External symbols that cannot be parsed by C + +

Error 3 LNK2001:
unresolved external symbol "public:static struct table * security::head" ([email protected]@@[email protected]@a) F:\github\membership\ Security\security\security.obj

This error occurs when a static variable is declared in the class, but is not defined outside the class, causing the error to be resolved by simply defining it outside the class.

Security.obj:error LNK2005: "public:static struct table * security::last" (email protected]@@[email protected]@a) already in Defined in Main.obj
1>f:\github\membership\security\debug\security.exe:fatal Error LNK1169: Find one or more multi-definition symbols

This error occurs when a static variable in a class is defined in the header file area, and a static variable is defined in a. cpp file to be resolved.

External symbols that cannot be parsed by C + +