Solved

Will deleting a CWnd through it's own PostNcDestroy message cause a memory leak if it was allocated on the heap?

Posted on 2006-10-31
2
545 Views
Last Modified: 2013-11-20
I have a splash screen window that is allocated on the heap and deleted in it's PostNcDestroy message handler.  Will this cause a memory leak?

The reason I'm asking is because a memory leak detection program pointed to the spot where I create a new Window on the heap with out deleting it before the function ended.  It may be wrong in this case.

Details below, if needed:

It is created like this:

BOOL CMainFrame::ShowSplashScreen()
{            
      pSplash=new CSplashScreen();      

      pSplash->Create(this,_T("My Splash"),1700,CSS_FADE | CSS_CENTERSCREEN | CSS_SHADOW);

      pSplash->Show();
}

And deleted like this:

void CSplashScreen::PostNcDestroy()
{
      CWnd::PostNcDestroy();
      delete this;
}


This is preferable because the splash screen is killed as soon as a timer runs out:

void CSplashScreen::OnTimer(UINT nIDEvent)
{
      KillTimer(0);
      ShowWindow(SW_HIDE);
      DestroyWindow();
}
0
Comment
Question by:bigsteve87
2 Comments
 
LVL 86

Accepted Solution

by:
jkr earned 500 total points
ID: 17843587
This is absolutely OK, see http://msdn2.microsoft.com/zh-tw/library/5zba4hah.aspx resp. http://msdn.microsoft.com/library/en-us/vcmfc98/html/_mfcnotes_tn017.asp ("TN017: Destroying Window Objects"):

Auto Cleanup with CWnd::PostNcDestroy

When destroying a Windows window, the last Windows message sent to the window is WM_NCDESTROY. The default CWnd handler for that message (CWnd::OnNcDestroy) will detach the HWND from the C++ object and call the virtual function PostNcDestroy. Some classes override this function to delete the C++ object.

The default implementation of CWnd::PostNcDestroy does nothing which is appropriate for window objects allocated on the stack frame or embedded in other objects. This is not appropriate for window objects that are designed to be allocated by themselves on the heap (not embedded in other C++ object).

Those classes that are designed to be allocated by themselves on the heap override the PostNcDestroy member function to perform a "delete this". This statement will free any C++ memory associated with the C++ object. Even though the default CWnd destructor calls DestroyWindow if m_hWnd is non-NULL, this does not lead to infinite recursion since the handle will be detached and NULL during the cleanup phase
0
 

Author Comment

by:bigsteve87
ID: 17843811
Great answer, exactly what I needed.  Thanks!
0

Featured Post

Announcing the Most Valuable Experts of 2016

MVEs are more concerned with the satisfaction of those they help than with the considerable points they can earn. They are the types of people you feel privileged to call colleagues. Join us in honoring this amazing group of Experts.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
xyBalance chalenge 58 96
Folder Comparison 12 54
not able to insert into temp table 68 169
Excel Use VBA to get user's Mac Address for their computer 5 252
Introduction: Ownerdraw of the grid button.  A singleton class implentation and usage. Continuing from the fifth article about sudoku.   Open the project in visual studio. Go to the class view – CGridButton should be visible as a class.  R…
Introduction: The undo support, implementing a stack. Continuing from the eigth article about sudoku.   We need a mechanism to keep track of the digits entered so as to implement an undo mechanism.  This should be a ‘Last In First Out’ collec…
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.
Two types of users will appreciate AOMEI Backupper Pro: 1 - Those with PCIe drives (and haven't found cloning software that works on them). 2 - Those who want a fast clone of their boot drive (no re-boots needed) and it can clone your drive wh…

828 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question