Re: [Swig-user] how can I return an array who's size is not static?

[William S F. <ws...@fu...>]

Valient Gough wrote:
> I'm creating a Java wrapper using Swig 1.3.29 and having some trouble
> with arrays.
> 
> I have a struct which contains a byte array, the size of which is not
> known at compile time.  I would like the regular get accessor to
> return a byte[].    I've reduced the code to a simple example:
> 
> test.h:
> typedef const char * buffer_p;
> struct Test
> {
> #ifdef SWIG
>     %immutable;
> #endif
>     buffer_p buf;
>     int bufSize;
> };
> 
> test.i:
> %module TestWrapper
> %{
> #include "test.h"
> %}
> %include "typemaps.i"
> %include "arrays_java.i"
> 
> %apply signed char[] { buffer_p }
> %include "test.h"
> 
> Then I run "swig -java test.i"
> 
> The problem here is that swig doesn't know the size of Test.buf.  It
> produces JNI code which contains the following in the buf_get method:
> 
> jresult = SWIG_JavaArrayOutSchar(jenv, result,
> FillMeInAsSizeCannotBeDeterminedAutomatically);
> 
> How can I tell SWIG that the size of Test.buf is Test.bufSize?
> 
> I figured my options would go something like:
> 1. replace the JNI code for buf_get.
>    I tried to use %native to replace the JNI code for Test_buf_get ,
> but then I get errors from swig saying that Test_buf_get is defined
> more then once.
> 2. somehow tell SWIG what the size is
>    I tried adding "%apply signed char [bufSize] { buf }" before the
> buf definition, but then I get an error message "test.h:8:
> Warning(453): Can't apply (signed char [Test::bufSize]). No typemaps
> are defined.
> "
> 3. post-process the wrapper function to fill in the FillMeIn...
> vars... Possible but ugly.
> 

Copy and modify the original typemap that is being used:

%typemap(out) signed char[]
%{$result = SWIG_JavaArrayOut##JFUNCNAME(jenv, $1,
FillMeInAsSizeCannotBeDeterminedAutomatically); %}

and put inbetween the %include "arrays_java.i" and %apply so that you
override the original typemap.

William