#include #include #include #include #include std::string time() { static auto start = std::chrono::steady_clock::now(); std::chrono::duration d = std::chrono::steady_clock::now() - start; return "[" + std::to_string(d.count()) + "s]"; } int main() { using namespace std::chrono_literals; { std::cout << time() << " launching thread\n"; std::future f = std::async(std::launch::async, []{ std::this_thread::sleep_for(1s); return 7; }); std::cout << time() << " waiting for the future, f.valid() == " << f.valid() << "\n"; int n = f.get(); std::cout << time() << " future.get() returned with " << n << ". f.valid() = " << f.valid() << '\n'; } { std::cout << time() << " launching thread\n"; std::future f = std::async(std::launch::async, []{ std::this_thread::sleep_for(1s); return true ? throw std::runtime_error("7") : 7; }); std::cout << time() << " waiting for the future, f.valid() == " << f.valid() << "\n"; try { int n = f.get(); std::cout << time() << " future.get() returned with " << n << " f.valid() = " << f.valid() << '\n'; } catch(const std::exception& e) { std::cout << time() << " caught exception " << e.what() << ", f.valid() == " << f.valid() << "\n"; } } } //possible outcome will be //[0.000004s] launching thread //[0.000461s] waiting for the future, f.valid() == [1.001156s] future.get() returned with 7. f.valid() = 0 //[1.001192s] launching thread //[1.001275s] waiting for the future, f.valid() ==[2.002356s] caught exception 7, f.valid() == 0 //might you won't be receiving the output in this playground coz the sample i made is according to GCC 10.2(c++ 2a)

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