如何在没有boost :: timer的情况下以毫秒为单位计时

Question

我正在使用boost 1.46，它不包括boost :: timer，还有什么方法可以计算我的功能。

我目前正在这样做：

time_t now = time(0);
<some stuff>
time_t after = time(0);

cout << after - now << endl; 

但它只是在几秒钟内给出答案，所以如果函数小于1，则显示0。

谢谢

Answer 1

在linux或Windows中：

#include <ctime>
#include <iostream>

int
main(int, const char**)
{
     std::clock_t    start;

     start = std::clock();
     // your test
     std::cout << "Time: " << (std::clock() - start) / (double)(CLOCKS_PER_SEC / 1000) << " ms" << std::endl;
     return 0;
}

祝好运 ;）

Answer 2

使用std::chrono ：

#include <chrono>
#include <thread>
#include <iostream>

// There are other clocks, but this is usually the one you want.
// It corresponds to CLOCK_MONOTONIC at the syscall level.
using Clock = std::chrono::steady_clock;
using std::chrono::time_point;
using std::chrono::duration_cast;
using std::chrono::milliseconds;
using namespace std::literals::chrono_literals;
using std::this_thread::sleep_for;

int main()
{
    time_point<Clock> start = Clock::now();
    sleep_for(500ms);
    time_point<Clock> end = Clock::now();
    milliseconds diff = duration_cast<milliseconds>(end - start);
    std::cout << diff.count() << "ms" << std::endl;
}

std::chrono是C ++ 11， std::literals是C ++ 14（否则你需要milliseconds(500) ）。

Answer 3

原来有一个版本的时间在boost 1.46（只是在不同的位置）。 感谢@jogojapan指出它。

它可以这样做：

#include <boost/timer.hpp>

timer t;
<some stuff>
std::cout << t.elapsed() << std::endl;

或者使用std libs作为@Quentin Perez指出（我会接受最初的问题）

Answer 4

在Quentin Perez的解决方案的基础上，您可以使用std :: function和lambda将任意函数传递给时间。

#include <ctime>
#include <iostream>
#include <functional>

void timeit(std::function<void()> func) {
    std::clock_t start = std::clock();

    func();

    int ms = (std::clock() - start) / (double) (CLOCKS_PER_SEC / 1000);

    std::cout << "Finished in " << ms << "ms" << std::endl;
}

int main() {
    timeit([] {
        for (int i = 0; i < 10; ++i) {
            std::cout << "i = " << i << std::endl;
        } 
    });

    return 0;
}

Answer 5

您可以使用long将当前时间值保存为起始值，然后将当前时间转换为double。 这里有一些片段代码用作示例。

#include <iostream>
#include <stdlib.h>
#include <time.h>
#include <sys/types.h>
#include <sys/timeb.h>
int main()
{

struct      _timeb tStruct;
double      thisTime;
bool        done = false;
long        startTime;

 struct _timeb
 {
 int   dstflag;   // holds a non-zero value if daylight saving time is in effect
 long  millitm;   // time in milliseconds since the last one-second hack
 long  time;      // time in seconds since 00:00:00 1/1/1970
 long  timezone;  // difference in minutes moving west from UTC

 };

  _ftime(&tStruct); // Get start time

thisTime = tStruct.time + (((double)(tStruct.millitm)) / 1000.0); // Convert to double
startTime = thisTime;                                             // Set the starting time (when the function begins)


while(!done)     // Start an eternal loop
    {
    system("cls");  // Clear the screen
    _ftime(&tStruct);    // Get the current time
    thisTime = tStruct.time + (((double)(tStruct.millitm)) / 1000.0); // Convert to double
    // Check for 5 second interval to print status to screen
    cout << thisTime-startTime; // Print it. 

    }
}