Re: Boost::Python

From: daveh-lists_at_[hidden]
Date: 2001-10-01 09:03:50

Another method that I have used is to create a class interface to 
your buffer which includes a copy constructor, maybe something along 
these lines (This is not complete, just for an idea):

class AccessBuffer
{
public:
  AccessBuffer(const void *pData) : m_pData(pData)
  {
  }
  AccessBuffer(const AccessBuffer &rBuffer)
  {
    m_pData = rBuffer.m_pData;
  }
  AccessBuffer &operator=(const AccessBuffer &rBuffer)
  {
    m_pData = rBuffer.m_pData;
    return *this;
  }
  // Add your data manipulation functions here
  unsigned char GetByte(int n)
  {
    return ((const unsigned char *)m_pData)[n];
  }
private:
  const void *m_pData;
};

Then you just need to declare the class and the data manipulation 
methods in boost and pass a reference (not pointer) to this class in 
your function call.

I have successfully used boost::python to support embedding python 
and have objects that simultaneously exist (can be called from) in 
python and c++ and that have virtual methods that can be overriden in 
python.

Dave Hawkes

--- In boost_at_y..., "David Abrahams" <david.abrahams_at_r...> wrote:
> Mike,
> 
> First of all, you'll need to pick a different interface 
for "function" (or
> wrap a different function and have it call your function), because
> Boost.Python can only convert a single Python object into a single 
function
> parameter.
> 
> Probably the easiest thing you can do is to write a function taking 
a
> boost::python::ref (which is kind of a smart pointer to a 
PyObject), and
> just use the regular Python 'C' API to extract the buffer data.
> 
> If you want to get fancier, you could create a type which 
corresponds to a
> Python buffer (perhaps struct my_buffer { void* data; int size; };) 
and
> write a family of from_python(PyObject*, type<buffer>) functions 
which check
> the argument type and convert Python buffers into your buffer type. 
You can
> look at boost/python/conversions.hpp for some examples. That would 
allow you
> to automatically wrap functions which accept my_buffer arguments.
> 
> HTH,
> Dave
> 
> ===================================================
>   David Abrahams, C++ library designer for hire
>  resume: http://users.rcn.com/abrahams/resume.html
> 
>         C++ Booster (http://www.boost.org)
>           email: david.abrahams_at_r...
> ===================================================
> 
> ----- Original Message -----
> From: "Mike Ensor" <MikeEnsor_at_C...>
> To: <boost_at_y...>
> Sent: Saturday, September 29, 2001 7:47 PM
> Subject: [boost] Boost::Python
> 
> 
> > I am using Boost.Python to build c++ to python wrappers.  I am
> > trying to make binary data available to python and visa versa.  I 
have
> tried
> > many different approaches.  The functions in C++ look similar to 
this:
> >
> > void function(const void* buffer, int size);
> >
> > and in python I can create a "buffer" of information.  When I 
check
> > the type of the "buffer" it is a "buffer".
> >
> > When I compile the c++ it won't let me because "none of the 425
> > overloads can convert prameter 2 from type 'struct
> boost::python::type<void
> > const*>'"
> >
> > How do I make the const void * be seen in Python and how do I send
> > in binary data into this function from python?
> >
> > Thank you for your help,
> > Mike Ensor
> > mikeensor_at_c...
> >
> >
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