Re: How to Pass c++ object across ATL DLL - COM Discussion Boards

How to Pass c++ object across ATL DLL

26-Jan-06 21:30

I don't have the exact link to the document, but you will find interesting things in this link:

http://www.sellsbrothers.com/links/#unmanlinks

Regards.

annjose2425-Jan-06 2:37

25-Jan-06 2:37

I need to pass a c++ object to the COM client. I saw a few articles on the same.
But those were objects in which there was just a single memeber. I need to pass a
c++ object which has several subclasses as its members.

If anyone could shed some light on this it would be very helpful.

Thanks in advance,

ann

Stephen Hewitt25-Jan-06 22:23

25-Jan-06 22:23

In short, you don't. COM is designed to be langauge neutral, as such it only knows about COM objects, not C++ objects. Can you give more details? If so I may be able to be more helpful!

Steve

annjose2426-Jan-06 16:33

26-Jan-06 16:33

thanks for the response steve..

I can give u the exact situation..

Say i have a class clsA

class clsA
{

public:
clsB obj1; //class B obj
clsC obj2; //class C obj
char name[10];
void show();
}

Now if i create an object of clsA say obj3, is it possible to pass
obj3 to the COM client. Please let me know if there is a way to do this
even if its twisted...

ann

Stephen Hewitt26-Jan-06 16:56

26-Jan-06 16:56

It's possible, but the solutions are definately "twisted", I would suggest they are worse then the problem. You could do this:

// WARNING: POOR CODE - THIS NULLIFIES THE BENIFITS OF USING COM!
 
// Your class:
class clsA
{
public:
     clsB obj1; //class B obj
     clsC obj2; //class C obj
     char name[10];
     void show();
};
 
// In an IDL file:
HRESULT DirtyHack_PassInCPPObject([in]INT_PTR pObj);
 
// And in a .CPP file.
STDMETHODIMP CYouCOMObject::DirtyHack_PassInCPPObject(INT_PTR pObj)
{
     clsA* pA = reinterpret_cast<clsA*>(pObj);
 
     return S_OK;
}
 
// A call would look something like this:
clsA a;
spObj->DirtyHack_PassInCPPObject(reinterpret_cast<INT_PTR>(&a));

As you've probably guessed, I do not approve of this - But you wanted twisted. None of your coworkers will thank you for putting this in production code - If I were a manager I'd fire someone for doing so. COM objects written in any language can be called from any other language, this is one of the reasons for using COM. Breaking the rules like this destroys all this.

Steve

annjose2426-Jan-06 17:07

26-Jan-06 17:07

You are right steve... its real twisted...

but u think such a situation never comes..? like the need to pass a collection
of values which are dependent on each other..? If such a situation comes, wat is the
perfect way to do it..?

thanks,
ann

Stephen Hewitt26-Jan-06 17:15

26-Jan-06 17:15

Model the data as a COM object. Once that's done you can consume the data from any COM compatible langauge. e.g. C/C++, JavaScript, VB, any of the dotNET langauges, etc......

Steve

annjose2426-Jan-06 17:25

26-Jan-06 17:25

sorry to bug u again steve...But can u explain a bit more on modelling the data a COM object
using the example i gave before as i am pretty new to COM..

Ann

Stephen Hewitt26-Jan-06 17:31

26-Jan-06 17:31

It would help if I knew how the COM server was implemented. Does it use ATL, MFC, etc....

Steve

annjose2426-Jan-06 18:15

26-Jan-06 18:15

yup... currently it is done using ATL...

Ann

Gizzo26-Jan-06 21:22

26-Jan-06 21:22

annjose24 wrote:
Now if i create an object of clsA say obj3, is it possible to passobj3 to the COM client.

The "clean" way to do that is implementing COM objects to expose the funcionality of clsA, clsB and clsC. So you will have IClsA implemented by clsA, IClsB implemented by clsB, and so on...
Then, instead of passing the object, you can pass the interface via COM. In your current COM object you need a method like:

(I suppose that you have a pointer to an object of type ClsA in your COM object called m_pClsa)

HRESULT CYourCOMObject::GetObjectClsA ( IClsA ** ppObjClsA)
{
HRESULT hr = m_pClsa->QueryInterface(IID_IClsa, (void**)ppObjClsA);
if (SUCCEEDED(hr))
return S_OK
*ppObjClsa = NULL;
return S_FALSE;
}

The same methods for ClsB and ClsC should be in ClsA.

Do you get the idea more or less?

Regards.

Gizzo26-Jan-06 1:49

26-Jan-06 1:49

As Stephen said, you can't, but you have the alternative of modeling the objects you want to pass with COM interfaces, as you can pass via COM that interfaces. I'm not sure if I was clear... D'Oh! | :doh:

This alternative is much more tedious but is better than nothing.

Regards.

annjose2426-Jan-06 16:36

Help with ENTRYID type and ENTRYLIST type

26-Jan-06 16:36

Can u explain a bit more on what you meant by modelling the
objects.

Thanks,
ann

Chris Meech24-Jan-06 10:40

Chris Meech

24-Jan-06 10:40

I'm having difficulty intializing a variable of type ENTRYLIST and I think I'm just missing something simple. I need to call IMAPIFolder::CopyMessage and the first variable is to be an LPENTRYLIST. So my code has

ENTRYLIST   elMessage[] = {1, &messageEID};
m_Folder->CopyMessage(&elMessage, ...

The compiler is not liking my initialization where the variable messageEID is of type ENTRYID and is the entry ID of a message within an Exchange folder. The error from the compiler makes sense, but I'm still unsure what needs to be change.

error C2440: 'initializing' : cannot convert from 'ENTRYID *' to 'struct _SBinary *'

What type of cast or type conversion do I need to do? Thanks.

Chris Meech

I am Canadian. [heard in a local bar]

When I want privacy, I'll close the bathroom door. [Stan Shannon]

Nice sig! [Tim Deveaux on Matt Newman's sig with a quote from me]

Re: Help with ENTRYID type and ENTRYLIST type

Chris Meech26-Jan-06 7:15

Chris Meech

26-Jan-06 7:15

This code is passing all compiler rules okay and I believe it is the correct way to set it up

SBinary      sbMessage[] = {1, pMessageEID->abFlags};
ENTRYLIST    elMessages[] = {1, sbMessage};
HRESULT      hr = m_pFolder->CopyMessages(elMessages, N...

However the call to CopyMessage is returning an error which indicates that I do not have permissions to create a message in the folder I'm trying to copy to. I suspect at the moment that my initialisation of elMessages[] is incorrect, but I don't know what else I can use to identify the message that I want to have copied.

I'm still searching but if anyone can shed some more light on extended MAPI, that whould help me out. Thanks.

Chris Meech

I am Canadian. [heard in a local bar]

When I want privacy, I'll close the bathroom door. [Stan Shannon]

Nice sig! [Tim Deveaux on Matt Newman's sig with a quote from me]

COM DLL with IShellPropSheetExt

souso2024-Jan-06 4:00

souso20

24-Jan-06 4:00

Hello All,

i have an com dll which implemts the IShellPropSheet Interface.

Now i will call the function AddPages from an application.

The Property Page from the comm dll should be showing in the application on an Tab Control.

All i must do is to call the function
AddPages(LPFNADDPROPSHEETPAGE lpfnAddPage, LPARAM lParam).

I don't understand the LPFNADDPROPSHEETPAGE parameter. I think it is an callback function, but how must i implement it in my application?

Thanks for you help.

If something is unclear, because my english is bad, please let me know. Wink | ;-)

send error message to vb from c++ com

mack scynox24-Jan-06 3:07

mack scynox

24-Jan-06 3:07

hi,

i want to send my custom error message to vb (or asp) from my c++ com object. i wrote a simple dll with one method

// C++ code
STDMETHODIMP _Test::TestErr ( ){
//AFX...

AfxThrowOleDispatchException( 1001 , "error occured" ); //just wrote this but tried many other methods

return S_OK;
}

'' VB code
Public Sub Test()
Dim obj as object
set obj = CreateObject("TestObj.Test")

on error goto ErrOccured
obj.TestErr
set obj = nothing
exit sub

ErrOccured:
MsgBox err.Description
set obj = nothing
End Sub

i want to see "error occured" message and also get 1001 as error number from vb exe.

i have tried many things but couldnot solve it.

Help needed!!!

thanx.

NOTE: com dll registrations WORKS, if i do not throw exception then no problem but i want to throw some error message to vb...

Re: send error message to vb from c++ com

Gizzo24-Jan-06 5:00