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global dialog object

Posted on 1998-08-06
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Last Modified: 2013-11-19
Is it illegal to define a program-global dialog box object?  It compiles perfectly, but when I run it, it gives me a runtime debug assertion error.

This is a dialog based app so I have a main dialog class called CTheDlg which is run in a modal loop in CTheApp.
What I need to do is have access (inspect and change) to a data member in CTheDlg throughout the whole program.  Is there a better method?
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Question by:VEngineer
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by:nietod
Comment Utility
MFC is not my area of expertise, but the problem could be that the constructor for the global dialog object needs to use MFC elements that are not initialized.

The solution would be to use a global pointer to a dynamically allocated object.  Allocate the object at startup, after MFC is done initializing.
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Expert Comment

by:danny_pav
Comment Utility
Why not try this:
CTheDlg * get_the_only_CTheDlg() {
  static CTheDlg dlg(...);
  return &dlg;
}

This will delay the initialization until the object is ready to be used and you will not have to explicitly call constructors and destructors.  I use this kind of thing a lot and have boilde it down to a template.

template<class T>T& get_the_only() {
  static T only_T;
  return only_T;
}

and then call it:

class CWhatever {
  public:
    CWhatever();

  public:
    func();
};





get_the_only<CWhatever>().func();

of course, this will only work if you have a constructor that takes no parameters.  This obviously will work without MFC.
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by:danny_pav
Comment Utility
oops, sorry.  I meant to make that a comment.
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by:VEngineer
Comment Utility
Ok.. it's a comment again.
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by:VEngineer
Comment Utility
Let me try some of these options and see which one works out.
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by:danny_pav
Comment Utility
My comment is complementary to nietod's.  I am agreeing with what he says, just giving an easier way to manage the memory.
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Accepted Solution

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Priyesh earned 10 total points
Comment Utility
I haven't tried this.. But do have a feeling that it should work...
             You might have seen the following code in the BOOL CDlgApp::InitInstance()
       m_pMainWnd = &dlg;
Well, u can always access the m_pMainWnd.. It's AfxGetApp()->m_pMainWnd.
This is a CWnd pointer and now contains the pointer of u'r dialog window. Get this and typecast to the Dialog class.
ie CDlgDlg* pDlg = (CDlgDlg*)(AfxGetApp()->m_pMainWnd);
U get a pointer to the dialog.. watch or change any member variable in this dialog through the above pointer.. it's easy isn't it?? Or did i miss u somewhere???
             Best wishes..

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by:danny_pav
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the only problem with a global dialog box (or any global object) is thread/concurrency.  If you have but one thread (most common case), this is not an issue.  
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by:VEngineer
Comment Utility

Thanks for the help.  I found a hybrid solution with everyone's comments.
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Expert Comment

by:danny_pav
Comment Utility
use AfxGetMainWnd() instead of AfxGetApp()->m_pMainWnd
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