You open the file by calling the in function of the DL_Dxf object and passing a pointer to a class that inherits from the DL_CreationAdapter abstract class.

通过调用 DL_Dxf 对象的 in 函数并将指针传递给一个继承 DL_CreationAdapter 抽象类来打开此文件。

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If I have a pointer to an object cast to one of its base classes, I can call the correct member functions through the abstract base class.

如果我有一个对象的指针，转换到它的基类指针对象上，我能通过基类指针调用合适的成员函数。

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