yjc01@doc.ic.ac.uk wrote:
> The code I came up with is as follows: 

I forgot to add, there is no reason to use a reference for buff:

> 
> open Unix;;
> 
> let file_reader = openfile "sudent.cd" [O_RDONLY] 0o640;;
> let buff = ref "empty";;

let buff = "empty";;

> 
> let main () =
>   let file_content = read file_reader !buff 1 5 in

let file_content = read file_reader buff 0 5 in

>   print_int file_content;
>   print_string !buff;;

print_string buff;;

> main ();

This is because you are actually writing directly on the string, so 
there is no need for indirection.