请教关于UG OPEN API不同的调用方式的问题

针对不同的调用方式，用户对话框程序有3个函数入口：“MENUBAR_COMMENTED_OUT"
(通过菜单调用）、”DISPLAY_FROM_CALLBACK“（通过回调函数调用）和”DISPLAY_FROM
_USER_EXIT“（通过用户操作调用）。
哪位高手能否帮助说的更具体一点，更详细一点。谢谢！

[ 本帖最后由 angel2004 于 2005-10-30 18:59 编辑 ]

User Exits
A user exit is an internal Open C and C++ API program with a unique entry point that occurs at a specific location within Unigraphics NX. The argument list for each function is identical to ufusr. You can obtain full details on user exits from the Reference Help or the header file uf_exit.h. Each user exit has a unique environment variable that points to the image that is to be executed. When this environment variable is defined and you select the correct menu option within UG, your internal Open C and C++ API Program is executed. For example, there is a user exit that occurs at File—>Execute UG/Open.

There is a special user exit that occurs at the startup of Unigraphics NX. The user exit function name is ufsta(). This exit uses the environment variable USER_STARTUP. However, this entry point can also be used by MenuScript and User Defined Objects (UDOs). Unlike MenuScript, in the UDO case, this entry point is encountered when an external Open C and C++ API program runs.

能不能搞点中文的，我的英文很菜的！

简单一点说：第一个入口是用菜单调用的；第二个可以做为一个函数被别的程序调用；第三个是用user-execute function那里调用的（函数名为ufusr）。