From: Tobias Peters <tpeters@...>
Date: 2004-11-21T22:58:07+09:00
Subject: Re: SWIG and Arrays (of ints)

Kurt Dresner wrote:
> Hi all,
> 
> I'm trying to get SWIG to create a wrapper for some C code.
> Specifically, there are several functions that take, as parameters, an
> int* (they also take the length of the array).  I don't know how to do
> the typemap for this - I want to be able to write
> 
> My_module.my_c_function([1,2,3])
> 
> for the corresponding C function
> 
> void my_c_function(int size, int* ary)
> 
> Additionally, one of the functions takes an integer array as a
> parameter, and I'd like it instead to return an array in Ruby (full of
> Nums).  I know how to get it to return the argument (instead of doing
> the pointer passing thing), but then it just thinks I want to pass it
> an integer instead of an array of integers.
> 
> Anyone have any idea how to help me? Everything I've seen pertains to
> char** and I'm not sure how to convert it to work how I want with
> int*.

Passing an array of integers from Ruby to C with SWIG requires 
multi-argument "in" and "freearg" typemaps:

%typemap(ruby,in) (int size, int *ary) {
   int i;
   if (!rb_obj_is_kind_of($input,rb_cArray))
     rb_raise(rb_eArgError, "Expected Array of Integers");
   $1 = RARRAY($input)->len;
   $2 = malloc($1*sizeof(int));
   for (i=0; i<$1; ++i)
     ($2)[i] = NUM2INT(RARRAY($input)->ptr[i]);
}
%typemap(freearg) (int size, int *ary) {
    if ($2) free($2);
}

There's room for improvement in handling (or better: preventing) 
exceptions raised from NUM2INT (proper error message and deallocation of 
C array).

Regarding output: It's not clear to me if you want in/out semantics or 
output only. I think you can achieve in/out with an additional 
multi-argument "argout" typemap. Output only implementation depends on 
which function is responsible for allocating/freeing the array and which 
is responsible for determining the array's size. You may need an 
additional "arginit" typemap for this one.

   Tobias