[Caml-list] input_line for zero-terminated strings

[Caml-list] input_line for zero-terminated strings

[Joel Reymont]

I'm trying to read C-style strings terminated with \0.

Does Pervasives.input_line provide the optimal implementation for me to clone?

    Thanks, Joel

---
let input_line ic =
  let buf = ref (string_create 128) in
  let pos = ref 0 in
  begin try
    while true do
      if !pos = string_length !buf then begin
        let newbuf = string_create (2 * !pos) in
        string_blit !buf 0 newbuf 0 !pos;
        buf := newbuf
      end;
      let c = input_char ic in
      if c = '\n' then raise Exit;
      !buf.[!pos] <- c;
      incr pos
    done
  with Exit -> ()
     | End_of_file -> if !pos = 0 then raise End_of_file
  end;
  let res = string_create !pos in
  string_blit !buf 0 res 0 !pos;
  res

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AW: [Caml-list] input_line for zero-terminated strings

[Gerd Stolpmann]

Am 07.06.2012 19:37:08 schrieb(en) Joel Reymont:
> I'm trying to read C-style strings terminated with \0.
> 
> Does Pervasives.input_line provide the optimal implementation for me  
> to clone?

Algorithmically, yes. I'd replace the manual buffer management (for  
buf) with a Buffer.t, though, because this is exactly what is done  
inside Buffer, and with inlining, the performance should be the same.  
(I guess Buffer can simply not be called from Pervasives, because it is  
defined later.)

The input_char is probably non-optimal here, because it is a C call,  
and cannot be inlined. If you afford to have your own input buffering  
this will even be better (I say "afford" because you will finally read  
beyond the last 0-terminated line, so do this only when you read until  
EOF).

Gerd


>     Thanks, Joel
> 
> ---
> let input_line ic =
>   let buf = ref (string_create 128) in
>   let pos = ref 0 in
>   begin try
>     while true do
>       if !pos = string_length !buf then begin
>         let newbuf = string_create (2 * !pos) in
>         string_blit !buf 0 newbuf 0 !pos;
>         buf := newbuf
>       end;
>       let c = input_char ic in
>       if c = '\n' then raise Exit;
>       !buf.[!pos] <- c;
>       incr pos
>     done
>   with Exit -> ()
>      | End_of_file -> if !pos = 0 then raise End_of_file
>   end;
>   let res = string_create !pos in
>   string_blit !buf 0 res 0 !pos;
>   res
> 
> --------------------------------------------------------------------------
> AlgoKit: EasyLanguage trading strategies, on the server, w/ Rithmic  
> R|API
> ---------------------+------------+---------------------------------------
> http://wagerlabs.com | @wagerlabs |  
> http://www.linkedin.com/in/joelreymont
> ---------------------+------------+---------------------------------------
> 
> --
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> 
> 



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Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
Creator of GODI and camlcity.org.
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Company homepage:       http://www.gerd-stolpmann.de
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