[Caml-list] Returning a file handle from C (fopen)

[Caml-list] Returning a file handle from C (fopen)

[Jeremy Cowgar]

Greetings,

I am trying to return a file handle from C. A simple Val_long does not
work, so I did some research and found something like the following:

  return caml_alloc_channel(caml_open_descriptor_out(myhandle));

This compiles (with 2 warnings):

  warning: implicit declaration of function `caml_alloc_channel'
  warning: implicit declaration of function `caml_open_descriptor_out'

However, the functions should be avaliable once running in ocaml, no?

Anyway, my real problem lies in the fact that when I do something like:

let fh = get_my_out_handle () in
Printf.fprintf fh "Hello, World!\n";;

nothing appears in my output file. No warning, errors or anything. In my
C source, I can do the exact thing and the contents are written.

Can anyone help me return a file handle from C to OCaml that can be used
with the OCaml output/input functions? I do realize a different type
would have to be returned for input/output. I was working on the output
portion first.

Thanks,

Jeremy Cowgar

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Re: [Caml-list] Returning a file handle from C (fopen)

[David Brown]

On Tue, Sep 21, 2004 at 06:06:20PM -0400, Jeremy Cowgar wrote:
> Greetings,
> 
> I am trying to return a file handle from C. A simple Val_long does not
> work, so I did some research and found something like the following:

You could just return the Val_long, and use Unix.out_channel_of_descr in
the ocaml world to get an ocaml channel.

Dave

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Re: [Caml-list] Returning a file handle from C (fopen)

[Eric C. Cooper]

On Tue, Sep 21, 2004 at 06:06:20PM -0400, Jeremy Cowgar wrote:
> I am trying to return a file handle from C. A simple Val_long does not
> work, so I did some research and found something like the following:
> 
>   return caml_alloc_channel(caml_open_descriptor_out(myhandle));
> [...] 
> Anyway, my real problem lies in the fact that when I do something like:
> 
> let fh = get_my_out_handle () in
> Printf.fprintf fh "Hello, World!\n";;
> 
> nothing appears in my output file. No warning, errors or anything. In my
> C source, I can do the exact thing and the contents are written.

Have you called either flush or close_out on your handle?  The OCaml
channel values add a layer of buffering, similar to C stdio, on top of
the file descriptor.

-- 
Eric C. Cooper          e c c @ c m u . e d u

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