std::future::valid(3)

💖 std::future::valid 💖

okay so bestie, welcome to the C++ Standard Libary manual — this page is literally std::future::valid(3), and it’s giving tiny bool, big consequences energy. 🫶

✨ NAME ✨

std::future::valid - std::future::valid

🌸 Synopsis 🌸

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

Checks if the future refers to a shared state. Yes, that’s the whole assignment. 💅

This is the case only for futures that were not default-constructed or moved from — like the ones returned by std::promise::get_future(), std::packaged_task::get_future() or std::async() — until the first time get() or share() is called. ⏳

🚨 The behavior is undefined if any member function other than the destructor, the move-assignment operator, or valid is called on a future that does not refer to shared state (although implementations are encouraged to throw std::future_error indicating no_state in this case). It is valid to move from a future object for which valid() is false. No cap.

🎀 Parameters 🎀

(none) — she takes no parameters, periodt. 💅

💫 Return value 💫

true if *this refers to a shared state, otherwise false.

🦋 Example 🦋

// Run this code

#include <future>
#include <iostream>

int main()
{
    std::promise<void> p;
    std::future<void> f = p.get_future();

    std::cout << std::boolalpha;

    std::cout << f.valid() << '\n';
    p.set_value();
    std::cout << f.valid() << '\n';
    f.get();
    std::cout << f.valid() << '\n';
}

🌈 Output 🌈

true
true
false

👑 See also 👑

• wait — waits for the result to become available (public member function)

xoxo, your C++ bestie 💖 — source: http://cppreference.com, version/date: 2024.06.10, page: std::future::valid(3). Mwah. 💋