Compiling... FrameUn.cpp Linking... PP.obj : error LNK2005: "class CDialogUn * m_lpDialog" (?m_lpDialog@@3PAVCDialogUn@@A) already defined in FrameUn.obj PP.obj : error LNK2005: "class CFrameUn * m_lpFrame" (?m_lpFrame@@3PAVCFrameUn@@A) already defined in FrameUn.obj PPDlg.obj : error LNK2005: "class CDialogUn * m_lpDialog" (?m_lpDialog@@3PAVCDialogUn@@A) already defined in FrameUn.obj PPDlg.obj : error LNK2005: "class CFrameUn * m_lpFrame" (?m_lpFrame@@3PAVCFrameUn@@A) already defined in FrameUn.obj Debug/PP.exe : fatal error LNK1169: one or more multiply defined symbols found Error executing link.exe.

请问各位高手出现这种错误，都有哪些情况！？