NAME

std::shared_future::valid - std::shared_future::valid

Synopsis

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.

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: