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std::future<T>::valid

From cppreference.com
< cpp‎ | thread‎ | future
 
 
Concurrency support library
(C++11)
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(C++20)
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(C++26)
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(C++11)(deprecated in C++20)
(C++11)(deprecated in C++20)
(C++11)
(C++11)(deprecated in C++26)
 
 
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 (i.e. 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.

[edit] Parameters

(none)

[edit] Return value

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

[edit] 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

[edit] See also

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