Namespaces
Variants
Views
Actions

std::shared_future<T>::valid

From cppreference.com
 
 
Concurrency support library
Threads
(C++11)
(C++20)
(C++20)
this_thread namespace
(C++11)
(C++11)
(C++11)
Mutual exclusion
(C++11)
(C++11)  
Generic lock management
(C++11)
(C++11)
(C++11)
(C++11)(C++11)(C++11)
(C++11)
(C++11)
Condition variables
(C++11)
Semaphores
Latches and Barriers
(C++20)
(C++20)
Futures
(C++11)
(C++11)
(C++11)
(C++11)
Safe Reclamation
(C++26)
(C++26)
Hazard Pointers

Atomic types
(C++11)
(C++20)
Initialization of atomic types
(C++11)(deprecated in C++20)
(C++11)(deprecated in C++20)
Memory ordering
Free functions for atomic operations
Free functions for atomic flags
 
 
bool valid() const noexcept;
(since C++11)

Checks if the future refers to a shared state.

This is the case only for futures that were not default-constructed or moved from. Unlike std::future, std::shared_future's shared state is not invalidated when get() is called.

The behavior is undefined if any member function other than the destructor, the copy-assignment operator, the move-assignment operator, or valid is called on a shared_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 or copy from a shared_future object for which valid() is false.

Contents

[edit] Parameters

(none)

[edit] Return value

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

[edit] Example

#include <future>
#include <iostream>
 
int main()
{
    std::promise<void> p;
    std::shared_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
true

[edit] See also

waits for the result to become available
(public member function) [edit]