Memory Leak returning QVariant containing a list of Qvariants from a com-call

Two windows applications communicate via the windows com interface. By calling a function which returns a QVariant containing a list of QVariant with approx 2000 items of double.
Memory is leaked.

Loooking into the details

The windows VARIANT is not cleaned up after the result is copied into a QVARIANT

This fixes it

diff --git a/src/activeqt/container/qaxbase.cpp b/src/activeqt/container/qaxbase.cpp
index fa3eacf..0b3b03c 100644
--- a/src/activeqt/container/qaxbase.cpp
+++ b/src/activeqt/container/qaxbase.cpp
@@ -3685,6 +3685,8 @@ int QAxBase::internalInvoke(QMetaObject::Call call, int index, void **v)
     if (hres == S_OK && ret.vt != VT_EMPTY)
         QVariantToVoidStar(VARIANTToQVariant(ret, slot.typeName()), v[0], slot.typeName());

+    clearVARIANT( &ret );
+
     // update out parameters
     for (p = 0; p < int(params.cArgs); ++p) {
     bool out;

It is hard for me to provide a small example, as it interacts with out "old"software and a new application on top of that. But I can simply reason about this bug by looking at the provided patch.

the line

QVariantToVoidStar(VARIANTToQVariant(ret, slot.typeName()), v[0], slot.typeName());

Does a deep copy from a VARIANT (ret) to a QVARIANT.

And the variable ret is never used afterwards not is it cleared.

Looking at the MS documentation https://msdn.microsoft.com/en-us/library/windows/desktop/ms221165%28v=vs.85%29.aspx?f=255&MSPPError=-2147217396

Or this Article http://www.roblocher.com/whitepapers/oletypes.html

If the VARIANT contains an array/List/pointer to something then it needs to be freed by hand.
Which is clearly not the case.

And as ret is nowhere used anymore we can call clearVARIANT( &ret ) in any case

I really hope this helps to see the issue and the proposed patch. However I still try to think about a easy way for you to reproduce this.