菜单问题: CMenu, DeleteMenu不起作用?

对话框程序:OnInitDialog()中,
... m_pMenuMain = new CMenu;
if( ! m_pMenuMain ->LoadMenu( IDR_MAINFRAME ) )
return;
... CMenu * pMenu;
int i;
//清空菜单
pMenu = m_pMenuMain ->GetSubMenu( 0 );
for( i=0; 3; i++)
pMenu ->DeleteMenu( i, MF_BYPOSITION);
... this ->SetMenu( m_pMenuMain );
...
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DeleteMenu后,菜单怎么仍然存在?