计算时间间隔（高精度）

#include 
#include 
#include 
#include 

using namespace std;

int main(){
    auto beginTime = std::chrono::high_resolution_clock::now();
    sleep(5);
    auto endTime = std::chrono::high_resolution_clock::now();
    auto elapsedTime = std::chrono::duration_cast(endTime-beginTime);

    double programTimes = ((double) elapsedTime.count());
    std::cout << "time: ";
  	std::cout << programTimes << std::endl;
}