Edit box which will have fixed digits and DOTS between digits

>> You can use some kind of mask edit control.

Why would you do that if MFC already has a control for *exactly* this purpose?

I have used the maskedit control without problems with eVC++, here is an IP variation of the control from codeproject. I have translated it, hope there are not errors:

ipmaskedit.h
---------------
#include "maskedit.h"       /* original maskedit control, also you must add maskedit.cpp to your project  */

class CEditIPAddr : public CMaskEdit
{
public:
      typedef struct {
            unsigned dir1:8;
            unsigned dir2:8;
            unsigned dir3:8;
            unsigned dir4:8;
      } TIPAddr;

public:
      DWORD m_Address;

      CEditIPAddr () : CEditIPAddr () {
            m_Address= 0;
      }
      virtual void PreSubclassWindow() {
            Init("[0-2][0-9][0-9].[0-2][0-9][0-9].[0-2][0-9][0-9].[0-2][0-9][0-9]");
            CMaskEdit::PreSubclassWindow();
      }
      static void AFXAPI DDX_EditIPAddr (CDataExchange* pDX, int nIDC, CEditIPAddr & rControl, DWORD& addr);
      static void AFXAPI DDV_EditIPAddr(CDataExchange* pDX, CEditIPAddr & rControl);
};


IPmaskedit.cpp
-----------------

#include "ipmaskedit.h"

void AFXAPI CEditIPAddr::DDX_CEditIPAddr(CDataExchange* pDX, int nIDC, CEditIPAddr &rControl, DWORD& addr)
{
      DDX_Control(pDX, nIDC, (CWnd&)rControl);
      CString data;
      TIPAddr IPaddr;

      if (!pDX->m_bSaveAndValidate) {
            memcpy(&IPaddr, &addr, sizeof(IPaddr));
            data.Format(TEXT("%03i.%03i.%03i.%03i"), (int)IPaddr.dir4, (int)IPaddr.dir3, (int)IPaddr.dir2, (int)IPaddr.dir1);
            rControl.SetData(data);
      } else {
            data = rControl.GetData();
            IPaddr.dir4 = LOBYTE(_ttoi(data.Mid(0,3)));
            IPaddr.dir3 = LOBYTE(_ttoi(data.Mid(4,3)));
            IPaddr.dir2 = LOBYTE(_ttoi(data.Mid(8,3)));
            IPaddr.dir1 = LOBYTE(_ttoi(data.Mid(12,3)));
            memcpy(&addr, &IPaddr, sizeof(addr));
      }
}

void AFXAPI CEditIPAddr::DDV_CEditIPAddr(CDataExchange* pDX, CEditIPAddr& rControl)
{
      if (pDX->m_bSaveAndValidate) {
            CString data = rControl.GetData();
            int dir4 = _ttoi(data.Mid( 0,3));
            int dir3 = _ttoi(data.Mid( 4,3));
            int dir2 = _ttoi(data.Mid( 8,3));
            int dir1 = _ttoi(data.Mid(12,3));
            if (dir1*dir2*dir3*dir4==0 || dir1>255 || dir2>255 || dir3>255 || dir4>255) {
                  ::MessageBox(NULL, TEXT("Values must be between 1 and  255."), TEXT("IP Address Error"), MB_OK|MB_ICONEXCLAMATION);
                  pDX->Fail();
                  rControl.SetFocus();
            }
      }
}