COM object and QtVariant casting issue

[mlago]

Hi, thankyou for answer.

I've tried how you say with error: error: '__mingw_uuidof' was not declared in this scope

QVariant var = JswAttrList.GetItem(Some_attribute);
HRESULT hr = AttrList.queryInterface(__uuidof(JSWSCAPILib::IJswAttrList),(void **)&var);

QVariant var = JswAttrList.GetItem(Some_attribute);
HRESULT hr = AttrList.queryInterface(__uuidof(JSWSCAPILib::IJswAttrList),(void **)&var);

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__uuidof is a MVC++ extensión. I have to say that I am using mingw as compiler. Them I've tried to get UUID Class from Visual C++ with this simple test:

String^ s = __uuidof(JSWSCAPILib::IJswAttrList);

String^ s = __uuidof(JSWSCAPILib::IJswAttrList);

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with this compiler error: error C2787: 'SCAPILib::IAttrList' : No GUIDs have been associated with this object

[anda_skoa]

I think (void**)&var does not make sense, that is retinterpreting a pointer to a QVariant, no?

You write that the QVariant type is IUnknown*, does this compile?

IUnknown *obj = var.value<IUnknown*>();

IUnknown *obj = var.value<IUnknown*>();

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Cheers,
_

[mlago]

Thankyou for reply.

I think (void**)&var does not make sense, that is retinterpreting a pointer to a QVariant, no?

In a sense yes.

You write that the QVariant type is IUnknown*, does this compile?

IUnknown *obj = var.value<IUnknown*>();

IUnknown *obj = var.value<IUnknown*>();

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Cheers,
_

Yes, compile Ok. What do you suggest?.

[anda_skoa]

Yes, compile Ok. What do you suggest?.

I haven't worked with COM or ActiveQt, but if the object is stored as a IUnknown in the QVariant, then just extract it as such and then use whatever API is provided for working with COM interfaces on that pointer.

I.e. the QVariant is just a transport wrapper, like an envelope. You take the transported item out of the envelope and forget about the envelope.

Cheers,
_

[mlago]

It sounds really easy

Seriously, I was thinking about something like that but still not know very well as how. What amazes me is that I can not do it any other way.

I appreciate your effort.

[d_stranz]

I've tried how you say with error: error: '__mingw_uuidof' was not declared in this scope

So that sounds like mingw knows about it, but you haven't included the header file where it is defined. I don't use mingw, so I can't really tell you where to look. What does Google tell you if you paste "__mingw_uuidof" into the search box?

[mlago]

Hi,
__uuidof is defined in _mingw.h

#define __uuidof(type) __mingw_uuidof<__typeof(type)>()

#define __uuidof(type) __mingw_uuidof<__typeof(type)>()

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The _mingw.h file begins by saying:

/**
 * This file has no copyright assigned and is placed in the Public Domain.
 * This file is part of the mingw-w64 runtime package.
 * No warranty is given; refer to the file DISCLAIMER.PD within this package.
 */

/**
 * This file has no copyright assigned and is placed in the Public Domain.
 * This file is part of the mingw-w64 runtime package.
 * No warranty is given; refer to the file DISCLAIMER.PD within this package.
 */

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and my compiler versión is 32 bits

The most usable that I found in google is this thread https://forum.qt.io/topic/35324/solv...ce-to-canoe/15, but it is not applicable to me in the same way that it is exposed there. I've already tried compiling it with ole32.lib and nothing has changed.

As I said I have also tried to capture the value returned by __uuidof in MS visual C ++ with the idea of using that UUID in my application in Qt. From this test what I consider relevant is the returned message by compiler error C2787: 'SCAPILib::IAttrList' : No GUIDs have been associated with this object. Which suggests to me that this class has no definite UUID. Then I have tried to define an IID_IATTRLIST variable in the IAttrList class without getting QueryInterface to return anything other than a null pointer. I think this is a dead end