Re: How to update a string in C++ MFC CListBox - C / C++ / MFC Discussion Boards

Pavan_Putra25-Jun-09 19:29

25-Jun-09 19:29

//Open the registrey and check that is it writable

lRet=RegOpenKey(HKEY_LOCAL_MACHINE, strKeyPath,hKey);

//if lRet != ERROR_SUCCESS then go to read registrey

unsigned char* lpBufferValue = new unsigned char [dwSize];
unsigned long dwType = 0;
unsigned long dwSize = 0;

lpBufferValue = new unsigned char [dwSize];

ASSERT(lpBufferValue);
lRet = RegQueryValueEx(hKey,strValueName, NULL,dwType, lpBufferValue,dwSize);

// if dwSize is not 0 then it is success
// close registrey (either success or failure )

RegCloseKey(hKey);

I hope this will work.

It's not enough to be the best, when you have capability to be great..

Re: Reading from registry

Pavan_Putra26-Jun-09 3:36

Pavan_Putra

26-Jun-09 3:36

It's not enough to be the best, when you have capability to be great....

How to update a string in C++ MFC CListBox

CodeMacDaddy25-Jun-09 4:31

CodeMacDaddy

25-Jun-09 4:31

I am creating an app where I have CListBox object. I call .AddString() to add 10 string to the list. After the list is initialized, I want to update some of the string data in the list. How to do ? I reviewed all the class member of CListBox and I do not see any type of update string method. The only way I see to do this type of operation is to use Add/Delete methods. There must be a bette way Frown | :(

Please help, so much time wasted on this class.

Re: How to update a string in C++ MFC CListBox

led mike25-Jun-09 4:33

led mike

25-Jun-09 4:33

Perhaps your requirements call for using a ListView rather than a ListBox?

Re: How to update a string in C++ MFC CListBox

CodeMacDaddy26-Jun-09 8:41

CodeMacDaddy

26-Jun-09 8:41

Hi, thank you for the reply I will look into ListView. As I found out yesterday ListBox is very good for what I am trying to do. I'm basically trying to create a window that is a comm monitor. I have 10 CAN message I receive at a very high rate 20-100ms that I want to display. With CListBox I am getting "flickering" and I know the app is probably getting tons of Window messaging !!

Re: How to update a string in C++ MFC CListBox

David Crow25-Jun-09 5:30

David Crow

25-Jun-09 5:30

CodeMacDaddy wrote:
The only way I see to do this type of operation is to use Add/Delete methods.

That's about it. Do you have an aversion to this approach?

"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

Re: How to update a string in C++ MFC CListBox

Rajesh R Subramanian25-Jun-09 7:17

Rajesh R Subramanian

25-Jun-09 7:17

Adding and removing items repeatedly may affect the performance of the application. You might want to use a CListCtrl[^].

It is a crappy thing, but it's life -^ Carlo Pallini

Re: How to update a string in C++ MFC CListBox

Maximilien25-Jun-09 7:21

Maximilien

25-Jun-09 7:21

For a small list (small number of items) the Add/Delete will work (maybe add a CWnd::LockWindowUpdate rto prevent flickering)

You could also use the list box in "virtual mode".

This signature was proudly tested on animals.

Different mutex handle even though it was created already?

Souldrift25-Jun-09 3:48

Souldrift

25-Jun-09 3:48

Hi again,

I got another one. This time regarding mutexes. I am using the following locking routine:

HANDLE Thread::Lock( const char* name )
{
	// first convert const char* to LPCWSTR -> for CreateMutex()
	wchar_t buffer[FILENAME_MAX];
	mbstowcs_s( NULL, buffer, FILENAME_MAX, name, FILENAME_MAX-1 );

	HANDLE hMutex = CreateMutex(NULL, 
				FALSE,    
				buffer); 
 
	if (!hMutex)
	{
	      return NULL;
	}
	 
	if (GetLastError() == ERROR_ALREADY_EXISTS)
	{
		// not really important, just for debugging
	}

	WaitForSingleObject(hMutex, INFINITE);

	return hMutex;
}

Now I found out that my locking mechanism does not work properly. And the thing is this: Thread 1 calls the Lock()-function. A Mutex is created and everything is fine. While it is locked the same thread actually (which is an error, but that´s how I found out) calls the Lock()-function again with the same name parameter. CreateMutex returns a DIFFERENT handle this time but the GetLastError query returns ERROR_ALREADY_EXISTS. But since it is a different handle WaitForSingleObject() grants access again, before the first Unlock() call occured.
So how does this work. Shouldn´t I get the same handle everytime I call CreatMutex() with the same parameters? Otherwise I get a new handle everytime and nothing is really ever locked.

Thanks again.

Souldrift

Re: Different mutex handle even though it was created already?

led mike25-Jun-09 4:29

led mike

25-Jun-09 4:29

Souldrift wrote:
But since it is a different handle WaitForSingleObject() grants access again, before the first Unlock() call occured.

Or since the handle is to the same mutex and the thread already has a lock on it the wait call does not block. Wink | ;)

Not all synchronization objects work the same, particularly when you lock them multiple times in the same thread. There are different object because they are designed to work differently.

Also I seriously recommend one obtains a good book on multi-threading if one intends to learn the subject.

Re: Different mutex handle even though it was created already?

Joe Woodbury25-Jun-09 8:33

Joe Woodbury

25-Jun-09 8:33

The main problem here is that you are returning a local variable. In addition, every time your function is called, it creates a new mutex handle (referencing the same mutex.) You are leaking handles like crazy.

To properly use a mutex you need to first create it (and you don't need to do a conversion from a char to wide string--just call CreateMutexA.) The locking is done separately.

BTW, only use mutexes if you are synchronizing between processes or you have to have multiple waits on a lock, otherwise use critical sections.

Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke

Re: Different mutex handle even though it was created already?

norish25-Jun-09 20:14

norish

25-Jun-09 20:14

It is not important the handle value of CreateMutex are different or same becuase the handle will never be compared its value but only be used with WaitForXXXXXX function.
Others wrote that mutex can not lock with the same thread and this implementation may cause handle leaks.
I suggest another locking mechanism using InterlockedIncrement and InterlockedDecrement like;

extern long some_locker = 0;

bool lock(long& name) {
  if (1 == InterlockedIncrement(&name))
    return true;
  InterlockedDecrement(&name);
  return false;
}

void unlock(long& name) {
  InterlockedDecremtn(&name);
}

Note that this implementation dose not wait, so you must write wait loop for this for example;

while (!lock(some_locker)) Sleep(10);
// ... some task
unlock(some_locker);

This may not be quite your requirement, but one way of some practical technique.

How to change the background color of an EditBox

Deepu Antony25-Jun-09 3:34

Deepu Antony

25-Jun-09 3:34

Hi all

Can anybody tell me how to change the back ground color and text color dynamically in an edit box.

Thanks and regards
Deepu.

Re: How to change the background color of an EditBox

David Crow25-Jun-09 3:41

David Crow

25-Jun-09 3:41

Check out WM_CTLCOLOREDIT.

Re: How to change the background color of an EditBox

Deepu Antony25-Jun-09 4:12

Deepu Antony

25-Jun-09 4:12

Thank you very much.

File Explorer Properties in MFC/Vista

Software200725-Jun-09 3:16

Software2007

25-Jun-09 3:16

I noticed the explorer properties that used to show in XP for my MFC generated files are gone in Vista. I did find something about including XML file .propdesc file to include properties that I need the file to have... Any one dealt with this before?

Thanks

B/B+ tree template

alikalik25-Jun-09 3:03

alikalik

25-Jun-09 3:03

Hi, does anyone know where sources for B/B+ tree implementation can be found?
The main requirements are:
- fast access to an element by index
- fast writing to a file

Re: B/B+ tree template

Rajesh R Subramanian25-Jun-09 3:06

Rajesh R Subramanian

25-Jun-09 3:06

alikalik wrote:
Hi, does anyone know where sources for B/B+ tree implementation can be found?

See here[^].

It is a crappy thing, but it's life -^ Carlo Pallini

Re: B/B+ tree template

CPallini25-Jun-09 3:10

CPallini

25-Jun-09 3:10

Nobody knows about, even Wikipedia [^], [^] (and you surely won't find links to C/C++ implementations at the bottom of the pages).
Smile | :)

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]

How to manually implement ID_FILE_NEW for MDI application?

transoft25-Jun-09 2:26

transoft

25-Jun-09 2:26

Hi

I have a MDI application. I don't want to use MDI default "ID_FILE_NEW". How can I manually implement this?

(1) What classes should I instance and create?
(2) The steps to do this?

Best regards,

Re: How to manually implement ID_FILE_NEW for MDI application?

David Crow25-Jun-09 3:44

David Crow

25-Jun-09 3:44

transoft wrote:
How can I manually implement this?

Implement what?

transoft wrote:
(1) What classes should I instance and create?

To do what?

transoft wrote:
(2) The steps to do this?

Steps for what?

Notice a theme here?

Re: How to manually implement ID_FILE_NEW for MDI application?

transoft25-Jun-09 6:39

transoft

25-Jun-09 6:39

Hi
I don't want to use MDI default "File-New" to instance a Child Window. I want to create Child Window myself. I need to do special processing during "File-New" process.

My question is: How can I implement the "File-New" operation without using MDI defaults? I don't want to use "Sending message "ID_File_New" message to Client window to get a Child Window. What is other way to do it (Instancing a new Child Window)?

Thanks,

Re: How to manually implement ID_FILE_NEW for MDI application?

David Crow25-Jun-09 7:17

David Crow

25-Jun-09 7:17

Look in your app's BEGIN_MESSAGE_MAP(). See ID_FILE_NEW? Just change the associated handler.

Re: How to manually implement ID_FILE_NEW for MDI application?

transoft25-Jun-09 7:42

transoft

25-Jun-09 7:42

That is what I don't want to do. I want to get rid of "ID_FILE_NEW". But I want to mimic the what "ID_FILE_NEW" does.

Do I need to instance and create "CSplitfrm", "CmyView, and "CMyDoc" class? How can I do it? what is sequence?

Thanks,

Re: How to manually implement ID_FILE_NEW for MDI application?

David Crow25-Jun-09 7:45

David Crow

25-Jun-09 7:45

transoft wrote:
I want to get rid of "ID_FILE_NEW".

Are you talking about the #define directive in afxres.h?

transoft wrote:
But I want to mimic the what "ID_FILE_NEW" does.

Have you looked at CWinApp::OnFileNew()?

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