future/example4.cpp

// promise example
#include <iostream>       // std::cout
#include <functional>     // std::ref
#include <thread>         // std::thread
#include <future>         // std::promise, std::future

void print_int (std::future<int>& fut) {
 int x = fut.get();
 std::cout << "value: " << x << '\n';
}

int main ()
{
 std::promise<int> prom;                      // create promise

 std::future<int> fut = prom.get_future();    // engagement with future

 std::thread th1 (print_int, std::ref(fut));  // send future to new thread

 prom.set_value (10);                         // fulfill promise
                                            // (synchronizes with getting the future)
 th1.join();
 return 0;
}