FIX: Messagebox Shows in DDX_FieldCBString & DDX_FieldLBString

   if (nLen > value.GetAllocLength()) ...
				

RESOLUTION

Create a new function by copying the DDX_FieldCBString or DDX_FieldLBString from Daoview.cpp located in the \Msdev\Mfc\Src directory. In the new function, add an additional parameter to be used as the maximum allowable length (the size of the field). You'll then need to replace the DDX call in your DoDataExchange() function with the new function you created.

For the DDX_FieldCBString function, change the function prototype to something like this:

   void DDX_MyFieldCBString(CDataExchange* pDX, int nIDC, CString& value,
   CDaoRecordset* pRecordset, int nMaxFieldLength)
				

Replace these lines:

   if (nLen > value.GetAllocLength())
      AfxFailMaxChars(pDX, value.GetAllocLength());
   // get known length
   ::GetWindowText(hWndCtrl, value.GetBuffer(0), nLen+1);
				

with these lines:

   if (nLen > nFieldLength)
      AfxFailMaxChars(pDX, nFieldLength);
   // get known length
   ::GetWindowText(hWndCtrl, value.GetBuffer(nLen), nLen+1);
				

Note that GetBuffer() is no longer receiving 0 but is using the value in nLen.

For the DDX_FieldLBString() function, change the prototype to:

   void DDX_MyFieldLBString(CDataExchange* pDX, int nIDC, CString& value,
   CDaoRecordset* pRecordset, int MaxFieldLength)
				

Replace these lines:

   if (nLen > value.GetAllocLength())
     AfxFailMaxChars(pDX, value.GetAllocLength());
   ::SendMessage(hWndCtrl, LB_GETTEXT, nIndex,
                 (LPARAM)(LPSTR)value.GetBuffer(0));
				

with these lines:

   if (nLen > nFieldLength)
     AfxFailMaxChars(pDX, nFieldLength);
   ::SendMessage(hWndCtrl, LB_GETTEXT, nIndex,
                (LPARAM)(LPSTR)value.GetBuffer(nLen));
				

You will need to include a prototype for AfxFailMaxChars() in your code. Here's the prototype:

   void _stdcall AfxFailMaxChars(CDataExchange* pDX, int nChars);