# Ruby \<-SWIG-\> C arrays

**URL:** <https://www.ruby-forum.com/t/ruby-swig-c-arrays/75953>\
**Category:** Ruby\
**Created:** [November 14, 2006, 6:04pm UTC](https://www.ruby-forum.com/t/ruby-swig-c-arrays/75953 "2006-11-14T18:04:12Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![buendia](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/54ee81/32.png) [@buendia](https://www.ruby-forum.com/u/buendia)\
**Post date:** [November 14, 2006, 6:04pm UTC](https://www.ruby-forum.com/t/ruby-swig-c-arrays/75953/1 "2006-11-14T18:04:12Z")

</div>

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’?

---

<div class="post-metadata">

**Author:** ![buendia](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/54ee81/32.png) [@buendia](https://www.ruby-forum.com/u/buendia)\
**Post date:** [November 15, 2006, 10:51am UTC](https://www.ruby-forum.com/t/ruby-swig-c-arrays/75953/2 "2006-11-15T10:51:31Z")

</div>

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_nn39)

[http://www.swig.org/Doc1.3/Ruby.html#Ruby\_nn47](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

---

<div class="post-metadata">

**Author:** ![buendia](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/54ee81/32.png) [@buendia](https://www.ruby-forum.com/u/buendia)\
**Post date:** [November 15, 2006, 1:41pm UTC](https://www.ruby-forum.com/t/ruby-swig-c-arrays/75953/3 "2006-11-15T13:41:47Z")

</div>

Hi,

In [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
“Ruby \<-SWIG-\> C arrays” on Wed, 15 Nov 2006 02:04:14 +0900,  
Aureliano B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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,

---

<div class="post-metadata">

**Author:** ![buendia](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/54ee81/32.png) [@buendia](https://www.ruby-forum.com/u/buendia)\
**Post date:** [November 15, 2006, 3:52pm UTC](https://www.ruby-forum.com/t/ruby-swig-c-arrays/75953/4 "2006-11-15T15:52:20Z")

</div>

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