C / C++ / MFC

Re: C++ questions: limiting number of class instantiation and volatile keyword

10-Jun-04 18:35

Oops, sorry i didnt notice the 'delete this' is your code earlier.

Calling delete this for a stack-based object will cause an exception, because the stack cannot be "freed" until a function returns.

If you are using this technique in your code, you should not be using stack-based objects at all.

Consider this:

void First(void)<br />
{<br />
  MyClass a;<br />
}<br />
<br />
void Second(void)<br />
{<br />
  MyClass b;<br />
  First();<br />
}

In this scenario, how would you prevent the second stack-based object being created in the call to First() ?

For this reason, either you should only use object instantiation via the new operator, or use some a BOOL data member to disable unwanted-instances' functionality. The latter is ofcourse tedious, and prone to errors.

You could, throw an execption in the constructor when you detect that a class instance is not the first instance.
Then, in every place you use this class via stack/freestore, you could use exception handling.

Bikram Singh

bikram singh10-Jun-04 18:41

Re: C++ questions: limiting number of class instantiation and volatile keyword

10-Jun-04 18:41

Anonymous wrote:
And regarding the 2nd question, if the callback function is called by another thread, I have to declare the variable as volatile, right?

Yes, you should declare the variable as volatile. Also, note that if you declare a struct to be volatile, all it's members are automatically made volatile.

Bikram Singh

palbano10-Jun-04 15:43

palbano

10-Jun-04 15:43

Would a Singlton work for you situation?

"No matter where you go, there your are." - Buckaroo Banzai

-pete

how to check if BDE installed

kzyczynski10-Jun-04 12:18

kzyczynski

10-Jun-04 12:18

as in subject.
What is the simplest way to check programatically if
Borland Database Engine is installed on local computer?
Thanks

Re: how to check if BDE installed

bikram singh10-Jun-04 15:32

Executing EXE from Memory?

10-Jun-04 15:32

Easiest to try and initialize it:

if(DbiInit(NULL) == DBIERR_NONE)<br />
{<br />
  ShowMessage("BDE is installed");<br />
}

Bikram Singh

NodeX10-Jun-04 11:35

10-Jun-04 11:35

Hi,
I wonder if there is a way to execute a program from memory.
I've read exe-data from resources and I must execute it without writing to disk.

How could it be done?

NodeX

Neville Franks10-Jun-04 12:09

Neville Franks

10-Jun-04 12:09

Not an area I know much about but trying doing a Google search for: Exe Packers or something like that. These are programs that compress Exe's and then decompress them when they are run.

Neville Franks, Author of ED for Windows www.getsoft.com and coming soon: Surfulater www.surfulater.com

David Crow10-Jun-04 16:48

10-Jun-04 16:48

Not a way that I know of. Why are not able to write to disk first?

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

NodeX10-Jun-04 21:37

10-Jun-04 21:37

I'm thinking about simple protection against debugging

NodeX

David Crow11-Jun-04 2:10

11-Jun-04 2:10

What does debugging an application have to do with anything? And why do you want to be protected from it? If an application has errors, I would think you'd want to know about them.

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

NodeX11-Jun-04 5:10

11-Jun-04 5:10

i have encoded exe-data (flash projector) in resources and i don't want others to get stuff (images etc.) from it...
ok.. it will only protect from simple resource-hackers etc. not from debugging (sorry for imprecision Frown | :(

)

NodeX

David Crow11-Jun-04 5:32

11-Jun-04 5:32

Can you not write it to some temporary folder using an obscure name (i.e., nothing obvious), and then delete it when done? Other than that, I know of no way to run something from memory. It's a stretch, but you might search for something about "injecting code into another process' address space."

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

NodeX11-Jun-04 5:39

11-Jun-04 5:39

As a last resort i will do it with temp folder...
but i can't assume that the person who will have my cd-rom with exe, grant me an access to temp folder...

NodeX

David Crow11-Jun-04 6:23

11-Jun-04 6:23

NodeX wrote:
but i can't assume that the person who will have my cd-rom with exe, grant me an access to temp folder...

Why not use SHGetFolderPath() with CSIDL_LOCAL_APPDATA or CSIDL_PROFILE as the CSIDL?

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Alexander ^M.,11-Jun-04 7:09

Alexander ^M.,

11-Jun-04 7:09

lol forget it, if someone wants to debug it, he will be able to!

Don't try it, just do it! Wink | ;-)

bikram singh10-Jun-04 18:16

Modeless Dialog in DLL: Message Confusion

10-Jun-04 18:16

In Windows, the EXE file is mapped as virtual memory. The os loader and other parts of the os perform this task. The idea of running a program from memory, even if it could be done, would be meaningless.

Not worth spending time over. Remember, using this technique, you could bypass some anti-virus programs, but the good ones out there will catch it anyway...

Bikram Singh

Justin Cooke10-Jun-04 11:31

Justin Cooke

10-Jun-04 11:31

Greetings All,

I've been burning up all of my time over the past two days trying to debug this. Please help!

I've written a DLL that creates a modeless dialog (in this case allowing the user to watch an aiming video image of a Laser Tracker.) This DLL is used by various client applications including my test app.

I need the user to be able to use the arrow keys to "jog" the Tracker from the dialog. Also, all of the normal dialog keyboard control needs to work (tabbing, typing into CEdit boxes, etc.)

At first, I couldn't even get key messages in the dialog...as soon as a key was pressed (with focus on the dialog), the message came to the client app. I found a way to fix this from MS' website involving having the app call a FilterDLLMsg() func from its PreTranslateMessage(). However, now when a key is pressed in the dialog, the dialog and app freeze.

I spent a long time tracing this freeze and it seemed to be freezing around the MFC code for _AfxFindNextMnem. I was stumped and thought it had to do with a tabstop or group setting for my dialog controls. Then I tried changing the m_pMainWnd = &dlg; line in my client application's InitInstance() to m_pMainWnd = NULL;. (It's a dialog based app.)

That corrected the freeze problem, but now any AfxMessageBoxes() I call from my client app seem to belong to the desktop instead of the main app dialog. There may be other, more serious, ramifications, but I haven't tested any further.

So, I don't want to change the m_pMainWnd = &dlg; if I don't have to, but for now, it's the only way I've found to keep the DLL/app from freezing. Is that safe? I'd prefer a different solution.

Has anyone out there ever seen this type of behavior? Any ideas? My brain is getting all mushy Unsure | :~

as I haven't made much progress on this Confused | :confused:

Thanks,
Justin

Re: Modeless Dialog in DLL: Message Confusion

bikram singh10-Jun-04 19:02

10-Jun-04 19:02

If your problem is AfxMessageBox(), dont use it. Use
MessageBox(dlg,"some text",0,0) instead.

The desktop is the parent of the Message Box bcos MFC probably uses the m_pMainWnd, which you set to 0, as the first param to the MessageBox() function.

I dont know why the dialog should freeze, cos i havent tried it yet.

Bikram Singh

Keeping Menu Open

cje10-Jun-04 11:29

cje

10-Jun-04 11:29

I am using TrackPopupMenu to display a dropdown menu from a toolbar button that has an arrow on the right side. Things are working as I expect. The menu is basically a list of items that my user checks on/off. Someone in the office has seen an application where you can click an item in a menu and the menu stays open so the user can "select" multiple menu items and then click off of the menu to close it...they now want this in my app.

Any ideas on how to keep the menu from closing after someone makes a selection?

thanks in advance
cje

Re: Keeping Menu Open

bikram singh10-Jun-04 14:43

10-Jun-04 14:43

You could try setting a WH_GETMESSAGE hook using SetWindowsHookEx() and intercept WM_LBUTTONDOWN ?

Bikram Singh

Help-Data Transfer

Design1863010-Jun-04 11:04

Design18630

10-Jun-04 11:04

I need to figure out a way to communicate with an A/D converter and send and receive data bytes from the PC.

Any suggestions and comments are appreciated.
Thanks.

JB

Re: Help-Data Transfer

bikram singh10-Jun-04 19:20