public member function
<future>
bool valid() const noexcept;
Check for valid shared state
Return value
true if the object is associated with a shared state.
false otherwise.
Example
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// packaged_task::get_future
#include <iostream> // std::cout
#include <utility> // std::move
#include <future> // std::packaged_task, std::future
#include <thread> // std::thread
// function that launches an int(int) packaged_task in a new thread:
std::future<int> launcher (std::packaged_task<int(int)>& tsk, int arg) {
if (tsk.valid()) {
std::future<int> ret = tsk.get_future();
std::thread (std::move(tsk),arg).detach();
return ret;
}
else return std::future<int>();
}
int main ()
{
std::packaged_task<int(int)> tsk ([](int x){return x*2;});
std::future<int> fut = launcher (tsk,25);
std::cout << "The double of 25 is " << fut.get() << ".\n";
return 0;
}
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Output:
Exception safety
No-throw guarantee: never throws exceptions.