Re: Get pointer to parent of parent (2 levels back) - NEWBIE QUESTION

David Wilkinson <>
Thu, 09 Oct 2008 10:40:06 -0400
Jimbo_Jimbob_Jiminator wrote:

My application is dialog-based.
The App creates a dialog. The dialog creates a property sheet. The property
sheet creates 4 property pages.
The dialog opens a file. I want the property pages to be able to write to
the file. How can I get access back to that file pointer? I found
m_pParentWnd in the Property Page. But, I can't go back like this
m_pParentWnd->m_pParentWnd to get two levels back.

I thought about passing the pointer to the CFile in via the contructors of
the dialog, then to the sheet, then to the pages but I am not sure how to do
that either.

Any help is greatly appreciated.

// --- FILE: Test.h
class CMFCTestApp : public CWinApp

// --- FILE: Test.cpp
CMFCTestApp theApp;
CMotmanDlg dlgTest;
m_MainWnd = &dlgTest;
nResponse = dlgTest.DoModal;

// --- FILE: TestDlg.h
class CMFCTestDlg : public CDialog
CFile* pDataFile;

// --- FILE: TestDlg.cpp
m_pPSheetTest = new CPSheetTest(m_sWinTitle, (CWnd*)this, 0);
... open("datafile.dat"); // Open the data file at the dialog level

WARNING! EX_CONTROLPARENT MUST be here for tabbed pages to work correctly!!!!
See WS_EX_CONTROLPARENT.txt file in project directory for more explanation.
m_pPSheetTest->Create(this, dwStyle, WS_EX_CONTROLPARENT);


// --- FILE: PSheetTest.h
class CPSheetTest : public CPropertySheet

// --- FILE: PSheetTest.cpp

// --- FILE: PPageTest1.cpp
// --- FILE: PPageTest2.cpp
// --- FILE: PPageTest3.cpp
// --- FILE: PPageTest4.cpp


"Reaching out" by using GetParent(), and casting, is not a good OOP technique.
Passing the CFile pointer through the constructors is the way to go.

What is stopping you? Just add CFile* arguments to the sheet and page
constructors, and create private CFile* member variables in each of the pages.

David Wilkinson
Visual C++ MVP

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