COM Discussion Boards

7-Dec-06 22:48

Hi All,

Description of Problem:-

I have a interface pointer to some custom dual interface. I am creating a object of _variant_t class like "_variant_t vtSample(pICustom);".

vtSample is created and assigned value as 'TRUE' and its vt as VT_BOOL.
It should have been VT_DISPATCH instead of VT_BOOL and value as some memory address.

Can anyone explain the above behavior?

Thanks...

Suraj Gupta

prasad_som7-Dec-06 23:02

7-Dec-06 23:02

Can you show some code ?

Gupta Suraj wrote:
I am creating a object of _variant_t class like "_variant_t vtSample(pICustom);".

vtSample is created and assigned value as 'TRUE' and its vt as VT_BOOL.

Why you are assigning its vt as VT_BOOL.

Gupta Suraj wrote:
It should have been VT_DISPATCH instead of VT_BOOL and value as some memory address.

Can anyone explain the above behavior?

I'm confused here to understand your problem. Can you explain in detail.

Prasad
Notifier using ATL | Operator new[],delete[][^]

Gupta Suraj7-Dec-06 23:26

7-Dec-06 23:26

Hi Prasad,

Thanks for the reply...

I am not explicitly assigning vt to VT_BOOL.

"_variant_t vtSample(pICustom);"

The above statement is causing vtSample object to be instantiated and initialized with vt= VT_BOOL and its value as 'TRUE'.

As pICustom is dual interface pointer so value of vtSample should be pointer to v-table and its vt should be VT_DISPATCH not VT_BOOL.

I don't know why it so?

Am I able to make you understand the problem?

Thanks...

Suraj Gupta

prasad_som8-Dec-06 1:49

8-Dec-06 1:49

Gupta Suraj wrote:
"_variant_t vtSample(pICustom);"

Can you show code snippet, how you are using this interface? There is no way it should assign vt as VT_BOOL , unless pICustom is BOOL.
While debugging, you can step through the contructor of _variant_t , see which contructor is been called.

Prasad
Notifier using ATL | Operator new[],delete[][^]

Gupta Suraj8-Dec-06 3:26

8-Dec-06 3:26

Thanks Prasad...

Actually,pICustom is a smart pointer. So when "vtSample(pICustom)" is executed, bool operator of _com_ptr template class is called. What I think is that the best matching constructor of _variant_t class is that which takes a bool as its paramter.So first bool operator of _com_ptr is called to convert the parameter to bool.

We don't have a overloaded constructor of _variant_t class which takes smart pointer as its parameter.

Please send your comment on this. Am i thinking in right direction?

Suraj.

Suraj Gupta

Ed Gadziemski8-Dec-06 18:29

Ed Gadziemski

8-Dec-06 18:29

Try explicitly casting your object to an IDispatch pointer, for example (IDispatch *)pICustom. That should eliminate falling through to bool.

Gupta Suraj10-Dec-06 17:44

10-Dec-06 17:44

Thanks...It worked...

Suraj Gupta

prasad_som10-Dec-06 21:29

10-Dec-06 21:29

Though, you had a solution to your problem;

Gupta Suraj wrote:
bool operator of _com_ptr template class is called.

Which operator bool you are talking about ? In fact, it should return you custom interface type.
Its implementated like this,

operator T*()   {
    return p;

So I feel, it should return interface pointer.
Can you show how you have declared this interface ?

Gupta Suraj wrote:
We don't have a overloaded constructor of _variant_t class which takes smart pointer as its parameter.

No, CComPtr, will be called for operator T*. Which returns appropriate interface pointer.
i.e. consider this declaration,

CComPtr<IMyInterface> pMy;
_variant_t f(pMy);

Here,in second statement pMy->Operator T* will be get called first. Which returns IMyInterface*.
So, it will set for VT_IDISPATCH automatically.
You dont even need to cast it.

Prasad
Notifier using ATL | Operator new[],delete[][^]

Gupta Suraj11-Dec-06 18:28

11-Dec-06 18:28

Hi Prasad,

Here is code snippet of my application..

// Smart pointer(SampleObjects::ISampleSetDualPtr) typedef declarations
_COM_SMARTPTR_TYPEDEF(ISampleSetDual, __uuidof(ISampleSetDual));
// Smart pointer typedef declarations

SampleObjects::ISampleSetDualPtr pMutipleValues = SampleObjects::ISampleSetDualPtr )propertyPtr->Value;

_variant_t vtMultiValue(pMutipleValues);//This statement first causes bool operator of template class _com_ptr_t being called and then overloaded constructor of _variant_t class being called which takes bool as input parameter.

template<typename _iiid=""> class _com_ptr_t
{
......
......
......
operator bool() const throw()
{
return m_pInterface != NULL;
}
}

Please let me know your input on this.

Thanks,
Suraj

Suraj Gupta

prasad_som11-Dec-06 19:22

11-Dec-06 19:22

Now I got your point.
I was in assumption, you are using CComPtr, where as you are using _com_ptr_t . Both are having different implementations.

Gupta Suraj wrote:
_variant_t vtMultiValue(pMutipleValues);//This statement first causes bool operator of template class _com_ptr_t being called and then overloaded constructor of _variant_t class being called which takes bool as input parameter

Here, compiler looks for mathcing constructor of _variant_t. It doesn't find one with given smart pointer. _com_ptr_t is overloaded for operator bool(). Hence, there is match betn constructor with bool parameter of _variant_t and passed smart pointer variable.

Type casting as said in one of previous replies is one solution.
Or you can Use

_variant_t vtMultiValue(pMutipleValues.GetInterfacePtr());//

to resolve ambiguity .

Prasad
Notifier using ATL | Operator new[],delete[][^]

Gupta Suraj11-Dec-06 19:36

11-Dec-06 19:36

Thank you...

Solution you suggested works.

I thought another solution that works in this case is

_variant_t vtMultiValue(pMutipleValues, true);

You have being a great help.
Suraj

Suraj Gupta

prasad_som11-Dec-06 19:51