Help Needed for getting record from database - C / C++ / MFC Discussion Boards

Re: Problem with CreateMutex() and CloseHandle()

Member 75496020-Dec-07 3:37

20-Dec-07 3:37

"And Every time I run application then it shows the message indicating that another Instance is running but CloseHandle() function does not remove process."

I think this is the source of the problem. The CloseHandle API doesn't control the running process. It is used to tell the running process that a previous instance exists and that it should not run. It is not clear from the code snippet that application is terminated when the first instance of the application is detected.

For a MFC CWinApp this text would occur in the InitInstance member function,

BOOL CMyApp::InitInstance()
{
	m_hMutex = ::CreateMutex(0, FALSE, "TestApp");
	if (::GetLastError() == ERROR_ALREADY_EXISTS) {
		TRACE("TestApp: Already running");
		// explicitly close the mutex handle
		::CloseHandle(m_hMutex);
		
		return FALSE;	// do not run second time
	}
}

A return value of FALSE from CMyApp::InitInstance will terminate the second instance of the program. The important point is that the Mutex is a resource used by the process, not the process itself. When you detect the ERROR_ALREADY_EXISTS condition you must terminate the application yourself. You must close the handle because CreateMutex returned a valid handle.

Re: Problem with CreateMutex() and CloseHandle()

ashishbhatt24-Dec-07 18:18

ashishbhatt

24-Dec-07 18:18

Thanks to you.

Sorry For the very late Reply on this htread becaz I do not want to create new thread for the same problem.

As you told in your post to test the code you show ,, I tested it and works fine.But i want to know some more things,, As you told that I have to terminate my application myself but how can I do that??? D'Oh! | :doh:

My problem is that when I run another instance of application then from my code it shows the message that another instance is running and I also close the Mutex Handle,But it creates new entry into the Process list(in TaskManager->Process tab).So how can I remove this entry when one is already running?? D'Oh! | :doh:

Ashish Bhatt,
System Developer,
Avinashi System Pvt. Ltd.

Re: Problem with CreateMutex() and CloseHandle()

Member 75496026-Dec-07 4:51

Member 754960

26-Dec-07 4:51

It is not clear to me which instance of the process you are trying to terminate. I have been assuming you want to terminate the second instance. I'll address that.

First what are the results we are looking for? The test program I use is the MFC program generated by MSVC App Wizard. The produces a program that will run two instances. When you do the Windows task manager will show both instances in the process list. To make the test results easy to see, sort the Task Manager process list by name in order to see the two processes listed together. If you then terminate one instance it will be removed from the process list after it has terminated. This is the result we are seeking. What we want is a way for the second instance of the program to detect the first instance of the program. When the first instance is detected the second program instance should terminate itself, just as if we had done it from the application. As before, the task manager process list will reflect that the second instance of the program terminated and remove it from the process list, leaving just the first instance running.

The way we detect the second instance of the program is to use a mutex object. Each instance of the program tries to create the mutex. This is doen when the application starts during InitInstance().

BOOL CMfctestApp::InitInstance()
{
	//...

	m_hMutex = ::CreateMutex(0, FALSE, "TestApp");
	if (::GetLastError() == ERROR_ALREADY_EXISTS)
	{
		TRACE("TestApp: Already running");
		// explicitly close the mutex handle
		::CloseHandle(m_hMutex), m_hMutex = 0;
		return FALSE;	// do not run second time
	}
	
	// ...
}

Note the use comma sequence operator and the explicit assignment of the mutex handle. A second instance of the application will get a valid handle to the existing mutex. Once we have closed the handle we do not want to use it again. We declare the m_hMutex handle as a private member variable in the application class,

class CMfctestApp : public CWinApp
{
	// ...
private:
	HANDLE m_hMutex;
};

Finally, we insure that the first instance of the application will properly release the mutex when the application terminates. This is done in ExitInstance()

int CMfctestApp::ExitInstance() 
{
	if (m_hMutex)
		::CloseHandle(m_hMutex);
	
	return CWinApp::ExitInstance();
}

The first instance of the program will have a valid, non null mutex handle and will close it. All other instances will have handle of 0.

If now run the program outside of the debugger and look at the Task Manager process list and you will see the first instance running. In the MSVC IDE place a breakpoint in the InitInstance member function and run the program under the debugger. When the breakpoint is hit look at the process list in the Task Manager and you will see both instances running. Let the second instance of the program, in the debugger, continue and you should see the process get removed from the task list.

Re: Problem with CreateMutex() and CloseHandle()

DevelopmentNoob16-Dec-09 19:56

DevelopmentNoob

16-Dec-09 19:56

Hi, i follow your way to create the program, so far is okay.
but i try to add the code below in

ExitInstance()
{
	if(m_hMutex)
	{
		::CloseHandle(m_hMutex);
                ReleaseMutex(m_hMutex);
	}
       //here suppose the program will not run to following code.
       //but it did now.ReleaseMutex should release the m_hMutex already right?
	if(m_hMutex)
	{
		::CloseHandle(m_hMutex);
                ReleaseMutex(m_hMutex);
	}
		
	return CWinApp::ExitInstance();

Re: Problem with CreateMutex() and CloseHandle()

NehaMishra286846-Dec-10 19:31

NehaMishra28684

6-Dec-10 19:31

The CreateMutex does not work on Win 7 32 bit. Even if the application already exists it returns a success..

Any thought?

Thanks..

Drag Drop

john563219-Dec-07 18:01

john5632

19-Dec-07 18:01

Hi Experts,

Hi have 2 view(both ListView) in my application. One conataind the full path of files. I want to drag drop a file in other ListView from first ListView.

How can I do this ?

Thanx in advance.

Re: Drag Drop

Hamid_RT19-Dec-07 18:17

Hamid_RT

19-Dec-07 18:17

Did you search on the codeproject?

Help Needed for getting record from database

Y_Kaushik19-Dec-07 17:53

Y_Kaushik

19-Dec-07 17:53

Hi..all's
I am making a program. I need to fetch record from Oracle database and
print these record to .txt file . I write a program for this . Although
i fetch record from database and store these record to result set .

Now i can exteract these record from object of CRecordset class and how can i write these record to .txt file although . I have create file successfully. My code is written below.

CDatabase *Dbase = new CDatabase();
CRecordset rs;

int count=0;
if(!Dbase->Open("aixmmapping_72",FALSE,FALSE,"ODBC;DSN=aixmmapping_72;UID=aixmmapping_72;PWD=aixmmapping_72"))
{
MessageBox(" Can Not Connect With Database");
}else
{
rs.Open(CRecordset::dynaset,_T("Select * from vor"));
while(!rs.IsEOF())
{
rs.MoveNext();
}
CFile obj;
obj.Open( "D:\\Yogi\\Test\\abc.txt", CFile::modeCreate|CFile:: modeReadWrite);

char TextData[800];
strcpy(TextData, "rs");
obj.Write(TextData,800);
MessageBox("File Write Successfully");
rs.Close();
}

Please help me

Regard's
Kaushik

Re: Help Needed for getting record from database

Roger Broomfield19-Dec-07 18:57

Roger Broomfield

19-Dec-07 18:57

Refer CRecordset::GetFieldValue[^] and pay particular attention to the Note in the remarks section, which mentions that you should NOT have the ODBC Cursor Library loaded.

Re: Help Needed for getting record from database

Y_Kaushik19-Dec-07 19:22

Y_Kaushik

19-Dec-07 19:22

First of all Thanks for reply.....

I can get record from database and can print it to .txt file.
but all the record print in a single line.

Can you told me how can make formatting of file so that each and every row print in a saprate line.

Again Thanks for help

Regard's
Kaushik

Re: Help Needed for getting record from database

Roger Broomfield19-Dec-07 19:41

Roger Broomfield

19-Dec-07 19:41

Here is what I get from the code you posted:
Open database
Open a recordset of all fields of table "vor"
Walk through all records in the recordset, doing nothing with each record
Open a file
Write the single string "rs" to the file
close the file
close the recordset

the MSDN article I linked includes a piece of sample code that:
walks through all the records of the recordset
walks each of the fields of each record

what I think you need to do is:
figure out how to write each varValue to the file
include a write to file of a cariage-return line-feed pair before the rs.MoveNext()

Re: Help Needed for getting record from database

Y_Kaushik19-Dec-07 19:53

Y_Kaushik

19-Dec-07 19:53

I am trying to do this like
sStr.Empty();
sStr="\n";
strcpy(TextData, sStr);
obj.Write(TextData,sStr.GetLength());
rs.MoveNext();
But its not working....

Can u told me where i am making wrong

Regard's
Kaushik

Re: Help Needed for getting record from database

Y_Kaushik19-Dec-07 20:01

Y_Kaushik

19-Dec-07 20:01

My code is runnign fine Thanks for Help

Regard's
Kaushik

Re: Help Needed for getting record from database

Y_Kaushik19-Dec-07 20:36

Y_Kaushik

19-Dec-07 20:36

Hello sir,
Although i can print the value of table field in .txt file .
in well manage order but , Now i want to show its field name at top of
its raw

I am trying it using GetFieldName() function but i am unable to fetch field name . Can u please told me how can i do this

Regard's
Kaushik

Need help with restricting window movement to the screen...

demxine19-Dec-07 16:35

demxine

19-Dec-07 16:35

Could anyone tell me how to restrict a window from being dragged outside the visible screen of the desktop?

Your help would be much appreciated, thank you.

-> Demsen

Re: Need help with restricting window movement to the screen...

Maxwell Chen19-Dec-07 16:45

Maxwell Chen

19-Dec-07 16:45

Try handling either of the below...
1. CWnd::OnWindowPosChanged()
or
2. WM_WINDOWPOSCHANGED

Maxwell Chen

Re: Need help with restricting window movement to the screen... [modified]

demxine19-Dec-07 19:47

demxine

19-Dec-07 19:47

I've used OnWindowPosChanging already and my code looks like this:

void CSnapDialog::OnWindowPosChanging( WINDOWPOS* lpwndpos )
{
int m_EdgeSnapGap = 1;

RECT rcScrn;
SystemParametersInfo (SPI_GETWORKAREA, 0, &rcScrn, 0);

//Snap X axis
if (abs(lpwndpos->x - rcScrn.left) <= m_EdgeSnapGap)
{
lpwndpos->x = rcScrn.left;
//???
//Code is needed here to prevent window from drifting
//outside the left edge of visible screen
}
else if (abs(lpwndpos->x + lpwndpos->cx - rcScrn.right) <= m_EdgeSnapGap)
{
lpwndpos->x = rcScrn.right - lpwndpos->cx;
//???
//Code is needed here to prevent window from drifting
//outside the right edge of the visible screen
}

//Snap Y axis
if (abs(lpwndpos->y - rcScrn.top) <= m_EdgeSnapGap)
{
lpwndpos->y = rcScrn.top;
//???
//Code is needed here to prevent window from drifting
//outside the top edge of the visible screen
}
else if (abs(lpwndpos->y + lpwndpos->cy - rcScrn.bottom) <= m_EdgeSnapGap)
{
lpwndpos->y = rcScrn.bottom - lpwndpos->cy;
//???
//Code is needed here to prevent window from drifting
//outside the bottom edge of the visible screen
}
}

Can anyone help me on what code I should supply to make this work correctly?
<div class="ForumMod">modified on Thursday, December 20, 2007 2:01:10 AM</div>

Fake Memory Leak!!

Lea Hayes19-Dec-07 16:06

Lea Hayes

19-Dec-07 16:06

Hi,

The program that I am working on uses two external DLL modules.

[program.exe] uses [library.dll]
[library.dll] uses [another_library.dll]

I have stepped through the program line by line, and have used the CRT break on allocation debugging feature. Upon exiting the program in debug mode within visual studio, it reports a lot of memory leaks. However, I believe these messages to be false.

Here is basically what happens.

[program.exe]
-->CMFCApplication
---->Initialise();
------>[library.dll]
-------->AllocateSomeMemory();
---------->[another_library.dll]
------------>AllocateSomeMoreMemory();

When the application closes I have confirmed that the processes exit in the following order:

[library.dll], [another_library.dll], [program.exe].

When [library.dll] exits the 'Output' panel within visual studio indicates that there is a memory leak. The memory is then released by [another_library.dll] after the leak has been reported within the output panel.

All three modules use the /MDd (Debug) /MD (Release) switches for multi-threaded dll, so they each share exactly the same memory manager.

Is there a way which I can force the DLL processes to be terminated in the specific order:
[another_library.dll], [library.dll], [program.exe]? Because I am confident that this will resolve the issue. I understand that it is probably safe for me to ignore this warning output...but future (problemsome) memory leaks will be masked by the fake ones. This could lead to some serious problems.

Any advice would be greatly appreciated...this is driving me nuts! Dead | X|

Lea Hayes

Re: Fake Memory Leak!! [modified]

Maxwell Chen19-Dec-07 16:34

Maxwell Chen

19-Dec-07 16:34

1. Shouldn't another_library.dll be released first? Library.dll is using another_library.dll, but library.dll dies in the half way. Therefore the system has no clue to release the resources of another_library.dll currently being used by library.dll.
2. Unreleased threads (suspended) can also cause memory leak warnings. Before the program exits, you should let all the threads exit.

Maxwell Chen

modified on Wednesday, December 19, 2007 10:56:20 PM

Re: Fake Memory Leak!!

Lea Hayes19-Dec-07 21:14

Lea Hayes

19-Dec-07 21:14

Hi,

Thanks for your quick reply.

[another_library.dll] is a core library which is actively used by both [library.dll] and [program.exe].....I should have mentioned this before.

So we have [another_library.dll] which uses [library.dll]
and [program.exe] which uses [another_library.dll] as well as [library.dll].

The threads are all executing their detatch command upon program exit....just in the wrong order, in that the memory leak is warned before the offending objects even have a chance to be cleaned.

Thanks,
Lea Hayes

Re: Fake Memory Leak!!

Roger Broomfield19-Dec-07 17:09

Roger Broomfield

19-Dec-07 17:09

This is the primary reason why I follow Microsofts recommendation of having Initialization and Termination routines exported from the dll's that are separate from DllMain. Its basically the only way you can guarantee the calling order. Refer: DllMain Callback Function[^]

Re: Fake Memory Leak!!

Lea Hayes19-Dec-07 22:02

Lea Hayes

19-Dec-07 22:02

Hi,

Thank you for your advice, I have created an exported class object which has an initialise and deinitialise method. They are automatically called by the constructor and destructor for added security. The main application calls the global objects deinitialise method which forces the library to be cleaned upon exit, and before any modules are terminated. This appears to have solved the problem.

Many thanks!
Lea Hayes

Destroy/Close the window

CodingLover19-Dec-07 14:21

CodingLover

19-Dec-07 14:21

Hi all,

I've create a window using CreateWindowEx windows API and do some work on it. Thats fine. But for the safer operation at the end of all the processing I want to close/destroy the window.

I've try this code, Here m_hwnd_RTFBox is the handle to the window. On the above code there is no compile error, but gives a runtime error and saying there is a unhandled exception on the first line. Where I'm going wrong. I found this from the MSDN, but it wont work.

	BOOL clsWin = DestroyWindow(m_hwnd_RTFBox);
	if(clsWin != 0)
	{
		printf("SS");
	}
<pre>

I appreciate your help all the time...
Eranga Smile | :)

Re: Destroy/Close the window

CodingLover19-Dec-07 17:54

CodingLover

19-Dec-07 17:54

I've test another thing also. First send a message to the window and then try to destroy the window. Sending message is ok, but on destroy window gives a error.

BOOL sendMess = PostMessage(m_hwnd_RTFBox, WM_DESTROY, 0, 0);
if(sendMess != 0)
{
    DestroyWindow(m_hwnd_RTFBox);
}

Access violation gives on the DestroyWindow() function.

I appreciate your help all the time...
Eranga Smile | :)

Re: Destroy/Close the window

Mark Salsbery20-Dec-07 6:01

Mark Salsbery

20-Dec-07 6:01

What do you mean it won't work?

Does the exception actually occur on that line?

As for your second post:
Do NOT send WM_DESTROY message to a window. The system does that
for you and also it won't destroy the window.

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

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