I have to compute execution time of a C++ code snippet in seconds. It must be working either on Windows or Unix machines.
I use code the following code to do this. (import before)
clock_t startTime = clock();
// some code here
// to compute its execution duration in runtime
cout << double( clock() - startTime ) / (double)CLOCKS_PER_SEC<< " seconds." << endl;
However for small inputs or short statements such as a = a + 1, I get "0 seconds" result. I think it must be something like 0.0000001 seconds or something like that.
I remember that System.nanoTime() in Java works pretty well in this case. However I can't get same exact functionality from clock() function of C++.
Do you have a solution?
You can use this function I wrote. You call GetTimeMs64(), and it returns the number of milliseconds elapsed since the unix epoch using the system clock - the just like time(NULL), except in milliseconds.
It works on both windows and linux; it is thread safe.
Note that the granularity is 15 ms on windows; on linux it is implementation dependent, but it usually 15 ms as well.
#ifdef _WIN32
#include <Windows.h>
#else
#include <sys/time.h>
#include <ctime>
#endif
/* Remove if already defined */
typedef long long int64; typedef unsigned long long uint64;
/* Returns the amount of milliseconds elapsed since the UNIX epoch. Works on both
* windows and linux. */
uint64 GetTimeMs64()
{
#ifdef _WIN32
/* Windows */
FILETIME ft;
LARGE_INTEGER li;
/* Get the amount of 100 nano seconds intervals elapsed since January 1, 1601 (UTC) and copy it
* to a LARGE_INTEGER structure. */
GetSystemTimeAsFileTime(&ft);
li.LowPart = ft.dwLowDateTime;
li.HighPart = ft.dwHighDateTime;
uint64 ret = li.QuadPart;
ret -= 116444736000000000LL; /* Convert from file time to UNIX epoch time. */
ret /= 10000; /* From 100 nano seconds (10^-7) to 1 millisecond (10^-3) intervals */
return ret;
#else
/* Linux */
struct timeval tv;
gettimeofday(&tv, NULL);
uint64 ret = tv.tv_usec;
/* Convert from micro seconds (10^-6) to milliseconds (10^-3) */
ret /= 1000;
/* Adds the seconds (10^0) after converting them to milliseconds (10^-3) */
ret += (tv.tv_sec * 1000);
return ret;
#endif
}