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[Caml-list] closing file descriptors and channels
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Date: -- (:)
From: Christian Schaller <Christian.Schaller@s...>
Subject: [Caml-list] closing file descriptors and channels
Hi,

Can anyone tell me how to close a file descriptor successfully?  In the
code below

(* Append new line if condition cond is not satisfied on any line.
   Otherwise, raise exception and return the line that fulfills the
condition. *)
let append_line_cond file_name line cond = 
  let file_descr = Unix.openfile file_name [Unix.O_RDWR; Unix.O_APPEND]
0o644 in
  let ic = Unix.in_channel_of_descr file_descr in
  let oc = Unix.out_channel_of_descr file_descr in
  try
  (* Read line by line and check if condition is true.  If so, leave the
     function and return the line that satisfied the condition *)
  while true do 
    let line = input_line ic in
    if cond line
    then raise (Found line)
  done          
  with          
  End_of_file -> output_string oc (line ^ "\n");
  (* close all channels *)
  Unix.close file_descr;
  close_out oc;
  close_in ic

I get a Sys_error "Bad file descriptor".  As far as I figured out, the
problem is related with the creation of the two channels for input and
output.  If I comment out the Unix.close, everything works fine, but I
don't know if the file_descr will be automatically closed.  Hm...

Yet another closing-channels-question.  If I use streams instead of
reading a file line by line, where exactly do I have to close the
channel?  Is close_in on the right position below?

let read_lines ch =
  let read_new_line n =
    try Some (input_line ch)
    with End_of_file -> close_in ch in
  Stream.from read_new_line

Thank you so much, but working with files in OCaml is kind of pain in
the butt :(

Cheers,
  Chris

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