Compiler Error C2517

'identifier' : right of '::' is undefined

The identifier on the right side of the scope resolution operator (::) was not defined.

The identifier on the right side of the scope resolution operator must be a defined member of the class, structure, or union found on the left side of the operator. If no class, structure, or union is named, then the identifier on the right side of the operator must be declared with global scope.