Date: Wed, 7 Sep 2005 22:17:36 +0200
From: benedikt-grundmann at web.de
To: romildo at uber.com.br
Cc: lablgtk at math.nagoya-u.ac.jp
Subject: Re: Help in C interface
Message-ID: <20050907201736.GA4858 at localhost.localdomain>
References: <20050907192141.GA7177 at malaquias>
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Sender: benedikt-grundmann at web.de

Use OCaml's Bigarrays. Let me cite the manual:

Large, multi-dimensional, numerical arrays.

This  module  implements  multi-dimensional  arrays of integers and floating-point
numbers, thereafter referred to as  ``big  arrays''.   The  implementation  allows
efficient  sharing  of  large  numerical arrays between Caml code and C or Fortran
numerical libraries.


Cheers,

Bene

On Wed, Sep 07, 2005 at 04:21:41PM -0300, romildo@uber.com.br wrote:
> Hello.
> 
> I am just trying to build an OCaml interface to
> the gtkdatabox (http://www.eudoxos.de/gtk/gtkdatabox/)
> C library.
> 
> This library has the function:
> 
> gint gtk_databox_data_add (GtkDatabox * box, guint length, gfloat * X,
>                            gfloat * Y, GdkColor color,
>                            guint type, guint size);
> 
> which is used to add two arrays of float values
> (X and Y) to the list of data of the GtkDatabox
> (these are the data plotted by GtkDatabox).
> GtkDatabox will not copy or backup the data. The
> user has to make sure that X and Y pointers will
> stay valid until the data is removed from the
> GtkDatabox or until the user destroys the
> GtkDatabox itself.
> 
> I am having difficults in making an interface
> for this function in OCaml, because it seems
> that it is not possible to construct a C
> array in OCaml. So the two arrays would be
> constructed in C. Then I do not know how to
> control their lifetimes.
> 
> The following attempt is not good because
> of the memory leaks:
> 
> CAMLprim value ml_gtk_databox_data_add(value box,
> 				       value length, value X, value Y,
> 				       value color, value type, value size)
> {
>    const gint n = Int_val(length);
>    double vetx = malloc(n * sizeof float); // memory leak
>    double vety = malloc(n * sizeof float); // memory leak
>    int i;
>    for (i = 0; i < n; i++)
>       {
> 	 vetx[i] = Float_field(X,i);
> 	 vety[i] = Float_field(Y,i);
>       }
>    return Val_int(gtk_databox_data_add(GtkDatabox_val(box),
> 				       n, vetx, vety,
> 				       GdkColor_val(color),
> 				       Int_val(type),
> 				       Int_val(size)));
> }
> 
> Note this function can be made better, but
> the memory leak will be there.
> 
> Any clues on how to solve this problem?
> 
> Romildo