extern HWND hDlgShow;//窗口句柄
 HWND hReceieve = ::FindWindowEx(hDlgShow,0,"Edit",0);//取文本框句柄
 
 CString strOld;
 ::GetWindowText(hReceieve,strOld.GetBuffer(2000),2000);
 strOld.ReleaseBuffer();//必须释放缓冲

 str.MakeUpper();//转换为大写
 ::SetWindowText(hReceieve,strOld + str);