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std::shared_future<T>::valid

From cppreference.com
 
 
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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]