[PyQt] SIP and virtual functions

[Jens Thoms Toerring]

Hi Phil,

On Tue, Nov 23, 2010 at 02:42:59PM +0000, Phil Thompson wrote:
> Not every C++ class can be wrapped. SIP often has to create temporary
> instances which obviously requires support from the underlying C++.

Thanks for the quick reply! It's a bit unlucky in my case since
creating public constructors with no arguments or a single int
argument simply doesn't make sense:-( And can you tell me why
in some cases a constructor with no argument and in others one
with an int are used? Without that information I wouldn't even
know which constructors I have to define (if I find a way to do
that).

BTW, looking at the sipVH_PyFoo_0() function it looks a bit as
if an instance of A is only created to obtain enough memory for
an object returned by sipParseResult(). So I'm wondering if the
constructor call couldn't be avoided when generating the function
instead in this way:

A sipVH_PyFoo_0(sip_gilstate_t sipGILState,PyObject *sipMethod)
{
	std::auto_ptr<char> sipRes(new char[sizeof(A)]);
    PyObject *resObj = sipCallMethod(0,sipMethod,"");

    if (!resObj || sipParseResult(0,sipMethod,resObj,"H5",sipType_A,
	                              reinterpret_cast<A*>(sipRes.get())) < 0)
        PyErr_Print();

    Py_XDECREF(resObj);
    Py_DECREF(sipMethod);

    SIP_RELEASE_GIL(sipGILState)

	return *reinterpret_cast<A*>(sipRes.get());
}

As far as I know new() should return memory properly aligned for
arbitrary objects and using a std::auto_ptr should take care of
not creating a memory leak . But then I'm not 100% sure if retur-
ning the content of an auto_ptr is ok, so an alternative might
be:

A sipVH_PyFoo_0(sip_gilstate_t sipGILState,PyObject *sipMethod)
{
	char *tmp = sipRes(new char[sizeof(A)]);
    PyObject *resObj = sipCallMethod(0,sipMethod,"");

    if (!resObj || sipParseResult(0,sipMethod,resObj,"H5",sipType_A,
	                              reinterpret_cast<A*>(tmp)) < 0)
        PyErr_Print();

    Py_XDECREF(resObj);
    Py_DECREF(sipMethod);

    SIP_RELEASE_GIL(sipGILState)

    A sipRes = *reinterpret_cast<A*>(tmp);
	delete [] tmp;
	return sipRes;
}

But perhaps that's a stupid idea (especially since I have no
good knowledge of the innards of the sipParseResult() function).
It's just an idea I came upon while pondering what's going on;-)

                      Thank you and best regards, Jens
-- 
  \   Jens Thoms Toerring  ________      jt at toerring.de
   \_______________________________      http://toerring.de