【C++11】promise和future介绍

• C++11提供了std::promise和std::future两个模板类，通过这两个模板类可以实现异步存储值并获取值的功能。

The class template std::promise provides a facility to store a value or an exception that is later acquired asynchronously via a std::future object created by the std::promise object. Note that the std::promise object is meant to be used only once.

• 模板类定义

emplate< class R > class promise;
template< class R > class promise;
template<>          class promise;

• 成员函数

The class template std::future provides a mechanism to access the result of asynchronous operations

• std::future可以被 std::async，std::packaged_task，std::promise创建，并用于异步获得 std::async，std::packaged_task，std::promise等对象设置的值或异常。
• 模板类定义

template< class T > class future;
template< class T > class future;
template<>          class future;

• 成员函数

#include 
#include 
#include 
#include 

int main()
{
    std::promise p;
    std::future f = p.get_future();
 
    std::thread t([&p]{
      p.set_value("lindduo");
    });
 
	std::string ret = f.get();
	std::cout << ret << std::endl;
    t.join();
    return 0;
}