CODEWITHSUNDEEP
c++classoperator-overloadingvirtualfunction-definition
Martian
Martian

Reputation: 225

Virtual overloaded operators >> and <<

I need an interface that would require its subclasses to overload << and >>, but I'm not quite sure how since these operators aren't overloaded as member functions:

std::istream& operator>> (std::istream& in, Student& student) {
    in >> student.name >> student.group;
    for (int& i : student.marks) { in >> i; }
    return in;
}

Maybe there's a way to make it a member function?

Upvotes: 3

Views: 220

Answers (2)

Jeffrey
Jeffrey

Reputation: 11420

You could do something like this:

class StudentInterface
{
public:
    virtual void readSelfFrom(std::istream& in) = 0;
};

std::istream& operator>> (std::istream& in, StudentInteface& student) 
{
    student.readSelfFrom(in);
    return in;
}

And then let users derive from StudentInterface, eg:

class Student: public StudentInterface
{
public:
    void readSelfFrom(std::istream& in) override
    {
        in >> name >> group;
        for (int& i : marks) { in >> i; }
    }
};

Upvotes: 10

Vlad from Moscow
Vlad from Moscow

Reputation: 311038

A general approach in such a case is to declare in the base class a virtual member function like 

virtual std::ostream & out( std::ostream &os = std::cout ) const;

In derived classes the function will be overriden.

Then the operator << can look like

std::ostream & operator <<( std::ostream &os, const Base &obj )
{
    return obj.out( os );
}

A similar way can be defined the operator >> only in this case the virtual member function will not be constant..

Upvotes: 5

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