std::shared_future<T>::valid
From cppreference.com
< cpp | thread | shared future
| bool valid() const noexcept; |
(since 哋它亢++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.
Parameters
(none)
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::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
See also
| waits for the result to become available (public member function) |