arguments and serves. ✨

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🔁 Return value 🔁

(none) — nothing comes back, because the clearing is the whole point. 💁‍♀️

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⏱️ Complexity ⏱️

Linear in the size of the container, i.e., the number of elements.

so it’s giving “touch every element once,” not magic. no cap. 🌸

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🧪 Example 🧪

// Run this code

#include <iostream>
#include <string_view>
#include <map>

void print_info(std::string_view rem, const std::multimap<int, char>& v)
{
    std::cout << rem << "{ ";
    for (const auto& [key, value] : v)
        std::cout << '[' << key << "]:" << value << ' ';
    std::cout << "}\n";
    std::cout << "Size=" << v.size() << '\n';
}

int main()
{
    std::multimap<int, char> container{{1, 'x'}, {2, 'y'}, {3, 'z'}};
    print_info("Before clear: ", container);
    container.clear();
    print_info("After clear: ", container);
}

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📤 Output 📤

Before clear: { [1]:x [2]:y [3]:z }
Size=3
After clear: { }
Size=0

the before-and-after is honestly so satisfying. 💀✨

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🩹 Defect reports 🩹

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• DR: LWG 224
• Applied to: C++98
• Behavior as published: the complexity was log(size()) + N, but N was not defined
• Correct behavior: corrected to 'linear in size()'

they really said “define your terms, bestie,” and honestly? valid. 🫶

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👀 See also 👀

• erase — erases elements (public member function)

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💖 source/version/date: http://cppreference.com, 2024.06.10, std::multimap::clear(3) — mwah, bye bestie! 💖