count execution time using clock() in milliseconds

[nik]

i have implemented an algorithm and the execution time is really small and when I use clock() I get a 0 as a result

is it possible to make clock() display results in milliseconds or even smaller like microseconds?

if yes, how is this possible? what parameters should I change?

all I do is

time_t before, after;

before = clock();

algorithm

after = clock();

time <- (double)(after-before)/CLOCKS_PER_SEC

i need to gather statistical data in seconds in order to see how my implementation reacts on different inputs

[brewbuck]

If you know the time in seconds, then surely the time in milliseconds is 1000 times that. Right?

[nik]

If you know the time in seconds, then surely the time in milliseconds is 1000 times that. Right?

the problem is that i dont know the time in seconds, it always returns 0

[brewbuck]

the problem is that i dont know the time in seconds, it always returns 0

Then the code you are trying to time is taking less than a single clock tick. That means clock() isn't going to be a good way of timing it.

On UNIX, you can use gettimeofday() to get better resolution. On Windows, you can use QueryPerformanceCounter().

[kmdv]

There is no standard way to do this. You need to use the functions mentioned or an external library.

[Mozza314]

Let me assure you it is possible to get really accurate time measurements (even more than microsecond resolution). I used them many times at a job I was working over the summer. You need to research tsc clocks and high frequency timers.

[novacain]

Let me assure you it is possible to get really accurate time measurements (even more than microsecond resolution). I used them many times at a job I was working over the summer. You need to research tsc clocks and high frequency timers.

Not on most MS OS systems, except CE.

Most of the time you will be +/- 50 msec, getting anywhere near a msec requires a filter driver (or realtime OS).

Both the methods you mention are unreliable, especially on multi core / variable speed CPUs.