How to get edit control value from sub tabControl in mainTabControl.?

Hi, all..
i'm now using Visual c++ in Visual Studio 2005 for my project. i faced problem in getting other tab value in main tab ..Below are details of my problem.
In the main tab control(CTabDialogControl), i have another sub tab . IDD_MACHINE is my other dialog ID while the CTabFourthDialog is this tab class name.. and IDD_EDITMCNO is a edit control in this tab, IDD_EDITMCNO passing value to a variable called m_McNo.

Code:

DDX_Control(pDX, IDC_EDITMCNO, m_McNo)

>> this is the edit control in CTabFourthDialog.
When i retrieved value from IDC_EDITMCNO within CTabFourthDialog, below statement can work properly:

Code:

CString sMachNo;
m_McNo.GetWindowText(sMachNo);

but when i trying to retrieve the value IDC_EDITMCNO from CTabFourthDialo in CTabDialogControl , it return me a error. below shown the code i wrote in CTabDialogControl.

Code:

 CString sMachNo;
CTabFourthDialog::m_McNo.GetWindowText(sMachNo)

and i getting this error when compile the program.

Please guide me to solve this problme..
Your help i will very appreciate..
Thanks very much
Regards
Alice