Generating array of unique random numbers in C

I am writing a function that is supposed to populate an array with random numbers from 0 to n (where n is passed argument to the function), but all numbers in array should be unique. I basically need to shuffle the array of numbers from 0 to n

I found this answer here: Unique random numbers in an integer array in the C programming language

And used the "Knuth Algorithm" suggested by user:

void generate_random_array(int count)
{
  int in, im;

  im = 0;
  srand(time(NULL));

  for (in = 0; in < count && im < count; ++in) {
    int rn = count - in;
    int rm = count - im;
    if (rand() % rn < rm) random_array[im++] = in; 
  }
}

However this function does not generate random numbers for me at all, its simply creates an array of numbers from 0 to count. How can I generate the actual random sequence of unique numbers.