纯虚函数和抽象类。一个有关VC++虚函数的源程序，比较适合VC++初学者。以后我上传一系列这种类型的源程序供大家学习之用。-pure virtual function and abstract category. The VC a virtual function of the source, more suitable for beginners VC. After I uploaded a series of this type of source for all learning.
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