Question

How to truncate file to size N in ocaml ?

I don’t see a function in Pervasive. The closest thing is “open_trunc” flag which I’m not really sure what it does.

Answer 1

If you’re under Unix, you can use

val Unix.truncate : string -> int -> unit

It “runcates the named file to the given size”.
But this function is not implemented in the Windows version of OCaml (or more precisely, it is not emulated).

If you’re under Windows and want to emulate it, you might be interested in

val really_input : in_channel -> string -> int -> int -> unit

“really_input ic buf pos len reads len characters from channel ic, storing them in string buf, starting at character number pos. Raise End_of_file if the end of file is reached before len characters have been read. Raise Invalid_argument "really_input" if pos and len do not designate a valid substring of buf.”