link_error 2001.怎么解决啊？

inking...
dbconnect_sybase.obj : error LNK2001: unresolved external symbol "public: virtual __thiscall CTDateTime::~CTDateTime(void)" (??1CTDateTime@@UAE@XZ)
dbconnect_sybase.obj : error LNK2001: unresolved external symbol "public: char * __thiscall CTDateTime::GetASCTime(void)" (?GetASCTime@CTDateTime@@QAEPADXZ)
dbconnect_sybase.obj : error LNK2001: unresolved external symbol "public: __thiscall CTDateTime::CTDateTime(long)" (??0CTDateTime@@QAE@J@Z)
dbconnect_sybase.obj : error LNK2001: unresolved external symbol "public: long __thiscall CTDateTime::GetTime_T(void)" (?GetTime_T@CTDateTime@@QAEJXZ)
Debug/TestDbConn.exe : fatal error LNK1120: 4 unresolved externals
Error executing link.exe.请教高手啊