Hi Rainer,
On 2011-05-12 08:57, Rainer Kluger wrote:
Hi
I try to expose the following class to python (using gcc 4.5.1, boost
1_44_0, Python 2.7.1):
// C++
class A
{
public:
int getName(const char*& name); // suppose the implementation
assigns the const char* x = "foo"; variable to the ref-pointer
}
I'd like to expose this API as is and not alter the method interface so I
think I'll have to do s.th. like this:
====================================
# intended usage in Python:
import test
a = A()
x = const_char_ptr_ref()
y = a.getName(x)
x()
'foo'
====================================
I followed the "recipes" of the python test example, realizing that
- m1.cpp
-extract.cpp
and tried to get the things together, knowing that those example do not
really match my use case.
My understanding for what I need to do, are the following steps:
(1) encapsulate the const char*& variable in a container class, let's
say ConstCharPtrRef""
(2) expose the ConstCharPtrRef class to Python
(3) provide a factory function for the class exposed in the step (2)
(4) expose the factory function from step (3)
Right.
(5) provide an extractor function which extracts the "const char*&"
variable from within the given python argument
(6) register a from_python converter for the given type and the
provided extractor function
I'm not sure I understand the need for (5) and (6). If you have defined
a ConstCharPtrRef C++ type, and exported it to Python, you will already
have converters between the two, so from within C++ you then can simply
access the ConstCharPtrRef members by whatever API you define in C++.
There is no need for extra converters at that point.
I'm also not sure the reference needs to be captured at that level, as
that's more of a call policy (for the A::getName member function) than
an aspect of the type.
Here is how I would approach it (caution: fully untested code):
struct ConstCharPtr
{
char const *x;
};
// A factory...
ConstCharPtr make_ccp(...);
// the A::getName, adjusted to work with a ConstCharPtr argument
int get_name(A const &a, ConstCharPtr const &ccp) { return a.getName(ccp);}
BOOST_PYTHON_MODULE(test)
{
// Export the ConstCharPtr type...
class_<ConstCharPtr, boost::noncopyable> ccp("ConstCharPtr", no_init);
// ...and define how to construct it
ccp.def("__init__", make_cpp);
// Export the A type...
class_<A> a("A");
// and export the getName member function
a.def("getName", get_name);
//...
}
I believe this should actually do what you want.
Stefan
--
...ich hab' noch einen Koffer in Berlin...
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