How to Achieve Millisecond Precision Timing in C on Linux Without Relying on clock()?

C : How to Obtain Milliseconds on Linux Without Clock() Limitations

Unlike Windows where clock() returns milliseconds, Linux's implementation rounds the result to the nearest 1000, resulting in second-level precision only. The need for millisecond-level timing prompts the question: Is there a standard C solution without using third-party libraries?

The Answer: gettimeofday()

The answer lies in the standard POSIX function gettimeofday(). This function provides high-precision timing information by populating a timeval structure with the current time. Here's a C example employing gettimeofday():

#include <sys/time.h>
#include <stdio.h>
#include <unistd.h>

int main()
{
    struct timeval start, end;

    long mtime, seconds, useconds;    

    gettimeofday(&start, NULL);
    usleep(2000);
    gettimeofday(&end, NULL);

    seconds  = end.tv_sec  - start.tv_sec;
    useconds = end.tv_usec - start.tv_usec;

    mtime = ((seconds) * 1000 + useconds/1000.0) + 0.5;

    printf("Elapsed time: %ld milliseconds\n", mtime);

    return 0;
}

This code demonstrates how to calculate the elapsed time in milliseconds by combining the seconds and microseconds components obtained from gettimeofday(). Note that the 0.5 addition is applied to round the result to the nearest integer.

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