This function retrieves a handle to the drop-down menu or submenu activated by the specified menu item.
HMENU GetSubMenu( HMENU hMenu, int nPos )
If the function succeeds, the return value is a handle to the drop-down menu or submenu activated by the menu item. If the menu item does not activate a drop-down menu or submenu, the return value is NULL.
SetMenu, GetMenu, IsMenu
origin.h