UNIX & GNU/Linux - System calls - Using gettimeofday()

The system call function gettimeofday() is a really helpful one.

Indeed, we can retrieve milliseconds of the time.

But in this tutorial, we are going to see how to generate random numbers every millisecond.

Here the code:

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

int my_random()
{
    double seed;
    struct timeval  tv;

    gettimeofday(&tv, NULL);
    seed = (tv.tv_sec) * 1000 + (tv.tv_usec) / 1000;
    srand(seed);
    usleep(10000);
    return (rand() % 255);
}

int main ()
{
    int i = 0;

    while (i < 10)
    {
        printf("R = %d\n", my_random());
        ++i;
    }
    return (0);
}

Nice example of random every millisecond.