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Re: [Discuss-gnuradio] Exporting C++ hier_block2s via SWIG

From: Martin Braun
Subject: Re: [Discuss-gnuradio] Exporting C++ hier_block2s via SWIG
Date: Mon, 23 Feb 2009 21:21:11 +0100
User-agent: Mutt/1.5.17 (2007-11-01)

On Mon, Feb 23, 2009 at 05:18:57PM +0100, Martin Braun wrote:
> I was wondering if it's possible to write a gr_hier_block2 in C++ and
> then export it to SWIG just like the the gr_blocks are.
> [...]
> Is there any easy way to do this? Basically, what I want is a
> GR_SWIG_HIERBLOCK_MAGIC() function, I suppose.
> Has anyone done something like this before?

I had a bash at it (not very elegant, though), and tried copying
gnuradio-core/src/lib/swig/gr_swig_block_magic.i into my own i-file. I
then simply modified everything from gr_block to gr_hier_block2. It now
looks like this (slightly truncated for readability):

<<<<< CODE >>>>>
%include "gnuradio.i"

#include "specest_welch.h"

// ----------------------------------------------------------------
class specest_welch;
typedef boost::shared_ptr<specest_welch> specest_welch_sptr;
%template(specest_welch_sptr) boost::shared_ptr<specest_welch>;
%rename(welch) specest_make_welch;
%inline {
  gr_hier_block2_sptr specest_welch_block (specest_welch_sptr r)
    return gr_hier_block2_sptr(r);

%pythoncode %{
specest_welch_sptr.block = lambda self: specest_welch_block(self)
specest_welch_sptr.__repr__ = lambda self: "<gr_hier_block2 %s (%d)>" %
(self.name(), self.unique_id ())

%ignore specest_welch;

specest_make_welch(unsigned fft_len, int overlap = -1, int ma_len = 8)

class specest_welch : public gr_hier_block2
<<<<< CODE >>>>>

It kind of works, but not as smoothly as I could. Here's an example
python session:

<<<<< COMMAND LINE >>>>>>
[insfl4:gnuradio]% python
Python 2.5.2 (r252:60911, Jul 31 2008, 17:31:22)
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from gnuradio import specest
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.5/site-packages/gnuradio/specest.py",
line 6, in <module>
    import _specest
/usr/local/lib/python2.5/site-packages/gnuradio/_specest.so: undefined
symbol: _ZN14gr_hier_block24lockEv
>>> from gnuradio import gr,specest
<<<<< COMMAND LINE >>>>>>

As you can see, I get an error when I only import specest, but not if
import gr and specest. Yep, I'm a nitpicker, but if I run 'from gnuradio
import trellis', I don't get this behaviour, so there must be a bug
somewhere down the line. If there's some SWIG experts out there, I'd
appreciate any advice, but this is already a good enough start for me.


Dipl.-Ing. Martin Braun           Phone: +49-(0)721-608 3790
Institut fuer Nachrichtentechnik  Fax:   +49-(0)721-608 6071
Universitaet Karlsruhe (TH)       http://www.int.uni-karlsruhe.de/

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