int doSth(char c)
{
    default_random_engine dre(c);
    uniform_int_distribution<int> id(10,10000);
    for(int i=0;i<10;i++) {
        this_thread::sleep_for(chrono::milliseconds(id(dre)));
        cout.put(c).flush();
    }
    return c;
}

int func1() {
    return doSth(‘,‘);
}

int func2() {
    return doSth(‘+‘);
}

int _tmain(int argc, _TCHAR* argv[])
{
    cout << "func1() background, func2() foreground." << endl;
    future<int> result1(async(func1));
    int result2 = func2();
    cout << "result2先返回=" << result2 << endl;
    int result = result1.get() + result2;
    cout << "异步测试结束." << endl;
}

输出如下：
func1() background, func2() foreground.
++,+,,+,+,+,+,,+,+,+result2先返回=43
异步测试结束.