MFC Edit control produces debug assert on first action

The underlying Windows controls have yet to be created in a CDialog constructor.
Do such initialisation in the dialog's OnInitDialog handler.

Answer looks good, but, what is the initialization code needed?

From another thread I found:

            CEdit* pEditCtrl = (CEdit*)this->GetDlgItem(IDC_EDIT1);

            ``if (pEditCtrl)

            ``{

                        ``pEditCtrl->SetWindowText(newValue);

            ``}

But that creates a pointer forcing the use of that pointer.  The object already exists.  What is the code to initialize it?  Maybe even better, where can I find a description of the class and the initialization code?  I did a search and found a description of CEdit Class here:  CEdit Class | Microsoft Learn  But it creates a new instance and a pointer.  I already have an instance in the MFC app.  I just need to initialize it and don’t recognize that code. 

That is code you could use if you haven't mapped a control variable to the underlying control (which you may have done from what you showed - though I can't be sure).

If you already have a control member variable then you can use it directly in OnInitDialog as you had tried to do in the constructor.

Have a read about the MFC dialog framework here.

I followed the link, and several threads that it led to.  I could not recognize the code to initialize the Edit Control.

So simplify a bit.  Create an MFC project with a dialog, build, and run it.  OK.

Use the Toolbox and add an Edit Control.  Use the default ID of IDC_EDIT1.  Build, run, the dialog is present.  It has been initialized to some degree.

The edit control appears to be CEdit.  With that control in my project, search the entire project for CEdit.  Not found.  How is this created if the class is not mentioned?  Maybe an including class is used, but what is that class?

Search the solution for IDC_EDIT1.  It is declared in Resource.h.  Looks like it is placed in MFCButton4.rc. But not found anywhere else.

So, I guess, back to the original question.  Please show the code needed to initialize the edit control and write text “123” to the control.  Preferably in the constructor. So the app starts with that text displayed.

Thank you in advance for your time and patience.

If you want to attach text to an edit control in an MFC dialog box, you can do this:

Right click on the edit control in the dialog editor and choose Add Variable...

In the Add Control Variable dialog, change the Category from Control to Value. Give your variable (now a CString) a name and proceed to create it.

In your program's InitInstance (where your dialog class is instantiated in a simple dialog application), prior to calling DoModal, set your text member variable, something like this:

	CMFCApplication1Dlg dlg;
	m_pMainWnd = &dlg;
	dlg.m_strText = "Hello world";
	INT_PTR nResponse = dlg.DoModal();

Build and run your program, you should see the text in your dialog's edit control.

Note that you can only do this for values, if you map an MFC control class to the Window control on the dialog you need to do the operations in the dialog's OnInitDialog handler - where the underlying Windows control has been created and the MFC mapping to your control class variable has taken place.

Have a look at this documentation too.