c – 如何以毫秒为单位获取当前时间?

我是C的新手,我对它的图书馆知之甚少.我需要对不同的排序算法进行时间分析,为此我需要以毫秒为单位获取当前时间.有没有办法做到这一点?
只需使用std::chrono.一般示例下面是“打印1000颗星”的任务:

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

int main ()
{
  using namespace std::chrono;

  high_resolution_clock::time_point t1 = high_resolution_clock::now();

  std::cout << "printing out 1000 stars...\n";
  for (int i=0; i<1000; ++i) std::cout << "*";
  std::cout << std::endl;

  high_resolution_clock::time_point t2 = high_resolution_clock::now();

  duration<double, std::milli> time_span = t2 - t1;

  std::cout << "It took me " << time_span.count() << " milliseconds.";
  std::cout << std::endl;

  return 0;
}

您不必打印星星,而是将排序算法放在那里,并按时间测量它.

如果您打算进行一些基准测试,请不要忘记为编译器启用优化标志,例如:对于,你需要-O3.这很严重,检查我没有这样做时发生了什么:Why emplace_back is faster than push_back?

Ps:如果您的编译器不支持,那么您可以查看我的Time Measurements (C++)中的其他方法.

使用我的Quicksort (C++)的特定(玩具)示例将是:

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

void quickSort(int a[], int first, int last);
int pivot(int a[], int first, int last);
void swap(int& a, int& b);
void swapNoTemp(int& a, int& b);

using namespace std;
using namespace std::chrono;

int main()
{
    int test[] = { 7, -13, 1, 3, 10, 5, 2, 4 };
    int N = sizeof(test)/sizeof(int);

    cout << "Size of test array :"  << N << endl;

    high_resolution_clock::time_point t1 = high_resolution_clock::now();

    // I want to measure quicksort
    quickSort(test, 0, N-1);

    high_resolution_clock::time_point t2 = high_resolution_clock::now();

    duration<double> time_span = t2 - t1;

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

    return 0;
}

现在的输出是:

Georgioss-MacBook-Pro:~ gsamaras$g++ -Wall -std=c++11 -O3 main.cpp 
Georgioss-MacBook-Pro:~ gsamaras$./a.out 
Size of test array :8
It took me 3.58e-07 seconds.

就这么简单.快乐的基准! =)

编辑:

high_resolution_clock::now() function returns time relative to which time?

std::chrono开始:

Time points

A reference to a specific point in time, like one’s
birthday, today’s dawn, or when the next train passes. In this
library, objects of the time_point class template express this by
using a duration relative to an epoch (which is a fixed point in time
common to all time_point objects using the same clock).

可以检查这个epoch and time_point example哪个输出:

time_point tp is: Thu Jan 01 01:00:01 1970
翻译自:https://stackoverflow.com/questions/41077377/how-to-get-current-time-in-milliseconds

转载注明原文:c – 如何以毫秒为单位获取当前时间?