This small program prints a timestamp with milliseconds included

formattedtime.c

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

void printTime()
{
    char buffer[32];
    struct timeval timevalue;
    struct tm *timeinfo;

    gettimeofday(&timevalue, NULL);
    timeinfo = localtime(&timevalue.tv_sec);

    strftime(buffer, 32, "%Y.%m.%d-%H.%M.%S.%03d", timeinfo);
    // adding milliseconds to it
    sprintf(buffer, buffer, timevalue.tv_usec / 1000);

    puts(buffer);
}

int main(int argc, char *argv[])
{
    printTime();
    return 0;
}