C / C++ / MFC Discussion Boards

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Re: LNK2001 Error when creating a Multithreaded Debug DLL

James Spibey16-Dec-01 0:38

James Spibey

16-Dec-01 0:38

Did you manage to fix this? I'm having the same problem.

James Spibey

I love the word naked, it's brilliant isn't it, 'naked'. When I was a kid I used to write the word naked on a bit of paper hundreds of times and rub my face in it - Jeff, Coupling, BBC2

Eject CD by DeviceIoControl

Masaaki Onishi10-Oct-01 4:17

Masaaki Onishi

10-Oct-01 4:17

Hello, the codegurus around the world.;)

I wrote the code to eject the cd from my application.

First time, I use mciSendString () to do this, and this works fine.
But, QA pointed out that this code didn't work on Windows 95 and NT without installing
MCI. Cry | :((

So, I use DeviceIoControl function since I found some sample code for Windows 9x and NT.
However, since I'm lazy Dead | X|

, I omitted the code to check if the other application
uses CD or lock and unlock CD.

Without these codes, my code works fine on Windows OS including Windows XP. Big Grin | :-D

But, I'm curious that we need these kind of codes - check if the application uses CD or lock or unlock CD.
(In fact, the time of executing my code rarely faces these kinds of situation, so I omitted these.)

Have a nice day!

-Masaaki Onishi-

CProperty Sheet

10-Oct-01 4:14

How to add control on the CProperty Page .

Re: CProperty Sheet

Erik G. Poel10-Oct-01 4:33

Erik G. Poel

10-Oct-01 4:33

Add a new resource. (Insert->Resource->Dialog->Property Page)
Create the property page as you would any standard dialog.
When you create a class for the new resource, make sure you derive from CPropertyPage. That's it. Smile | :)

Creating a COM object in another thread?

NormDroid10-Oct-01 2:49

NormDroid

10-Oct-01 2:49

Not for the faint hearted. I recently changed the way my project was designed and parts of it stopped working, I tracked this down to a media com object being created in my worker thread and not the thread where my *mainframe* window resides.

Question?
If I'm in a worker thread is there anyway to create a com object under the context of another thread i.e the thread where my mainframe resides, I'm sure I've done this before, but have'nt touched COM for 6months.

Thanks In Advance

Norm Almond
Chief Technical Architect
FS Walker Hughes Limited

Re: Creating a COM object in another thread?

10-Oct-01 3:12

Does the com object work in a worker thread (does it have a window or need a message pump)? You may need to create it in your main thread or a user-interface thread instead.

If you create a com object from the worker thread, then it cannot be called from other threads directly because the com implemenation uses windows messages to call objects in other threads.

Re: Creating a COM object in another thread?

NormDroid10-Oct-01 3:42

NormDroid

10-Oct-01 3:42

Here goes, hope this is clean Smile | :)

[CMainframe]
|
+-W A S----> OnTimer
| new ATLMediaPlayerWrapperWnd *This Worked*
|
+ N O W----> ActionThread (Responsible for creating objects etc)
| new ATLMediaPlayerWrapperWnd *This Doesn't play but screen a single frame*
if I put DoEvents( PeekMessage etc) in the while (1) loop is works fine.

Ideally I *dont* the DoEvents code, the the object needs to be create in the ActionThread code.

Norm Almond
Chief Technical Architect
FS Walker Hughes Limited

Re: Creating a COM object in another thread?

10-Oct-01 3:53

if I put DoEvents( PeekMessage etc) in the while (1) loop is works fine.

That means you DO need to have a message pump for the object to work. Why not change the ActionThread to a user interface thread derived from CWinThread so that you don't need to DoEvents explicitly.

Re: Creating a COM object in another thread?

NormDroid10-Oct-01 3:59

NormDroid

10-Oct-01 3:59

Owwww noooo, can't do that. Need especially CWinThread (horrid) need to keep the object in a worker thread. I think I have a solution see other postings on this thread.

Norm Almond
Chief Technical Architect
FS Walker Hughes Limited

Re: Creating a COM object in another thread?

10-Oct-01 4:08

"Owwww noooo, can't do that. Need especially CWinThread (horrid) need to keep the object in a worker thread. I think I have a solution see other postings on this thread."

Good for you. Comeback when it doesn't work. Wink | ;)

Re: Creating a COM object in another thread?

NormDroid10-Oct-01 4:16

NormDroid

10-Oct-01 4:16

Got it working, do you won't a copy for reference Poke tongue | ;-P

Norm Almond
Chief Technical Architect
FS Walker Hughes Limited

Re: Creating a COM object in another thread?

10-Oct-01 4:41

No, thanks. But you did move the creation of your com object to the main thread which has a message pump, right?

Otherwise, you need to write an article to explain how it is working. Wink | ;)

Re: Creating a COM object in another thread?

Not Active10-Oct-01 3:20

Not Active

10-Oct-01 3:20

You can create the object and then marshal it to the other thread via CoMarshalInterThreadInterfaceInStream.

Re: Creating a COM object in another thread?

NormDroid10-Oct-01 3:52

NormDroid

10-Oct-01 3:52

I know where your coming I reckon this should do the trick?

CMyActionThread::CreateObject()
{
SendMessage(m_hWnd, WM_CREATE_OBJECT, 0, 0);
//
Now get the marshedPointer!

}

LRESULT CMainFrame::OnMyCreateObjectMessage(WPARAM wParam, LPARAM lParam)
{
// Create the object

// Marshal the object
return 0;
}

and it's coming back now, in essential com, there's helper functions, WritePtrToGlobalVariable and ReadPtrFromGlobalVariable

Norm Almond
Chief Technical Architect
FS Walker Hughes Limited

How i manage Events of a run time created DBGrid control

Khalil10-Oct-01 2:36

Khalil

10-Oct-01 2:36

I have create DBGrid controls at run time and want to catch event corresponding each instance but find no way.
so if someone know about it plz tell me Smile | :)

CRuntimeClass::CreateObject() and delete

BruteBertus10-Oct-01 2:18

BruteBertus

10-Oct-01 2:18

I tried to create a cobject derived class:

CObject*t=(CObject*)RUNTIME_CLASS(CHScrollTitle)->CreateObject();

and then i tried to free it with:
delete t; or CHScrollTitle::operator delete(t);

but the delete operator failes in debug-mode with an assert-notice. (something with pHead->nBlockUse==nblockuse)

does anybody know how to free a with CreateObject(or CArchive::ReadObject()) created object?
\
TIA B.Bruggeman

Re: CRuntimeClass::CreateObject() and delete

Tomasz Sowinski10-Oct-01 3:53

Tomasz Sowinski

10-Oct-01 3:53

This problem isn't probably related to CRuntimeClass::CreateObject - seems that you've corrupted the heap somehow.

BTW: calling CRuntimeClass::CreateObject makes absolutely no sense when you know the exact type of object - in your case, it's CHScrollTitle. You can just write

t = new CHScrollTitle;

Tomasz Sowinski -- http://www.shooltz.com

Re: CRuntimeClass::CreateObject() and delete

BruteBertus10-Oct-01 22:05

BruteBertus

10-Oct-01 22:05

I also thought it was a memoryleak/overwrite but i wrote a simple test program and than already it assert's about the debug-memory-tracing-variable m_nBockUse,
but when i use new/delete it doesn't assert..

i have different kind of classes in a list and i want to serialize them using Write/ReadObject, so i can't use an ordinary new/delete operator. but when i tested this it asserts in the (debug) operator delete, so i tested it with the lines i posted before, but it still asserted..

so do you have other suggestions?
btw in the file afxmem.cpp are many operator delete which (in debugmode) either call _free_dbg(p, _CLIENT_BLOCK); or _free_dbg(p, _NORMAL_BLOCK);, so probably the wrong deconstructor is called.. but how do I fix this?

TIA. B.Bruggeman

Re: CRuntimeClass::CreateObject() and delete

Tomasz Sowinski11-Oct-01 1:50

Tomasz Sowinski

11-Oct-01 1:50

1) memory overwrites: the fastest way to detect/remove them is by using automatic diagnostic tools, like BoundsChecker (www.numega.com) or Purify (www.rational.com)

2) serializing different CObject-derived classes from list: just use operator << with pointers to objects. MFC is smart enough to write metadata containing type information to archive. You don't need to write type information yourself.

// write
// p points to something derived from CBaseClass
CBaseClass *p = list.GetHead();
ar << p;
// ...
// read
CBaseClass *p;
ar >> p;
// now p contains address of dynamically created
// object derived from CBaseClass. The type is 
// correctly restored. p should be deleted with a
// call to plain delete when you no longer need 
// this object:
delete p;

Tomasz Sowinski -- http://www.shooltz.com

Remote MS-ACCESS database connect.

10-Oct-01 0:09

hi there,

I'm writing a client to manage a remote ms-access database, how can i do that is it with SQLConfigDataSource
or something else ??

my problem is that my db is on my website ie:
www.mywebpage.com/database/mydb.mdb

a sample code will help me lot
thanks in advance ...
Confused | :confused:

How can i do this?

zhangyifei10-Oct-01 0:00

zhangyifei

10-Oct-01 0:00

how can i add a version number to the CDocument class?

ZHANGYIFEI

Re: How can i do this?

Jon Hulatt10-Oct-01 0:41

Jon Hulatt

10-Oct-01 0:41

1. Don't double post.

2. You really DON'T want to add _anything_ to the CDocument class.

The whole idea of MFC is that it encapsulates base functionality. To extend it for specific requirements, you inherit an MFC class and extend and customise to your hearts content.

Sorry to dissapoint you all with my lack of a witty or poignant signature.

Adding MFC class to ATL object

9-Oct-01 23:34

Is my dll will be matched for another language (delphi, vb ect) if I created it in ATL COM APP Wizard and I use in class CDialog into this project ? Confused | :confused:

Re: Adding MFC class to ATL object

Michael P Butler10-Oct-01 0:48

Michael P Butler

10-Oct-01 0:48

Delphi and VB will be able to call a COM dll generated by ATL/WTL Wizard. I don't tend to use MFC but rather ATL for my dialog classes. As long as you don't export any MFC/C++/C Datatypes then a COM dll should be able to be called from any lanugage that supports COM.

Michael Smile | :)

Re: Adding MFC class to ATL object

Bill Wilson10-Oct-01 11:27

Bill Wilson

10-Oct-01 11:27

MSDN contains an article titled How to add MFC code to an ATL project. It explains all.

Thanks for the help,
Bill

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