[Caml-list] getting fd behind a channel from C

[Caml-list] getting fd behind a channel from C

[Jeremy Fincher]

I can't for the life of me figure out how, from C, to take an in_channel and
get the file descriptor of it.  How do I write a C function that takes an
in_channel and then does some work on the underlying file descriptor?

Thanks,
Jeremy
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Re: [Caml-list] getting fd behind a channel from C

[Olivier Andrieu]

 Jeremy Fincher [Tuesday 4 September 2001] :
 >
 > I can't for the life of me figure out how, from C, to take an in_channel and
 > get the file descriptor of it.  How do I write a C function that takes an
 > in_channel and then does some work on the underlying file descriptor?

in the OCaml source tree, look at byterun/io.h : it contains
definitions and macros to access caml channels from C :

 - struct channel has a field fd for the file descriptor.
 - the macro Channel takes a Caml value and gives you a struct
   channel*

so (Channel(ml_channel))->fd does what you want.

There's also the Unix.descr_of_in_channel and
Unix.descr_of_out_channel functions.

			  Olivier
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Re: [Caml-list] getting fd behind a channel from C

[Jeremy Fincher]

I already found this, but there's no way to get to this from the standard
C/O'Caml interface.

Jeremy

> in the OCaml source tree, look at byterun/io.h : it contains
> definitions and macros to access caml channels from C :

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Re: [Caml-list] getting fd behind a channel from C

[Olivier Andrieu]

 Jeremy Fincher [Tuesday 4 September 2001] :
 > > in the OCaml source tree, look at byterun/io.h : it contains
 > > definitions and macros to access caml channels from C :
 > I already found this, but there's no way to get to this from the standard
 > C/O'Caml interface.

You just have to take the io.h from the OCaml tree, put with your C
files, #include it, at it works !

You can just keep the relevant parts :

<<<<< 
#ifndef IO_BUFFER_SIZE
#define IO_BUFFER_SIZE 4096
#endif

struct channel {
  int fd;                       /* Unix file descriptor */
  long offset;                  /* Absolute position of fd in the file */
  char * end;                   /* Physical end of the buffer */
  char * curr;                  /* Current position in the buffer */
  char * max;                   /* Logical end of the buffer (for input) */
  void * mutex;                 /* Placeholder for mutex (for systhreads) */
  char buff[IO_BUFFER_SIZE];    /* The buffer itself */
};

#define Channel(v) (*((struct channel **) (Data_custom_val(v))))
>>>>>


       Oliv
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