Re: [Swig-user] passing Python buffer/string to C++ function as void *

[Haoyu B. <div...@gm...>]

On Fri, Aug 28, 2009 at 1:45 AM, Angus McMorland<am...@gm...> wrote:
> 2009/8/26 Josh Cherry <jc...@nc...>:
>> On Wed, 26 Aug 2009, Angus McMorland wrote:
>>
>>> I'm not sure that we're looking for an integer representation: in
>>> Python, SWIG's ".this" attribute is a <Swig Object of type
>>> 'MDF_TEST_DATA *' at ...>, which seems like some special thing that
>>> swig uses to keep track of its objects. I looked inside the swig
>>> wrapper code, to see how ".this" was generated, but it comes from the
>>> binary .so generated during the swig build, so I follow that lead any
>>> further.
>>
>> I had in mind, in the crudest form, something like this:
>>
>> %inline %{
>>    void *void_ptr(long long n) {
>>        return (void *) n;
>>    }
>> %}
>>
>> Adding a bit of code with %pythoncode could hide this all from your users,
>> so they can just pass the ctypes pointer (they wouldn't even need to pass
>> the size; the Python code could get that from the ctypes pointer).
>>
>> Josh
>
> I just want to say a public "big thanks, Josh". That void_ptr code
> snippet was just what I needed. With it, and a dash of %pythoncode to
> wrap the copying of data to and from the ctypes structures (as you
> suggested), everything works seamlessly, without the need for lots of
> boilerplate code for each data type.
>
> Angus.
> --
> AJC McMorland
> Post-doctoral research fellow
> Neurobiology, University of Pittsburgh
>

Hi,

FYI, do you aware there's SWIG's support for Python buffer protocol
(http://www.swig.org/Doc1.3/Python.html#Python_nn75)? This should be
able to used for any Python types that support the buffer protocol,
eg., string, unicode. But I'm not sure whether it is suitable for your
case.

-- 
Haoyu BAI
School of Computing,
National University of Singapore.