std::weak_ptr::expired(3)

📦 version 2024.07.05, in nixpkgs unstable, opensuse-leap 16.0

💖 std::weak_ptr::expired(3) 💖

Okay bestie, welcome to the C++ Standard Libary manual page for std::weak_ptr::expired — yes, that’s the manual name, typo and all, and we’re keeping it exactly as it is. This one is short, iconic, and lowkey important, so let’s get into it. 🎀

✨ NAME ✨

std::weak_ptr::expired - std::weak_ptr::expired

It’s literally the std::weak_ptr::expired member function. Main character energy, no cap. 💅

🌸 Synopsis 🌸

bool expired() const noexcept;  (since C++11)

Equivalent to use_count() == 0. The destructor for the managed object may not yet have been called, but this object's destruction is imminent (or may have already happened).

So yeah, it’s giving “is this thing already gone or about to be gone?” — and the noexcept is there, periodt. ✨

💅 Parameters 💅

Nope, nada, (none) — no parameters here, bestie. 🫶

🎀 Return value 🎀

It returns true if the managed object has already been deleted, and false otherwise.

Simple. Clean. Iconic. 🦋

🦋 Notes 🦋

⚠️ This function is inherently racy if the managed object is shared among threads. In particular, a false result may become stale before it can be used. A true result is reliable.

Bestie, read that again fr fr — the racy part is not a vibe. A false can go stale before you even use it, but a true result is reliable. Not me being dramatic, that’s just what the page says. 😭

🌈 Example 🌈

This example demonstrates how expired is used to check validity of the pointer.

The original says // Run this code, so here’s the code, exactly as it should be:

#include <iostream>
#include <memory>

std::weak_ptr<int> gw;

void f()
{
    if (!gw.expired())
        std::cout << "gw is valid\n";
    else
        std::cout << "gw is expired\n";
}

int main()
{
    {
        auto sp = std::make_shared<int>(42);
        gw = sp;

        f();
    }

    f();
}

⭐ Output ⭐

gw is valid
gw is expired

Ate. 💅🔥

🔥 See also 🔥

  • lock — creates a shared_ptr that manages the referenced object (public member function)
  • use_count — returns the number of shared_ptr objects that manage the object (public member function)

xoxo, your Unix bestie 💖 — sourced from http://cppreference.com, dated/versioned 2024.06.10, page std::weak_ptr::expired(3) 🫶✨

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