setwindowtext在sdk中的应用问题

我编写了个小程序，但并不能显示，有哪位大哥给解释下，谢了！
hWnd=GetDlgItem(hDlg, IDC_LIST1);
switch (message)
{
case WM_COMMAND:
switch(LOWORD(wParam))
{
case ID_IN:
len=GetDlgItemText(hDlg, IDC_ENTER, com, sizeof(com));
com[len]='\0';
SetWindowText(hWnd,com);
LPVOID   lpMsgBuf;
FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER |   
                              FORMAT_MESSAGE_FROM_SYSTEM |   
                              FORMAT_MESSAGE_IGNORE_INSERTS,   
                              NULL,
  GetLastError(),    
                              MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),   
                              (LPTSTR)   &lpMsgBuf,   
                              0,   
                              NULL
  );
MessageBox(hDlg, (LPCTSTR)lpMsgBuf, "Error3 ", MB_OK | MB_ICONINFORMATION);   
LocalFree(lpMsgBuf); 
break;
case IDCANCEL:
EndDialog(hDlg, LOWORD(wParam));
return TRUE;
}