With the "%.*s" format you need no null at the end. It just counts out the characters:

    #include <stdio.h>

    void main()
    {
      char buff[10] = {'R', 'o', 'b', 'o', 't', 't', 'y', 'p', 'e', 's'};
      printf("=>%.*s<=", 4, ((char *)&buff + 3));
    }

prints

    =>otty<=