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[Caml-list] Apparent I/O bug
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Date: -- (:)
From: Xavier Leroy <xavier.leroy@i...>
Subject: Re: [Caml-list] Apparent I/O bug
> I have encountered what appears to be a bug in out_channels created with
> Pervasives.open_out_gen:
> 
>   bash-2.05a$ ocaml
>           Objective Caml version 3.07+2
>   
>   # let oc = open_out_gen [Open_creat; Open_text] 0o644 "/var/tmp/foo";;
>   val oc : out_channel = <abstr>
>   # output_string oc "Fubar Baz\n";;
>   - : unit = ()
>   # close_out oc;;
>   Exception: Sys_error "Bad file descriptor".
> 
> Well, that's disturbing. Or is there something I don't understand about
> the proper usage of open_out_gen (documentation problem?)?

In your call to open_out_gen, you didn't request write permission
(the list of flags doesn't contain "Open_wronly").  So, attempts to
write to the underlying file descriptor will fail.  Since out_channels
are buffered, the error isn't reported at the first output_string, but
only when an actual OS write takes place, i.e. at close_out in your example.

> BTW, I'm running OCaml on Debian GNU/Linux 3.0 (Woody), with glibc
> 2.2.5. I installed OCaml 3.07pl2 from source, with no apparent
> compilation errors. I am seeing the same problem on two similarly
> configured systems.

It is standard POSIX behavior.

- Xavier Leroy

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