Get/Set WindowText questions

Part of my program has to get information from a dialog box and format and display the information into the current document.  This is easy using SetWindowText().  The only problem is that I must create an obsurd number of CStrings in the formatting process and I get memory reading errors.  If the answer is use GetWindowText, what kind of type declaration should be used for the buffer that will hold the window's text?  Is there a better way to do this?  Also, is there a way to GetWindowText relative to the cursor so something could be displayed at the cursor location.  

Example:

CString fubar = GetWindowTextBeforeCursor();
CString  marsupial = "text";
CString foo = GetWindowTextAfterCursor();
CString alltogethernow = fubar + marsupial + foo;
SetWindowText(alltogethernow);

Is there any way to do this?