C / C++ / MFC

Re: Using CoCreateInstance from C to use class in VB DLL

26-Jun-09 8:08

Hi all,

I've beating this around for a few days now and I'm totally lost.

I was given a DLL written in VB by a client with the idea of instantiating a class and calling some of the methods. I created a small test app (from code I found here) and attempted to use CoCreateInstance. This worked fine in the code shown below. The client then gave me a more up-to-date version of the DLL and with this new version, CoCreateInstance failed with a E_NOINTERFACE.

I've gone back and forth with the client about this and they have said that it was compiled with the same compiler (really old was the comment) and that all that was changed with the new release was couple of lines of code. They said they had recompiled the DLL under the highest compatibility. A couple of years has gone by since releases, so there may be underlying OS changes, if that would make a difference. They have said they have other users using the DLL without issues, though perhaps not with C/C++.

I modified the code so that instead of using CoCreateInstance, it uses CoGetClassObject and CreateInstance. CreateInstance fails with E_NOINTERFACE, the same error.

I would appreciate all help in understanding how to debug this, bearing in mind that I'm unfamiliar with COM.

This is a snippet from stdafx.h:

//{{AFX_INSERT_LOCATION}}
// Microsoft Visual C++ will insert additional declarations immediately before the previous line.

#import "TTExt.dll" no_namespace

This is a snippet from the area where I do the CoCreateInstance:

void CVCClientDlg::OnButton1() 
{
	HRESULT hresult;
	CLSID clsid;

		CoInitialize(NULL);

		hresult=CLSIDFromProgID(OLESTR("TTExt.WebRes"), &clsid);
		if(FAILED(hresult))
		{
			switch (hresult) {
				case CO_E_CLASSSTRING:
					AfxMessageBox("CLSID Failed -- registered CLSID for the ProgID is invalid");
					break;
				case REGDB_E_WRITEREGDB:
					AfxMessageBox("CLSID Failed -- error occurred writing the CLSID to the registry.");
					break;
				default:
					AfxMessageBox("CLSID Failed -- unknown reason");
					break;
			}
		}
		
		_WebRes *wr;
		IClassFactory *pCF;

		hresult=CoGetClassObject(clsid, CLSCTX_INPROC_SERVER, NULL, IID_IClassFactory, (LPVOID *)&pCF);	
		hresult = pCF->CreateInstance(NULL, __uuidof(_WebRes), (LPVOID *)&wr);

		//hresult=CoCreateInstance(clsid, NULL, CLSCTX_INPROC_SERVER, __uuidof(_WebRes), (LPVOID *)&wr);
		
		if(FAILED(hresult))
		{
			switch (hresult) {
				case REGDB_E_CLASSNOTREG:
					AfxMessageBox("Creation Failed -- Class not registered");
					break;
				case CLASS_E_NOAGGREGATION:
					AfxMessageBox("Creation Failed -- class cannot be created as part of an aggregate.");
					break;
				case E_NOINTERFACE:
					AfxMessageBox("Creation Failed -- class does not implement the requested interface");
					break;
				case E_POINTER:
					AfxMessageBox("Creation Failed -- ppv parameter is NULL");
					break;
				default:
					AfxMessageBox("Creation Failed -- unknown reason");
					break;
			}
			return;
		}

		//bool bCon = wr->Connect("GEX", "./TeeTimes.ini");
		bool bCon = wr->Connect("GEX", "");

		if (bCon)
			MessageBox("Connect Succceded\n");
		else 
			MessageBox("Connect Failed **********\n");

		wr->Release ();

		CoUninitialize();

}

This is a snippet from the top of the .tlh file:

// Created by Microsoft (R) C/C++ Compiler Version 14.00.50727.42 (2ecf2b05).
//
// c:\documents and settings\phild\my documents\visual studio code\vbdll\vcclient\debug\ttext.tlh
//
// C++ source equivalent of Win32 type library TTExt.dll
// compiler-generated file created 06/24/09 at 17:14:13 - DO NOT EDIT!

#pragma once
#pragma pack(push, 8)

#include <comdef.h>

//
// Forward references and typedefs
//

struct __declspec(uuid("f5171c2c-b846-47bc-8c7f-19658cfc0086"))
/* LIBID */ __TTExt;
struct __declspec(uuid("787d47a3-020f-4b1f-912e-003523277942"))
/* dual interface */ _WebRes;
struct /* coclass */ WebRes;

//
// Smart pointer typedef declarations
//

_COM_SMARTPTR_TYPEDEF(_WebRes, __uuidof(_WebRes));

//
// Type library items
//

struct __declspec(uuid("787d47a3-020f-4b1f-912e-003523277942"))
_WebRes : IDispatch
{
    //
    // Property data
    //

I did a comparison of the .tlh files from the two different versions of the DLL and this is the result:

Compare: (<)C:\Documents and Settings\phild\My Documents\Visual Studio Code\VBDll\VCClient\Debug\tmp\v7.ttext.tlh (10755 bytes)
   with: (>)C:\Documents and Settings\phild\My Documents\Visual Studio Code\VBDll\VCClient\Debug\tmp\v6.ttext.tlh (10755 bytes)

6c6
< // compiler-generated file created 06/26/09 at 13:23:52 - DO NOT EDIT!
---
> // compiler-generated file created 06/26/09 at 13:25:49 - DO NOT EDIT!
17,19c17,19
< struct __declspec(uuid("e897466c-75b0-459f-9512-21d42e1f5703"))
< /* LIBID */ __TTExt;
< struct __declspec(uuid("dc8718c4-d07f-4542-a799-f2015a0614cf"))
---
> struct __declspec(uuid("f5171c2c-b846-47bc-8c7f-19658cfc0086"))
> /* LIBID */ __TTExt;
> struct __declspec(uuid("787d47a3-020f-4b1f-912e-003523277942"))
33c33
< struct __declspec(uuid("dc8718c4-d07f-4542-a799-f2015a0614cf"))
---
> struct __declspec(uuid("787d47a3-020f-4b1f-912e-003523277942"))
311c311
< struct __declspec(uuid("d00de9f1-98eb-4cd9-8685-0ea4f283971f"))
---
> struct __declspec(uuid("0cab506a-1b4d-473f-9a8b-051277ae5603"))

modified on Friday, June 26, 2009 2:32 PM

CPallini26-Jun-09 8:58

Re: Using CoCreateInstance from C to use class in VB DLL

26-Jun-09 8:58

Did you unregister the previous DLL and register the new one?

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

BeerFizz26-Jun-09 9:30

Re: Using CoCreateInstance from C to use class in VB DLL

26-Jun-09 9:30

Hi Pallini,

Thank you for responding.

Yes, in fact I can unregister the old DLL, register the new DLL, try the test code and it will fail. I can then unregister the new DLL and register the old DLL and it will work fine.

Other ideas?

CPallini26-Jun-09 9:38

26-Jun-09 9:38

BeerFizz wrote:
hresult=CLSIDFromProgID(OLESTR("TTExt.WebRes"), &clsid);

BeerFizz wrote:
hresult = pCF->CreateInstance(NULL, __uuidof(_WebRes), (LPVOID *)&wr);

Have you done, using the debugger, a constistency check between clsid and __uuidof(_WebRes) ?
Smile | :)

[Message Deleted]

BeerFizz26-Jun-09 10:00

Re: Using CoCreateInstance from C to use class in VB DLL

26-Jun-09 10:00

[Message Deleted]

BeerFizz26-Jun-09 10:06

Re: Using CoCreateInstance from C to use class in VB DLL

26-Jun-09 10:06

Look at this one... they appear to be different.

http://farm4.static.flickr.com/3403/3662825099_9b99748264_o.png[^]

Why would that be?

CPallini26-Jun-09 10:17

Re: Using CoCreateInstance from C to use class in VB DLL

26-Jun-09 10:17

Actually this picture shows that there is consistency.
Can you get an instance of the object via, for instance, OleView tool?

BeerFizz26-Jun-09 10:41

Re: Using CoCreateInstance from C to use class in VB DLL

26-Jun-09 10:41

This is from oleview. Not sure exactly how to use it, but this is an image from it. If you give me further instructions as to what you need to see I am sure I can provide the details, thanks for your continued help.

http://farm4.static.flickr.com/3615/3663707060_eb3f657c11_o.png[^]

CPallini26-Jun-09 11:00

Re: Using CoCreateInstance from C to use class in VB DLL

26-Jun-09 11:00

Hey, wait a moment. The code snippet of tlh file you provided in your OP is relative to the old DLL. I hope you aren't using it.
Smile | :)

BeerFizz26-Jun-09 11:11

Re: Using CoCreateInstance from C to use class in VB DLL

26-Jun-09 11:11

C.Palinni, you are a genius!!! That was the issue!

D'Oh! | :doh:

You know, at some point I had thought of that but obviously screwed it up. You would think that after the multitude of compiles I've done, registers and unregisters that at some point I would have lucked on the right combination.

Thank you so much for your help, it is very much appreaciated,

Best Regards
Phil

CPallini26-Jun-09 11:21

Refresh a form in C++ Builder

26-Jun-09 11:21

You're welcome.
Smile | :)

David21u226-Jun-09 6:12

26-Jun-09 6:12

I can not refresh the forms of my application when I execute the .exe file. Whether I click over my application then the screen seens to be frozen...same result if I do soemthing with another application like web browser...I've tried with refresh() and bringtofront() methods but it doesn't work.

I would really apreciate if someone could tell me how to keep the forms updated when it is running...

c u soon...

David

David Crow26-Jun-09 7:29

26-Jun-09 7:29

David21u2 wrote:
I would really apreciate if someone could tell me how to keep the forms updated when it is running...

How did you initially populate them?

"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

David21u226-Jun-09 7:42

26-Jun-09 7:42

Hi,

Thanks a lot for your help...

My issue is the following...when I'm running the .exe file... any further action I do with the mouse, lets say open another application or even click over my application cause that the screen gets frozen...i've added refresh() and Bringtofront() methods but they only work whether I run the application from the Builder IDE...

tks in advance for your help...

dg

David Crow26-Jun-09 7:47

26-Jun-09 7:47

David21u2 wrote:
...cause that the screen gets frozen...

Instead of what? Is your application doing something at that point?

David21u226-Jun-09 7:55

26-Jun-09 7:55

Yeah,

The application is a cellular networks simulator; some simulations are really heavy computationally speaking that the system I think is unable to refresh the graphical interface...but the curious thing is that only the app's screen gets frozen because the simulation itself keeps working properly; I've verified it because once the overall simulation process finishes then the application screen returns.

I've viewed some articles refering to threads but I have no idea how to use them...maybe there is another way !!

c u,
dg

David Crow26-Jun-09 7:57

26-Jun-09 7:57

David21u2 wrote:
...some simulations are really heavy computationally speaking that the system I think is unable to refresh the graphical interface...I've verified it because once the overall simulation process finishes then the application screen returns.

Put these computations into a worker thread.

David21u226-Jun-09 8:01

26-Jun-09 8:01

well,

could you give me please additional insight how to do that...i've never use such threads so a tutorial or maybe a sample file could be useful...

: )

tks
dg

David Crow26-Jun-09 8:12

26-Jun-09 8:12

See here.

David González G26-Jun-09 9:05

David González G

26-Jun-09 9:05

tks a lot for your help...I'm gonna go over that inmediately...

c u around..
dg

favorxx26-Jun-09 21:15

favorxx

26-Jun-09 21:15

maybe your frequent refresh leads to the frosen, try to create a thread to refresh Smile | :)

David González G26-Jun-09 22:46

David González G

26-Jun-09 22:46

hi,

do ou have a sample code showing how to do that...
I've never used threads and I found it a bit complicated...

well, tks a lot for your help...

c u around,
dg

favorxx27-Jun-09 2:23

favorxx

27-Jun-09 2:23

Multithreading Tutorial[^]

you can download the code here，although it isn't in c++ builder. It is written by api, hope it helpful.
anyway, i think the code in msdn is also valuable.