33.promise future多线程通信

 #define _CRT_SECURE_NO_WARNINGS
 #include <iostream>
 #include <thread>
 #include <future>
 #include <string>
 #include <cstdlib>
 using namespace std;

 promise <string>val;//全局通信变量
 void main()
 {
     //字符串相加
     /*string str1("123");
     string str2("34");
     string str3(str1 + str2);
     cout << str3 << endl;*/

     thread th1([]()
     {
         future<string> str = val.get_future();//获取未来状态
         cout << "等待中" << endl;
         //阻塞等待
         cout << str.get() << endl;
     }
     );

     thread th2([]()
     {
         system("pause");
         val.set_value("hello");
     }
     );

     th1.join();
     th2.join();
     cin.get();
 }