How to measure time in milliseconds using ANSI C?

Using only ANSI C, is there any way to measure time with milliseconds precision or more? I was browsing time.h but I only found second precision functions.

The best precision you can possibly get is through the use of the x86-only "rdtsc" instruction, which can provide clock-level resolution (ne must of course take into account the cost of the rdtsc call itself, which can be measured easily on application startup).

The main catch here is measuring the number of clocks per second, which shouldn't be too hard.

I always use the clock_gettime() function, returning time from the CLOCK_MONOTONIC clock. The time returned is the amount of time, in seconds and nanoseconds, since some unspecified point in the past, such as system startup of the epoch.


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

int64_t timespecDiff(struct timespec *timeA_p, struct timespec *timeB_p)
{
return ((timeA_p->tv_sec * 1000000000) + timeA_p->tv_nsec) -
((timeB_p->tv_sec * 1000000000) + timeB_p->tv_nsec);
}

int main(int argc, char **argv)
{
struct timespec start, end;
clock_gettime(CLOCK_MONOTONIC, &start);

// Some code I am interested in measuring

clock_gettime(CLOCK_MONOTONIC, &end);

uint64_t timeElapsed = timespecDiff(&end, &start);
}

#include <time.h>
clock_t uptime = clock() / (CLOCKS_PER_SEC / 1000);

Under windows:

SYSTEMTIME t;
GetLocalTime(&t);
swprintf_s(buff, L"[%02d:%02d:%02d:%d]\t", t.wHour, t.wMinute, t.wSecond, t.wMilliseconds);

There is no ANSI C function that provides better than 1 second time resolution but the POSIX function [`gettimeofday`][1] provides microsecond resolution. The clock function only measures the amount of time that a process has spent executing and is not accurate on many systems.

You can use this function like this:

struct timeval tval_before, tval_after, tval_result;

gettimeofday(&tval_before, NULL);

// Some code you want to time, for example:
sleep(1);

gettimeofday(&tval_after, NULL);

timersub(&tval_after, &tval_before, &tval_result);

printf("Time elapsed: %ld.%06ld\n", (long int)tval_result.tv_sec, (long int)tval_result.tv_usec);

This returns `Time elapsed: 1.000870` on my machine.

[1]:

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