Ruby <-SWIG-> C arrays

Ruby
1

Hi,

I am trying to wrap this function is C ro Ruby using SWIG:

typedef unsigned long uInt32
someFunction(uInt32 someArray[])

The array is simply some input. Calling the wrapped function in Ruby:

Wrapper.someFunction([1, 2, 3])

produces this error:

…in method ‘someFunction’, argument 1 of type ‘uInt32 []’ (TypeError)

Does this have anything to do with the argument being defined as ‘uInt32
someArray[]’ and not ‘uInt32 *someArray’?

2

Aureliano B. wrote:

typedef unsigned long uInt32
someFunction(uInt32 someArray[])

The array is simply some input. Calling the wrapped function in Ruby:

Wrapper.someFunction([1, 2, 3])

produces this error:

…in method ‘someFunction’, argument 1 of type ‘uInt32 []’ (TypeError)

It looks like you require some typemap here to convert a ruby array of
integers to a C array of longs. You probably want %typemap(in), which
mangles Ruby function/method params to something that the C function can
digest.

Your %typemap(in) will use the RARRAY($input)->len Ruby C macro to get
the length of the incoming ruby array. $input is a placeholder for the
ruby parameter being processed. Create a new empty uInt32[].

Then, for each element in the Ruby array use the NUM2LONG macro to
convert the Ruby integer to a C long, and add this to your uInt32[].
Lastly, assign the uInt32 to the special variable $1, which is a
placeholder for the actual value that will be passed to the C function.
SWIG will generate the appropriate wrapper code.

You will want to verify the types of the arguments passed in from ruby,
using TYPE and T_ARRAY etc macros.

Suggest you re-read the following sections of the Ruby/SWIG
documentation should be useful:

http://www.swig.org/Doc1.3/Ruby.html#Ruby_nn39

http://www.swig.org/Doc1.3/Ruby.html#Ruby_nn47

Sorry I can’t give you a complete example, but I’m not a C programmer,
just familiar with SWIG. Hopefully this will get you started.

alex

3

Hi,

In [email protected]
“Ruby <-SWIG-> C arrays” on Wed, 15 Nov 2006 02:04:14 +0900,
Aureliano B. [email protected] wrote:

typedef unsigned long uInt32
someFunction(uInt32 someArray[])

The array is simply some input. Calling the wrapped function in Ruby:

Wrapper.someFunction([1, 2, 3])

produces this error:

Here is a my answer:

%module “Example”;

%inline %{
typedef unsigned long uInt32;
%}

%typemap(in, numinputs=1) (uInt32 some_array[], int length)
{
int i;

$2 = RARRAY($input)->len;
$1 = ALLOCA_N(uInt32, $2);

for (i = 0; i < $2; i++) {
  $1[i] = NUM2INT(RARRAY($input)->ptr[i]);
}

};

%inline %{
uInt32
some_function(uInt32 some_array[], int length) {
int i;
uInt32 sum = 0;
for (i = 0; i < length; i++) {
sum += some_array[i];
}
return sum;
}
%}

Compile:
% swig -ruby a.i && ruby -r mkmf -e ‘create_makefile(“Example”)’ &&
make

Test:
% ruby -r Example -e ‘p Example.some_function([1, 2, 3])’
6

Thanks,

4

Kouhei S. wrote:

Note that RARRAY(x)->len is going away in future versions of Ruby. Use
RARRAY_LEN(x) if you can. If you don’t have it defined you can always
supply it:

#ifndef RARRAY_LEN

define RARRAY_LEN(x) RARRAY(x)->len

#endif

Roy