How do I filter characters in a CEdit?

A. Create a CEdit derivative (CMyEdit) and create an OnChar() message map entry.

   // Assume that CMyEdit is derived from the CEdit class.

   afx_msg void CMyEdit::OnChar(UINT nChar, UINT nRepCnt, UINT nFlags)

   {

      if (nChar == 'a' || nChar == 'A')

      {

          nChar = 'X';

      }

      DefWindowProc(WM_CHAR, nChar, MAKELONG(nRepCnt, nFlags));

   }