VC6.0编写的对话框无法关闭

在这里，OnCancel()函数和其它的按钮响应函数不太一样，它本身是CDialog类的虚函数。在基于对话框的程序中，点击关闭按钮，按键 ALT + F4，都会调用此函数（可加断点调试查看），注释掉调用基类函数的代码自然会导致无法手动关闭对话框。

可以查阅MSDN:
CDialog::OnCancel
virtual void OnCancel( );
If you implement the Cancel button in a modeless dialog box, you must
override the OnCancel method and call DestroyWindow from within
it Do not call the base-class method, because it calls EndDialog, which
makes the dialog box invisible but does not destroy it

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