Get time in milliseconds on Windows

Question

I need a way to get the time in a high precision (milliseconds or microseconds) for a PRNG algorithm I'm writing in C (C11), as time(0) is not precise enough.

I tried using several other possible solutions, which I found on StackOverflow, but none of them worked for me.

Anyways my problem is now fixed, with the help of the code @dbush provided

@Scott Hunter Technically all of them worked, but I would always get 0 as a time difference, due to my program running too quickly — ChaoticSomeone, Feb 08 '23 at 15:10
Normally, you'd get time and seed your PRNG once at the start of your program, not repeatedly. Or is the process stopping and starting multiple times per second? — Ruud Helderman, Feb 08 '23 at 15:15
@Ruud Helderman My PRNG works a bit differently, as I have a ```randint``` function, which generates a random integer based of the elapsed time — ChaoticSomeone, Feb 08 '23 at 15:19
ChaoticSomeone, "on Windows" --> It is a compiler issue, not an OS one. What compiler? — chux - Reinstate Monica, Feb 08 '23 at 15:19
Does this answer your question? [Getting the current time (in milliseconds) from the system clock in Windows?](https://stackoverflow.com/questions/1695288/getting-the-current-time-in-milliseconds-from-the-system-clock-in-windows) — vandench, Feb 08 '23 at 15:42
@van dech my problem has already been solved. Thanks anyways — ChaoticSomeone, Feb 08 '23 at 15:43
@SevaAlekseyev I suspect OP's interest in high precision time is not reinventing PRNG, but seeding it. — chux - Reinstate Monica, Feb 08 '23 at 15:44
ChaoticSomeone, you appear now to have a way to get a high precision time, yet how you use it for a PRNG may be questionable. Yet since that use is not posted, the real issue is not truly well solved. — chux - Reinstate Monica, Feb 08 '23 at 15:48
From the comment: "I have a randint function, which generates a random integer based of the elapsed time". Looks like it's not just a seed. — Seva Alekseyev, Feb 08 '23 at 18:13

dbush · Accepted Answer · 2023-02-08T15:15:16.930

2

You can use the GetSystemTimeAsFileTime function, which gives you the current time in 100ns intervals since 1/1/1601 UTC.

FILETIME ft;
uint64_t ts;
GetSystemTimeAsFileTime(&ft);

ts = 0;
ts |= ft.dwHighDateTime;
ts <<= 32;
ts |= ft.dwLowDateTime;

Note that the system clock is most likely not that precise, so don't expect 100ns granularity.

Another option is QueryPerformanceCounter, which will give you microsecond intervals from an undetermined starting point:

LARGE_INTEGER ticks;
QueryPerformanceCounter(&ticks);
uint64_t ts = ticks.QuadPart;

edited Feb 08 '23 at 15:15

answered Feb 08 '23 at 15:09

dbush

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How is ```uint64_t``` a datatype? I get the error: Use of undeclared identifier 'uint64_t' – ChaoticSomeone Feb 08 '23 at 15:16
1

@ChaoticSomeone You'll need to `#include `. – dbush Feb 08 '23 at 15:18
Now I don't get an error but I still get the same results in my for-loop – ChaoticSomeone Feb 08 '23 at 15:24
@ChaoticSomeone Try both options, and try printing the resulting vaule to see how much it changes between invocations. – dbush Feb 08 '23 at 15:27
what format specifier is it for ```uint64_t```? – ChaoticSomeone Feb 08 '23 at 15:31
@ChaoticSomeone `%I64u` – dbush Feb 08 '23 at 15:33
my results are: 133203440785961221(called before the loop), 5219627056065(called after the loop) – ChaoticSomeone Feb 08 '23 at 15:35
As of now I got my program to generate random numbers using the 2 code snippets provided by you. Thanks a lot! – ChaoticSomeone Feb 08 '23 at 15:41
`"%"PRIu64` is standard and portable (from `inttypes.h`). – Lundin Feb 08 '23 at 15:55
If possible, it would seem better to use `GetSystemTimePreciseAsFileTime` which should have greater precision (<1us according to the [docs](https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimepreciseasfiletime)) than `GetSystemTimeAsFileTime`. – Iridium Feb 08 '23 at 16:19

score 1 · Answer 2 · answered Feb 08 '23 at 15:13

1

Starting from C11, you can use struct timespec and timespec_get to get the same value as time(NULL) in seconds and nanoseconds:

#include <stdio.h>
#include <time.h>

int main(void)
{
    struct timespec ts;
    timespec_get(&ts, TIME_UTC);
    printf("Time since epoch: %ld seconds, %ld nanoseconds", ts.tv_sec, ts.tv_nsec);
}

answered Feb 08 '23 at 15:13

mediocrevegetable1

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This code just raises an error – ChaoticSomeone Feb 08 '23 at 15:15
@ChaoticSomeone can you tell what exactly the error is? I have tested and the program seems to work fine for me. – mediocrevegetable1 Feb 08 '23 at 15:18
Call to undeclared function 'timespec_get'; ISO C99 and later do not support implicit function declarations – ChaoticSomeone Feb 08 '23 at 15:19
Use of undeclared identifier 'TIME_UTC' – ChaoticSomeone Feb 08 '23 at 15:20
1

@ChaoticSomeone the only explanation I can think of is that your compiler doesn't fully conform with C11. Can you tell what compiler you're using and the version? – mediocrevegetable1 Feb 08 '23 at 15:24
Don't know about what compiler I'm using, I don't even know where to find that out, but in my CMakeLists it says version 3.23 – ChaoticSomeone Feb 08 '23 at 15:28
@ChaoticSomeone are you using Visual Studio? If not then I'm assuming you're using MinGW. – mediocrevegetable1 Feb 08 '23 at 15:31
I use CLion as my IDE – ChaoticSomeone Feb 08 '23 at 15:32
@ChaoticSomeone I'm fairly CLion only partially supports C11, and from what I can tell that doesn't include the C11 time utilities. If you want to use C11 fully and properly, you may want to switch. – mediocrevegetable1 Feb 08 '23 at 15:35
I will consider switching to a different IDE – ChaoticSomeone Feb 08 '23 at 15:38

Get time in milliseconds on Windows

2 Answers2