Hello,
I wonder if someone could help me with a tricky conversion between c++
and python types (well, tricky for me!)
I have a c++ library that I would like to use in python via Boost::Python
One function fills a c++ unsigned char* buffer. It has two overloads:
unsigned char * getPixels(int deviceID);
bool getPixels(int id, unsigned char * pixels);
How would I go about getting that data into a python object, a string in
particular? I seem to face several problems:
/////////////////////////
1) unsigned char* does not have a to_python converter to Py_String.
I tried this:
struct uchar_ptr_to_str
{
static PyObject* convert(unsigned char* p)
{
return incref( str(p).ptr());
}
static PyTypeObject const *get_pytype () {return &PyString_Type; }
};
struct uchar_to_str
{
static PyObject* convert(unsigned char& p)
{
return incref( str(p).ptr());
}
static PyTypeObject const *get_pytype () {return &PyString_Type; }
};
BOOST_PYTHON_MODULE(pyVideoInput)
{
to_python_converter< unsigned char*, uchar_ptr_to_str, true >();
to_python_converter< unsigned char, uchar_to_str, true >();
class_<videoInput>("videoInput")
.def("getPixels", &videoInput::getPixels,
return_value_policy<manage_new_object>())
;
}
/////////////////////////
2) How do I allocate memory in a python string and then pass the pointer
through boost python, to be filled by the c++ function?
In c++, the library would be used like this:
videoInput vi;
....
unsigned char * buffer = new unsigned char[size];
vi.getPixels(device, buffer);
The buffer could be pretty big so I want to pass by pointer, not by value
The alternative would be to use the overload which returns the pointer,
but I can't get that to compile with bjam. I get the dreaded:
make_instance.hpp(24) : error C2027:
use of undefined type 'boost::STATIC_ASSERTION_FAILURE<x>
when I try to return a pointer...
Thanks for any help freeing me from my confusion!
Regards
Si
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