You may want to try having Py++ do an example wrapping of a header file or
two, thats always what I did while I was wrapping parts of my code that I
was not sure about the right conventions in boost python.
That being said, I have also never tried passing a pointer to python for
python to edit and give back. That kind of design kind of stinks to me, I
think a better solution would be to write an interface for a python visitor
that you could apply to your C++ game objects, but that is not important
here.
There are a couple of suggestions I can make, if you switch back to passing
by reference, you need to remember to use boost::ref() for the arguments
you do not want copied.
Eg:
call_method<void>(self, "TickCharacter", boost::ref( character ),
boost:;ref( field ), ticks)
I use a constant ref in some of my functions and I found I always need to
tell boost about it other wise the object does not work right.
Also, why are you using call_method like this?
I thought the right way for calling python functions was
if( bp::override func = bp::get_override( "TickCharacter" ) )
func( boost::ref( character ), boost::ref( field ), ticks );
That is what I do anyway and it was in the docs at some point. Maybe the
difference in calling convention is causing boost python to not accurately
pass your pointers?
Charles
On , Jim Bosch <tallji...@gmail.com> wrote:
On 05/25/2011 02:26 PM, Jay Riley wrote:
I have some class functions that takes in parameters by pointer.
However, when I expose and override this class/these functions in
boost::python, any changes I make to the parameters are not reflected
back to the original, meaning it isn't being passed by pointer as I
expect. I previously had them as pass-by-reference, but the same problem
still occurred. For an example of what I mean, here's some of my code
with unimportant functions and details omitted.
I note two spots that bear further investigation.
The most likely source is here:
//In the actual scripting code
void StatusEffectWrapper::TickCharacter(Game::Character::BaseCharacter*
character, Game::Battles::BattleField *field, int ticks)
{
call_method(self, "TickCharacter", character, field, ticks);
}
I think there's a very good chance that call_method is copying your
character argument when it converts it to Python. Boost.Python is
extra-careful about making sure the C++ objects it puts inside Python
objects don't turn into dangling references, and it has no way to control
the lifetime of a raw pointer or reference. I think you could probably
fix this by using shared_ptr here, because Boost.Python does know how to
convert that safely to Python without copying the pointee.
If that fails, look here:
.def("TickCharacter", &StatusEffect::TickCharacter,
&StatusEffectWrapper::TickCharacterDefault)
I've personally never seen this invocation of .def, with two member
function pointer arguments. That doesn't necessarily mean it's incorrect,
because overloading virtual methods in Python is feature I almost never
use, and it seems like there are a half-dozen ways to do it and I never
know which one is considered best (perhaps someone else on this list
does?). But you might want to make sure this does what you expect.
HTH
Jim Bosch
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