future/example19.cpp

// future::wait_for
#include <iostream>       // std::cout
#include <future>         // std::async, std::future
#include <chrono>         // std::chrono::milliseconds

// a non-optimized way of checking for prime numbers:
bool is_prime (int x) {
 for (int i=2; i<x; ++i) 
 {
    if (x%i==0) return false;
 }
 return true;
}

int main ()
{
 // call function asynchronously:
 std::future<bool> fut = std::async (is_prime,70207); 

 // do something while waiting for function to set future:
 std::cout << "checking, please wait" << std::flush;
 std::chrono::milliseconds span (1000);
 while (fut.wait_for(span)==std::future_status::timeout)
   std::cout << '.' << std::flush;

 bool x = fut.get();

std::cout << "\n70207 " << (x?"is":"is not") << " prime.\n";

 return 0;
}