Re: [Swig-user] argout typemap for dynamically sized array

[Bob H. <bh...@co...>]

On 8/16/2011 10:53 PM, tn...@fa... wrote:
> Say you have a function takes values from an array, transforms the value
> and stores it in another array, like 
>
>     void transform(const int k, const in[], int out[])
>     {
>         int i;
>         for (i=0; i<k; i++) 
>             out[i]=in[i]*2; // or whatever...
>     }
>
> I want to be able to call this function as (from perl in my case):
>
>     my $x = swigmod::transform([1,2,3,4]); # $x is now [2,4,6,8]
>
> I can't figure out how to accomplish this without having to manually
> write a C wrapper function, or forcing the scripting language user to
> pass an array preallocated with k elements.  I thought I could write
> something analogous to non-array argouts, like this:
>
>     %typemap(argout) double *OUTPUT {
>         $result = sv_2mortal(newSVnv(*$1));
>         argvi++;
>     }
>     
>     %typemap(in,numinputs=0) double *OUTPUT(double junk) {
>     	$1 = &junk;
>     }
>
> But for arrays, I would need to allocate an appropriately sized 'double
> * junk', which I can't do b/c I don't have access to the length from
> within the typemap code (I know I can access the length variable k with
> something like 'k_0' where 0 is the position of 'k', but that seems
> extremely dirty).  I would also need to know the length in the argout.  
>
> Any ideas?

I don't know if this will help, but there's a section in the documentation
that might be relevant in this case.  Have a look at some of the examples in
"10.9 Multi-argument typemaps".  That might get you where you want to be with
this.


Render me gone,                       |||
Bob                                 ^(===)^
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