[C++-sig] Manipulating arguments with CallPolicies::precall?

[Arve Knudsen]

Hi

I want to wrap a native C Python object in a C++ object that takes care of 
constructing and destructing it properly (there isn't any way to specify 
custom allocation/deallocation routines are there?). However, I would like 
to send this object directly to the associated routines (its part of an 
existing Python extension). I haven't found any direct support for this 
kind of thing within boost::python, since everything seems strongly tied 
to the contained type (my wrapping C++ class). But, I figured it might be 
possible to manipulate the Python argument tuple within 
CallPolicies::precall?

So I experimented a little and it seems I am able to change the first 
argument to point to the contained C object, instead of it's wrapper. But, 
when the function (which takes a pointer to one such C object) receives 
the object something is not right. A member which was initialized to zero 
(verified within caller.hpp), now contains some other number. I suppose 
some conversion magic goes wrong? I've tried to figure out what's going on 
myself, but gdb tends to die on me in the process (no pun intended). It'd 
be great if someone could enlighten me as to why this won't work (fingers 
crossed), or perhaps present a better solution :)

Btw, I'm getting lots of warnings building boost::python from CVS (this is 
on Linux with GCC 3.3.2 and Python 2.3), because of this: 
/usr/include/python2.3/pyconfig.h:847:1: warning: "_POSIX_C_SOURCE" 
redefined. Is Python 2.3 to blame? I dont think I ever saw this warning 
with boost 1.30.2, though.

Thanks

Arve Knudsen