oop - virtual operator overloading c++ -

suppose wanted overload "==" operator derived class, need rewrite overload in derived class header file or there way implement operator overload in .cpp file without having add in header file? , if so, how implementation of derived operator in .cpp?

what header looks like:

class {     public:     a();     ~a();     virtual bool operator==(const &ref) = 0;     protected:     int year;     string note; } class b:a {     public:     b();     ~b();     bool operator==(const b &ref); //is needed or not?     private:      int month, day; } 

if want override virtual function in child-class, need declare function override in child class.

so yes, declaration needed.

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think way: class declaration used in many places , many source files, how else compiler know function has been overridden?