COM Discussion Boards

Re: Can COM interface functions be overloaded?

15-Dec-04 14:51

If you are looking at it from the client side then instead of trying to overload the com interface simply create an interface wrapper for the COM object in your client. Your code would then sit inbetween your main client and the COM interface. For info on interface wrappers look here[^]

Andy Hunter19-Dec-04 15:57

problem in CoCreateInstance()

19-Dec-04 15:57

You could also take a look at aggregation and containment if you are trying to perform it from the server side. It is not necessarily that COM doesn't support good programming practice, the whole reason for the development of COM was to insulate the client from the details of implementation; thus implementation inheritance is out of the question since it requires too much detailed information over how the "insides" work. COM does support interface inheritance, which is developed through aggregation and containment. These tools allow you to specialize COM interfaces.

biswaranjan_rath6-Dec-04 21:18

biswaranjan_rath

6-Dec-04 21:18

I wrote a piece of code as

hr = CoCreateInstance (&CLSID_DataAccessClient, NULL, CLSCTX_INPROC_SERVER, &IID_IDataAccessClient, &pCOM);

where pCom is of type IDataAccessClient.

The program throws a Fatal error as:

Fatal execution engine error.

Please help me out by giving some suggestions.

Biswa
Email: biswaranjan.rath@amdocs.com
Phone No: 09373311346

RChin7-Dec-04 1:20

7-Dec-04 1:20

Try this instead:

hr = ::CoCreateInstance(CLSID_DataAccessClient,
                        NULL,
                        CLSCTX_INPROC_SERVER,
                        IID_IDataAccessClient,
                        (void**)&pCOM);
if(FAILED(hr))
{...}

Notice the absence of the & operator.

I Dream of Absolute Zero

biswaranjan_rath7-Dec-04 1:28

biswaranjan_rath

7-Dec-04 1:28

I tried those options, but i'm using a reference so '&' is needed. again i tried this with (void**). still i got the error. Even this call doesn't return a status.

RChin7-Dec-04 1:33

7-Dec-04 1:33

Ok. I'm still not quite sure why you need to pass the address of the GUIDs like you did though.
The only other possibility that I can think of is that the COM library was not initialised. Have you called ::CoInitialize(NULL) at the start of your program?

I Dream of Absolute Zero

biswaranjan_rath7-Dec-04 17:27

biswaranjan_rath

7-Dec-04 17:27

I have initialized thye COM library by:

hr = CoInitialize(NULL);

after that i checked the status of hr, which is returning success.

then the program fails in CoCreateInstance()

ThatsAlok7-Dec-04 17:58

ThatsAlok

7-Dec-04 17:58

biswaranjan_rath wrote:
hr = CoCreateInstance (&CLSID_DataAccessClient, NULL, CLSCTX_INPROC_SERVER, &IID_IDataAccessClient, &pCOM);

What is Return Value of hr here

-----------------------------
"I Think this Will Help"
-----------------------------
Alok Gupta
visit me at http://www.thisisalok.tk

COM programming

Andy Hunter6-Dec-04 6:08

6-Dec-04 6:08

Hello everyone. I know this is a newbie question but I have to ask. I am pretty comfortable with windows programming in C and C++ as a whole however I am still sketchy over COM development. Specifically I would like to tie in my office solutions to my Visual studio solutions. I understand that interacting with Office requires COm deployment and I was hoping someone might point me in the right direction for finding a good reference. When I first started Windows programming I was told to get Petzold's book. I think it was one of the best investments I ever made. I was wondering and hoping frankly, that there was an equivalent to that with respect to COM programming.

Re: COM programming

User 2155978-Dec-04 4:17

User 215597

8-Dec-04 4:17

Hi,
You can check my COM BLOG[^]. I have listed some good book names and useful URL's (Notes: These are my personal favourites)

Have a great day ahead!
Regards,
Sohail Kadiwala
(My Blog - http://blogs.wdevs.com/sohail/[^])

modified 21-Apr-21 21:01pm.

Re: COM programming

Andy Hunter8-Dec-04 10:11

How to change name of coclass ?

8-Dec-04 10:11

I have just ordered a copy of Inside COM and I was looking into Inside OLE. I was wondering if anyone has read these books or have any other suggestions.

arun14056-Dec-04 2:02

arun1405

6-Dec-04 2:02

Hi Folks,

I am writing an Attributed COM component in Visual C++ 7.1. In standard cases, the name of the coclass is the same as the CLASS name. I want to know if it is possible to change the coclass name ?

For instance, in the following code of mine, IDL will be generated with the coclass named as "CMyData". But, I want to have the coclass name as "MyData" without changing the actual class name.

[CODE]
[
object,
uuid("19088A64-4E82-4FD7-A8A5-A9FEE2577FE8"),
dual, helpstring("IMyData Interface"),
pointer_default(unique)
]
__interface IMyData : IDispatch
{
[id(1), helpstring("method MyMethod")] HRESULT MyMethod();
}

[
coclass,
threading("apartment"),
support_error_info("IMyData"),
vi_progid("MyComponent.MyData"),
progid("MyComponent.MyData.1"),
version(1.0),
uuid("4AF80BC4-6A51-4E83-A3A0-9184230CD2AD"),
helpstring("MyData Class")
]
class ATL_NO_VTABLE CMyData : public IMyData
{
public:
CMyData();
virtual CMyData();

DECLARE_PROTECT_FINAL_CONSTRUCT()

HRESULT FinalConstruct()
{
return S_OK;
}

void FinalRelease()
{
}

STDMETHOD(MyMethod)(void);
}
[/CODE]

Any help would be appreciated.

Regards,
Arun.

Adding Button to Outlook Message Window

lukevandiest3-Dec-04 9:50

lukevandiest

3-Dec-04 9:50

I am trying to develop a COM addin for Outlook 2003 using C#. I have read Hannes Pavelka's article on creating toolbars and buttons in Outlook. But, every button that I added only shows up in the main Outlook window. I'm not able to get anything new to show up in the message composition window. Does anyone know how to do this?

Passing string array pointer from managed code to unmanaged .COM

Member 8391433-Dec-04 1:04

Member 839143

3-Dec-04 1:04

The GnucDNA is a component for building P2P applications. It is written in C++. Examples of how to call it from VB.NET and C#.NET can be seen at http://www.gnucleus.com/GnucDNA/docs/examples.html. Works fine for most methods in GnucDNA, but one crucial call to a method called SetSharedDirs is not shown in the examples, and for a good reason: It does not work, it requires the argument to be passed as a string array pointer.

Looks like Microsoft is trying to explain something about how to do it by marshalling at http://samples.gotdotnet.com/quickstart/howto/doc/Interop/StringMarshal.aspx. Also, seem like using unmanaged code in C# by declaring keyword “unsafe” and statement “fixed” may hold a key, but how?

The C++ - method in the .COM can be seen at http://cvs.sourceforge.net/viewcvs.py/gnucleus/GnucDNAR2/ComShare.cpp?sortby=date&view=markup, and looks like so:
void CComShare::SetSharedDirs(VARIANT* pDirPaths)

Anybody able to come up with a call from VB.NET or C#.NET that does not produce a type mismatch – error?

VBA method calling from an Object type

RChin3-Dec-04 0:28

Re: VBA method calling from an Object type

3-Dec-04 0:28

I hope someone might be able to answer this puzzle that I've found while testing a component of mine.

I am using Excel's VBA environment to quickly test a few of the methods in my component. Now if I create my component, specifying the type explicitly and run the method, everything works OK.

eg:

<code>
Dim Obj as MyItem
Dim strTitle As String
 
Set Obj = New MyItem
strTitle = "Some Description"
call Obj.SetTitle(2057, strTitle)
Set Obj = Nothing
</code>

Now here's the weird bit. If I create my item from an Object variable, it fails on my call to the same method. So if I change my code to:

<code>
dim Obj as Object
Dim strTitle As String
 
Set Obj = New MyItem
strTitle = "Some Description"
<font color=red>call Obj.SetTitle(2057, strTitle)</font><font color=green>' This FAILS with 'Type Mismatch' error </font>
Set Obj = Nothing
</code>

I can get access to the other properties of the item, but for some reason, it will not call this function.
Am I missing something?
There must be a simple explanation for this.

I Dream of Absolute Zero

RChin3-Dec-04 0:40

Re: VBA method calling from an Object type

3-Dec-04 0:40

UPDATE
Its gets stranger. Confused | :confused:

If I replace the String variable by a litteral text, it works!!

call Obj.SetTitle(2057, "Hello") 'Works!!

WTF! Are string types treated differently when called via an Object type?
Why is this happening ? Someone enlighten me.

I Dream of Absolute Zero

Vi26-Dec-04 3:07

Vi2

6-Dec-04 3:07

Are string types treated differently when called via an Object type?

Of course. Strings can be passed by VARIANT with VT_BSTR (your second case) or VT_BSTR|VT_BYREF (your first case).

Probably, the Invoke-helper for your class cannot process this vt-value.
Set the breakpoint inside Invoke(...) of your class and test it.

PS
Your can also get the valid result with extra parentheses around String.
call Obj.SetTitle(2057, (strTitle))

With best wishes,
Vita

Re: VBA method calling from an Object type

RChin7-Dec-04 1:14