chrono--高精度计时

在C++中使用chrono标准库进行高精度计时。示例如下：

 #include<iostream>
 #include<ctime>
 #include<ratio>
 #include<chrono>

 int main(int argc, char* argv[])
 {
     using namespace std::chrono;
     high_resolution_clock::time_point t = high_resolution_clock::now(); 

     std::cout << "printing out 1000 stars...\n";
     for (int i = ; i < ; i++)
     {
         std::cout << "*";

     }
     std::cout << std::endl;

     high_resolution_clock::time_point t2 = high_resolution_clock::now();
     duration<double> time_span = duration_cast<duration<double>>(t2 - t);

     std::cout << "It tooks me " << time_span.count() << "seconds";
     std::cout << std::endl;

     return ;
 }

参考： http://www.cplusplus.com/reference/chrono/high_resolution_clock/now/