On 05/04/2011 08:01 AM, zeb wrote:
hi, I have some problem about transfer-ownership. C++ code is like this:class RefCounter { int _count; public: RefCounter() : _count(1) {} virtual RefCounter() {} void addRef() { ++_count; } void release() { --_count; if (_count == 0) delete this; } }; class A : public RefCounter {...}; class B { public: void setA(A* a) { // B takes the ownership of A. _a = a; a.addRef(); } private: A* _a; }; So, in python, I use these classes like: a = A() # the reference count of a is 1 now. b = B() b.setA(a) # B take the ownership of A, and now the reference count is 2. a.release() # a should call release to decrease the reference count, but now a is invalid. Python says: did not match C++ signature. I can change the C++ code to solve this problem, but I really don't want to change C++ code. It's better to solve it by other way. Is there any one could give me some advice?
You should really to let Python (and C++, for that matter) handle your reference counting if at all possible.
The best way to do that would be to ensure your Python objects are held inside a smart pointer (boost::intrusive_ptr would probably work). If you set that up correctly, you should never have to call addRef() or release() from your Python code - think of it as allowing Python to always own one reference, which it is responsible for deleting when its done with it.
I realize I'm being a little vague about the details - feel free to ask more questions if you need more help, but a look through the Boost.Python reference documentation for setting the "HeldType" of a class_ instantiation to a smart pointer should get you started.
Good luck! Jim Bosch
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